Monday, May 10, 2010

Homogenizing Milk


How is Milk Homogenized?

There are 2 stages:

1)  In most cases, the milk is forced through a narrow opening at very high pressure until the turbulence causes the fat globules to break up into tiny pieces.  Typically the pressure is 2,000-4000 pounds per square inch (psi), but some super homogenizers produce 14,500 psi and higher.  (The heat from this can be so intense that it functions as a second pasteurization.)

2)  In the second stage, the little pieces of fat are broken up because they have a tendency to clump together.


Why is Milk Homogenized?

Milk used to be judged by the amount of cream that floated to the top of the bottle.  That was "cream-top" milk.  Then, the large dairies found that homogenizing the milk had 2 major advantages to them:

1)  They could lower the standard.  The 3.25% butterfat which is the norm in whole milk today is lower than the average amount of cream most cows provide- 4%.  (Some cows provide 8%!)  The dairies could then make butter and sell the cream separately with the extra butterfat they took from the milk

When the % was standardized by the industry, the dairies could also mix all kinds of milk together to achieve the final %.  In other words, nobody was looking in the bottle to see how much cream there was, so the weak milk went right into the mix and nobody was wiser.

2)  Homogenized milk lasts longer on the shelves than cream-top.

What does this mean for cheesemakers?

A lot of our customers are having good luck with cream-top milk.  The cream has formed on top because the fat globules are large enough to float to the top of the liquid.  (Most of this milk has been pasteurized because the sale of raw milk is still illegal in most states.)  They are having good luck because in most cases, unhomogenized milk is better for making cheese.  There are essentially three reasons why this is the case:

Flavor
When it comes to making cheese, it is widely accepted that when it is made from unhomogenized milk, it has more flavor.  This may or may not be true and there have been some studies that dispute this (Nair et al. 2001, Int. Dairy Journal 10:647).  But, in the Artisan Cheese world, milk is rarely homogenized before using it to make cheese.

We should note that flavor is very important, but if your only source of milk is homogenized, your homemade cheese is still going to taste much better (at least to you) than store bought.

Texture
Studies have been done and it is generally agreed that if you make your hard cheeses from homogenized milk, the curd may be too soft and your cheese may end up firmer and tougher than you would like it to be.

There are a few exceptions to this:  When making cheeses with cow's milk that are traditionally made with goat's or sheep's milk, (like Blue and Feta), homogenization may be beneficial.  Also, cream cheese made with homogenized milk may be smoother and creamier.

If you are making the pressed cheeses, and your only source of milk is pasteurized and homogenized, you might want to add calcium chloride to your milk.  We recommend adding as much CC as the amount of rennet your recipe calls for.

Anne Mendelson's book "Milk"
Nutrition
This is where the issue gets very controversial.  There was a study done by Kurt A. Oster which is widely touted, but has been disproved (Mary G. Enig, PhD).  After studying the effects of milk on the human body for twenty years, he theorized that the homogenization process contributes to a substance known as Xanthine Oxidase (XO) passing through intestinal walls into the circulatory system where it collects in the arteries. When you hear references to milk and heart disease this is usually the study they are citing.

Though Oster's theory is probably false, there are still concerns about homogenization. The process actually increases the surface area of the fat molecules. When the old membrane is lost, the new one contains a higher concentration of casein and whey proteins. This is thought to contribute to the higher incidence of milk allergies and lactose intolerance in our population.

Where do we stand?

In general, we here at NECS support the concept of processing foods as little as possible.  As far as we can see, homogenizing milk has no nutritional benefit to the consumer and there is some evidence that it might be detrimental.   We rarely use it to make cheese.

3 comments:

DavidM said...

My local dairy company advocates using skim milk (which obviously hasn't been homogenised), and adding whipping cream to it, essentially recreating cream-top milk, for cheesemaking. Makes some kind of logical sense (at least for the dairy, who gets to sell me the individual components which they have just laboriously separated). Does this make a difference in the cheese made from the re-constituted mailk vs. homogenised milk?

Jeri said...

David,
Your dairy is right about that. But, is the cream ultra-pasteurized? If it is, the benefit will be slight. If it isn't, the idea makes more sense. For more about this, contact our technical advisor, Jim Wallace at jim@cheesemaking.com.

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