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THE
P R O D U C TI O N O F C L E A N ML K
F I G . 63 . A n inexpensive barn, but one in which c lean
milk is produced by means of careful attention to methods .
R eprinted, with adap tations, from THE P R O D U C T I O N O F
C L E A N MI L K ,
”by T. I . Mclnerney , in
"C ornell ‘
R eaa’ing
C ourses .
”
J . 0 . K I N G , L td . ,
P rinters and Stat ioners,42-60, Goswell R oad ,
L ondon, E C . 1 .
THE P R O D U C T I O N O F C L E A N
MI L KT . J . Mc I N E BN E Y
We present herewith, as a basis for the di scussion o f
this top i c , the score card used in enforcing the MilkOrdinance , passed in N ew York on January l st , 19 15 .
F I G . 64 . I nterior of barn shown in F ig . 6 3 .
This score card (pages 5 to 7 ) attempts to enumeratethe po ints that a good dairy shoul d possess , and givesthese po ints a num erical value . This card may becopied and used in scor ing the reader
’s da iry. P robably
3
the dairy score card is most valuable in an educationalway . I t i s educational to the farmer or dairymanbecause i t points out certain defects and shows whereinhe can improve it i s educational to th
'é'consumer
because he can see which dair ies are best from a sanitarystandpoint . The score card is divided into two parts ,equipment and methods . The equi pment is g iven a
value of 40 per cent . and the methods 60 per cent . The
reason for this difference is that a man may have a poorda iry barn , that is , a poor equipment as to b uild ings andthe like , b ut i f he is neat and clean in his methods he
N ot brushed , bacteria.
Brushed, bacteria.
Increase , bacteria.
F I G . 65 . A diagram show ing the increas e inthe bacteria content of milk caused . by briishing
the coios immediately b efore milking .
can produce a god'
dg’
rade of milk and'
receiv e credi t . for
his clean methods on the score card.-
‘
I n Figs . 63 and 64
are shown the ext erior and the inter i or of an inexpensiveb arn . By careful attention to methods , milk was
produced in this b arn that had an average for one yearof 5 133 b acter ia per cub i c centimetre in
‘
morning’s milk
and b acteria per cub ic centim etre in night’s mi lk .
Because aman may have an excellent or a very expen
sive dairy farm , i t does not foll ow that a good grade o i
milk is produced . If the methods are unclean , the milkwill be of an inferior quali ty , and the score w ill b ereduced under methods .
SC O R E C A R D U SE D I N E N F O R C I N G THE MI L K
ORDIN A N C E .
Indorsed by the O fficial Dairy Instructors’
A ssociation.
O wner or lessee of farm
P . 0 . A ddress
Total number of c ows Number milking
Gallons of milk produced daily
Product is sold by producer to famili es, hotels, restaurants, stores,
or to dealer
F or milk supply of
Permit N o . Date of inspec tion
(S igned)
SC O R E
E quipment .
Cows.
Health apparent ly in good health , 1 ; if tested withtuberculin wi thin a y ear and no tubercul osis is
found, or if t ested within six months and all re
act ing animals removed , 5 . ( If test ed within a
y ear and react ing animals arefound and removed ,Food
,clean and wholesome .
Water,clean and fresh
SrT LA B E S.
L ocat ion of stable—Well drained 1 ; free from con
taminating surroundings, 1C onstruct ion of stable—Tight , sound floor and propergutter, 2 ; smooth
,t ight walls and ceiling , 1
proper stall , tie, and manger ,1
Provision for light : 4 sq . ft . of glass per cow
( 3 sq . ft . , 3 ; 2 sq . ft .,2 ; 1 sq . ft .
,1 . Deduct
for uneven distribution) .
BeddingVent ilation—Provision for fresh air
,c ontrollable flue
system,3 . (Windows hinged at bott om,
s'
ding windows, 1 ; other openings, Cubicfeet of Space per cow
,500 ft . ,
3 . ( L ess than 500 ft . ,
2 ; less than 400 ft . ,1 ; less than 300 ft . ,
P rovision for controlling t emperature, 1
U TENSILS.
C onstruction and c ondition of utensilsWater for cleaning ( clean,
convenient and abundant )Small -top milk pailMilk coolerClean milking suits
MI L K -R O OM O R MILK -HOU SE .
