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How is Milk Made


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How is Milk Made

http://www.pauls.com.au/information/information.cfm?/section/3/subsection/22/#s4


Step 1 - Cows Grazing

Step 2 - Harvesting Milk

Step 3 - Storing Milk

Step 4 - Transporting Milk

Step 5 - Laboratory Testing

Step 6 - Processing Milk

Step 7 - Selling Milk
Step 1 - Cows Grazing

Typically cows spend about 8 hours eating, 8 hours sleeping and 8 hours ruminating or chewing their cud. Cows are usually provided with a fresh paddock of grass in the morning after milking and another fresh paddock of grass in the evening after milking. They may also be fed some grain in the dairy while being milked and Hay or Silage (conserved forage) if there is not enough grass available.



Step 2 - Harvesting Mlik

Cows are normally milked 2 times per day, however some high producing herds are milked 3 times per day. Normally cows are milked at about 6 am in the morning and again at about 5 pm in the evening. Milking time takes about 5 minutes per cow but depends on the type of machine and the amount of milk the cow is producing. Most dairies have enough machines to milk 20 to 40 cows at one time, reducing the amount of time the cows wait to be milked. Milking machines mimic the action of a young calf by creating a pulsating vacuum around the teat, which causes the milk to be released from the udder.


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Step 3 - Storing Milk

Milk storage vats or silos are refrigerated and come in various shapes and sizes. Milk is stored on farm at 4 degrees Celsius and less for no longer than 48 hours. Vats and silos are agitated to make sure that the entire volume remains cold and milkfat does not separate from the milk. After milk has been collected, storage vats and stainless steel pipes are thoroughly cleaned before the farmer milks again.


Step 4 - Transporting Milk

Milk is collected from the farm every 24 or 48 hours. The tankers that are used have a special stainless steel body which are heavily insulated to keep the milk cold during transportation to the processing factory. Milk tanker drivers are accredited milk graders, which allows them to evaluate the milk prior to collection. Tanker drivers grade and if necessary reject milk based on temperature, sight and smell. A representative sample is collected from each farm pickup prior to being pumped onto the tanker. After collection, milk is transported to factory sites and stored in refrigerated silos before being processing.


Step 5 - Laboratory Testing

Samples of milk are taken from farm vats prior to collection and from the bulk milk tanker on arrival at the factory. Samples from the bulk milk tanker are tested for antibiotic and temperature before the milk enters the factory processing area. Farm milk samples are tested for milkfat/protein/bulk milk cell count and bacteria count. If milk is unsuitable for our quality products the milk will be rejected. Most farmers are paid on quality and composition of their milk and it is extremely important that these samples are collected and stored correctly.


Step 6 - Processing Milk

Whole milk, once approved for use, is pumped into storage silos where it undergoes pasteurization, homogenization and further processing.



Pasteurization:



Involves heating every particle of milk to a specific temperature for a specified period of time and cooling it again without allowing recontamination. Pasteurization is performed for two reasons;

1. Ensure all milk products are safe for human consumption by destroying all bacteria that may be harmful to health (pathogens).

2. Improve the keeping quality of milk by killing or inactivating some undesirable enzymes and spoilage bacteria.


Homogenisation:

Involves pushing the raw milk through an atomizer to form tiny particles so that the fat is dispersed evenly throughout the milk, stopping the fat from floating to the top of the container.


Further processing:

Includes, reducing the fat content by micro-filtration, increasing the storage life by ultra high temperature (UHT) treatment and mixing or culturing milk for flavored and yoghurt products.


Step 7 - Selling Milk

Then milk is sent off to your favourite store for sale to the general public.





Introduction to Dairy Science and Technology: Milk History, Consumption, Production, and Composition

http://www.foodsci.uoguelph.ca/dairyedu/home.html



Introduction

This course is about the study of milk and milk-derived food products from a food science perspective. It focuses on the biological, chemical, physical, and microbiological aspects of milk itself, and on the technological (processing) aspects of the transformation of milk into its various consumer products, including beverages, fermented products, concentrated and dried products, butter and ice cream.

Milk is as ancient as mankind itself, as it is the substance created to feed the mammalian infant. All species of mammals, from man to whales, produce milk for this purpose. Many centuries ago, perhaps as early as 6000-8000 BC, ancient man learned to domesticate species of animals for the provision of milk to be consumed by them. These included cows (genus Bos), buffaloes, sheep, goats, and camels, all of which are still used in various parts of the world for the production of milk for human consumption.

Fermented products such as cheeses were discovered by accident, but their history has also been documented for many centuries, as has the production of concentrated milks, butter, and even ice cream.

