How Milk Gets from the Cow to the Store

Although some dairies have their own unique methods of milk production, most dairies in the United States follow the eight-step process seen below. Those eight steps are (in order): grazing, harvesting, storing, transportation, lab testing, processing, packaging and selling.

Step 1 - Cows Grazing

Holstein cows grazing, 2007Dairy cows at the feeding trough, 2007

Dairy cows typically spend their days eating, sleeping, and ruminating or chewing their cud. Cows in some dairy farms wander around and eat fresh grass (i.e. grazing). In other farms, they are fed grain, hay, or silage (conserved forage) and remain in close quarters all day.

Step 2 - Harvesting Milk

Hand milking a cow, 2007

A cow is ready to be milked when her udder is full. The farmer has some flexibility when making a schedule of cow milking times. Usually, cows are milked in the early morning and again in the late afternoon. It is possible to milk a cow by hand. However, milking a whole herd of cows twice a day in this manner would take a great deal of time and energy. Before the invention of milking machines, people milked their dairy cows by hand by squeezing gently on the cow's teats using the thumb and forefinger. Some people continue to milk a little by hand today.

Cows are normally milked at least 2 times per day. 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 over 20 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.

Step 3 - Storing Milk

Milk storage vat, 2007

Milk storage vats or silos are refrigerated and come in various shapes and sizes. Milk is usually stored on farm at 39 degrees Farenheit 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 transportation truck, 2007

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 processing.

Step 5 - Laboratory Testing

Milk testing in a laboratory, 2007
Source: AgSource Food and Environmental Division

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 antibiotics 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 does not meet quality standards it is rejected. Most farmers are paid on the quality and composition of their milk.

Step 6 - Processing Milk

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

Involves heating every particle of milk to a specific temperature for a specified period of time and cooling it again without allowing recontamination.

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.

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 yogurt products.

Step 7 - Packaging Milk

Machine filling and packaging milk, 2007

Now the milk is ready to be packaged for delivery to the stores where it will be sold. The milk travels through pipes to the automatic packaging machines that fills and seals the milk into paper cartons or plastic jugs. As the containers move through the assembly line, a date is printed on each of them to show how long the milk will stay fresh.