L ocat ion free from c ontaminat ing surroundingsConstruct ion of milk -room—F loor , walls and ceiling ,
1 ; light , vent il at ion, screens 1
Separate rooms for washing utensils and handling
Facilities for steam (hot water,
Total
S core .
l?erfect . A ll owed
Methods.
A ll owed.
C ows.
C lean (free from visible dirt , 6 )STABLE
C leanliness of stable—Floor,2 ; walls , 1 ; ceiling and
ledges, 1 ; mangers and partit ions, 1 ; windows, 1Stable air at milking time—Freedom from dust
,3 ;
freedom from odours, 2
C leanl iness of beddingBarnyard- Clean
,1 ; gwell drained , 1
R emoval of manure daily ( to 50 ft . or more fromstable)
MILK -R OOM O R MILK -HOUSE .
C leanl iness of milk -room
U TENSILS A N D MILK I NGC are and cleanliness of utensils Thoroughlywashed
,2 ; sterilised in steam for 15 minut es . 3 .
(Placed over steam jet or scalded with boilingwater, Protected from c ontaminat ion,
3
C leanl iness of milking—Clean, dry hands, 3 ; udders
washed and wiped, 6 .
( U dders cleaned wi th moist cloth , 4 ; cleanedwith dry
1
cloth or brush at least 15 minutes beforemilking , 1
HAND LING THE MILK .
C leanliness of attendants in milk-roomMilk removed immediately from stable without
C ooled immediately after milking each cowCooled below 50
° F . ( 51°
to 4 ; 56°
toStored below 50
° F . (51°
t o 2 56°
toTr
gonspprtation below 50
°
F . ( 51°
to 1 .50 ; 56°
( If delivered twic e a day , allow perfect score forstorage and transportation. )
Total
E quipment Methods Final S core .
NOTE 1 .
—I f any except ionally filthy condition is found , part icul arlydirty utensils, the total score may be further limited .
NOTE 2 .
—I i thewater is exposed to dangerous c ontamination, or if thereis evidenc e of thepresenc e of a dangerous disease in animals or attendants,the score shall b e O
THE cow.
F ir st Of all in the production Of clean milk , i t isnecessary to have heal thy cows . If the cows ared iseased ,
the ir milk may contain disease -produc ing bacteria or
b e otherwise unfit for use. Spec ial attention shoul dbe given to the condition Of the udder , and any milkthat appears sl imy , ropy , watery , colour ed , or otherwiseab normal should be d iscarded . A skill ed veterinarianmay do much to determine the general health Of a cow b v
g iving her a thorough physi cal examination . C lean and
who lesome food , as well as plenty O f clean fresh water ,are essential . If the watering trough and surroundingsare kept clean , there is less chance Of the water supplyb eing contaminated .
The surface Of the cow ’s body i s one O f the mostimportant sources Of milk contamination . It i s therefore essential that extra care b e given to keep the cowclean . C ows kept on pasture usually keep cleaner thanthose kept in the b arn , b ut in e ither case thorough
grooming i s necessary to remove loose hairs , dust ,micro -organisms , and the like , so that they will not fallinto the milk pail . The process Of grooming , feedingor b edd ing the cows tends to fil l the air with dust andb acteria therefore these operations should be done longenough before milking to give the dust plenty Of timeto settle . The increase in the b acteria coun t in milkdrawn shortly after grooming and feed ing i s shown inF igs . 65 and 66 . The data used in the construction Of thesed iagrams were taken from experiments conducted at theC onnecticut (Storrs ) Agr icultural E xperiment Station .
!
“Quali ty O fMilk A ffe ct ed by C omm on Dairy P ractic es. By W. A .
S to cking, jun. C onne ct i cut ( S torrs ) A gri cul tural E xp erim entStat i on. Bull et in 42 .
A damp cloth used O n the cow’s udder and flanks
just b efore milking will remove most O f the dust and loose
Before feeding , bacteria.
A fter feeding , bacteria.
Increase , bact eria.
F I G . 66 . A diagram showing the increase in thebacteria c ontent of milk caused by feeding thecows
dry corn stover immediately beforemilk ing .
hairs that might otherwise fall into the milk pail . Thiswill reduce the b acteria count , as is shown in F ig . 67 .
THE STABLE .
High ground mping toward the south or the east i san ideal site for a b arnyard in this State , for a slope ine ither of these directions protects the animals from the
N ot wip ed , bacteria.
Wip ed, 715 bacteria.
D ecrease, bact eria.
