To pasteurize or not to pasteurize? It's a pretty big question.
A satisfying endeavor for the home chef, cheese making is a process that offers much creative control. From soft, creamy mozzarella to sharp aged cheddar, the possibilities are endless. At the heart of the cheese making process is, of course, milk. Whether it comes from cows, goats, sheep or even water buffalo, milk is the main ingredient in all types of cheese, affecting the flavor and the consistency. Homogenization and pasteurization are two processes most modern milk goes through before it hits the grocer's shelf. While these procedures do affect the cheese making process, they are independent of one another in that you wouldn't choose one or the other, nor do they impact each other.
Homogenization
Many decades ago, milk was judged by its cream top -- the layer of cream that rose to the top of the glass jar after the milk was bottled. The thicker the cream layer, the better the milk. The down side of this is that the milk underneath the cream was often thin. Thus, homogenization was born. When milk is homogenized, it simply means that it has gone through a process that breaks up the fat molecules and distributes them evenly throughout the milk, creating the uniform consistency most milk drinkers enjoy today. The process has nothing to do with the safety of the milk, and while there is speculation that it impacts the nutritional value of the milk, this is unproven. When it comes to cheese making, homogenized milk can be used successfully in most recipes. Some artisan cheese makers posit that unhomogenized milk imparts a superior flavor, but this is debatable. If you're a home cheese maker and have access to unhomogenized milk, try it in a few cheese recipes and decide for yourself if the flavor is better than your homogenized cheese.
Pasteurization
In the mid-19th century, French scientist Louis Pasteur discovered that heating milk would kill harmful bacteria associated with typhoid fever, tuberculosis, diphtheria, among other diseases. By about 1940, it was (and still is) common practice in both Europe and the U.S. to pasteurize commercial milk. As with homogenized milk, pasteurized milk can be used in most cheese recipes without problem. Because the pasteurization process disrupts the milk's calcium balance, the curd from a pasteurized milk may be softer and more difficult to work with. If you find this is the case, add some calcium chloride, a supplement available from cheese making suppliers.
Ultra-Pasteurization
Ultra-pasteurized (or UHT) milk is -- as its name suggests -- pasteurized to a greater degree than regular pasteurized milk. The milk is heated at higher temperatures, allowing it to sustain a longer shelf life. UHT is not recommended for cheese making, especially for soft cheeses like mozzarella, as the protein structure and calcium balance are altered so severely, the milk won't coagulate properly to form curds.
Raw Milk
For some cheese makers, raw milk is the ideal dairy product. It is the unadulterated milk that comes directly from the animal -- no homogenization and no pasteurization. It generally has a higher butterfat content (i.e., more flavor) and the protein structure and calcium balance are as nature intended. Raw milk may even have a higher nutritional value, since its original structure is undisturbed. However, if you plan to use raw milk for drinking or for cheese making, it is vital that you understand the risks and fully research the safety of the milk. This means checking out the farm for cleanliness and quality of product. Many experts maintain that raw milk from organic grass-fed cows is optimal for raw milk.
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