Tuesday, May 21, 2019
Our fourth stop in the journey of milk from the farm to the table is processing and packaging. This is the step in the process where the milk is pasteurized and packaged (and maybe turned into ice cream or your other favorite dairy products) at a dairy processing facility for shipment to grocery stores.
You’ll recall from our previous blog that milk is delivered to dairy processing plants in large tanker trucks. Once the milk is unloaded from the tanker truck, it is put through a separator – a machine that separates the milk into cream (fat) and skimmed milk. Regardless of the level of fat desired in the final fluid milk product, all milk goes through this step (yes, even whole milk) so that the precise amount of milk fat can be added back. While no fat is added back to skim milk, 1 percent, 2 percent and whole milk (3.5 percent fat) will have the respective amount of fat added back – this way, every time you choose 1 percent milk, it is the same amount of fat as the time before – exactly 1 percent.
The next step is to add vitamins A and D to the milk. Whole milk naturally contains vitamin A and some vitamin D, but it is supplemented in low-fat milk products to meet a certain “standard of identity” for milk (According to FDA rules, 2,000 international units of vitamin A and 400 international units of vitamin D are required for the milk to be allowed to be called milk). Supplementation of milk with vitamin D has helped to reduce the prevalence of rickets and other bone weakening conditions because vitamin D helps your body absorb milk’s calcium.
After vitamin supplementation, milk is homogenized. This is a process where milk is pumped through fine holes under high pressure to decrease milk fat globule size. Because fat is less dense than water, fat naturally separates and rises to the top of milk when it is not homogenized – while not harmful to have a layer of cream on the top of your milk, most people prefer homogenized milk. Homogenization helps create a smooth, uniform and appealing texture by dispersing the smaller fat molecules throughout the milk. Homogenization has no effect on the nutritional quality of milk.
Lastly, milk is pasteurized – the process of heating raw milk at a high enough temperature for a sufficient length of time to destroy bacteria, which can cause serious illnesses as well as yeasts and molds. Traditional pasteurization heats the milk to 161 degrees Fahrenheit for a minimum of 15 seconds while ultra-high temperature pasteurization heats the milk to 280 degrees Fahrenheit for a minimum of one to two seconds. Both methods ensure the milk is safe to drink and do not affect milk’s nutritive value. The high temperature method creates aseptic milk, you can read more about here.
Milk is then quickly cooled and packaged into bottles or cartons. During and after packaging, milk is kept cold in large refrigerated rooms. For every degree over 40 that milk reaches, the shelf life is reduced by 24 hours. This is why keeping milk cold is paramount to ensuring a high-quality product. It is also why you should pick up your milk last during your grocery store trip and take it home as soon as possible! Milk should stay below 40 degrees Fahrenheit to stay as fresh as possible for as long as possible.