Technological advances have only come about very recently in the history of milk consumption, and our generations will be the ones credited for having turned milk processing from an art to a science. The availability and distribution of milk and milk products today in the modern world is a blend of the centuries old knowledge of traditional milk products with the application of modern science and technology.

The role of milk in the traditional diet has varied greatly in different regions of the world. The tropical countries have not been traditional milk consumers, whereas the more northern regions of the world, Europe (especially Scandinavia) and North America, have traditionally consumed far more milk and milk products in their diet. In tropical countries where high temperatures and lack of refrigeration has led to the inability to produce and store fresh milk, milk has traditionally been preserved through means other than refrigeration, including immediate consumption of warm milk after milking, by boiling milk, or by conversion into more stable products such as fermented milks.



World-wide Milk Consumption and Production

The total milk consumption (as fluid milk and processed products) per person varies widely from highs in Europe and North America to lows in Asia. However, as the various regions of the world become more integrated through travel and migration, these trends are changing, a factor which needs to be considered by product developers and marketers of milk and milk products in various countries of the world.

Even within regions such as Europe, the custom of milk consumption has varied greatly. Consider for example the high consumption of fluid milk in countries like Finland, Norway and Sweden compared to France and Italy where cheeses have tended to dominate milk consumption. When you also consider the climates of these regions, it would appear that the culture of producing more stable products (cheese) in hotter climates as a means of preservation is evident. Table 1 illustrates milk per capita consumption information from various countries of the world. Table 2 shows the quantity of raw milk produced around the world.

Table 1. Per Capita Consumption of Milk and Milk Products in Various Countries, 2005 data.



Country

Fluid Milk (Litres)

Cheeses (kg)

Butter (kg)

Finland

117.0

10.8

1.4

Norway

100.8

14.8

1.7

New Zealand

94.3

4.8

3.9

Sweden

93.7

16.3

1.2

Spain

92.7

6.9

0.2

Australia

80.8

7.1

0.8

United Kingdom

75.2

6.3

2.2

United States

67.8

5.5

0.7

Netherlands

60.3

10.7

1.4

Italy

57.8

15.5

1.1

European Union (25 countries)

57.2

5.8

1.0

Germany

54.5

9.4

3.3

Austria

51.4

7.8

2.8

Switzerland

51.3

11.6

2.4

Mexico

51.3

5.0

N/A

Canada

48.5

6.0

1.4

France

46.4

13.6

2.9

Argentina

33.5

5.4

0.8

Greece

30.3

14.3

0.7

Ireland

19.1

3.5

2.3

China

2.5

N/A

N/A













Source: Agriculture and Agri-Food Canada, Canadian Dairy Information Centre. This is national "retail" consumption data (although I am not sure how that is defined and compiled) divided by population, but please note that there are discrepancies from the data presented by the International Dairy Federation, in Bulletin 399/2005.

Table 2. Cow milk production ('000 tonnes) in selected countries in the world (2005).



United States

77,470

India

38,500

Germany

28,180

France

23,970

Brazil

23,300

China

18,850

New Zealand (2004)

14,500

United Kingdom

14,400

Poland

12,700

Netherlands

10,630

Italy

10,400

Australia (2004)

10,700

Mexico

9900

Canada

7540

 Source: Agriculture and Agri-Food Canada, Canadian Dairy Information Centre

Milk Composition

The role of milk in nature is to nourish and provide immunological protection for the mammalian young. Milk and honey are the only articles of diet whose sole function in nature is food. It is not surprising, therefore, that the nutritional value of milk is high.

Table 3. Composition of Milk from Different Mammalian Species (per 100 g fresh milk).

 

Protein (g)

Fat (g)

Carbohydrate (g)

Energy (kcal)

Cow

3.2

3.7

4.6

66

Human

1.1

4.2

7.0

72

Water Buffalo

4.1

9.0

4.8

118

Goat

2.9

3.8

4.7

67

Donkey

1.9

0.6

6.1

38

Elephant

4.0

5.0

5.3

85

Monkey, rhesus

1.6

4.0

7.0

73

Mouse

9.0

13.1

3.0

171

Whale

10.9

42.3

1.3

443

Seal

10.2

49.4

0.1

502

Source: Webb, B.H., A.H. Johnson and J.A. Alford. 1974. Fundamentals of Dairy Chemistry. Second Ed. AVI Publishing Co., Westport, CT., Chap. 1.

Table 4. Gross composition of milk of various breeds, g/100g.



