Bacteria That Feed Your Family
TINY bacteria, too small to be seen by the unaided eye, produce a nourishing food for you and your family. It is a tasty food that can be enjoyed just as it is, or it can be used to enhance many other foods. This delicious food is cheese.
There are many varieties. But, of course, the ones you see in a market are not all of them. All together, there are approximately four hundred different kinds. When you look at the variety of cheeses where you shop, do you ever wonder how they are made and what makes one differ from another?
Cheese is usually made from cow’s milk, but the milk of any animal can be used. In India there are cheeses made from buffalo’s milk, and in the Middle East camel’s milk is used to make a cheese called Krutt. Laplanders make one from reindeer milk, and in Nepal yak milk is used. The milk of goats and sheep is also used in a number of countries.
But when you look at a glass of milk and a piece of cheese you do not see much resemblance, do you? Yet the one comes from the other. Bacteria make possible the remarkable transformation of milk to cheese.
Preparing the Milk
If you were going to make cheese, how would you go about it? First, remember that milk is ideally suited to the growth of microorganisms, so it can easily become contaminated. For that reason the containers as well as the utensils used in making cheese must be sterilized. If the wrong type of bacteria gets into the milk, your cheese-making efforts may not succeed.
To give a freer field to the bacteria used for making cheese, heat the milk so as to destroy a portion of the microorganisms already in it. Then put in the bacteria needed to transform the milk to cheese. It is a type of bacteria that produces lactic acid by fermentation of the milk.
The bacteria can be obtained, either in liquid form or in a powder, from companies that specialize in producing high-quality cultures. When the powder is put into a small amount of sterilized milk, the bacteria are reactivated. Regard this milk as your starter culture or mother culture. Carefully protect it from contamination by other microorganisms.
It takes about twelve to eighteen hours for a mother culture to become ready for preparing a bulk starter of milk. Then when the bulk starter is ready, mix it into the vat of milk that is to be made into cheese. This bulk starter should amount to about 4 percent of the entire vat.
Once the bulk starter has been mixed through the milk, a fermentation process begins. This establishes an acid condition in the milk as a result of bacterial action. To aid the activity of the bacteria, warm the milk to 85 degrees Fahrenheit for the first hour or so.
Forming the Curd
At the moment when the rising acid condition of the milk is just right, mix in some rennet. Rennet contains the enzyme rennin, from the cells in the stomach lining of a calf. Manufacturers obtain rennet by processing the lining taken from the fourth stomach of calves.
Rennet acts as a catalyst, causing a chemical action in which the casein in the milk coagulates as an insoluble, visible curd. If the acidity of the milk is at the optimum level, the curd will become firm in about forty to fifty minutes, filling the entire vat with a solid mass. It is much like yogurt in appearance.
The temperature at which rennet produces a curd that is best suited for many varieties of cheeses is approximately 86 degrees Fahrenheit. After the rennet has been stirred through the milk, stirring must stop, and the milk allowed to remain absolutely quiet while coagulation takes place.
Cutting the Curd
The solid mass of curd needs to be broken up so as to allow the serum or whey to drain out. A wire knife consisting of a series of parallel wires is usually used by cheese makers for this purpose. It is inserted in the curd and is used in such a fashion that the curd is cut into quarter-inch or half-inch cubes. Sometimes larger cubes are cut when a cheese is desired with a higher moisture content.
As the acid acts on the casein in the curd, the curd undergoes changes in its physical properties. It mats together and becomes smoother, firmer and more elastic. A cutting machine is then used by cheese makers to cut the matted curd of certain cheeses into small pieces.
In some instances the curd is salted at this point, but in others the salting is done later by soaking the brick of cheese in a salt solution. The pieces of curd are now packed into molds, and these are subjected to pressure of four to eight tons.
The amount of pressure varies according to the type of cheese that is being made. In some instances no external pressure is applied. This is so with Roquefort cheese. If it were compressed too compactly, no air could seep into it, and that would prevent a desirable mold from forming within it.
Cottage cheese is handled differently. Instead of allowing it to mat it is washed two or three times to remove the acidity. Pasteurized cream can then be added to make the cheese creamy. Since cottage cheese does not ripen, it cannot be kept for very long and so must be eaten while fresh.
From the presses the cheese goes to a storage room for the ripening process. This also involves bacterial action that causes a breakdown of fat, protein and carbohydrates. Enzymes produced by the bacteria bring about these chemical actions, and they continue throughout the ripening period.
For the ripening process to go well the temperature and humidity of the storage room must be carefully controlled. The temperature may range from 40 to 60 degrees Fahrenheit, depending upon the type of cheese, flavor, texture and appearance desired.
The time that a cheese stays in this temperature-controlled room varies according to the type of cheese. It may be from two to forty-eight months. During that time the bacteria and the enzymes they produce bring about chemical changes in the cheese, causing it to become softer, more pliable and to have a more aromatic flavor. Cheese coloring is obtained by adding a coloring agent.
As might be expected, there are pests that can ruin cheese. One is the cheese mite. It is a very small insect that resembles a spider. When cheese mites have infested a cheese they leave its surface covered with a brown dust. In a short time they can reduce a cheese to a heap of dust.
Another pest is the cheese fly. It deposits eggs in the cracks and crevices of very old cheeses. The maggots hatch from the eggs and penetrate the cheese as they feed on it. Then they stay in a hollowed-out place until they develop into flies. The cheese, of course, is ruined for human consumption. Still another pest is a virus called bacteriophage, which can be very destructive in a cheese plant.
Varieties of Cheeses
Cheeses are classified as belonging to eighteen distinct types, and these are usually divided according to texture and flavor. The texture may be soft, medium or hard, and the flavor may be mild, medium or sharp.
A soft cheese may include a ripened cheese such as Camembert, as well as an unripened one such as cottage cheese. The latter is the simplest of the cheeses.
A medium or semisoft cheese is a ripened cheese. It includes such cheeses as Limburger and Munster.
The hard cheeses are also ripened cheeses and include Swiss and Cheddar. About ten pounds of milk are needed to make one pound of hard cheese.
A very popular variety is processed cheese. It is made by mixing and heating several lots of natural cheese. After the addition of an emulsifying agent this mixture becomes a homogeneous plastic mass. People like to use it in cooking because of the smooth way it melts. However, an undesirable feature is the fact that chemicals are used to emulsify, color, preserve, stabilize and thicken it.
There is indeed a great variety of delicious cheeses from which you can choose. All of these cheeses are excellent protein foods that contain vitamins, calcium, phosphorus and other minerals. And in view of the important role bacteria play in cheese making, when you put cheese on the dinner table you might say that bacteria are feeding your family.