Fermentation Class Lecture

8/6/2019 Fermentation Class Lecture

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Fermentation


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Fermentation involves the action of desirable microorganisms, or

their enzymes, on food ingredients to make biochemical changes,which cause significant modification to the food.

Often lactic-acid bacteria convert the carbohydrate energy source

of food, such as lactose in milk, to lactic acid; examples are yogurt

and cheeses from milk, and pickles from fruits and vegetables.

Alternatively, yeasts, often of the Saccharomyces species, may

convert the glucose to ethanol and carbon dioxide in leavened

breads, or the sugars in grain or fruit beverages to beers and wines.

It is estimated that about one-third of all the food we consume is

fermented. World estimates for beer consumption are about 22

million gallons, and a total of 15 million tons of some one thousand

varieties of cheese are eaten annually.

What is Fermentation


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Alcoholic fermentation

Two stages:

Step 1: Glycolysis Results in the production of2 molecules of ATP

Step 2: Pyruvic acid is broken down into CO2 and alcohol

No ATP is produced in this stage

Total energy produced in both stages is 2 molecules of ATP

End products are CO2, alcohol, and 2 molecules of ATP

Used in the baking and brewing industry.

This is the process which for example yeast use. When there is a

lack of oxygen, the cells start to produce CO2 and alcohol as waste.

This is the reason why yeast is used in baking. Bread for example,

wouldn't rise without yeast, but it does rise because yeast creates CO2

which makes it rise.


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The smell that you get from baking, is from the alcohol burning

off. The reason we do not get intoxicated when eating bread

(because of the alcohol that is made from the fermentation) is

because the alcohol is burned off during baking because of high

temperatures.

LacticAcid Fermentation

Process occurs in two stages: Stage 1. Glycolysis

Stage 2. Pyruvic acidis broken down into lactic acid

Occurs in the cytoplasm

Total products are 2 molecules of lactic acid and 2 molecules ofATP

Occurs in humans during periods of prolonged physical activity

Oxygen levels become very low in the muscles involved and lactic

acid fermentation occurs


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Yogurt fermentation

Yogurt is made by fermenting milk with friendly bacteria, mainly

Lactobacillus bulgaricus and Streptococcus thermophilus. Yogurt fermentation was invented probably by accident by Balkan

tribes thousands of years ago. Yogurt remained mainly a food of

eastern Europe until the 1900s, when the biologist Mechnikov

created the theory that lactobacillus bacteria in yogurt are

responsible for the unusually long lifespan of the Bulgar people.

The milk sugar or lactose is fermented by these bacteria to lactic

acid which causes the characteristic curd to form. The acid also

restricts the growth of food poisoning bacteria. During the yogurt

fermentation some flavors are produced, which give yogurt its

characteristic flavor.


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KefirYogurt

Kefir means to froth and Yogurt in Turkish means dense or

thick.


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Kefir fermentation

Kefir is a fermented milk drink

Kefir fermentation is similar to yogurt fermentation.

Yogurt is only fermented by bacteria but kefir fermentation

involves the help of bacteria as well as yeasts.

These yeast produce some alcohol and carbon dioxide, whichgives kefir its typical fizzy aspect.

Kefir is inoculated with special kefir grains. These grains are

mixtures of bacteria and yeasts in a matrix of proteins, lipids and

carbohydrates.Kefir fermentation is done at room temperature, which makes the

process easier. On the other hand, not everyone likes the taste of

kefir.


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Considering the digestion, Kefir is easily digested than Yogurt.

As the Kefir curd size is smaller to that ofYogurt, it becomes

easier to get digested.

Another difference that can be noticed is that Kefirs yeast and

bacteria combination has more nutritional value than Yogurt. Kefir

also helps to keep the colon clean and healthy.


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What types of microorganisms cause fermentation to

occur?

The primary purpose of fermentation is to furnish

energy for metabolism and growth to

microorganisms including bacteria, yeast, and

mold.

A. Bacteria are typically one-celled organisms

that multiply by simple division and can be seenonly with a microscope; necessary for some

types of fermentation.