FIG . 6 7 . A diagram show ing the decrease in thebacteriac ontent of milk caused by wiping the c ows ’
udders witha damp cloth immediately before m ilking .
prevail ing winter winds . P ig-pens , Outhouses , piles of
manur e , and the like , left stand ing in the barnyard ,
may b e sources O f contaminat ion .
9
The construction O f the s tab le may be of less importance than careful methods in the production of cleanmilk ,
but i t shoul d b e such as to l ighten the lab our necessaryfor keeping the stab le and i ts equipment clean . The
most comm on defect in dairy stables is a lack Of cleanliness . The interior Of the b arn should be so constructedthat dirt , cobweb s , and the l ik e , cannot easily collect .
The stab le floor and the gutter shoul d b e made Of somematerial , such as cement , that will not absorb moistur e ,b ut that is easy to clean and disinfect in case Of necessity .
A swing stanchion is more comfortable for a cow than a
rig id one, and shoul d b e so constructed that i t does notcollect dirt . The length Of the stall s shoul d be suchthat the cows can stand comfortab ly and the dr oppingsfall into the gutter . A suffic ient amount Of c lean b edding
shoul d be used to insur e thecomfort and the cleanl inessOf the cows .
A nother requir ement Of asani tary cow stable is good
‘
ww oow l ight , which is necessary inorder that the work may beproperly done and that the
general health Of the animalsmay be good. A good coatOf whitewash appl ied to the
F I G 6 8 ° A dwgmfm' show interi or Of the stable at least
i ng a method of l ighti ng a
bas ement stab le .
tw I C e a year I S a very ln
expensive and e ffi c i e n tmethod Of keep ing i t l ight and clean ; a bright , cleanstable is a gr eat incentive to the production Of cleanmilk . Sunl ight is one Of our gr eatest natural disin
fectants , and the stable shoul d have plenty Of windowspace so that the sunlight can enter . If l ight i s
10
lacking on the underground side Of a basement stable ,a window may be cut in the floor above according to thediagram shown in F ig. 68 .
G ood ventilation , as well as plenty Of sunl ight , i snecessary for the health of the animals . E very da irystable shoul d have some system O f ventilation to keepthe air fresh and pur e and the cows comfortab le and
unexposed to injur ious draughts . P oor ventilation usuallymeans poor sanitary conditions . One good method O f
FIG . 69 . Types of sanitary milk pails.
ventilation is the K ing system, b ut this will no t workunl ess the b uilding i s tight . Simple d irect Openingsare very effect ive , b ut they are likely to make a directdraught , especially if they are exactly opposite each other .
The cloth cur tain system has two advantages in that iti s inexpensive and the curtains can b e easily replacedwhen they b ecome dirty , b ut the main disadvantagesare that this system may collect ( lust and may no t besuitable for cold cl imates .
11
THE CONSTRUCT ION AIN’ D THE CARE OF D A mY
UTENSI'LS .
P rob ably no one thing will have a more b eneficial effecton the production Of clean milk than the use of a small
top , or a covered , milk pail ( F ig . There seems to b ea prejudi ce on the par t Of many dairymen against thistype Of pail , b ased on the ground that i t is d ifficul t to use.
P erhaps a part O f this prejudice is due to the fact that
6 00 0 C O MO /f/O N S
O p en e tc b on er /o
C o / erea eluded
f exc/uded
C ave/ed
0 bac ter ia,9 7a” cen r ex C /u d c
’ d
FIG . 70. A d iagram showing the efi'
ectof a small top or c overed m ilk pa il in cl im i
nating bacteria from m ilk . The relat ivenumber of bacteria in each case is shown
by the length of the l ines , but a differentscale is required in each of thefour cases because of the great variat ion in the number
of bacteria,as shown by thefigures .
some impracticalpails have b e e np u t 0 n t h emarket . T h e r ea r e , h o w e v e r ,many good typesOf sani tary pails
(F i g . a n d
careful i n q ui r yh a 8 shown thatnot a single dairym a n w h 0 h a s
given this typ e Ofpail a fair tr ialwould go b ack tou s i n g t h e O l dwide -mouth type .
A pail t h a t i 8about two - thirdsor three - fourthsc o v e r e d is thetype that i s in
general use.
A l l dairy utensils should b e so constructed that theycan be easily cleaned . This means that all crevices andseems Of the utensils must b e well flushed with solder
12
( F ig .
