The milk you purchase at the grocery store has a consistent texture, color, and creaminess, both in the jug and in every other milk jug. This consistency is also known as homogenous.
However, milk was not commonly homogenous in the United States even one hundred years ago. Until the 1920s, discovering a layer of cream at the top of milk was normal. Milk consists of the milk fat–cream–and the remaining milk. Without homogenization, the cream rises to the top as the rest of the milk settles.
Milkfat naturally rises to the surface, creating a top layer of cream. Begun in 1899, milk homogenization mixes that top layer of milkfat into the rest of the milk by breaking the milkfat into smaller particles. Essentially, the milk is shaken until the top layer is broken up into the milk and evenly dispersed. That’s it! Once shaken, the small milk fat particles stay mixed into the milk, resulting in a uniform texture.
Milk is often homogenized to give milk its rich, smooth texture. Homogenization is a process that breaks up the fat globules in milk so that they stay evenly dispersed in the milk. The term “homogenized” is used in chemistry, describing the process of converting a mixture of two mutually non-soluble liquids into a uniform liquid throughout, and it’s the same with milk.
The milk is agitated to break up the cream so that it is found evenly throughout the beverage. There are no chemicals involved in the process and homogenization does not change the quality of milk. It simply makes drinking milk more convenient because you don’t have to shake up the bottle to distribute the cream before drinking.
Today, this distinctive layer identifies non-homogenized milk with another name: cream line. While still available, non-homogenized milk options declined with time as milk became more accessible in urban and suburban communities. When people drink non-homogenized milk, they either skim the layer of cream off the top or shake the milk to distribute the cream back into the milk, which are similar processes done to create homogenized milk.
Deciding if you will purchase non-homogenized milk is a matter of personal preference, not a matter of safety. Homogenized milk is the most readily available option on your shopping list, but you can buy non-homogenized or cream line milk—just check the label or visit a specialty farm store.
For more information about homogenization and other processes, visit our Milk Safety page.