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B. Yeasts are any of various unicellular (single-celled)

fungi in which little or no mycelium develops and that

ordinarily reproduce by budding; they live on sugary

solutions. The dry granules of yeast that are bought at

the store become active when they become moist.

C. Molds are a fungus that grows in a tangled mass of

filaments containing cells. Fungi are not plants and

therefore do not photosynthesize. They are eukaryotic

(have a cell membrane and membrane bound

organelles) heterotrophs (obtain energy by consumingother organisms). Fungi break down their food outside of

their bodies and then consume it.


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What food and non-food products are created by

fermentation?

A. Foods that undergo fermentation include

yogurt, cheese, wine, cider, bread, sauerkraut,flavorings, candy, fruit juice, silage, and beer.

Pickling involves fermentation. Foods that are

frequently pickled include beans, onions,

cauliflower, cucumbers, tomatoes, and cabbage.


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Yeast

Yeast is a unicellular fungi.

Yeast flourish in habitats where sugar is

present e.g. flowers, fruit and bark of trees.A few are pathogenic for animals and

humans.

The most important commercially are

bakers or brewers yeast which are spp. of

Saccharomyces.


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Bread and Yeast

Leavened bread is made from a

combinations offlour, sugar, milk or water,

yeast, and sometimes butter or oil.Yeast (Sacchromyces) ferments the sugar

to ethanol and CO2.

The

CO2 causes the bread to riseproducing the characteristic texture.

The ethanol evaporates during baking.


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1. Bread is made through alcoholic fermentation. Yeasts

eat the sugar from the granulated sugar and the maltose

(disaccharide or double sugar; made up of two glucose

molecules) from the flour. ATP is created helping the

yeast to multiply. One yeast cell can consume its weight

in glucose in one hour. The yeast initially uses oxygen to

obtain energy and reproduce. As the oxygen is used upthey undergo alcoholic fermentation and produce alcohol

and carbon dioxide as by-products.

The alcohol burns off during baking, but leaves a good

flavor in the bread. When flour is mixed with water and

then kneaded, an elastic dough is created because of

gluten. Gluten is a protein found in wheat. This elastic

dough holds in the carbon dioxide forming small air

pockets or bubbles causing the bread to rise.


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Wine

Produced from the fermentation of fruit juice,usually from grapes

The grapes are crushed to form a must

For white wines, white grapes are usually used,

and the skins are removed from the must(pressing) before fermentation

For red wines, red or black grapes are used, andthe skin is allowed to remain during

fermentationFor ros wines, red grapes are used and the juice

is allowed to remain in contact with the skins just long enough for a rose or pink color to

develop


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Wine Production

Grapes are crushed and thejuice extracted(Must).

Depending on the grapes used and its treatment,

white or red wine is produced.White wine: white grapes with skin removed.

Red wine: pomace (skin, seed and pieces of

stem) is left during fermentation.Yeast used are 2 types:

Wild yeast present on grapes

Cultivated yeast (S. ellipsoideus)


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Wine Making

Before fermentation the wild yeast is killed by

SO2 (100 ppm).

S. ellipsoideus is added as a starter culture.

Large amounts of CO2 produced during

fermentation escapes through a one-way valve.

With red wine after 3-5 days of fermentationthe pomace is separated from the wine and

allowed to ferment for another week or two.


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Wine Making

During racking the wine is separated from the

yeast cells etc. and stored at a high temperature

foraging, flavour development and

clarification. The final clarification is aided by the addition of

fining agents such as casein, tannins and

bentonite clay or the wine is filtered.

The wine is bottled and left for aging.

Red wine: age for several years.

White wine: sold without much aging.

Wine is 6-14% alcohol.


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Fermented Foods

Beer

Produced by the fermentation of malted grain

Malted grain: Grain that has been allowed to

germinate, then dried in a kiln & perhaps roastedGerminating the grain causes the production of a

number of enzymes, most notably - and -

amylase

Malted grains that may be used are barley, rye, or

wheat

Unmalted grains, such as rice or corn, may also be

used


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Brewing

Brewing is the manufacture of alcohol

beverage from malted grains e.g. beer,

ale and stout.Beer making can be divided 3 basic

stages:

Wort making

Fermentation

Bottling and aging


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Wort Making

Malt is prepared from geminating barley

seeds.