'
I f the seams and crevices are left Open , as
in d iagram A , milk will accumulate in these placesi t is practically impossib le to thoroughly wash and stei 1l ize such utensi ls . This deposi t Of partly decomposedmi lk forms an excellent b reed ing place for b acter ia,
which contaminate each fresh lo t Of milk put into theutensil . This contam inat ion may
b e so great as tovery s e r i o u s l yafiect the keep ingq u a l i t y O f themilk .
The proper procedure i n cleani n g an y d a i r y FIG . 7 1. A diagram showing thewronga t c u s l l i s a s and theright kinds of amilk pail . A shows
£ 9 110 w s = tw is ts;rms e the utensfl the samepail properly flushed with solder,i 11 111 k e w a r m so as to facilitate thorough cleaning . The
water s e c 0 n d ,
lowerfigurerep resents a j oint as ordinarily
wash a o ass;roughly Wl th a which they arenot readily dislodged . This
b rush in a strong j oint should befilled c ompletely with solder.
solution Of h O twater and washing powder , ab out a handful to a 12
O r l 4 -quart pai l Of water ; third , scald it with b o il ingwater or place i t in a steam steril izer . The reasonfor each step in the pro cedur e is as fo llows Lukewarmwater i s used for r ins ing the utensil b ecaus e milk containsab out . 7 Of l per cent . Of alb umen , which is coagulatedand prec ipitated on the utensil so that i t i s very hardto r emove if water Of a temperatur e Of 160° F . or above isused . The utensil should b e washed in a strong solution
13
Of alkal i powder and hot water because normal milkcontains about 4 per cent . Of milk -fat , and this solution willdissolve any fat tha t is on the utensil .
‘
A brush is bestto use for this work because it enters the seams and
crevices better and can be kept clean much more easilythan a cloth , which may be a breeding place for b acter iaunl ess great car e i s given to cleaning i t each time afterusing . The utensil must be ster ilized in order to b e
perfectly clean . If water is used for this purpose , i tmust have a temperature of 180
° F. or higher in orderto kill all bacteria that may be present. The utensilshoul d b e left in thi s water for at least several minutesin order to become sterile .
The value Of thorough steril iz ing of utensils is shownby the fo ll owing resul ts Of bacter iological tests Of milksamples taken from dair ies wher e the utens ils wereproperly scalded and where they were no t scalded.
A ll these samples were taken on the same days as theproducers del ivered the milk to the dealer . A
’
s utensilswere properly washed and scalded twice a day , b ut
B ’s were not s calded .
14
The equipment in B ’s case was about the same as inA
’
s , but the methods in A’s case were nearly 11 per cent.better ; methods and not equipment count most in theproduction Of clean milk .
THE I SI I L K ROOM O R THE MILK HOUSE .
The location and the construct ion O f the room or thehouse in which the milk is handled and the utensilswashed i s also a verv important factor in clean milk
production . The
milk house shoul dbe so located thatit will have gooddrainage and bef r 8 e f r 0 m a 11 Vco n t am in at i o n .
The p r i n c i p a lpurpose in building a milk housei s to provide a
p lace where them i l k a n d t h eutensils may beh a n d l e d apartfrom all 0 t h e rdairy Operat ions .
F I G .
'
72 . A galvanized iron sterilizer The milk roomThis is inexp ensive and saves lab our. ii or milk h 0 u s 6
should be so con
structed and car ed for that i t will b e thoroughly clean .
Smooth , tight walls and ceilings are des irab le for the samereason h ere as in the dairy b arn , that is , they prevent theco ll ect ion Of dirt . Milk house floors made Of cementaremore sanitary and durable than wood floors , because
16
they do not readily ab sorb moisture , are more easilycleaned , and are not injured b y water us ed in cleaningthe utensils and the floor itself.
be well suppl iedwith fresh air and
s u n l i g h t , and
spec ial care shouldb e taken to havethe air free fromodours . It is
.
a
well -known factt h a t m i l k willreadily take upodours , and , forthis reason if noother
, a clean milkhouse is necessaryif the milk is to b eproperly handled .
F l i e s and otherins ects m ay b ekept out Of them i l k hous e b y
having the doorsand the windowsproperly screened .
A good supply Off r e s h w a t e r isoneOf therequirements Of a welleq u i p p e d milkhouse .
Themilk house should
FIG. 73 . A ! stationary sterilizer com
structed of c oncrete and hollow tile .racks and doors are of wood.
The
The milk room should be provided with fac il ities forheating a l iberal supply of water for washing and ster i
17
lizing the utensils . This may be done on a stove or byturning steam into a half barr el . E ither bo iling water orsteam w ill do efii cient steril iz ing if properly used .
