DAIRY MICROBIOLOGY

Milk is extremely perishable and many means have been developedto preserve it. The earliest one which has been used for many thousands ofyears is fermentation. Milk can be fermented by inoculating fresh milk withthe appropriate bacteria and keeping it at a temperature which favorsbacterial growth. As the bacteria grow, they convert milk sugar (lactose) tolactic acid. You can detect its presence by the tart or sour taste (sour ishow we taste acid). The lowered pH caused by lactic acid preserves themilk by preventing the growth of putrefactive and/or pathogenic bacteriawhich do not grow well in acid conditions.

Milk contains components that are essential to humans such asproteins, carbohydrates, fat, water, all the B-vitamins, vitamins A and D,calcium and phosphorus. It also provides energy.

An important protein in milk is casein (in many cases 80% of themilk protein). This is the base for cheese making. Casein is linked tocalcium phosphate, which is why milk contains a relatively large amount ofthis salt that is a very important nutrient for humans and animals.

87% water13% solids

DAIRY : MILK

Types of Milk

• Whole Milk (3.25% fat) contains 150 calories and 8 grams (g) of fat per serving (8 fluid oz). Although not required, whole milk may be fortified with vitamin D at a level of 400 International Units (IU) per 1 quart. If vitamin D is added, the label must state this fact.

• 2% Reduced-Fat Milk (2% fat) contains 120 calories and 5 grams (g) of fat per serving(8 fluid oz). Vitamins A and D are removed with the milk fat. For this reason, these vitamins must be added to 2% reduced-fat milk so that it contains at least 2,000 IU of vitamin A and 400 IU of vitamin D per 1 quart. The addition of these vitamins must be stated on the label.

• 1% Lowfat Milk (also called Light Milk) (1% fat) contains 100calories and 2.5 grams (g) of fat per serving (8 fluid oz).Vitamins A and D must be added to a level of at least 2,000 IU ofvitamin A and 400 IU of vitamin D per 1quart. The label mustindicate the addition of these vitamins.

• Fat-Free Milk (also called Skim or Nonfat Milk) (0% fat)contains 80 calories and 0 grams (g) of fat per serving (8 fluidoz). Vitamins A and D must be added to a level of at least 2,000IU of vitamin A and 400 IU of vitamin D per 1quart The labelmust indicate the addition of these vitamins.

• Chocolate Milk (fat-free,1% lowfat, 2% reduced-fat, wholemilk) is milk to which chocolate or cocoa and a sweetener havebeen added. This milk is just as nutritious as its unflavoredcounterpart. Compared to plain milk, chocolate milk containsabout 60 more calories per serving (8 fluid oz).

• Evaporated Milk(6.5% fat) is made by removing about 60% of the water from whole milk. The milk is then homogenized, fortified with vitamin D to a level of 25 IU per 1fluid ounce, canned and heat sterilized. The addition of vitamin A is optional. If added, each fluid ounce must contain not less than 125 IU of vitamin A.

Evaporated Fat-Free Milk (0.5% fat or less) is a concentrated, fortified (vitamins A and D) fat-free (skim or nonfat) milk that is canned and sterilized

Sweetened Condensed Milk (8% fat or less) is a canned milk concentrate of whole milk to which sugar has been added. The sweetener used (usuallysucrose) prevents spoilage. Sweetened condensed fat-free milk contains no more than 0.5% milk fat.

Buttermilk refers to a number of dairy drinks. Originally, buttermilk wasthe liquid left behind after churning butter out of cream. This type ofbuttermilk is known as traditional buttermilk.

The term buttermilk also refers to a range of fermented milk drinks,common in warm climates (e.g., the Balkans, the Middle East, Turkey,Afghanistan, Pakistan, India, Sri Lanka and the Southern United States)where unrefrigerated fresh milk sours quickly, as well as in colder climates,such as Scandinavia, Finland, Ireland, Netherlands, Germany, Poland,Slovakia and Czech Republic. This fermented dairy product knownas cultured buttermilk is produced from cow's milk and has acharacteristically sour taste caused by lactic acid bacteria. This variant ismade using one of two species of bacteria—either Lactococcuslactis or Lactobacillus bulgaricus, which creates more tartness.

Buttermilk

The tartness of buttermilk is due toacid in the milk. The increased acidity isprimarily due to lactic acid produced by lacticacid bacteria while fermenting lactose, theprimary sugar in milk. As the bacteriaproduce lactic acid, the pH of the milkdecreases and casein, the primary milkprotein, precipitates, causingthe curdling or clabbering of milk. Thisprocess makes buttermilk thicker than plainmilk. While both traditional and culturedbuttermilk contain lactic acid, traditionalbuttermilk tends to be less viscous, whereascultured buttermilk is more viscous.

