tai lieu ve khu trung sua

8/7/2019 tai lieu ve khu trung sua

1/85

HOME HELP PREFERENCES

Search Titles Subjects Organizations

CONTRACT TEXTEXPAND CONTENTSDETACHNO HIGHLIGHTING

Technical Guide for SMEs in the Dairy Industry (CDI, 1999, 74 p.)

(introduction...)LIST OF ABBREVIATIONSFOREWORDPART 1 - DAIRY FARMINGPART 2 - THE DAIRYANNEXESTHE CDI's ACP ANTENNAE NETWORK THE CDI'S EUROPEAN INSTITUTIONAL NETWORK BACK COVER

(introduction...)

GUIDESERIES TECHNOLOGY NR. 13

Centre for the Development of IndustryACP-EU

52 Avenue Herrmann Debroux1160 BRUSSELS

BELGIUMTel: +322679.18.11
http://www.nzdl.org/gsdlmod?a=p&p=home&l=en&w=utf-8http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=p&p=helphttp://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=p&p=helphttp://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=p&p=preferenceshttp://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=p&p=preferenceshttp://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=qhttp://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&cl=CL1http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&cl=CL2http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&cl=CL3http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&cl=CL3.8&d=HASH42a2de12455398e80d1e7c&gt=0http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&cl=CL3.8&d=HASH42a2de12455398e80d1e7c&gc=1http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&cl=CL3.8&d=HASH42a2de12455398e80d1e7c&x=1http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&cl=CL3.8&d=HASH42a2de12455398e80d1e7c&hl=0&gc=0&gt=2http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2%2E2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&c=fnl2.2&cl=CL3.8&d=HASH42a2de12455398e80d1e7c.9#HASH42a2de12455398e80d1e7c.9http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2%2E2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&c=fnl2.2&cl=CL3.8&d=HASH42a2de12455398e80d1e7c.8#HASH42a2de12455398e80d1e7c.8http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2%2E2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&c=fnl2.2&cl=CL3.8&d=HASH42a2de12455398e80d1e7c.7#HASH42a2de12455398e80d1e7c.7http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2%2E2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&c=fnl2.2&cl=CL3.8&d=HASH42a2de12455398e80d1e7c.6http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2%2E2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&c=fnl2.2&cl=CL3.8&d=HASH42a2de12455398e80d1e7c.5http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2%2E2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&c=fnl2.2&cl=CL3.8&d=HASH42a2de12455398e80d1e7c.4http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2%2E2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&c=fnl2.2&cl=CL3.8&d=HASH42a2de12455398e80d1e7c.3#HASH42a2de12455398e80d1e7c.3http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2%2E2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&c=fnl2.2&cl=CL3.8&d=HASH42a2de12455398e80d1e7c.2#HASH42a2de12455398e80d1e7c.2http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2%2E2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&c=fnl2.2&cl=CL3.8&d=HASH42a2de12455398e80d1e7c.1#HASH42a2de12455398e80d1e7c.1http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2%2E2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&c=fnl2.2&cl=CL3.8http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2%2E2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=p&p=abouthttp://www.nzdl.org/gsdlmod?a=p&p=home&l=en&w=utf-8http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=p&p=helphttp://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=p&p=preferenceshttp://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=qhttp://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&cl=CL1http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&cl=CL2http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&a=d&cl=CL3http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&cl=CL3.8&d=HASH42a2de12455398e80d1e7c&gt=0http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&cl=CL3.8&d=HASH42a2de12455398e80d1e7c&gc=1http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&cl=CL3.8&d=HASH42a2de12455398e80d1e7c&x=1http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0fnl2.2--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00---4----0-0-11-1-0utfZz-8-00&cl=CL3.8&d=HASH42a2de12455398e80d1e7c&hl=0&gc=0&gt=2


2/85

Fax: +32 2 675.26.03Telex: 61427 cdi b

e-mail: [email protected] website: www.cdi.be

This document has been established on the basis of information obtained throughbibliographical research and communicated by the various bodies and companies thatare the subject of this publication. Although every effort has been made to verify andupdate these data, the Centre cannot be held responsible for any inaccuracies or omissions in the information in question. The fact that an organisation or a companyhas been included in this publication does not imply any obligation for them toprovide any of the services described under the corresponding heading.

Since it was formed in 1977, the Centre for the Development of Industry (CDI) hasacquired substantial technical and commercial know-how in the service of thecreation, development and rehabilitation of small and medium-sized enterprises inACP countries (Africa, Caribbean and Pacific), particularly through the setting up of lasting partnerships with companies in the European Union.

With the publication of the Practical Guides collection, the CDI is responding to aclearly expressed need among ACP promoters and EU entrepreneurs wishing toestablish industrial cooperation with these countries. The guides are aimed at allowingthem to adapt to the particular technical, commercial, financial, administrative andlegal environment of the different local contexts. Designed to offer concreteassistance in this task - in simple practical terms - in a specific field or on particular aspects of their activities, they are aimed above all at providing an effective tool in theservice of the manager.

In preparing these guides, the CDI calls upon the services of consultants, researchersand practitioners - in the ACP countries and/or the European Union - with extensiveexperience of the field concerned and of the practical problems encountered byentrepreneurs, along with the solutions to be applied. When circumstances allow it,the CDI teams up with a co-publisher (consultancy, research body, specialisedinstitution, etc.) in order to ensure that the guides have the widest possible circulation.

This guide has been prepared by two experts:

Professor Papa El Hassan Diop, veterinarian, for the Dairy Farming section, Jean-Luc Voisin, food engineer, for the Dairy section.

Under the supervision of Chf TourCDI sectoral coordinator.

Coordination: Tour./Adenaike B., CDINijborg G., CDI

1999 CDI, Brussels, first edition.This volume of the CDI Guides is a CDI publication.May not be sold by persons other than the CDI and its official distributors.Value: 20 Euro.Reproduction permitted with mention of the source, except for commercial purposes.


3/85

LIST OF ABBREVIATIONS

D Dornic Degree Al Artificial Insemination

D Day DM Dry Matter DNS Digestible Nitrogenous Substance FSH Follicle-Stimulating Hormone H Heat IU International Unit MFU Milk Fodder Unit Na Sodium PG Prostaglandin

PIPose Implant

PMSG Pregnant Mare Serum Gonadropin PP Polypropylene PS Polystyrene PVC Polyvinyl chloride Rl Retarit Implant rpm revolutions per minute TDN Total Digestible Nutrients UDM Useful Dry Matter

UHTUltra high temperature

FOREWORD

This brochure aims to promote the development of the dairy industry in the ACPregion. It follows several missions to evaluate this industry in 1997 and 1998 at theinitiative of the CDI in fifteen ACP countries (especially in East Africa and SouthernAfrica). It is mainly intended for company heads, farmers and/or processors operatingon a small to medium scale, i.e. with processing capacities of between 1 000 and 50000 litres of milk per day.

With a production level of 11 000 000 tonnes of milk, Africa produces only 2% of theworlds milk from a herd representing 14% of the worlds total dairy herd. This milk is intended for a young and growing population set to increase from 500 million in1990 to 1.5 billion in 2025.

Within the last ten years, driven by the liberalisation of the economy, milk productionand processing has really taken off in many countries. Around fifty new dairycompanies have been created in the last few years on this continent.

The CDI has been called upon to intervene by studying new projects (feasibility),helping companies in their start-up stage, financing experts, training productionmanagers or company heads in Europe in specific technologies and introducingquality-improvement programmes.


4/85

However, for many dairy entrepreneurs this is only the beginning of the path that theyhave embarked upon and many different problems are encountered in each company.

This guide is therefore designed as another stone in the edifice that is beingconstructed in numerous countries in the ACP region; it tackles problems relating to

milk production and collection and the technological aspects of the most commondairy products in this region and offers advice on cleaning and disinfecting. Finally, alist of specialised manuals and publications is given, to enable each dairy industrialistto build up an essential library to answer the countless questions arising every day for the people working in this industry, along with useful addresses of different suppliers.

I.1. LIVESTOCK

The area of Africa is 30 000 000 km 2. Stock-farming is present only in 3 000 000 km 2

of forest and 15 000 000 km 2 of savannah. In the latter, 8 000 000 km 2 are free of tsetse flies and have a density of 17.5 head/km 2, which is even higher in the highplateaux areas due to the climate and the abundant pasture. This density falls to 2.5head/km 2 in the 7 millions km 2 infested with tsetse flies. These areas are unfavourablefor the development of stock-farming.

African stock-farming consists of 192 180 000 cattle, 197 169 000 small ruminants,13 815 000 camels and 3 200 000 buffaloes. The African bovine breeds fall into 3groups:

- the taurine group- the zebu group

- the group consisting of various crosses.

