Homogenization
Sometimes used in cheesemaking, homogenized milk can have downstream effects on cheese texture and flavor.
Milk Chemistry Review
As we’ve discussed before, milk is an emulsion. An emulsion is a dispersion of droplets (called the dispersed phase) in another liquid (called the continuous phase). In milk, the dispersed phase is fat globules and the continuous phase is “water” (“water” being a mixture of water, minerals, proteins, etc.) The proteins contained in the water-portion play an important role in homogenization, which we’ll get to in a bit.
Milk is an emulsion, with dispersed fat globules
WARNING: Math
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Emulsions, left to their own devices, are usually very unstable. This means they want to separate. In our case, the fat in the milk wants to rise and form a “cream line” or “cream top”. This is the same phenomenon you see when a vinaigrette salad dressing separates in the bottle. The behavior of the fat globules can be described by Stokes’ Law.
Stokes' Law
The variables in the equation shed light onto how emulsion stability can be improved. V refers to the speed of the fat globule in milk. We want that speed as slow as possible so the fat stays in the milk and doesn’t rise quickly to the top. Homogenization effectively makes smaller fat globules therefore lowering the value of r in the above equation. This will lead to a smaller value for V and thus a more stable emulsion! This is a simplistic view of emulsion stability, but it gets the point across. Read on to see what homogenization does to the fat globules and how that effects cheese!
TopProcess
The goal of homogenization, for fluid milk, is to prevent that cream from rising. To accomplish this, we have to make the fat globules smaller so they are less likely to merge together and rise. Tremendous amounts of force is exerted on the milk breaking the fat globules into smaller pieces. These smaller globules are now more stable and less likely to rise and form the cream line. In addition to the fat globules being a smaller size, casein and whey proteins may also get embedded in their surface. These new fat globules can now behave as pseudo proteins. Since cheese structure is protein, these new fat/pseudo-protein particles can change final cheese texture.
Homogenization breaks down the fat globules and can embed proteins in their surface
(Not to scale)
Effects on Cheese
Homogenization isn’t that popular in cheese making outside of certain niche uses. The added cost and time don’t make it a worthwhile venture unless the cheese maker has a very specific need for it. Milk/cream may be homogenized for the production of blue cheese. The rough treatment of the fat globules can expose them to more enzymes and increase lipolysis, leading to more flavor. The final cheese may also have a whiter color due to homogenization. Cream cheese is another common example; homogenization results in smoother texture and better fat recovery.
Homogenization is often used for blue cheese
Some other effects could include: brittle curds during cheese make, less oiling off (e.g. mozzarella on pizza), and more easily fractured cheese. The overall effects are very dependent on cheese type, extent of homogenization, and many other parameters. Much of these structural changes are due to the presence of those small fat globules with embedded proteins. Fat, for the most part, is usually just along for the ride in the cheese structure. Now that the fat is homogenized and acts as a "pseudo-protein", it actively takes part in the cheese structure. There are many other ramifications and the cheese maker has to weigh the pros and cons in order to decide if homogenization is necessary.
TopFor More Information
- Wikipedia - Homogenization
- University of Guelph - Homogenization
- University of Guelph - Effect of Homogenization