If a supply Of steam can be had , the steriliz ing processcan b e simpl ified by plac ing all of the utensils in a ster il izer , where they are all treated at one time with lesslabour than is necessary to thoroughly scald each p iecewi th b oil ing water . There are several forms of good ,
effic ient ster il izers on the market Of the general typeshown in F ig . 72 . A l l O f the utensils used dur ing theentir e day can be sterilized at one time in one of thesemachines . Larger forms Of stat ionary steril izers can bebuilt of concrete or hollow tile , as shown in F ig . 73 .
If a steam ster il izer is used , the utensils will be dr ied b ythe ir own heat if the steam is allowed to escape imm edi
ately after the heating per iod . The door can then beclosed , and the utensils are thus protected from con
tam inat ion until ready for use. The length Of timenecessary to ster il ize the utensils or to heat the ster ilizerand i ts contents to the temperatur e Of the steam ,
shoul d be determined. In the small iron ster ilizers , thisrequires only a few minutes , while in the large concreteor tile ster il izers , i t may requir e from twenty to thirtyminutes .
C OOLIN G MILK .
H. E . Ross AND T . J . MO I N E R N E Y.
Bacteria and their products are the cause Of nu
wholesome mi lk . These small plants are present nearlyeverywhere , and some O f the comm onest sour ces fromwhich thev enter mi lk are the dust in the air , the bodyOf the cow, the person Of the milker , and dirty utensils .
18
Like other plants , b acteria requir e certain cond tionsfor their growth , one O f the most important b e ing a
favourab le temperatur e . Most germs thr ive b est at a
temperatur e o f ab out 98 ° F or 3 6 6°
C . , and this isvery nearly the temperature O f freshly drawn milk .
Milk should b e cooled to at least 50° F . as soon as possib leafter i t i s drawn ; i t i s still b etter to coo l i t to a temperature as low as 40
° F . Wh ile i t is true that manyO f the b acteria that are commonly found in milk eitherdo not develop at all , or at least develop very slowlyat 50
°F . , still there are some forms that grow with
comparat ive rap id ity at this temperature . F or thisreason the colder the milk is kept , the better it will b e,
provided it is no t frozen .
T A BLE l .—C O .\I P A R I SO N or BACTER IA C OUNT o r
SA MI P L E S O F MILK HELD AT D IFFERENTT E N EP E R A T U R E S F O R O N E HOUR .
Increase inNumber Bacteria Bacteria Bacteria bacteria per
Sample . of p ounds per c . c . in per in per in of milkoriginal milk held milk held held at 90° F .
used . at 50° F . at 90
° F . over milkheld at 50° F .
19
A comparison O f the bacteria count Of var ious samplesO f milk is given in Tab le 1. E ach sample was d ividedinto two parts , and one part washeld at a temperatur eOf 50° F. for one hour , the other at 90° F . for the sametime . In each case the samples were thoroughly mixedby pour ing the milk several times from one can toanother . b efore they were held at the ir respectivetemperatur es for the per iod stated . The table indicatesthat there was a large increase Of b acter ia, due to
keeping milk at the higher temperature ,
and also thatthose samples Of milk that had a high ini tial b acteriacorm t had a correspondingly high coun t at the end Ofan hour . This point is Of great practical importance .
and shows the necessity Of producing clean milk eventhough i t i s to be kept cold or i s to be pasteur ised. Ifcond itions favourab le to the growth of bacteria arise , alarge initial count means that the bacter ia have a
proportionately better chance to mul tiply.
It is interesting to note that in four of the ten testshere recorded , the bacter ia coun t Of the milk , after i thad b een held for one hour at 50
°F . , was less than the
initial bacter ia count . This is prob ab ly due to the factthat the low temperatur e was unfavourab le to theparti cular spec ies Of germs that happened to bepresent .
20
TA BLE 2.—E E F E C T O F HIGH TEMP ER ATU R E O N MI L K
HAVING A SMALL INIT IAL BACTERIA C OUNT .
Number of b ac l Increase of b acTem t eria per teria per c . c .
Number peraturei of F . ) at
Sample . pounds whi ch A t b e A t end
mil k milk was ginnin of 2used . held for of the hours i N umber
‘
P er
2 hours. 2-hours period . c entage .
period .