The taurine breeds are essentially trypanotolerant breeds, the most widespread of which are still the Ndama, originating from the region of Fouta Djallon in Guinea,followed by the Baoulthe Somba, the Kapsiki and the Kouri in Chad.

Zebus are in the majority, and are essentially found in the Sahel and in the savannah.We could mention in particular the Gobra zebu in Senegal, Moorish zebu in Mali andMauritania, the Azawak zebu in Niger, Chad, and Burkina Faso, the Goudali zebu inCameroon and the Ankolebu in East Africa (Rwanda, Burundi and the DemocraticRepublic of the Congo), the Afrikaner breed in Southern Africa and the Boran breed

in East Africa.

I.2. PRODUCTIVITY

The indigenous African breeds are not very productive: 1 to 2 kg of milk during therainy season and 0.4 a 1 kg in the dry season, i.e. 150 to 300 kg per lactation of 200days. The best, like the Azawak, can produce 2 to 4 kg/day, i.e. 600 to 800 kg per lactation of 250 days.

To make up for this low productivity, exotic milk-producing breeds have beenintroduced, mostly in East Africa and Southern Africa. The main breeds are still theHolstein, the Jersey and the Alpine Brown. The average production of this group is 6


5/85

to 15 kg/day, i.e. 1 500 to 5 000 kg per lactation of 200 to 250 days. This type of stock-farming is usually intensive.

This analysis reveals a number of constraints, the main ones being:

- the shortage of feed,- the low genetic potential of the local breeds,- animal health problems,- the organisation and fluctuation of trade flows,- the poor organisation of stock-farmers.

The problems are much more acute in West and Central Africa, whilst most countriesin East and Southern Africa tend to be self-sufficient in milk.

(introduction...)

The study on the reproduction of cattle will be focused on the female.

II.1. FROM THE ZOOTECHNICAL POINT OF VIEW

The indigenous breeds reach puberty at 26 months on average, whereas it takes only10 to 11 months for the exotic breeds. The variation factor is the feed, although afemale is considered to have reached puberty when its weight is 2/3 of the weight of the adult.

The age at which cows first calve is 3 years 9 months for local breeds and 24 months

for exotic breeds. The interval between calvings, an important factor in fertility andproductivity, is 473 days for local breeds and 360 days for exotic breeds. This intervaldepends on several factors, namely:

- Return to heat: this takes an average of 45 days for milk cows, and 60 to 90 days for suckler cows;

- Average number of inseminations per impregnation: 1.25 for heifers and 2.24 for cows;

- Interval between calving and first insemination: 56 days 28.

Consequently, these are factors that depend on farming practice and herdmaintenance, and therefore the post-calving period.

II.2. FROM THE SEXUAL POINT OF VIEW

During her genitally active period, the female experiences a number of structuralmodifications which occur in the same order at periodic intervals: these constitute thesexual cycle or oestrous cycle. These activities are only interrupted by gestation or certain gynaecological problems.

The length of the cycle is 21 days for cows and 20 days for heifers.


6/85

The cycle is subdivided into 3 stages:

- pro-oestrus, which corresponds to the stage of follicle growth,

- oestrus

- and post-oestrus. The follicle, which has ovulated, turns into a corpus luteum with astage of formation, functioning and dehiscence.

The most important element for the farmer is oestrus. This is the only visible element.It is marked by the arrival of the females heat and, above all, acceptance of coupling.It is therefore the favourable period for artificial insemination or covering, andsubsequently impregnation.

It is essential for this strategic period to be identified.

There are several identification methods:

- Direct observation by the farmer, which can be continuous for 24h/24h or discontinuous for 20 minutes an hour.

- Indirect observation with the help of markers placed either in the male (ink system)or the female (paste placed on the sacrum, which is rubbed off during coupling).

Direct observation produces better results than indirect observation, which can bemisleading due to unproductive couplings.

The duration of the heat is very short for native breeds: 10 to 13 hours, whilst it is 12to 24 hours for exotic breeds.

Signs of a cow being on heat comprise:

- A major sign is acceptance by the cow in question of coupling with one of her fellow creatures,

- secondary signs such as:

emission of cervical mucus congestion of the vulva tonus of the uterine horn extreme mobility on the part of the cow

III. 1. OBJECTIVES

Controlling reproduction allows animal production to be improved and rationalised,namely:

- planning the birth of calves at favourable periods, but also planning milk production;


7/85

- limiting the periods when cows are unproductive;

- large-scale use of biotechnological tools such as artificial insemination and thetransfer of embryos.

(introduction...)

Controlling reproduction is based on the use of hormones, namely progesterone andits derivatives and a reproductive substance, prostaglandin.

III.2.1. Progesterone

Progesterone is secreted by the corpus luteum of the ovary, but its syntheticderivatives are 100 times more active and constitute the group of progestogens. Theyare used in cows that have not had cycles and can cause oestrus 2 to 3 days after the

treatment is stopped. In general, these progestogens are used in conjunction with aprostaglandin 2 days before the progestogen treatment is stopped; the day on which itis stopped, a substance called PMSG is administered to the cow, which stimulates theovarian follicle. The two most common progestogen METHODS are the vaginal coiland the subcutaneous implant.

The vaginal coil is a coil made of a silicon elastomer impregnated with 2.3 g of progesterone, which is released continuously at regular intervals, remaining in thecows vagina for 12 days. The coil has a capsule containing 10 mg of oestradiolbenzoate which is released on the day on which it is inserted, destroying any existingcorpora lutea. It is recommended to carry out a double insemination 48 and 72 hours

after removal of the coil (diagram No. 1).

The subcutaneous implant. This contains 3 mg of Norgestomet. It is fittedunderneath the skin at the base of the cows ear. When the implant is fitted, the cow isgiven an intramuscular injection of a 2 ml solution of Norgestomet and oestradiolvalerate to destroy the existing corpora lutea.

The implant remains in place for 9 days and double insemination is carried out 48hours and 72 hours after it is removed (diagram No. 2).

Diagram No. 1: Diagram showing the use of the coil


8/85

Diagram No. 2: Diagram showing use of the implant

III.2.2. Prostaglandin

This is used above all in cows with cycles, i.e. coming on heat regularly and havingan active corpus luteum. Its action destroys the corpus luteum and encourages the startof a new cycle 2 to 3 days after the treatment.

A dose is injected at intervals of 11 days. It is generally after the second injection thatthe cow comes on heat. Insemination is then carried out 72 hours and 96 hours after the second injection.

From a practical point of view, progestogens are used to trigger off a cycle in cowswith prolonged anoestrus, i.e. more than 60 days for milk-producing cows and 90days for suckler cows, whilst prostaglandins are reserved for cows whoseinsemination periods it is wished to group together.

(introduction...)

Artificial insemination (Al) is a reproduction method allowing the use on a large scaleof bulls semen collected beforehand by artificial means, to impregnate femalesduring their fertile period.

The bull producing the semen must be suitable on two levels:

- zootechnical: in terms of its genetic quality;

- health: it must be free of all legally contagious diseases.

By means of dilution and preservation techniques, especially through freezing,artificial insemination has an action that is both spatial (1 diluted ejaculate allows 300-700 cows to be inseminated) and temporal (liquid nitrogen makes it possible to savealmost indefinitely the semen of a bull that disappeared several years previously).

The semen is collected by means of an artificial vagina. It is then examined in thelaboratory and diluted. The fresh semen can be kept in a refrigerator at +5C for 2 to 3days, whilst the semen for freezing must be diluted with glycerol.

Regardless of the type of semen, it is mostly stored in straws of 0.25 ml or 0.50 mlThese straws are identified beforehand in accordance with an internationalnomenclature giving information on the breed, the bulls identification number, theinsemination centre, etc. The frozen straws are immersed in tanks of liquid nitrogen,where they are stored at a temperature of -196C

From a practical point of view, a weekly check must be made of the level of liquidnitrogen in the tank. This level must not fall below 1/3 of the total volume of the tank.At a level lower than that, there is a risk of endangering the lives of the spermatozoa.


9/85

a) Method

The frozen straw must be thawed out in warm water at 35C for 15 to 20 seconds. It isthen inserted in an insemination gun called a Cassou gun. The upper part is sectionedand the whole of the gun is covered with a protective sheath. The inseminationtechnique used is the recto-vaginal method, i.e. the gun is inserted into the vagina andthe uterus with one hand whilst the other grips the cervix to ease it through thecervical folds.

Insemination is carried out 12 hours after the cow first comes on heat. Generally, themorning-evening rule is applied, i.e. a cow coming on heat in the morning isinseminated in the evening, whilst one coming on heat in the evening is inseminatedthe following morning. It should be remembered that ovulation occurs 24 hours after the cow starts to come on heat and the spermatozoid must be at the fertilisation site atleast 2 hours before the ovum descends to this site.

b) Results

The results obtained with artificial insemination are very good indeed. The successrate varies from 60% to 70%, which is comparable to results with natural coupling.However, this rate can vary according to the state of health of the cow, its feedinglevel, the moment of insemination and the insemination technique used.