 

Body Wt. (kg)

Milk Yield (kg)

Fat (%)

Protein (%)

Lactose (%)

Ash (%)

Total Solids (%)

Holstein

640

7360

3.54

3.29

4.68

0.72

12.16

Brown Swiss

640

6100

3.99

3.64

4.94

0.74

13.08

Ayrshire

520

5760

3.95

3.48

4.60

0.72

12.77

Guernsey

500

5270

4.72

3.75

4.71

0.76

14.04

Jersey

430

5060

5.13

3.98

4.83

0.77

14.42

Shorthorn

530

5370

4.00

3.32

4.89

0.73

12.9

Holstein: 12.16% T.S. x 7360 kg/lactation = 895 kg of total solids produced/lactation (140% of her body wt.!)

Jersey: 14.42% T.S. x 5060 kg/lactation = 730 kg of total solids produced/lactation (170% of her body wt.!)

Source: Webb, B.H., A.H. Johnson and J.A. Alford. 1974. Fundamentals of Dairy Chemistry. Second Ed. AVI Publishing Co., Westport, CT., Chap. 1.

Now you can return to the home page and work through the various topics within this Education Series systematically, or you can select any topic of interest for further, in-depth information. I hope you enjoy!


Milk Production and Biosynthesis


Milk Production


Milk is the source of nutrients and immunological protection for the young cow. The gestation period for the female cow is 9 months. Shortly before calving, milk is secreted into the udder in preparation for the new born. At parturition, fluid from the mammary gland known as colostrum is secreted. This yellowish coloured, salty liquid has a very high serum protein content and provides antibodies to help protect the newborn until its own immune system is established. Within 72 hours, the composition of colostrum returns to that of fresh milk, allowing to be used in the food supply.

The period of lactation, or milk production, then continues for an average of 305 days, producing 7000 kg of milk. This is quite a large amount considering the calf only needs about 1000 kg for growth.

Within the lactation, the highest yield is 2-3 months post- parturition, yielding 40-50 L/day. Within the milking lifetime, a cow reaches a peak in production about her third lactation, but can be kept in production for 5-6 lactations if the yield is still good.

About 1-2 months after calving, the cow begins to come into heat again. She is usually inseminated about 3 months after calving so as to come into a yearly calving cycle. Heifers are normally first inseminated at 15 months so she's 2 when the first calf is born. About 60 days before the next calving, the cow is dried off. There is no milking during this stage for two reasons:



  1. milk has tapered off because of maternal needs of the fetus

  2. udder needs time to prepare for the next milking cycle

The life of a female cow can be summerized as follows:

Age
0 Calf born

15 mos Heifer inseminated for first calf

24 mos First calf born - starts milking

27 mos Inseminated for second calf

34 mos Dried off

36 mos Second calf born - starts milking

Cycle repeats for 5-6 lactations


Automatic Milking




Effects of Milk Handling on Quality and Hygiene

Cleanliness


The environment of production has a great effect on the quality of milk produced. From the food science perspective, the production of the highest quality milk should be the goal. However, this is sometimes not the greatest concern of those involved in milk production. Hygienic quality assessment tests include sensory tests, dye reduction tests for microbial activity, total bacterial count (standard plate count), sediment, titratable acidity, somatic cell count, antibiotic residues, and added water.

The two common dye reduction tests are methylene blue and resazurin. These are both synthetic compounds which accept electrons and change colour as a result of this reduction. As part of natural metabolism, active microorganisms transfer electrons, and thus rate at which dyes added to milk are reduced is an indication of the level of microbial activity. Methylene blue turns from blue to colorless, while resazurin turns from blue to violet to pink to colourless. The reduction time is inversely correlated to bacterial numbers. However, different species react differently. Mesophilics are favoured over psychrotrophs, but psychrotrophic organisms tend to be more numerous and active in cooled milk.


Temperature


Milk production and distribution in the tropical regions of the world is more challenging due to the requirements for low-temperature for milk stability. Consider the following chart illustraing the numbers of bacteria per millilitre of milk after 24 hours:

5°C 2,600


10°C 11,600
12.7°C 18,800
15.5°C 180,000
20°C 450,000

Traditionally, this has been overcome in tropical countries by stabilizing milk through means other than refrigeration, including immediate consumption of warm milk after milking, by boiling milk, or by conversion into more stable products such as fermented milks.


Mastitis and Antibiotics


Mastitis is a bacterial and yeast infection of the udder. Milk from mastitic cows is termed abnormal. Its SNF, especially lactose, content is decreased, while Na and Cl levels are increased, often giving mastitic milk a salty flavour. The presence of mastitis is also accompanied by increases in bacterial numbers, including the possibility of human pathogens, and by a dramatic increase in somatic cells. These are comprised of leukocytes (white blood cells) and epithelial cells from the udder lining. Increased somatic cell counts are therefore indicative of the presence of mastitis. Once the infection reaches the level known as "clinical' mastitis, pus can be observed in the teat canal just prior to milking, but at sub-clinical levels, the presence of mastitis is not obvious.