The importance of cool ing milk and of keeping i tcold is st ill further emphasised in Tab le 2, which setsforth the resul ts O f keep ing at a high temperatur e milkthat had a low initial b acter ia count . In each case themilk was held at a high temperatur e for a period O f twohours , and i t will be noted that in every case there wasa large increase in germ content .
The place where the milk is cooled must be cleanand free from dust. Bacter ia ar e carried on dust p art icles , whi ch float ab out in the air therefore the handlingof hay or grain at the time and the p lace that milk isb e ing coo led is a b ad practice because the dust fromb oth of these feeds is loaded with germs . Furthermore ,milk takes up odours very readi ly, and for this reasonshould be coo led in a place free from odour s of any
kind . Straining and coo ling milk d irectly behind the
21
cows is a parti cularly b ad practice . The odour s fromstab le manure , and oftentimes from silage , are thustransmitted to milk .
If milk is cooled slowly , many germs may developdur ing the process , although a low temperature may bereached ul timately . If germs should develop thus , and
if conditions shoul d again become favourab le for thegrowt h of b acter ia, the mi lk would soon spo il .
FIG . 74 .—A c ement tank for c o oling milk.
Thewalls ext ending above the level of the floor prevent dirt fromwashing int o the tank .
22
The fat i s not evenly distr ibuted in frozen milk ,there
fore it is no t so good as normal milk .
TA NK S .
On farms , milk is most often cooled b y setting thecans containing i t in a tank of water . The most conv enient and in the long run the cheapest kind of tankfor this purpose is mad e of cement and sunk in the floorso that onl y ab out twelve inches of the s ides extendab ove it . This arrangement obviates l ifting the cansto any great height , and prevents dirt from washinginto the tank . The top of the walls of the tank shouldbe faced with strap iron to prevent the cans crackingthe cement as they are l ifted in and out . Some out-let
should be provided in the bottom of the tank so that i tcan b e easily and thoroughly cleaned as Often as may b e
necessary . It is alm ost impossible to prevent milk fromsp ill ing into a cool ing tank of this sort , and unl ess thi si s cleaned out the tank soon b ecomes unfit for use
from a sanitary standpo int . Outlets should b e madeat the top O f the tank in order to carry off surplus waterand to pr event the cans from b e ing flooded .
A nother type of coo l ing tank is made of galvani zediron faced with iron at the top and the b ottom. Such a
tank is not so serviceable as one made of cement , buti t i s more durab le than a wooden one and i s easier tokeep clean ( F ig . A galvanized iron tank
'
large enoughfor cool ing four or fiv e cans of milk mav bebought forfrom eight to ten dollars .
In size the tank should b e large enough to hold therequired numb er of cans and to allow ab out three inchesb etween each can and ab out four inches between thecan s and the walls of the tank . The larger the tank ,
24
the gr eater is the amount o f ice needed to cool thewater around the cans ; therefore the tank shoul d be
FIG . 76 .-Metal tank for cooling milk.
no larger than necessary . It must , of course , be deepenough to allow the water to r ise around the necks ofthe cans .
R efrigerating Materia l .
The refr igerating mater ial most comm only us ed incool ing milk in tanks is cold water o r i ce water . It isgenerally necessary to use ice , since few well s or spr ingsfurnish water sufficiently cold to cool milk to the propertemperatur es . The amount Of i ce necessary can bestb e determined b y exper iments b ecause it varies withthe amount of milk to b e cooled , the temperatur e ofthe surrounding atmosphere , and the temperatur e Of thewater in whi ch the ice is placed .
L 5
E fiect of S tirring Milk during C ooling in Tanks .
The cool ing process , in order to b e thorough , requir esmore than setting the can ofmi lk in a tank of i ce waterthe milk mus t be stirred frequently . If the milk '
is no t
stir red , that which is near the walls of the can willb ecome cold , whi le that in the centre of the can willfor a long t ime maintain a high temperatur e favourab leto the growt h of b acter ia. Resul ts showing the rateof cooling ,when milk was and was no t stirred dur ingthe cooling process are given in Table 3 . In eachexper iment in Table 3
.
can 1 was st irred at intervals of
fiv e minutes , and the temperatur e recorded can 2 was
st irred at intervals of ten minutes and the temperatur er ecorded ; can 3 was
g
no t st irred at all , but the tem
perature O f the milk in the centre of the can was recordedat intervals of ten minutes ; C an 4 was st irred con
t inuously , and the temperatur e recorded at intervalso f ten minutes .