(introduction...)

Embryonic transplantation is a reproduction technique using hormonal treatment

which allows numerous embryos to be produced in what is called a donor cow. Theseembryos are then taken out and transferred individually to another category of cowscalled recipient cows.

a) Advantages

From the genetic point of view:

This technique allows the efficiency of the selection system to be improved bymultiplying the number of offspring with a smaller number of mother bulls.

From the zootechnical point of view:

- Possibility of using cows of low genetic value as recipients;

- The great advantage of making maximum use of the genetic qualities of anexceptional cow.

The different stages in embryonic transplantation are as follows:

- in the donor cow: there is - superovulation

- and collection- in the recipient cow, there is - synchronisation of the heat


10/85

- and the transfer of embryos

b) Superovulation

This is a hormonal treatment based on the principle of stimulating the production of ova. The substances used are FSH, which is a hormone from the pituitary gland,PMSG, which is a hormone secreted by the endometrium of a pregnant mare.

FSH is administered twice-daily for 4 days, whilst PMSG is administered in a singledose. The cows are generally inseminated 48 hours and 72 hours after administrationof the PG.

Diagram 3: General treatment applied to donor/recipient cows

Seven days after insemination, the ovaries of the cows are examined, and only cowswith at least 4 corpora lutea are used for collection.

c) Collection of embryos

This is mainly done by the non-surgical method, i.e. via the cervix. A catheter isplaced in the uterine horn, allowing the collecting liquid to be injected and recoveredalong with the embryos. The latter are examined and classified in the laboratoryaccording to the rules of the International Embryo Transfer Society (IETS).

d) Synchronisation of the heat in recipient cows


11/85

This is done by means of progestogens or prostaglandins. The basic rule is that therecipient cow that is to receive the embryo must be at the same physiological stage asthe donor cow, because when the embryo changes site it must find identicalnutritional conditions. An asynchronism of 24 hours is tolerable.

The synchronisation must be organised so that donor and recipient come on heat at thesame time.

e) Transfer of embryos

This takes place 8 days after the recipient cow comes on heat. As with collection,transfer of the embryo is essentially carried out via the cervix, with the help of aspecial Cassou gun. The embryo is deposited as far forward as possible in the uterinehorn whose ovary has the largest corpus luteum.

f) Results

The results obtained offer a success rate of 60% to 70% for fairly experienced teams.

(introduction...)

The objective of milking is to extract the maximum amount of milk of goodorganoleptic and bacteriological quality. This is an extremely important stage in dairyfarming because it is here that the fruit is reaped of all the work carried out upstream,i.e. genetic improvement, feed, health and habitat. There are two sorts of milking:

- milking by hand, reserved for small scale farming,

- machine milking, reserved for large herds. It has become very common and has evenled to the selection of cows for their suitability for machine milking.

IV.1. ANATOMY OF THE UDDER

The udder consists of 4 independent quarters. Each quarter comprises the gland in theupper part and the teat in the lower part. The gland secretes alveolar milk (75% of total milk), which is extracted by triggering a neuro-hormonal reflex. The startingpoint is a local mechanical or thermal stimulus. This excitation gives rise to adischarge of oxytocin from the pituitary gland. This substance is then carried by theblood to the udder, where it causes the muscles around the alveoli to contract. Thisaction leads to expulsion of the milk from the alveoli towards the cisterna and the teat.The internal mammary pressure increases and the udder becomes hard and the teatserect. The amount of time between excitation and the discharge of oxytocin is 25seconds. The oxytocin act for 8 to 12 minutes. This discharge can be inhibited bystress, noise or pain.

The milk in the cisterna represents 30% of the total milk. It is extracted by a purelymechanical action.

IV.2. MILKING RULES


12/85

There are 5 basic rules:

Milking must be carried out in calm surroundings, at the same time and in the sameplace if possible.

The udder must be well prepared, i.e. washed and massaged.

Milking must be carried out quickly in order to benefit from the action of theoxytocin.

Milking must be complete, to optimise the useful matter in the milk. However, thereis a residual rate of 15 to 20%.

Milking conditions must be clean: animal, dairyman and milking machine.

IV.3. MILKING BY HAND

Technique for milking by hand: pressure and slight massage to bring out the milk.

- full-hand milking

- milking with the thumb

- teat pinched between fingers and thumb

(introduction...)

Machine milking uses the same principle as sucking by the calf, which alternatelysucks and massages by moving its tongue.

During the suction stage, there is a depression in the milk chamber. All around theteat there is a vacuum system. This depression causes dilation of the tissue which isdrawn towards the rigid cup, leading to the opening of the sphincter and making themilk flow.

Massage stage: this corresponds to restoring atmospheric pressure. When the sheath

of the cup grips the teat, pressure is established and the milk stops flowing: this is therest stage.

IV.4.1. Standards

- Pulse frequency: 50-60 cycles/min.

- Milking depression 38 cm of Hg = 50 Kpa = bar


13/85

IV.4.2. Parts of the milking machine

These can be divided into 3 categories:

Parts creating and directing the vacuum, i.e. the vacuum pump and its accessories,the switch, the regulator and the pressure gauge

Pulsator: its role is to receive the milking vacuum and cause an alternation, puttingthe pulsation chamber successively in communication with the milking vacuum andatmospheric pressure

Teat cup cluster: this is a unit comprising 4 cups, 2 short tubes per cup and 1collector unit which is a sort of crossroads where the milk flows and the pulsationarrives separately. The volume of the collector unit is 150 - 250 ml. It is made of plastic or stainless steel.

a) Milking in the cowshed

Installation with a milking bucket: the milk flows from the milking cluster into acontainer close to the animal; the container (on the ground or suspended) is connectedto the vacuum system.

Installation with milk pipeline: the milk is carried along a special pipeline towards amilk storage room. The milk pipeline may be made of stainless steel or plexiglass.

b) Milking parlours

Milking parlours are used in conjunction with the loose housing system. The milkingparlour is incorporated in a milking block comprising a waiting area and a milk storage room.

The waiting area is designed to organise and facilitate access for the animals to themilking parlour, with the storage room being used to keep the milk afterwards.

Using milking parlours offers several advantages:

The work of the dairymen is made easier by having a milking pit allowing them towork standing up at a suitable height in relation to the cows udders.

It allows better control over hygiene.

Possibility of automating certain milking operations.

There are two types of milking parlour:

Milking parlour with fixed stalls: in this, the cow is placed in a stall and it is thedairyman who moves from one place to another. This is the most widespread method,and there are several types.


14/85

Milking parlour with mobile stalls: for large herds. The cows are placed on a sort of mobile stand.

(introduction...)

The protocol comprises 3 stages:

- preparation of the udder - fitting of the cups- end of milking operation

a) Preparation of the udder

The objective is twofold: hygiene (producing milk of good bacteriological quality)and physiology (instilling a good milk ejection reflex).

Preparation consists of washing and massaging of the udder.

- Washing is by means of a solution of warm antiseptic followed by wiping to preventdripping. It is even recommended to use an individual cloth or sponge and to wipe theudder with a disposable towel.

- Massaging is carried out at the same time as washing. Massaging in warm water constitutes the physiological preparation.

Preparation for milking is completed by extracting the first jets of milk into a jar with

a black base so that any mastitis or blood in the milk can be detected and thebacteriological quality of the milk can be improved.

b) Fitting the cups

This must be done immediately after preparation. It is easy in the case of individualmilking, but with batch milking the dairyman tends to do the preparation for all thecows in the batch and then to fit the cups.

c) End of milking

The main operation at the end of milking is stripping. The purpose of this is to obtaincomplete milking. The need for stripping is explained by the milking cups climbingup the teats, causing the obstruction of communication between the lactiferous sinusand the papillary sinus and, consequently, stopping the flow of milk, which causescreeping.

The dairymans hand pulls the claw downwards for about 20 seconds, whilst the other hand massages the 4 quarters.

Milking finishes with disinfection of the teats. For this, soaking is recommended,

consisting in soaking each teat in a cup containing an iodine solution.


15/85

IV.4.5. Cleaning and maintenance of the milking machine

Milk is an excellent culture medium for germs; it is therefore essential to clean themilking equipment systematically after each use.

The best-known technique is to wash first in cold water and then with a solution of hot water and a detergent, followed by a rinsing with potable water.

The teat cup liners must be massaged and the regulators dusted.

The power of the pulsators must be checked once a week, together with all parts inrubber. Any cracked part must be replaced immediately.

