Cheese is one of the most universal fermented foods, and also one of the most commonly made at home.
The theory of cheesemaking
Cheesemaking at its simplest involves three steps: acidifying milk, coagulating or "curdling" it, and separating the curds from the liquid whey to create a solid cheese mass.
The first stage in cheesemaking is to acidify the mixture. Most commonly, this is done by introducing a culture of lactic acid bacteria and allowing it to generate lactic acid; this bacterial transformation is why cheese is considered a fermented food. However, a few cheeses are acidified directly, through the addition of a strong acid solution such as vinegar.
Next, the acidified milk is curdled. If the acidity of the cheese is high enough, it will curdle the milk on its own; however, most cheeses are curdled through the addition of an enzyme solution known as rennet, which is usually derived from the stomach lining of cows and other animals (although vegetarian rennets are available). Curdling separates milk into solid or viscous curds, containing milk protein and fat, and liquid whey, containing primarily water and sugar.
Separating curds from whey
Once the curds are set, they are processed to separate out the liquid whey while retaining as much of the protein and fat contained in the curds as possible. The way in which this processing takes place determines the final form and consistency of the cheese.
Choosing and finding ingredients
The required ingredients for making cheese at home are a bacterial starter culture; rennet; and salt.
The milk used for cheesemaking will play a significant role in the flavor of the finished cheese. Any kind of milk may be used, with the exception of "ultra-heat treated" (UHT) milk or ultra-pasteurized milk. Both of these processes heat milk to such a degree that the proteins in the milk are denatured, preventing good coagulation.
A number of bacterial starters are available from cheesemaking supply companies for making different kinds of cheeses; the main varieties are "mesophilic" culture, used for making many soft cheeses, and "thermophilic" culture, used for making most hard and aged cheeses. However, in a pinch, the home cheesemaker can use a small amount of plain yogurt to inoculate and acidify the milk.
Rennet is also available in solid and liquid forms from specialty suppliers. The only alternative for most home cheese makers is the lower-quality "junket" rennet, sold in many supermarkets for custard making.
Salt is necessary to achieve the best flavor in most types of cheese. Any kind of non-iodized salt can be used, including specialty cheesemaking salt or fine sea salt. The iodine in iodized salt interferes with the bacterial reactions that give the cheese its flavor.
Making soft cheeses at home
Making soft cheeses at home is simple and easy, and requires very little equipment beyond what a home brewer or winemaker already has.
To make a simple soft cheese, simply add bacterial starter culture and rennet to milk that has been warmed gently on a stove or in a double boiler or water bath. After the curds have set, strain them through a fine cheesecloth known as "butter muslin," then tie up the ends of the butter muslin and hang the curds over a sink or bowl to drain. Once enough liquid whey has drained out of the cheese to reach the desired consistency, it may be eaten immediately.
Making hard cheeses at home
Hard cheeses require some additional equipment. Most important is a cheese press, which places constant pressure on a cheese to compact the curd and expel additional whey. Cheese presses can be expensive, but they can also be made at home fairly easily.
A hard cheese is made the same way as a soft cheese, except that instead of allowing the curds to drain in butter muslin, they are pressed in a cheese press until they are firm, then dried and aged. Hard cheeses are often coated in cheese wax or wrapped in bandages to prevent them from drying out or spoiling during the aging process.
The standard book on home cheesemaking is "Home Cheese Making" by Ricki Carroll, which contains detailed instructions and recipes and is a must read for aspiring home cheesemakers.
Ricki also runs the New England Cheesemaking Supply Company, at www.cheesemaking.com, which sells cheesemaking ingredients and equipment, including kits for beginners.