In each exper iment , with the exception of one, recordedin Tab le 3 , the milk in can 4 , which was st irred cont inuously , registered the lowest temperatur e at the endof an hour while the milk in cans 1 and 2 , which wasst irred every fiveminutes and every ten minutes respect ively , reg istered about the same final temperatur e , butno t so low as that obtained in can 4 . Themilk in can 3 ,
which was not stirred at all dur ing the hour , had a
higher temperatur e than that in the thr ee o ther cans .Thi s was due to the fact that the milk in the centr eof the can was not near enough to the cool ing mixtur ehowever
,when the milk in this can was stirred at the
end of the hour , the mixed mi lk had a temperatur e thatcompar ed very favourably with that of the milk incans 1 and 2. This woul d indicate that the milk nearthe walls of the can had a low temperatur e .
26
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T A BLE 4 .—C OMP AR ISON O F T EMP ERATURE O F MILK IN
C ENTRE O F C A N AT E N D O F C O OLING P ERIOD
BEFORE STIRRIN G AND AF TER ST IRR I NG .
Temperatur e ofmilk F . ) incentre of can .
Sample .
Before A f terstirring . stirring.
Stirr ing milk dur ing cooling produces a rapid dr op intemperatur e , which is advantageous b ecause i t checksthe growt h of b acter ia. They develop more slowly , as
has b een stated , as the temperatur e of the milk decreases .
In each experiment recorded in Tab le 3 , all the milkih - can 4— which was stirred continuously—was coo ledvery rapidly , and the largest drops in temperatur e
29
occurred near the b eginn ing of the period ; while incan 3 , which was no t stirred at all , the temp erature of
the milk ranged as high as 72° F . at theend of the hour .
The point is fur ther illustrated in Tab le 5 , according towhich at the end O f twenty minutes the difierence intemperature due to stirring the milk varied from 3
° to17
° F . and the average difierence in temperature b etweenthe milk stirred and not stirred was 9 7
° F . Thisaverage drop in temperature , F . , in twenty minutesdue to stirr ing means an effective check on the development of b acteria. For all practical purposes i t seemsthat stirr ing the contents of the can once every tenminutes for an hour is sufficient .
TA BLE 5 .
—E FFECT O F ST I R R INGMI LK O N RAP ID ITY'
O F
C O OLING .
Stirred at intervalsof 10 minutes. N ot stirred .
Difference
Temperature of milk Temperature of milk temp éfiatureF . ) at a
due to
Beginning of E nd of 20 Beginning of E nd of 20experiment . minutes. experiment . minutes.
When a suffic ient amoun t of i ce and water are used ,
stirring the water in the tank at frequent intervals has
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The comparative results of cooling milk with a conicalcoo ler in which the water and i ce wer e stirred and wereno t stirred , are g iven in Tab le 7 .
TA BLE 7 .—C OMP ARATIVE R E SU L TS O F C O OLING MI L K
WITH A C ONICAL C O OLER WHEN THE WA T E R AND
I C E WERE ST IRRED AND WERE N O T ST IRRED .
Temperature of Temperature of Differenc emilk F . ) at water F . ) at inNumberNumber fini sh of finish of t empera
of of exp eriment . experiment ture ofSample . pounds pounds milk
of milk of ice F . )used . used . WaterWater not Wat erWater not due t o
stirred . stirred . stirred . stirred . st irring .
O O O O O O O
0 0 0 0 0 0 0
0 0 0 0 0 0 0
0 0 0 0 0 0 0
A verage difference 154°
The Tubular Typ e.
Where comparat ively large quantities of milk are tobe cooled , tub ular cooler s are generally used (F ig .
This type consists of a series of tub es , usually corrugated ,
33
over which the mi lk flows and through which the reir i
gerat ing mater ial i s forced. The corrugation increases
F I G . 7 7.—A conical cooler.
the surface over whi ch them ilk has to flow , and therefore makes the cooler moreeffi c ient .
Therefr igerat ing substanceshoul d enter the lower partof the cooler and flow outat the top . By thi s arrangement milk has part of i tsheat r emoved by the warmest refr igerat ing substance ,and as the milk flows downover the cooler , i t passesover the tubes that containthe coldest substance . In thisway the highest efficiency ofthe refrigerating substancei s ob tained . Tubular coolersr equi r e e ither a pump or theforce of grav ity to cir culatethe cooling mater ial . Small
tubular coolers , such as theone shown in F ig. 7 8 , are
sometimes used on farmswhere ther e i s an abundantwater supply. Wh en so usedthe cooler is attached d irectly
to the well pump or to a r eservo ir situated above thecooler and the water i s then allowed to run to wasteafter passing thr ough it .
