In most cases, milk processing begins in a dairy. A dairy is a type of farm devoted to raising and tending cattle in order to use them for milking. After the milk is collected, it goes through a process of clarification and separation, after which it is fortified with vitamins. Once fortified, the milk must be pasteurized and homogenized, processes that kill bacteria and reduce the amount of fat content. Once these procedures are complete, the milk is ready to be packaged and sold.
On most dairy farms, cows are milked twice per day. Milking is done using vacuum equipment that transfers the milk to refrigerated holding tanks. This milk is later collected by refrigerated trucks that transfer the milk to a processing facility. Before transport, the drivers check to be sure that the milk in the refrigerated tanks is suitable for use, a process normally done by testing temperature and flavor. When the truck arrives at the processing plant, milk is pumped from the truck into tanks that will hold the milk ready for the separation and clarifying process.
Clarification is a step in milk processing that ensures the milk will be free of bacteria and debris. Milk is put into large vats that continually spin. The spinning causes the milk to separate from debris and floating bits of bacteria. After clarification is completed, the milk is spun once again to separate heavier and lighter milks. Heavier milks might be used for butter, cream, or buttermilk, while lighter milks are reserved for the majority of table milks.
The next step in milk processing is typically fortifying with vitamins. Most of the time, vitamins A and D are pumped into the milk in carefully measured amounts. Once the vitamins are in the milk, it is ready to be pasteurized. Pasteurization is an added step that helps kill any remaining bacteria present in the milk. Pasteurization is usually done by heating the milk as it passes through steel pipes.
Homogenizing is a step in milk processing that eliminates some of the remaining milk fat. This is done by using heat to reduce the size of fat particles. Without homogenization, fat particles would eventually separate from the milk and float to the top.
The final step in milk processing is putting the milk into retail containers. Some of the containers may be paper cartons, while others are plastic jugs. Most countries require that milk containers be stamped with dates that indicate their shelf life. Once the containers are ready for shipping, they are sent to distribution warehouses where they are kept refrigerated until they are delivered to grocery stores.