How Is Skim Milk Made?

Sometimes my fridge contains too many varieties of milk — whole milk for my toddler, 2% low-fat milk for the other kids who hang out here, and skim milk for my husband. Seeing the lineup got me thinking recently: How exactly do you get all the fat out of skim milk, and is that the only difference between it and the other kinds of milk?

Skim milk goes by “skimmed milk” in the United Kingdom and Canada. It is also sometimes referred to as nonfat or fat-free milk.

For comparison, these are the minimum fat contents of the different kinds of milk as mandated by law:

• Whole Milk: 3.5% fat
• Low-Fat Milk: 1% or 2% fat
• Skim Milk: 0-0.5%, usually has an average fat content of 0.1%

So how is skim milk made? Traditionally, the fat was removed naturally from milk due to gravity. If fresh milk is left to sit and settle, the cream — which is where most of the fat is — rises to the top, leaving behind milk with much less fat.

The quicker, modernized way of making low-fat and skim milks is to place the whole milk into a machine called a centrifugal separator, which spins some or all of the fat globules out of the milk. This occurs before the milk is homogenized, a process which reduces all the milk particles to the same size so that natural separation doesn’t occur anymore.

Federal law mandates that most skim milk has to be fortified with vitamin A and sometimes vitamin D. This is due to the fact that even though whole milk naturally has a fair amount of both, the vitamins are fat soluble and thus lost when the milk fat is removed during the skimming process.

Milk solids in the form of dried milk are also added since they contain proteins that help thicken the watery consistency of skim milk.

Because of the lack of fat in skim milk, it is not a good substitute for whole or low-fat milk in cooking, as the lighter flavor and the thinner consistency would probably compromise the recipe.

There is one instance, though, where skim milk is better than whole milk: foaming! For foamed drinks like lattes and cappuccinos, skim milk is the most easily foamed because it’s fortified with protein that helps to foam and keep it stabilized.