Ice water and brine are the two substances generallyused as refr igerat ing mater ials . Of these brine is the
34
more effic ient b ecause lower temperatur es can b e
ob tained with it than wi th ice water alone , due to thefact that when ice and salt unite to form a liquid theyab sorb heat . The temperatur e ob tained depends on thepercentage of salt in the solution , the amount of i ceused , the temperatur e o f the milk coo led , and thetemperatur e of the atmosphere . The amount of refri
gerat ion that can b e suppl ied b y a g iven amoun t ofic e and salt can b e definitely computed , b ut the otherfactors mentioned have so great an influence that thetheoret ical amount is usuall y only approximate . The
theoretical temperatures that would resul t fromsolutions conta ining different percentages of salt in icewater at 32
° F . are g iven in Tab le 8 , which is takenfrom a pub l ication of the U nited States Departmentof A gricul ture.
>k
TA BLE 8 .—A P P R ox r.\L i T E TEMP ERATURES RESULTIN G
FROM THE MI ! TURE O F D I FFERENT P ERCENTAGESO F S A L T AND I C E .
P ercentage of Salt in Temperature ofMixtureMixtur e . E ) .
The App li cat i on of R efrigerat i on t o t heHandling of Milk . ByJohn T . Bow en, U S . D epartm ent of A g ri cul t ure . Bull e tin 98
(new seri es) .
35
One of the least expensive and at the same time mosteffic ient methods of cool ing milk b y the use of b r ine isby means of a brine barrel (F ig . 7 The b arrel selected
FIG . 78 .— A typ e of tubular cooler .
for this p u r p o s es h o u l d b e of goodqual ity , since it getsalmost cons tan t use .
The salt and i ce are
m i x e d in it , and
the brine is pumpedfrom t h e b a r r e lthr ough the cooleran d b a c k to theb arrel , ‘ from whichit is pumped againinto the cooler . Itis necessary to usea b rasslined pump ,
f o r o n e o f i r o nwould soon b e rustedout by the b rine .
Most of the coolersare constructed of
mater ial such as willwiths tand the actiono f b r i n e . In thismethod o f c o o l i n gmilk , ice water can
of cour se be usedi n s t e a d o f brine ,
b ut the latter is much more effi c ient , and i s com
parat ively inexpensive . C omparative resul ts ob tainedb y the use of ice water and of brine and ice in a
tubular coo ler are g iven in Table 9.
3 6
TA BLE 0 C OOL I NG MILKI N A TUBULAR C O OL ER BYTHE I
'
s‘
E O F
I C E WATER A N D O F BRINE AND I C E .
’
Tempera Temper a D ifferenceNumberNumber Number ture of ture of in tem
of of of perature requiredSamp l e pounds pounds pounds F . ) at F . ) at of milk to c ool
milk ice salt b eginning end of F . ) due milk .
used . us ed . used . of experi experi to use (minment . ment . of brine . ut es) .
Brine and i ce are much more effi cient as a refrigerantthan is ice water alone , ac cording to the figures inTable 9 . In “ the ten experiments
‘
recorded , the milkcooled b y b rine and i c e averaged 6 . 5
°lower than the
milk cooled by ice water under the same condi tions.
These are important from the standpoint of checkingbacter ial growth .
37
F I G . 7 9 .— A brine barrel and a typ e of tubular cooler in
which brine may be used as the refrigerating material .
38
QU E STION S .
From the standpoint of the dairy farmer critic isethe score card on equipment and methods ,pointing out i ts good points and b ad points .
Describe the care and management of the cow inthe production of clean , wholesome milk .
C l eanl iness and coldness are the dairyfarmer ’s watchwords . G ive reasons why this is
Outl ine the essentials of a stable for the productionof clean milk .
G ive a l ist of utensils necessary , and describe theirconstruction and care b r iefly.
How would you wash out a metal vessel in’
wh ich
milk had b een kept
Descr ib e the fittings of a convenient milk room .
Describe a cement tank and - a galvanised iron tanksui table for cool ing milk.
How does stirring the milk affect its cooling ?Descr ibe in detail .
Descr ibe the conical cooler , the tubular cooler ,and tell how they are operated and the cool ingmedium used.
40