Buttermilk can be drunk straight, andit can also be used in cooking. Soda bread is abread in which buttermilk reacts with therising agent, sodium bicarbonate, toproduce carbon dioxide.

Cultured Sour Cream

• Sour Cream (cultured sour cream) isthe product resulting from adding lacticacid bacteria to pasteurized cream atleast 18% milk fat.

• Acidified Sour Cream results fromsouring pasteurized cream with safe andsuitable acidifiers, with or without lacticacid-producing bacteria. One tablespoonof sour cream contains about 26 caloriesand 2.5 grams (g)of fat.

• Reduced-Fat Sour Cream and AcidifiedSour Cream contain at least 25% less fatper serving than a serving (2tablespoons) of sour cream or acidifiedsour cream, respectively. Reduced-fatsour cream contains 20 calories and 1.8grams (g) of fat per tablespoon.

Bulgarian milk refers to a fermentedmilk product obtained with Bulgariansymbiotic starter from L.bulgaricus andS.thermophilus by an original technologywithout any additives.

Heat the fresh (skimmed) milk to boilingpoint, stirring all the time. Cool it down to 18 –20°C, for instance in a large pan with cold water.Add 10 – 30 ml of sour milk or buttermilk or astarter culture per each litre of milk (1%). Leavefor it 18 - 24 hours at room temperature (18 –20°C); if the surrounding temperature is higher,fermentation time will be somewhat shorter. Afterthis the milk is ready. Store it in a cold place (coolbasement or a refrigerator), if you want to keep itfor some days.

Bulgarian milk

Acidified buttermilk is a related product made by adding a food-grade acid (such aslemon juice) to milk. It can be produced by mixing 1 tablespoon of vinegar orlemon juice with 1 cup of milk and letting it sit until it curdles, about 10 minutes.Any level of fat content for the milk ingredient may be used, but whole milk isusually used for baking. In the process which is used to produce paneer suchacidification is done in the presence of heat.

Acidophilus milk

Yoghurt is produced when milk issoured by certain lactic acid bacteria, whichprefer growing temperatures far above roomtemperature: 37 – 45°C. The milk should firstbe heated to 85°C or higher. A highpasteurisation temperature (above 72°C)gives a better consistency (thickness) to thefinal product. After the milk has been soured,the resulting yoghurt can be used to makemore fresh yoghurt by adding it to fresh milk.

Heat the milk to 85°C or higher andkeep it at this temperature for 3 minutes. Coolthe milk to 45°C. Add 30 ml (2 - 3 tablespoons)of fresh yoghurt to each litre of milk; theyoghurt should not be more than 2 days old.Instead of fresh yoghurt you can use a yoghurtstarter culture. Mix the milk and the starterand leave it to ferment. The time required forthe milk to turn sour depends on thetemperature.

The Lactobacillus bulgaricus bringacidity to the milk.

The Streptococcus thermophilusdevelop aroma

Yogurt Nutrition

Nonfat Yogurt/1 cup

Calories 100

Total fat (g) 0

Saturated fat (g) 0

Monounsaturated fat (g) 0

Polyunsaturated fat (g) 0

Dietary fiber (g) 0

Protein (g) 10

Carbohydrate (g) 19

Cholesterol (mg) 5

Sodium (mg) 135

Calcium (mg) 300

Low-fat Yogurt/1 cup

Calories 155

Total fat (g) 3.8

Saturated fat (g) 2.5

Monounsaturated fat (g) 1

Polyunsaturated fat (g) 0.1

Dietary fiber (g) 0

Protein (g) 13

Carbohydrate (g) 17

Cholesterol (mg) 15

Sodium (mg) 172

Riboflavin (mg) 0.5

Vitamin B12 (mcg) 1.4

Calcium (mg) 448

Phosphorus (mg) 353

Potassium (mg) 573

Zinc (mg) 2.2

Types of Yogurt

Set Yogurt- this type of yogurt is incubated and cooled in the final package. Firm “jelly like” texture.

Stirred Yogurt- incubated in a tank and final coagulum is broken by stirring before cooling. Less firm then set yogurt (like a thick cream). A little reformation of coagulum will occur after packaging.

Drinking Yogurt-also has coagulum broken before cooling. Very little reformation of coagulum will occur.

Types of Yogurt (continued)

Frozen Yogurt- Incubated like stirred yogurt. Cooling is achieved by pumping through a freezer like ice cream. Has a texture like ice cream.

Concentrated Yogurt-incubated like stirred yogurt. After coagulum is broken, some water is boiled off. Produces rough and gritty textures.