Once a year, a specialist must check that the machine is working properly, withseveral surveys revealing that there is a high percentage of badly adjusted machines.

a) Cow-related incidents

The cow retains her milk. Possible causes:- Poor preparation of the udder - Cow used to taking concentrate- Cow is ill, on heat, stressed- Preparation water too cold- Intervals between milking too short and irregular - Cow used to stripping (by hand or mechanically)- Long milking, the effect of the oxytocin has worn off The cow is too nervous and kicks. Possible causes:- Primiparous cow- Painful teats- Mastitis- Unskilled dairyman- Too many flies or mosquitoes disturbing her - The cow wants more concentrate- Pulsator out of order - Milking dry Milking takes a long time. Possible causes:- Flow of milk too slow- Teat too long- Sphincter closed- Cup liner worn and too loose- Partial vacuum level too low- Claw in wrong position Cow that does not empty her 4 quarters at the same time. Possible causes:- Teat suffering from an old mastitis- Teat or sphincter injured- Liner twisted in cup- Milk tube affected

- Leak in the milk line or pulsation line


16/85

- Teat folded in the liner - Pulsator out of order Cow with hard blue teats after milking. Possible causes:- Teats too tender (primiparous cow)- Oedema in the udder - Milking dry- The pulsators massage time is too short- High vacuum level- Teat cup liner worn and deformed Cow with hard skin on teats. Possible causes:- Milking with a vacuum level too high and lasting too long- Pulsator out of order - Milking dry (over-stripping)- Diameter of the liners does not correspond to the teats- Milk flow too slow Difficult cow. Precaution:- Let primiparous cows get used to the machine- Do not rush cows- Switch on and off quickly- Attach the teat cluster from the rear, between the cows legs, in the milking parlour - Use a stifle grip, hock grip or a rope around the feet- Do not give concentrate Cows with 3 teats. Precaution:- Close or fold a cup- Close the vacuum inlet Cow with an udder that is too low. Precaution:

- Grasp the milk pipeline, then fit the cups one by one (the two rear teats first, then thefront two) Cow with teats pointing outwards. Precaution:- Milk two at a time or fold over the short milk pipelines and pulsation lines Milking of freshly calved cows. Precaution:- Do not completely empty the cow during the first days of milking (risk of milk fever)

- Do not mix with the rest of the milk for at least 4 days.

b) Machine-related incidents

The machine does not produce enough vacuum. Possible causes:- The pump is not running fast enough (worn belt)- Blades stuck or jammed- interceptor cover open- Vacuum valve open- Pressure gauge out of order (broken) The machine produces too much vacuum. Possible causes:- Regulator valve stuck - Regulator badly fitted

The pulsator does not work. Possible causes:


17/85

- Pulsator cracked- Hole in the membrane- Pulsator jammed- Not enough vacuum Number of pulsations too high or too low. Possible cause:- Pulsator out of order or poorly maintained

c) Dairyman-related incidents

Poor milking can cause mastitis (the udder is hard, red and painful, and the milk changes structure and colour).

Treatment in the event of mastitis:

- Drain the quarter well into a separate bucket. Repeat this operation several timesover the course of the day. If there is no improvement, call the veterinarian.

- Take hygiene measures to prevent contamination of the other cows.

- Leave the cow with mastitis until the end of the milking.

- Disinfect the teats.

(introduction...)

Feed represents 60 to 80% of production costs on the dairy farm. Quality feeding

stuffs are required to produce good milk. Consequently, the transformation of feedinto milk must be as efficient as possible.

V.1. PRINCIPLES

The feed received by the cow must cover two types of needs: sustenancecorresponding to a vital minimum and production requirements, i.e. gestation,growth and lactation.

V.2. NATURE OF NEEDS

There are 5 main needs, namely:

V.2.1. Energy

This constitutes the animals primary need. It is necessary for the functioning of theorganism through the production of new milk tissues. It is achieved throughcarbohydrates, fats or proteins.

V.2.2. Nitrogenous substances

These are essential for the metabolism, tissue growth and the secretion of milk. Theyare obtained in the form of proteins.


18/85

V.2.3. Minerals

Elements such as salt, phosphorus, calcium and magnesium are essential for theformation of the skeleton and for milk production.

V.2.4. Vitamins

These contribute towards proper functioning of the cells. The animal does notsynthesise them, with the exception of vitamin D when it is exposed to sunlight. Theimportance of vitamin A is undeniable in protecting young animals from diarrhoea.Transmission is via the clostridium and the mothers milk.

V.2.5. Water

This is involved in all nutritional exchanges. It plays a vital role in the secretion of milk and control of body temperature. It represents 70% of the animals weight.Adults can consume up to 100 litres of water a day.

V.3. FEEDING DAIRY CATTLE

Feeding dairy cattle depends on a knowledge of a number of factors such as the liveweight of the animal, its age, its stage of gestation, its daily milk output and the foodvalue of the fodder that the farmer has.

During the course of its reproductive life, a cow can calve 5 to 7 times and havelactation periods of 7 to 10 months followed by a rest period (drying up) of 2 months.

The lactation curve passes through a maximum of 1 to 2 months after calving andfalls to 10% every month until drying up.

Consequently, the farmer has to feed 3 categories of cows: cows at the start of lactation (rising production), cows in the middle of lactation (decreasing period)and cows that are drying up.


19/85

Figure 1: Lactation curves

V.3.1. Needs as regards energy and nitrogenous substances

Energy needs can be expressed in milk fodder units (UFL*) whilst needs in proteinsare expressed in digestible nitrogenous substances (MAD***) in grams. Sustenancerequirements are expressed by means of the following formulae:

MAD = 0.6 X live weight

As far as production needs are concerned:

0.43 UFL and 60 g DNSare required per litre of milk

The table below summarises the daily requirements of a milk cow for both sustenanceand production.

Table No. 1: Daily of dry matter (DM), UFL and MAD requirements


20/85

L of milk with 4% DM** Cow of 500 kg Cow of 600 kg Kg DM UFL g MAD Kg DM UFL g MAD

8 11-12 7.8 780 13-14 8.4 84016 13-14 11.3 1,620 15-16 11.9 1,32024 15-16 14.7 1,740 17-18 15.3 1,80032 18-19 18.1 2,220 20-21 18.8 2,280

* UFL (Unitourrag Lait) as used by INRA/FRANCE** Dry Matter *** MAD = Matis Azot Digestible as used by INRA/FRANCE

However, there are other ways of measuring energy, such as TDN (Total DigestibleNutrients) and starch equivalents.

V.3.2. Diet

The milk cows diet comprises:

a basic diet preferably in the form of fodder (greenstuff, hay) and availablebyproducts (harvest residues). This basic diet must meet sustenance, growth andgestation requirements and part of milk production requirements.

A supplementary diet comprising balanced concentrates either bought in or producedon the farm. These are agro-industrial by-products (cake made of groundnut, cotton,palm-kernel, rice bran, wheat, molasses, pulp, etc.).

In practical terms,

For cows at the start of lactation, the energy concentration of the diet must begradually increased by giving 8 to 12 kg of concentrate a day.

In the middle of lactation: the quantities of concentrates must be rectified, reducedto 4 to 5 kg a day.

For dried-up cows: the diet must cover sustenance requirements plus productionrequirements for 5 litres of milk a day for the first month.

During the second month, the diet must cover sustenance requirements plusproduction requirements for 10 litres of milk a day.

Whatever the cows output, she must have a mineral supplement with added vitaminsto correct the basic diet.

V.4. FEEDING COWS IN FIRST LACTATION


21/85

It is noticed that after calving, cows are lighter and have a smaller appetite than adultcows, even though they have growth needs; they must put on 50 to 60 kg after calvingat the age of 2 years and 20-30 kg after calving at the age of 3. To take these twophenomena into account, the diet must be increased by the equivalent of 6 kg of milk if calving takes place at 2 years of age and 3 kg of milk if calving is at the age of 3.

V.5. FEEDING BULLS FOR SERVICE

In general, bulls for service are delivered to farmers during the full growing stage. Onaverage, a young bull of 400 kg with an average daily weight gain of 500 g mustreceive:

- 30 kg of greenstuff - 4 kg of hay- 3 kg of concentrate

When the bull is in full sexual activity, the diet must be increased by 30 to 50%.

(introduction...)

The choice of species and varieties depends on several factors such as climaticconditions, the type of soil, the fodder storage system and water requirements. Thereare essentially two categories of fodder crops:

- grasses: maize, sorghum, oats, barley. Ray grass, Pannicum and Pennisetum melinis,

- legumes: lucerne, Stylosanthes and beans

The amount of fodder stored must take account of both the need to feed the animalsall year round and the fact that 60% of fodder crops are produced in less than 3months.

After the harvest, the fodder can be stored either in the form of hay or as silage.

a) Hay

Hay is a dried fodder, but its quality can be assessed:

- by sight, by its green colour and the presence of leaves,- by smell,- by touch: the hay must be flexible.

The reaping period is:

- for grasses, when they are in the ear,- for legumes, at the start of flowering.

The dried hay must retain 80-85% of dry matter. This stage is reached when sapcannot be drawn from the stems by pressing with the fingernails.