Natural enzymes in the seed convert starch

to sugar (yeast cannot digest starch).

Mixed in with the malt are other grains e.g.

corn, rice and wheat.

The mixture is cooked and steeped. Theheat and enzyme convert starch to sugar.

After cooking the wort is filtered and hops

(female flower of the hop plant) is added.


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Hops


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Wort Making/Fermentation

The hops add flavour and has antimicrobial

properties.

Wort and hop is boiled for several hours toextract flavour from the hops and the

coagulated proteins are removed.

Fermentation

There are 2 types of brewing yeast

Top (S. carlsbergenis)

Bottom (S. cerevisiae)


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Fermentation/Bottling

Yeast is added to the wort and

fermented (6-23 C) for 5-14 days.

After this the beer is removed to largetanks and stored at a lower temperature

for several days to weeks.

Beer is taken from the storage tank andbottled.


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Beer Making


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What are some advantages and disadvantages of

fermentation in food processing?

A. Advantages include:

1. Fermentation can increase the shelf life of foods by

inhibiting the enzymatic deterioration of plant tissues.

2. Fermentation improves the dough handlingcharacteristics of bread by softening the gluten because

the gluten proteins are hydrated. This allows the dough to

be handled easier, especially by machines.

3. It can enhance the texture, flavor and odor of foods. For

example, the compound diacetyl is produced by variouslactic acid bacteria during dairy fermentations (i.e.

cottage cheese, sour cream, buttermilk). This compound is

responsible for the buttery aroma and taste typically

associated with these products.


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4. Fermentation helps food to be stored safely.

5. Fermentation allows humans to enjoy their favorite foods

in a different way by creating a variety of flavors, textures,

color, and appearance of some foods.

6. Fermentation is also used to create new energy sources

such as ethanol.

7. The vitamin content of some foods can be increased.

8. Digestibility can be improved.

9. The toxicity of some foods (particularly oriental) may be

decreased.

10. Some scientists believe that particular types of

fermented milk products (i.e. acidophilus milk, yogurt) havea therapeutic value and can be beneficial in cases of

alimentary disorders (i.e. constipation, diarrhea, etc.) and

may even preclude the development and outgrowth of

harmful bacteria.


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What factors can affect the fermentation process?

A. Fermentation time determines how long the yeast has to

act on the sugars. As time passes the rate of fermentation

decreases, but never stops under favorable conditions.

B. Yeast cells can tolerate a pH of4.08.5 with the optimum

pH between 4.0 and 6.0. Before fermentation begins in

bread dough, the pH is around 5.5 5.8. As fermentation

begins the pH drops to around 5.0. This is caused by the

production of organic acids including carbonic acid (carbondioxide dissolved in water; H2CO3 ). Carbonic acid is more

acidic than the dough. Flour and milk act as buffers to help

maintain the pH level. Calcium carbonate is a common

additive that bakeries use to buffer the pH.


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C. The presence of air affects fermentation and is

probably the most critical factor in producing somefood products. Since fermentation is anaerobic, the

presence of air will allow for yeast/mold growth and

result in softening, off flavors and darkening of the

product.

D. Optimum fermentation occurs at 75-85F for

yeast. The higher the temperature, the faster

fermentation will occur, but the flavor can be inferior

and the product will darken readily. Scientistsestimate that for every one degree increase in

temperature that fermentation of yeast will increase

three to five percent.


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E. The presence of salts affects the fermentation

process. The salt withdraws water and nutrients from

vegetative tissue in order to enable lacticmicroorganisms to grow. It also inhibits the growth of

undesirable microorganisms and delays enzymatic

spoilage.

The proper concentration of salt (2.5% for sauerkraut)favors lactics, while low salt results in softening of the

tissue because not enough water is pulled form the

tissues. High salt (over 3.5% for sauerkraut) inhibits all

lactics, including the desirable ones, slows anaerobiosis,

and results in undesirable yeast growth. Also, high saltconcentration favors lactic microorganisms that produce

only lactic acid, resulting in a rather bland product.


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Fermentation Class Lecture