Flavored Yogurt-Flavors are added just before yogurt is poured into pots. Add in usually contain about 50 % sugar.

http://www.cip.ukcentre.com/yogurt.htm

10 Reasons Yogurt is a Top Health Food…

1. Easier to digest then milk

2. Contributes to colon health

3. Increases the absorption of other nutrients such as calcium

4. Boosts immunity

5. Aids in healing process after infections in the intestines

6. Decreases yeast infections

7. A rich source of calcium

8. Good source of protein

9. Lowers cholesterol

10. It is a “grow food” meaning it helps children to grow

Kefir, like yoghurt, is a milk productfirst discovered by the nomadic tribes livingin the cold areas of the Caucasus. Whenmaking kefir, acid, gas and some alcohol areproduced. Like sour milk and buttermilk, ithas a special aroma which is different fromthat of yoghurt. Kefir is made by using a'yoghurt plant', which is actually a misleadingname as it is not a plant and it has nothing todo with yoghurt.The 'yoghurt plant' is in fact a cauliflower-likelump of chalky crystals and micro-organismsconsisting of yeasts and bacteria. The yeastsproduce alcohol and gas, while the bacteriaconvert the milk sugar into lactic acid. Youmay be able to obtain a piece of this fromsomeone who regularly makes kefir. If not,get some dried kefir granules at the localmarket.

Kefir

Boil the milk and put it into a bottle,which has been thoroughly cleaned andrinsed with hot water. Do not fill thebottle completely; let the milk cool downto 20°C (use a thermometer). Add onetablespoon of kefir granules soaked inwater to each half litre of milk in thebottle and cover it loosely so that the gasproduced can escape. You can use a freshyoghurt plant instead of the soakedgranules. Keep the bottle at atemperature of 16 to 18°C. After 24hours the milk will have become a littlethicker, forming some froth: this is kefir.Sieve the kefir and use the (washed withclean water) granules, which remain inthe sieve to make fresh kefir again. Thekefir is now ready for consumption orcan ripen for some days to get moreflavour.

Ripening of the kefir

The kefir can be left to ‘ripen’, during which time furtherfermentation takes place. This is essential to create kefir’scharacteristic qualities. Pour the kefir into a well-cleaned bottle,which can be closed, or a bottle with a clip fastening and do not fillmore than 3/4 because gas forms during ripening.

Leave the bottle at about 15°C, but do not store it for morethan 3 days. Towards the end of the ripening process the wheyseparates and can be incorporated again by stirring or turning thebottle. The end product is a thick, creamy, frothy drink with a sourtaste and smell and the produced carbon dioxide is perceivable. If thekefir is left to ripen for more than 3 days, the milk may curdle and thedrink becomes too sour. The temperature and the time are importantas they determine the flavour. The kefir can be kept in a refrigeratoror a cellar for a few days.

Koumiss is a sour milk product similar to Kefir. It ismanufactured from mare milk.

Koumiss often called "milk wine" or "milk brandy" asit is a fermented drink of milk beralkhohol.The name ofkoumiss obtained from asia tribes in ancient times, namelykumanes or komans.

Traditional koumiss made from mare's milk fromgrazing horse races kumanes that sustain life on the steppesof Central Asia until 1235.

Koumiss fermentari result is a product of thebacterium L.Bulgaricus and yeast talura alcohol producer.Due to lack of milk production of koumiss horse is now oftenmade from cow's milk, but the milk has a composition that isnot the same.

Koumiss

Cheese is a product made from curd obtained from the whole,partly fat free/non-fat, or fat-free/non-fat milk of cows or frommilk of other animals, with or without added cream, bycoagulating with rennin, lactic acid or other suitable enzyme oracid and with or without further treatment of the separatedcurd by heat or pressure, or by means of ripening ferments,special molds, or seasoning.

Cheese

There is a huge assortment of cheeses. They can havevarious compositions; we make a rough distinction betweenfresh cheese and matured cheese, and between soft cheese andhard cheese.

Fresh cheese can be consumed immediately afterproduction, whereas matured cheese has to be stored afterprocessing to develop flavour and a good consistency.

Soft cheese has a higher water content than hard cheese;moreover hard (or semi-hard) cheese generally has a clean, dryrind. Soft cheeses and hard cheeses can be matured for someweeks or even up to a number of years.

Production

• Coagulation: enzyme or acid

• Curd treatment involves:

• Cutting: to increase surface area- to remove more whey

• Heating: to evaporate water, to destroy bacteria

• Salting: to dehydrate curd, to control bacterial growth, flavor, texture

• Knitting: the use of heat to combine curd

• Pressing to create more solid mass before ripening

• Curing or ripening: exposure of cheese to controlled temperature and humidity conditions to promote chemical and physical changes in cheese.

Spoilage of Milk

The presence of too many micro-organisms in the milkcontamination by diseased animals (tuberculosis, brucellosis) and/orpeople.

Bacterial and/or chemical conversion of certain substances in themilk contamination of the milk with antibiotics (used for treatment ofdiseased animals), disinfectants, pesticides and so on.

Milk should be handled with care. There are several factors that can make milk gooff and become unsuitable for further consumption. These include: