DAIRY MICROBIOLOGY

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

Milk contains components that are essential to humans such as proteins, 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 the milk protein). This is the base for cheese making. Casein is linked to calcium phosphate, which is why milk contains a relatively large amount of this 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 100 calories 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 of vitamin A and 400 IU of vitamin D per 1quart. The label must indicate 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 fluid oz). Vitamins A and D must be added to a level of at least 2,000 IU of vitamin A and 400 IU of vitamin D per 1quart The label must indicate the addition of these vitamins.

• Chocolate Milk (fat-free,1% lowfat, 2% reduced-fat, whole milk) is milk to which chocolate or cocoa and a sweetener have been added. This milk is just as nutritious as its unflavored counterpart. Compared to plain milk, chocolate milk contains about 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 was the liquid left behind after churning butter out of cream. This type of buttermilk 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 known as cultured buttermilk is produced from cow's milk and has a characteristically sour taste caused by lactic acid bacteria. This variant is made using one of two species of bacteria—either Lactococcus lactis or Lactobacillus bulgaricus, which creates more tartness.

Buttermilk

The tartness of buttermilk is due to acid in the milk. The increased acidity is primarily due to lactic acid produced by lactic acid bacteria while fermenting lactose, the primary sugar in milk. As the bacteria produce lactic acid, the pH of the milk decreases and casein, the primary milk protein, precipitates, causing the curdling or clabbering of milk. This process makes buttermilk thicker than plain milk. While both traditional and cultured buttermilk contain lactic acid, traditional buttermilk tends to be less viscous, whereas cultured buttermilk is more viscous.

Buttermilk can be drunk straight, and it can also be used in cooking. Soda bread is a bread in which buttermilk reacts with the rising agent, sodium bicarbonate, to produce carbon dioxide.

Cultured Sour Cream

• Sour Cream (cultured sour cream) is the product resulting from adding lactic acid bacteria to pasteurized cream at least 18% milk fat.

• Acidified Sour Cream results from souring pasteurized cream with safe and suitable acidifiers, with or without lactic acid-producing bacteria. One tablespoon of sour cream contains about 26 calories and 2.5 grams (g)of fat.

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

Bulgarian milk refers to a fermented milk product obtained with Bulgarian symbiotic starter from L.bulgaricus and S.thermophilus by an original technology without any additives.

Heat the fresh (skimmed) milk to boiling point, 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 a starter culture per each litre of milk (1%). Leave for it 18 - 24 hours at room temperature (18 – 20°C); if the surrounding temperature is higher, fermentation time will be somewhat shorter. After this the milk is ready. Store it in a cold place (cool basement or a refrigerator), if you want to keep it for some days.

Bulgarian milk

Acidified buttermilk is a related product made by adding a food-grade acid (such as lemon juice) to milk. It can be produced by mixing 1 tablespoon of vinegar or lemon 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 is usually used for baking. In the process which is used to produce paneer such acidification is done in the presence of heat.

Acidophilus milk

Yoghurt is produced when milk is soured by certain lactic acid bacteria, which prefer growing temperatures far above room temperature: 37 – 45°C. The milk should first be heated to 85°C or higher. A high pasteurisation temperature (above 72°C) gives a better consistency (thickness) to the final product. After the milk has been soured, the resulting yoghurt can be used to make more fresh yoghurt by adding it to fresh milk.

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

The Lactobacillus bulgaricus bring acidity to the milk.

The Streptococcus thermophilus develop aroma

Yogurt NutritionNonfat Yogurt/1 cup

Calories 100

Total fat (g) 0

Saturated fat (g) 0Monounsaturated fat (g) 0

Polyunsaturated fat (g) 0

Dietary fiber (g) 0Protein (g) 10

Carbohydrate (g) 19

Cholesterol (mg) 5

Sodium (mg) 135

Calcium (mg) 300

Low-fat Yogurt/1 cupCalories 155Total fat (g) 3.8Saturated fat (g) 2.5Monounsaturated fat (g) 1Polyunsaturated fat (g) 0.1Dietary fiber (g) 0Protein (g) 13Carbohydrate (g) 17Cholesterol (mg) 15Sodium (mg) 172Riboflavin (mg) 0.5Vitamin B12 (mcg) 1.4Calcium (mg) 448Phosphorus (mg) 353Potassium (mg) 573Zinc (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 milk2. Contributes to colon health3. Increases the absorption of other nutrients such as calcium4. Boosts immunity5. Aids in healing process after infections in the intestines6. Decreases yeast infections7. A rich source of calcium8. Good source of protein9. Lowers cholesterol10. It is a “grow food” meaning it helps children to grow

Kefir, like yoghurt, is a milk product first discovered by the nomadic tribes living in the cold areas of the Caucasus. When making kefir, acid, gas and some alcohol are produced. Like sour milk and buttermilk, it has a special aroma which is different from that of yoghurt. Kefir is made by using a 'yoghurt plant', which is actually a misleading name as it is not a plant and it has nothing to do with yoghurt. The 'yoghurt plant' is in fact a cauliflower-like lump of chalky crystals and micro-organisms consisting of yeasts and bacteria. The yeasts produce alcohol and gas, while the bacteria convert the milk sugar into lactic acid. You may be able to obtain a piece of this from someone who regularly makes kefir. If not, get some dried kefir granules at the local market.

Kefir

Boil the milk and put it into a bottle, which has been thoroughly cleaned and rinsed with hot water. Do not fill the bottle completely; let the milk cool down to 20°C (use a thermometer). Add one tablespoon of kefir granules soaked in water to each half litre of milk in the bottle and cover it loosely so that the gas produced can escape. You can use a fresh yoghurt plant instead of the soaked granules. Keep the bottle at a temperature of 16 to 18°C. After 24 hours the milk will have become a little thicker, forming some froth: this is kefir. Sieve the kefir and use the (washed with clean water) granules, which remain in the sieve to make fresh kefir again. The kefir is now ready for consumption or can ripen for some days to get more flavour.

Ripening of the kefir

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

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

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

Koumiss often called "milk wine" or "milk brandy" as it is a fermented drink of milk beralkhohol.The name of koumiss obtained from asia tribes in ancient times, namely kumanes or komans.

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

Koumiss fermentari result is a product of the bacterium L.Bulgaricus and yeast talura alcohol producer. Due to lack of milk production of koumiss horse is now often made from cow's milk, but the milk has a composition that is not 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 from milk of other animals, with or without added cream, by coagulating with rennin, lactic acid or other suitable enzyme or acid and with or without further treatment of the separated curd by heat or pressure, or by means of ripening ferments, special molds, or seasoning.

Cheese

There is a huge assortment of cheeses. They can have various compositions; we make a rough distinction between fresh cheese and matured cheese, and between soft cheese and hard cheese.

Fresh cheese can be consumed immediately after production, whereas matured cheese has to be stored after processing 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, dry rind. Soft cheeses and hard cheeses can be matured for some weeks 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 milk contamination by diseased animals (tuberculosis, brucellosis) and/or people.

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

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