22/85

b) Ensilage

This is a fermentation process consisting in storing green fodder while it is wet. Thefodder is cut when young for good digestibility and a good DNS content. The cuttingperiod is the same for hay. The fodder is stored away from the air in silos, of whichthere are various kinds.

(introduction...)

The accommodation must provide relaxing conditions for the cow and comfortableworking conditions for the farmer.

VI.1. BASIC DESIGN

Temperature

A comfortable temperature, for imported cows especially, is between -5 and +25C;relative humidity should be between 60 and 80% and the air flow less than 1 m/sec.There should be sufficient ventilation to eliminate harmful gases.

VI.2. STALL-BARN SYSTEM

In this principle, the cow is tethered. There are two types of stall:

- the long stall, where the length is greater than that of the cow; it has been abandonednow;

- the short stall, where the length is slightly less than that of the cow. It is used for large units. There are several tethering systems (American, Dutch, etc.). In thissystem, the excrement is removed to a platform, usually automatically.

VI.3. LOOSE-HOUSING SYSTEM

This has several advantages, namely:

- It is easier to monitor cows coming on heat- Reduction in the frequency of foot and mammary diseases- Flexibility in follow-up.

In practice, there are 3 different areas:

- an area with straw for resting or sleeping: 4 to 5 m 2/cow- an exercise area: of concrete or hard-packed earth: 5 m 2/calf - a feeding area: of concrete: 2 m 2/cow

There is also a loose-housing system with compartments. Here, the sleeping area isdivided up into individual sections or compartments.

CONCLUSION


23/85

In practice, dairy farming is a delicate process. The cow and the feed are the major elements. In effect, the cow only yields what you put into her.

The best exotic dairy cow, if poorly fed, will produce a quantity of milk comparableto that from indigenous breeds. A good diet is required, adapted to the cows output.

Dairy-farming policy is synonymous with genetic improvement programme, wherethe biotechnological tools have a select place.

Finally, a close watch must be kept on the cows environment, since the slightestdisturbance acts as an inhibiting factor on milk secretion.

I.1.1. Payment by density

The density is always measured with temperature correction using an abacus;densities are expressed in g/l at 20C.

Payment by density can be done in two ways:

Reduction or increase in the quantity delivered; e.g. if the basis is 1028 a producer delivering 50 litres of milk at 1024 will only be paid 50 X 1024/1028 = 49.8 l.

Penalty or bonus on the basic price.

Price = basic price base X density of the milk.

I.1.2. Payment by composition (Fat and Protein)

Generally speaking, the price paid to producers according to the composition of themilk is the result of the application of a so-called differential calculation methodexpressed by the formula:

P = Po + X. TB + Y. ATP

in which:

P Is the price of milk paid to each producer for a litre or a kilogram;Po Is the basic price determined in accordance with the technical (fat and protein

content) and economic data relating to the administrative region, part of theregion or collection area of the establishment;

X Is the nominal value of the differential gram of fat;Y Is the nominal value of the differential gram of protein; TB

Is the difference between the average fat content of the milk delivered by theproducer and the content used to fix the Po price;

TP

Is the difference between the average protein content of the milk delivered by theproducer and the content used to fix the Po price.


24/85

Others pay for the useful dry matter by using a so-called unit method instead of thedifferential. All the useful fat has the same value, in effect, unlike the differentialsystem. The unit method, although little used in fact, is expressed as follows:

P = X.TB + Y.TP

In the case of payment by useful dry matter, the unit values (X and Y) given to the fatand protein are the same: X = Y.

Normally, for each producer, the fat and protein content used for payment of the milk is equal to the average of the rates observed in the samples of milk taken during themonth, after these rates have been weighted in accordance with the quantities of milk delivered on the day of sampling (3 samplings a month).

Unlike payment by fat content, which was fairly widespread, payment for milk byprotein content is more difficult to apply in view of the analytical equipment that itrequires.

I.1.3. Payment by quality of the milk

At the end of the month, the milk delivered by the producers is placed in threecategories (A, B and C) according to the marks obtained during the month for all thechecks, which take account of the microbe level in the milk. The marks are awardedon the basis of the following scale:

- 1: milk containing over 200 000 germs/ml;

- 2: milk containing between 100 000 and 200 000 germs/ml;- 3: milk containing less than 100 000 germs/ml.

Comment: payment by quality generally also takes account of:

the cell level (average of three samples a month):

3 < 300 000 cells/ml2 300 to 450 000 cells/ml1 > 450 000 cells/ml Presence of inhibitors: no payment for the collection concerned.

a) Mixing in the collecting tanks of refrigerated milk and milk in non-refrigerated churns

On collection, for two and sometimes four milkings, milk in churns is often mixedwith refrigerated milk in tanks. This is a major cause of poor quality milk in the tanks.

Non-refrigerated milk or milk cooled only to a temperature of over 4C must becollected every day.

b) Adding milk of very poor bacteriological quality to the milk-collection tank


25/85

It has been amply demonstrated that the poor quality of milk in tanks is often a resultof small quantities of milk of very poor quality being added.

Separating good and poor quality milk on collection, by means of different tanks or tanks with two compartments, is very useful to avoid mixing the milk.

c) Length of collection rounds

When the collection tanks are properly cleaned and disinfected, virtually no microbialmultiplication is observed during transport in the case of rounds not exceeding twohours.

The generalised use of thermally insulated tanks does not seem to be indispensable,given the cost of insulating them, provided that the rounds do not exceed two hours.However, it is recommended to insulate the trailers used at times of high productionduring the hot season if they remain stationary in summer before being taken to thedairy.

I.2.2.1. Cooling

a) Purpose and bacteriological aspects of cooling

The purpose of cooling is to maintain the initial quality of the milk until it is used or processed. In no way, therefore, can it improve the quality of milk collected inmediocre conditions.

It is necessary to cool quickly to a temperature of less than 15C to prevent thedevelopment of mesophilic acidifying bacteria.

In practice, it is recommended to cool the milk to 12C less than an hour after milking. In this way, one can avoid a multiplication to more than 100 times the initialnumber of germs and remain at 10 000 germs/ml at the farm; 1 000 000 germs/ml atthe factory. Cooling must start right after milking; it is even more effective if the milk has few germs. The length of time between collection and utilisation of the milk mustbe taken into consideration; the longer this is, the more energetic the cooling must be.

b) Technical aspects

There are numerous types of equipment on the market, so it is easy to find onesuitable for the particular operating conditions concerned. The choice usually dependson economic conditions: price, water availability, electrical installation, payment of milk by quality, etc.

Cooling in running water is generally the only method on small farms. For this to beeffective, fresh water (temperature around 10-15C) must be available in sufficientquantities, something that is difficult to come across in most countries in the ACParea.


26/85

Artificial cooling is used in various types of equipment:- cooling in the churn: Immersion tank cooled directly by a cooling hose;

Spraying of chilled water by means of a spray unit placed between the churns, witha collar attached to each churn, or a sprinkler. The water can come from an adjoiningrefrigerator; after use, it is collected by a pump and returned to the coolant;

Formation of milk ice: part of the milk is frozen in blocks of 5 kg between twomilkings; one block is added to 15 litres of warm milk;

Cold store (cooling is very slow);

Immersible cooler.

- cooling in bulk: Running water cooler;

Chilled tank.

The advantage of artificial refrigeration is that it safely allows just one collection aday to be made or, in very favourable conditions, even a collection every other day.Reducing the frequency of an expensive operation is to the advantage of the dairyand, ultimately, the producer too. Usually it is at the prompting of the milk factorythat the practice of cooling milk becomes more widespread.

The chilled tank is the most commonly used equipment in the bulk milk collectionsystem. The more sophisticated models consist of a stainless steel tank with doublewalls between which the coolant flows. These tanks range from 200 to severalthousand litres.

Milk stored in a tank must be of very good bacteriological quality when it is obtained;cooling must quickly bring the temperature of the milk down to less than 4C; thetank and its accessories must be thoroughly cleaned and disinfected. The proliferationof psychrophilic germs is to be feared, generating bad smells during prolongedstorage, if these rules are not observed.

Case of collective coolers: in regions where individual production is low, where theproducer cannot equip himself with a cooling system, it may be advantageous to setup a centre to gather milk together in an inhabited area (milk brought in); the centrecan also be supplied by a double collection in a small zone.

I.2.2.2. Collection

a) General conditions

It is preferable for transport to be carried out on the responsibility of the processor.The independent transport operator does not have the same interest in the quality of


27/85

the goods; for him, it is the quantity that counts above all. The collection equipmentmust be appropriate for this purpose and the personnel aware of the care requiredwhen handling and transporting milk. They must be able to recognise defectivesupplies by their appearance and smell and have the authority to refuse milk of poor quality.

Collection must be regarded as a race against time, especially with the conventionalmethod. The organisation of rounds is a delicate business. The duration of thetransport process must be as short as possible. But it is essential to take account of certain practical necessities: not all the milk collection rounds can reach the factoryunloading bay at the same time; they must follow each other according to thecollection diagram.

Milk must never leave the coolest building on the farm until it is taken over by thetransport operator. Leaving milk at the roadside is a practice that should be banned.

b) Collection in churns

This is a classic method, with churns generally containing between 20 and 40 litres.They are made of either aluminium or plastic (lighter); the aluminium churn is themost widespread but its main drawback is corrosion by acidic or chlorinateddetergents.

Collection in churns has the advantage of allowing the individualisation of suppliesuntil reception. For the producer it is a favourable factor. Inspection and weighing of the milk are carried out at the factory, which facilitates sampling for payment byquality. The milk can be sorted. It is worth keeping evening milk and morning milk separate.

It is preferable for the factory to have its own churns and to carry out the cleaning in amachine, which successively rinses, washes in a very hot detergent solution (75C)and sterilises with steam.

Returning by-products to the farm in milk churns is a dangerous practice.

Transport in churns has several serious disadvantages:

- heavy weight of the containers;

- upkeep of a host of containers requiring a repair shop and a large and expensivewashing machine.

- practical impossibility of refrigerated transport. During a round of 3 to 6 hours, milk that has been well cooled by the producer and other milk quickly end up at the sametemperature.

c) Collection in tanks:

The most rational collection method is that using a cooled tank at the farm and acooled or refrigerated tank on the collection lorry.


28/85

Lorries carry up to 18 000 litres of milk. This method requires a certain uniformity of milk supplies, because it makes sorting difficult. It is only profitable with fairly highproduction on each farm.

I.3.1. Information for farmers

There are several aspects to be developed by the company as regards information for milk producers:

Results of inspections for payment of the milk

Information on the quality of the milk collected

Information on milk purchasing policy, company results cooperative system

Information on and training in improving milk production

Introducing a quality challenge for producers and a quality assurance system for milk production

Information and services on various retrocessions.

I.3.2. Farm liaison agent

Employed by the company, this agent has the task of monitoring milk producers andproviding them with assistance and information so as to improve the quality of themilk delivered and to maintain relations between the company and milk producers;

The position of farm liaison agent is very varied and calls for good diplomatic,technical and legal qualities, whilst gaining the respect of the partners in thesector, producers and other internal factory departments.

II.1.1. Raw milk

In Africa, milk is often sold directly to the consumer without any form of treatment.Untreated milk does not undergo any standardisation or heat treatment and must not

contain any chemical preservative. Most of the time, it is produced directly at the farmor after filtration. It is packaged and brought down to 4C; Use-by date = 2 days.

II.1.2. Pasteurised milk

Pasteurisation is a heat treatment that is capable of destroying the agent that transmitstuberculosis (Koch bacillus). It is done by means of equipment with plates or tubes.

In practice, the treatment is carried out at a temperature much higher than thatrequired to destroy the Koch bacillus: 75C - 85C for a time of between 15 and 30seconds. It can be checked that this degree of heat treatment has been attained bylooking for an enzyme: phosphatase (destroyed at that temperature).


29/85

The storage life between packaging and consumption is seven days maximum at+4C.

Manufacturing process (see plate 1).

II.1.3. Sterilised milk

This is a processed milk - sterilised after packaging in a hermetically sealed container,made impervious to liquids and microorganisms by heat, which destroys enzymes andpathogenic microorganisms. Sterilisation is carried out at a temperature of 120C for about twenty minutes. More and more, milk undergoes bulk pre-sterilisation (142Cfor 2 seconds) to reduce the sterilisation treatment (117C for 5 minutes) and thusavoid browning. Containers used: glass or polyethylene bottle, aluminium lined bag,metal can.


II.1.4. UHT milk

This is a heat-treated milk, to destroy enzymes and pathogenic microorganisms. Themilk is then packaged aseptically in a sterile, hermetically sealed container impervious to liquids and microorganisms (tetra brik type container or multilayer plastic bag).

The heat treatment can be either direct (steam injection) or indirect. It is carried out at135C - 150C for about 2 to 5 seconds.



30/85

Plate 1: manufacture and inspection of different milks

II.2.1. Fermented milks

Fermented milks are certainly the most widespread milk products in the world; oneonly has to mention the many different names that they are given in each region: Skyrin Iceland, Naja or Naya and Mladost in Bulgaria, Miciurata in Yugoslavia, Zivdaor Zivdah in Israel. In Turkey, they have Eyran, a sort of diluted yoghurt. In the


31/85

Middle East, they eat Zabady and Leben (or Labban), which is obtained by churningacidified milk. There are also alcoholic fermented acidified milks (Koumiss andKefir) in Russia. In Eastern Europe, there is Karmdinska in Poland and Biokys inCzechoslovakia. In the United States, as well as yoghurt, there is another type of fermented milk that is very popular. Cultured Buttermilk which, unlike its name

suggests, is not produced from buttermilk but from skimmed milk.

In Asia we find Iranian Dough and Indian Dahi (or Dadhi).

In Africa they have fermented or curdled milk going under different traditional or commercial names such as Lacto in Zimbabwe, Mala in Kenya or Leito Dormido inCape Verde. It is appreciated above all for its digestive qualities, its price and the factthat it keeps better than pasteurised milk.

II.2.2.1. Definition (by the international club of yoghurt manufacturers)

Yoghurt or yogurt is a fermented milk obtained by multiplication in the milk of twoassociated specific lactic bacteria: Streptococcus thermophilus and Lactobacillusbulgaricus. These lactic bacteria are cultivated on previously pasteurised milk, inorder to eliminate most if not all of the pre-existing microbial flora. After fermentation, the yoghurt is cooled to a temperature of between 1C and 10C, to theexclusion of any other heat treatment. It is then ready to be consumed.

II.2.2.2. Technology

There are two types of yoghurt:

Traditional or set or incubated yoghurts which ferment in pots, (often plain andflavoured yoghurts).

Stirred yoghurts plus liquids, which ferment in a vat before being packed incontainers, (plain yoghurt with fruit). There are several stages in the manufacture of yoghurt:

a) Preparation and treatment of the milk

To increase the dry extract of the milk, one can either add milk powder (2% to 3%) or concentrate the milk to reach a final skimmed dry extract of about 12%.

The enriched milk is then pasteurised at 90-95C (held for 3 to 5 minutes) or sterilised(a few seconds at 135-140C); during the pasteurisation process, the milk ishomogenised (250 atmospheres at 85-90C) in order to stabilise the fat. For low-fatyoghurts, the milk can also be homogenised two or three times, which improves itsconsistency (effect on the casein).

b) Development of fermentation

This stage consists of the sowing and incubation phase.


32/85

Sowing is the inoculation of Lactobacillus bulgaricus and Streptococcus thermophilusin a Strepto/Lacto ratio of 1.2 to 2/1 (for plain yoghurt) or even up to 10/1 for yoghurts with fruit. The minimum sowing required varies according to the vitality of the cultures, from 0.5% to 1%, up to a maximum of 5-7%. It is essential not to exceedthese values because otherwise the amount of lactic acid and curdled milk may be too

great (risk of grainy texture) and acidification may be too quick.

It is after sowing that the particular technologies differ for sweated yoghurts andstirred yoghurts. In the case of traditional yoghurts, the mixture of milk/bacteria isdrawn off and packed in pots (it is when the mixture is drawn off that the fruit andsugar is added in the case of flavoured yoghurts) which are sweated (in hot air) wherethe acidity develops. In the case of stirred yoghurts, the cultured milk is acidified invats.

The incubation phase corresponds to the development of acidity in the yoghurt; itdepends on two factors: temperature and duration; a temperature is chosen close to theoptimum temperature for the development of Streptococcus thermophilus, i.e. 42-45C rather than a temperature close to the optimum for Lactobacillus bulgaricus (47-50C), because it is preferable for the Streptococci to trigger off the lacticfermentation.

c) Stopping fermentation

When the acidity reaches a certain level (70-80D in the case of sweated yoghurts,100-120D in the case of stirred yoghurts), it is necessary to stop acidification byinhibiting the development of lactic bacteria by cooling. This cooling phase is carriedout in ventilated cold rooms or cooling tunnels before being stored in a cold store at+2/+4C for sweated yoghurts, whilst stirred yoghurts are cooled by passing over exchangers-coolers with plates, tubes or even a grooved surface.

d) Packing:

This is the final manufacturing stage. The yoghurts are generally packed in plasticpots with a heat-sealed aluminium closure. For small production speeds (less than5000 pots an hour), the packing machines use pre-formed pots (PS or PP) whilst for high-speed production the machines are of the form, fill and seal type using PVCtype film.

e) Stirring of stirred yoghurts

This stirring is what makes the product unctuous; it is carried out by the lamellationtechnique (passing gel through a filter or sieve), by mechanical agitation (screw or turbine agitator), or by homogenisation at low pressure (less than 50 bars) for drinkingyoghurt because the product is more liquid with this technique.