Somatic Cell Count (000's/ml) Daily Milk Yield (kg): 1st Lactation Older Lactations

0-17 23.1 29.3

18-34 23.0 28.7

35-70 22.6 28.0

71-140 22.4 27.4

141-282 22.1 27.0

282-565 21.9 26.3

566-1130 21.4 25.4

1131-2262 20.7 24.6

2263-4525 20.0 23.6

>4526 19.0 22.5

Antibiotics are frequently used to control mastitis in dairy cattle. However, the presence of antibiotic residues in milk is very problematic, for at least three reasons. In the production of fermented milks, antibiotic residues can slow or destroy the growth of the fermentation bacteria. From a human health point of view, some people are allergic to specific antibiotics, and their presence in food consumed can have severe consequences. Also, frequent exposure to low level antibiotics can cause microorganisms to become resistant to them, through mutation, so that they are ineffective when needed to fight a human infection. For these reasons, it is extremely important that milk from cows being treated with antibiotics is withheld from the milk supply.

The withdrawal time after final treatment for various antibiotics is shown below:



Amoxcillin 60 hrs.
Cloxacillin 48 hrs.
Erythromicin 36 hrs.
Novobiocin 72 hrs.
Penicillin 84 hrs.
Sulfadimethozine 60 hrs.
Sulfabromomethozine 96 hrs.
Sulfaethoxypyridozine 72 hrs.

Anti-Microbial Systems in Raw Milk


There exists in milk a number of natural anti-microbial defense mechanisms. These include:

  • lysozyme - an enzyme that hydrolyses glycosidic bonds in gram positive cell walls. However, its effect as a bacteriostatic mechanism in milk is probably negligible.

  • lactoferrin - an iron binding protein that sequesters iron from microorganisms, thus taking away one of their growth factors. Its effect as a bacteriostatic mechanism in milk is also probably negligible.

  • lactoperoxidase - an enzyme naturally present in raw milk that catalyzes the conversion of hydrogen peroxide to water. When hydrogen peroxide and thiocyanate are added to raw milk, the thiocyanate is oxidized by the enzyme/ hydrogen peroxide complex producing bacteriostatic compounds that inhibit Gram negative bacteria, E. coli , Salmonella spp , and streptococci. This technique is being used in many parts of the world, especially where refrigeration for raw milk is not readily available, as a means of increasing the shelf life of raw milk.


Milk Biosynthesis


Milk is synthesized in the mammary gland. Within the mammary gland is the milk producing unit, the alveolus. It contains a single layer of epithelial secretory cells surrounding a central storage area called the lumen, which is connected to a duct system. The secretory cells are, in turn, surrounded by a layer of myoepithelial cells and blood capillaries.


The raw materials for milk production are transported via the bloodstream to the secretory cells. It takes 400-800 L of blood to deliver components for 1 L of milk.

  • Proteins: building blocks are amino acids in the blood. Casein micelles, or small aggregates thereof, may begin aggregation in Golgi vesicles within the secretory cell.

  • Lipids:

    • C4-C14 fatty acids are synthesized in the cells

    • C16 and greater fatty acids are preformed as a result of rumen hydrogenation and are transported directly in the blood

  • Lactose: milk is in osmotic equilibrium with the blood and is controlled by lactose, K, Na, Cl; lactose synthesis regulates the volume of milk secreted

The milk components are synthesized within the cells, mainly by the endoplasmic reticulum (ER) and its attached ribosomes. The energy for the ER is supplied by the mitochondria. The components are then passed along to the Golgi apparatus, which is responsible for their eventual movement out of the cell in the form of vesicles. Both vesicles containing aqueous non-fat components, as well as liquid droplets (synthesized by the ER) must pass through the cytoplasm and the apical plasma membrane to be deposited in the lumen. It is thought that the milk fat globule membrane is comprised of the apical plasma membrane of the secretory cell.

Milking stimuli, such as a sucking calf, a warm wash cloth, the regime of parlour etc., causes the release of a hormone called oxytocin. Oxytocin is relased from the pituitary gland, below the brain, to begin the process of milk let-down. As a result of this hormone stimulation, the muscles begin to compress the alveoli, causing a pressure in the udder known as letdown reflex, and the milk components stored in the lumen are released into the duct system. The milk is forced down into the teat cistern from which it is milked. The let-down reflex fades as the oxytocin is degraded, within 4-7 minutes. It is very difficult to milk after this time.


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