33/85

Plate 2: Yoghurt manufacture

II.3.1. Fresh cheeses

In all countries of the world, fresh cheese accounts for a significant proportion of cheese uses of milk. These cheeses:


34/85

Moulded fresh cheese, where the curd keeps its individuality in the block or grainstate (cheese basket or country type);

Fresh cheese with a homogenous structure:

- with a low dry extract content and an oily texture, like beaten or smoothed freshcheese,

- with a higher dry extract content and a spreadable texture like petits suisses

It is possible to include in this classification various products manufactured in other regions of the world:

Quark or Tworog in Western and Eastern Europe,

Mascarpone and Ricotta in Italy,

Bakers Cheese, Neufchatel Cheese and, above all, Cottage Cheese in the Anglo-Saxon countries,

Labneh in the Middle East (based on thermophilic ferments).

Fresh cheeses have developed substantially over the last twenty years in newcountries but also in those countries which traditionally produce them: in Germany,for example, annual per capita consumption rose from 4.4 kg in 1970 to 6.6 kg in1986; in France over the same period, consumption increased from 3.5 to 5.7 kg, andwas 8 kg in 1996, an annual increase of 3.5%.

This worldwide development can be explained by a combination of a number of favourable factors:

- high nutritional aspect as a protein concentrate;

- high hygienic quality: firstly, because of the design of the production and packaginglines and, secondly, due to the positive role played by the lactic species contained inthe cheese;

- varied and inexpensive packaging, ranging from the individual portion to the drumof several kg;

- high yield in terms of the milk used: the new techniques (thermo-quark process,ultra-filtration) produce a whey with a low protein content;

- simple process, generally continuous and requiring little labour,

- possibility of manufacture not only from natural milk but also, for countries with aninsufficient milk production, from milk powder and butter oil;

- general development of cold chains in the distribution trade;


35/85

- lends itself to ranges of products in small portions: with fruit, jam, herbs; culinarypreparations (sauces, pastries); processed cheese; use of individual portions rapidlydeveloping;

- development and dynamism of major national and international brands.

II.3.2. Moulded and smoothed fresh cheeses

Plate 3: Fresh cheeses

II.3.3. Pressed cheeses


36/85

Pressed cheeses are quick-curdling cheeses (2 hours), where draining is accelerated bymechanical and thermal action.

a) Maturation: the milk is put into a vat, heated to 32-35C and then sown with 0.2%to 1% of lactic bacteria. The maturation period depends on the initial acidity of the

milk. Pressed cheeses can be manufactured using pasteurised milk (72C -20 s) or heat-treated milk (63C - 20 s). Maturation will then be 1 hour at 32C, sown with 1%acidifying mesophilic bacteria.

b) Rennet is added at the same temperature as maturation, at the rate of 30 ml per 100litres of milk (force 1/10 000). 20 to 100 minutes is sufficient for the curds to reachthe requisite consistency. The setting time is about 10 to 15 minutes and the hardeningtime 5 to 10 minutes. The higher the acidity and the temperature of the milk when therennet is added, the shorter the coagulation time.

c) Working in the vat: this makes it possible to separate the whey from the curds andconsists of four stages:

- Breaking up of curds: the finer the grain, the drier the cheese.

- Stirring for 5 to 10 minutes: this makes the grain size uniform. For milks that aretoo acidic, whey is removed to make the cheese softer (10% to 20% of the whey isreplaced by 5% to 15% pasteurised water).

- A slight heating by stirring, to make the grain firmer if it is too soft. (34-35C for uncooked cheeses, 39C for semi-cooked cheeses and more for cooked cheeses).

- Pressing in whey to facilitate the binding of the grains.

d) Moulding: to make moulding easier, as much whey as possible is removed. Thecurds are placed in moulds with a cloth and covered with a lid.

e) Pressing: this takes place in the manufacturing room, and three parameters must bemet to make this stage successful: the ambient temperature at 18-20C, the weightput on the cheese and the duration of pressing (from 4 to 12 hours); the longer thepressing, the drier the cheese will be. After 15-20 minutes, the cheeses are turned over to give them a regular shape. When pressing has been completed, draining continues

in the mould for 12 hours. When the pH is between 5 and 5.5, the cheeses can then beremoved from the moulds.

f) Salting: this can be done either by adding salt directly (1% to 2%) or by soaking for 6 to 24 hours in brine. The brine is prepared from boiled water saturated with salt andpossibly acidified by adding boiled whey. During soaking, the brine is kept at atemperature of 12 to 15C and an acidity of 35 to 40 Dornic. The salting can becompleted by spraying with mould to encourage the develop of the rind.

g) Drying and ripening: drying is usually carried out in the ripening room, at atemperature of 12-14C and a hygrometry of 98%.


37/85

Plate 4: Pressed cheese technology

II.4.1.1. The different creams


38/85

Light cream: minimum milkfat content of 12% to be mentioned on the packaging,pasteurised or sterilised, ideal for tea or coffee.

Normal cream: minimum milkfat content of 30%, used in cooking or pastries.Untreated or pasteurised, cream is sown with lactic or aromatic bacteria whichproduce diacetyl and viscosity; acidity is 80-100 D in the non-fatty stage. Theaddition of sucrose (


39/85

The different treatments consist, in order, of:

a) Standardisation

This preliminary operation consists in fixing the fat content of the cream at between

35% and 40% for traditional manufacture and 40% to 45% for continuousmanufacture.

b) Deacidification

This is necessary when one wants to pasteurise left-over creams whose acidity couldpose problems in the heating equipment. Two techniques allow the acidity level of thenon-fat matter to be reduced by 15 to 20 Dornic: washing the cream or addingneutraliser.

c) Pasteurisation

In the case of creams of good quality, the temperatures applied are between 90C et95C for 15 to 20 seconds. In the opposite case, it may be necessary to reach 105C to110C in order to inactivate the microbial lipases.

d) Degassing

Very widely used in industry, this operation takes place in two stages:

First degassing: this is carried out before pasteurisation at 70-75C, in a depression

of 70 cm of mercury in order to remove dissolved gases from the cream and thusreduce the risk of clogging up the heating equipment.

Second degassing: carried out after the cooler section of the pasteuriser at atemperature of 90-95C and in a depression of 40 cm of mercury in order to limit anytaste of cooking from the cream after it has been heated to a high temperature. Thecream is then cooled to the maturation temperature.

e) Physical maturation

After pasteurisation, the fat globules are in liquid form and physical maturation will

lead to it becoming partially solidified by causing directional crystallisation of thetriglycerides. The objectives, therefore, are:

- to give the butter the proper consistency in view of the variability of the compositionof the butterfat,

- to ensure appropriate yields by limiting losses in the buttermilk,

- to optimise the butter-making machinery utilisation rate,

- to lower the basic moisture content of the butter to allow re-injections.


40/85

The solid fat/liquid fat ratio allows better control over the maturation of creams, asshown in the table below:

LIQUIDFAT

SOLID FAT

Soft butter 85% 15% (crystals with a high melting point)Hard butter 55% 45% (crystals with a high and a low

melting point)Butter with good spreadingproperties

65% to 78% 22% to 35 %

f) Biological maturation

Conventional system: forced biological maturation (3% to 6% lactic acid bacteria)

allowing pH levels of 4.7 to 4.8 to be attained. The drawback to this technique is thatthe product does not keep as well, with a greater risk of oxidation and thedevelopment of a metallic taste. Lowering the pH, on the other hand, makes itpossible to reduce fat losses in the buttermilk.

Improved system: moderate sowing with lactic ferments after crystallisation,completed by re-injections during mixing using lactic acid bacteria enriched with dryextract or lactic acid bacteria concentrate, so as to:

- adjust the dry non-fat matter to meet the legal standards (economic interest),

- lower the pH so that the product keeps longer,

- develop the flavour of the butter (lactic ferments rich in diacetyl).

The most commonly used strains are Lactococcus lactis and Lactococcus cremoris,Leuconostoc lactis and Streptococcus diacetilactis.

II.4.2.2. Butter-making in a churn (discontinuous technique)

The traditional churning technique may seem a little outdated compared to theperformances achieved from the new generations of butter-making machines, yet itdoes have the great advantage of being able to be adapted for small capacities (20 to2000 litres of cream). This traditional technology is shown in figure 2 below:


41/85

Figure 2: traditional churning


42/85

Plate 5: Comparison of butter-making technologies (conventional method and NIZO method)

II.5.1.1. Preparation of the mix

Sugar syrup is mixed in with the other raw materials - milk and cream, to which isadded a very small amount of stabiliser in vats with a fast agitator and a heating jacket(the mix dissolves better at 50-60C). Before pasteurisation, the acidity may becorrected to avoid any sticking, which would be even more harmful if the product wasviscous and flowed poorly through the pipes. Usually, the acidity is neutralised byadding sodium bicarbonate.

II.5.1.2. Pasteurisation


43/85

Low pasteurisation (63-66C for 25/30 minutes in vats) or high pasteurisation, (85-90C for a few seconds)

II.5.1.3. Homogenisation

The pasteurised mixture is then homogenised to 150/200 kg/cm 2 at 65-70C, whichcauses the fat globules to burst and disperse in the mass. This operation is essential tomake the ice cream homogenous and to give it a good taste and better unctuosity (topromote a subsequent operation: swelling).

II.5.1.4. Cooling of the mix

The mixture is brought down to + 4C through heat exchangers with tubes or plates or through spray coolers.

II.5.1.5. MaturingThis corresponds to storing the mix. It is done in sanitary tanks with a slow agitator at0C to 4C for 4 to 6 hours (24 hours maximum). There is an increase in viscosity dueto the fact that ice forms in the liquid phase and the protids are hydrated. Thestabilisers are completely hydrated, swelling and maintaining the structure of the icecream.

It is at this stage that the flavours are added.

II.5.1.6. Chilling or pre-freezing

This process has two essential functions: to solidify the mix and to bring in air toobtain the requisite swelling and texture.

Chilling is done in a freezer, which the mix moves through. It goes in at a temperatureof 0-4C and the ice cream comes out at a temperature of -2C to -7C (adjustedaccording to shaping requirements).

Chilling is a complex operation which ensures simultaneously and continuously:

- quick cooling of the mix,- crystallisation of 30% to 70% of the water,- homogeneous distribution of fine crystals,- emulsion of air in the product (until the finished product is twice the volume).

II.5.2. Shaping

The ice cream, still malleable when it comes out of the freezer, is given its final shapebefore freezing in two different ways:

moulding: the product is poured into metal or plastic moulds, reusable or

disposable, and then extracted when it is frozen.


44/85

direct filling of retail packages: this is what happens in the vast majority of cases(pots, cones, etc.).

II.5.3. Freezing or hardening

There are three possible methods:

Immersion: water-tight moulds. Brine at -40C, which is stirred vigorously to ensurethat the exchange gradient between the medium and the mould is kept constant.

Contact: this consists in squeezing the products between two hollow plates, insidewhich there is a partial ammonia vacuum at -40C.

Tunnel hardening: an insulated chamber through which a air is passed at -40C atspeeds varying from 3 to 8 m/s. A conveyor moves the freezing products from the

entrance to the exit of the tunnel, 45 minutes to 4 or 5 hours depending on the volume(small pots). The quicker the operation, the quicker the temperature falls and thequicker the formation and the smaller the size of the ice crystals.

II.5.4. Ice cream lollies and choc-ices

Fully integrated lines are used, where shaping, freezing, removal from the mould andany subsequent treatment are all carried out at the same time.

The cream leaves the freezer at -2C to -4C and is distributed in metal moulds by ametering injector. The filled moulds move through a brine bath where freezing takesplace. When the consistency is right, wooden or plastic sticks are insertedautomatically by a synchronised mechanism. The pass through the brine lasts between3 and 8 minutes.

The moulds leaving the brine are then sprayed with hot water to ensure that the articlecomes out cleanly. Arms with grabs then extract the frozen products and dip them intothe chocolate covering if required. The finished products are then conveyed to abagging or wrapping machine.


45/85

Plate 6: Ice cream technology

II.6.1. Fermenting agents

Fermenting agents are used in the dairy industry to perform the following functions:


46/85

- lowering the pH (coagulation, draining),

- producing the taste (known aromatic: diacetyl),

- changing the texture and opening up the structure of cheeses (proteolysis and

production of gas),

- formation of rind (maturing flora).

There are four main groups of fermenting agents (see table 2).

Table 2: The different microorganisms used in the dairy industry

Type Usual name Taxonomic name Moulds: - Penicillium candidum - Penicillium caseicolum

- Penicillium album - Penicillium camenberti- Geotrichum candidum - Geotrichum candidum- Fusarium solani - Fusarium solani

Yeasts: - Kluyveromyces lactis - Kluyveromyces lactis- Debaryomyceshansenii

- Debaryomyces hansenii

Flavouring and maturingferments:

- Micrococci - Micrococcus varians

- Red ferment - Brevibacterium linens- Surface ferment - Arthrobacter globiformis

Lactic acid bacteria: Mesophiles - Streptococcus lactis - Lactococcus lactis ssp lactis- Streptococcuscremoris

- Lactococcus lactis ssp cremoris

- Streptococcusdiacetylactis

- Lactococcus lactis ssp lactis var diacetylactis

- Leuconostoc cremoris - Leuconostoc mesenteroides sspcremoris

Thermophiles: - Bifidobacteriumlongum

- Bifidobacterium longum

- Lactobacillusacidophilus

- Lactobacillus acidophilus

- Streptococcusthermophilus

- Streptococcus salivarius sspthermophilus

- Lactobacillushelveticus

- Lactobacillus helveticus

- Lactobacillus - Lactobacillus delbrueckii ssp


47/85

bulgaricus bulgaricus- Lactobacillus lactis - Lactobacillus delbrueckii ssp

lactis- Lactobacillus

delbrueckii

- Lactobacillus delbrueckii ssp

delbrueckii.


48/85

Plate 6 Ice cream technology

II.6.2.1. Definition

a) Rennets:

These are extracts from the abomasum of young bovids fed on milk and having anactive chymosin mass/active bovine pepsin mass ratio of 1.38.

b) Bovine pepsin:

This is the liquid extract from the rennet stomach of adult bovines, having an activechymosin mass/active bovine pepsin mass ratio of 0.154.

c) Mixture of rennet and bovine pepsin: 2/2 mixture of extracts of rennet and bovine pepsin = liquid extract with an activechymosin mass/active bovine pepsin mass ratio of 0.33.

3/1 mixture = liquid extract obtained by mixing rennet extract with bovine pepsinextract having an active chymosin mass/active bovine pepsin mass ratio of 0.66.

d) Mixture of rennet and pig pepsin:

This coagulant is no longer used in cheese-making.

e) Acid proteases of fungal origin for cheese-making:

Coagulating enzymes extracted from Endothia parasitica, Mucor pusillus and Mucor Miehei can be produced and used in cheese-making, without any limits in time.

II.6.2.2. Strength of coagulating enzymes

Usually, the strength given is 1/10 000th, i.e. 520 mg of active enzymes per litre of coagulant. This means that one litre of coagulant curdles 10 000 litres of milk at 35Cin 40 minutes. Strengths of 1/75 000th and 1/150 000th (powdered rennet) are alsofound.

II.6.2.3. Practical conditions for adding rennet to milk

a) Lactic coagulation products (fresh cheese type)

Rennet is used more for the draining properties that it offers than for its coagulatingaction properly speaking. Low doses of rennet are therefore used (1.5 to 5 ml of rennet to 1/10 000 for 100 litres of milk) at a fairly low temperature (15-20C).

b) Rennet coagulation products (Cantal, Gruy, Emmental type)


49/85

Large quantities of rennet are added to non-acidic milk (15 to 30 ml for 100 litres of milk) at a higher temperature (30 to 35C). Curds form after 30 to 60 minutes. Thesecurds must have highly pronounced rennet characteristics: flexible, elastic andcompact. This allows them to withstand mechanical draining and thermal draining (asin the case of Gruy).

c) Mixed coagulation products (Camembert, Carre IEst type)

A fairly large quantity of rennet is always used (15 to 25 ml for 100 litres of milk,strength 1/10 000th). Acidification is earlier than with the previous products, becausethe temperature applied allows optimum development of the mesophilic lactic acidbacteria (28C to 32C).

II.6.3. Sodium chloride: properties and utilisation in cheese-making

a) Salting of cheeses

Various methods are used to salt cheese:

dry salting, by hand, using a sieve or a machine allowing the desired amount of saltto be fixed on the wet surface of the cheese,

salting in brine, usually saturated. In this case, the difference in concentrationbetween the aqueous phase of the cheese and the brine causes diffusion of the salt intothe cheese and inverse migration of the aqueous phase into the brine. This is the mostcommonly used system in industry,

salting in the curds before moulding for certain cheeses, such as Cantal or Cheddar,

dissolving salt in the milk, a method used for some types craft cheeses produced inthe Middle East. Use of this technique is still limited by difficulties in the coagulationof salted milk.

b) Brining

Cheese-making brine consists of water and sodium chloride. However, as it is used itgradually becomes richer in various substances brought in by the cheese (fragments of casein, soluble proteins, lactose, lactic aci

Documents

tai lieu ve khu trung sua