The basic principle involved in making all natural cheese is to coagulate or curdle the milk so that it forms into curds and whey. As anyone knows who has left milk un-refrigerated for a period, milk will curdle quite naturally. The milk sours and forms into an acid curd.
Today’s methods help the curdling process by the addition of a starter (a bacterial culture which produces lactic acid) and rennet the coagulating enzyme which speeds the separation of liquids (whey) and solids (curds). There are two basic categories of starter cultures. Mesophilic starter cultures have microbes that can not survive at high temperatures and thrive at room temperatures. Examples of cheeses made with these bacteria are Cheddar and Gouda. Thermophilic starter cultures are heat-loving bacteria. They are used when the curd is cooked to as high as 55°C. Examples of cheeses made from these bacteria are Swiss and Italian cheeses.
The least sophisticated cheeses are the fresh, unripened varieties typified by Cottage Cheese. These are made by warming the milk and letting it stand, treating it with a lactic starter to help the acid development and then cutting and draining the whey from the cheese. The cheese can then be salted and eaten fresh. This is the simplest, most basic form of cheese.
Generally, cheese making starts with acidification. This is the lowering of the pH (increasing acid content) of the milk, making it more acidic. Classically, this process is performed by bacteria. Bacteria feed on the lactose in milk and produce lactic acid as a waste product. With time, increasing amounts of lactic acid lower the pH of the milk. Acid is essential to the production of good cheese. However, if there is too much acid in the milk the cheese will be crumbly. If not enough acid is present the curd will be pasty.
After acidification, coagulation begins. Coagulation is converting milk into curds and whey. As the pH of the milk changes, the structural nature of the casein proteins changes, leading to curd formation. Essentially, the casein proteins in the milk form a curd that entraps fat and water. Although acid alone is capable of causing coagulation, the most common method is enzyme coagulation. The physical properties of enzyme-coagulated milk are better than that coagulated purely with acid. Curds produced by enzyme coagulation achieve lower moisture content without excessive hardening.
Enzymes used to coagulate milk come from a number of sources: animals, plants, and fungi. The traditional source of enzyme is rennet. Rennet is a preparation made from the lining of the fourth stomach of suckling calves or kids. The most important enzyme in rennet is chymosin. Today, most chymosin is a recombinant product made possible by genetic engineering. Until 1990, the only source of rennin was calves. Around 1990, scientists created a system to make chymosin that doesn’t require calves. Using genetic engineering, the gene for chymosin was cut from a calf cell and inserted into the genomes of bacteria and yeast. The microbes make an exact copy of the calf chymosin. Microbes replicate and grow rapidly, and can be grown continuously. Thus, the supply of rennet is assured. Approximately 70% of the cheese made in the U.S. is coagulated using chymosin. The chymosin made by the yeast cells is the same as that made by the calf cells.
Cutting and Pressing the Curd
After the coagulation sets the curd, the curd is cut. This step is usually accompanied with heating the curd. Cutting the curd allows whey to escape, while heating increases the rate at which the curd contracts and squeezes out the whey. The purpose of this stage of the process is to make a hard curd. The term hard curd is relative; the cheese at this stage is still quite pliable. The main difference between a soft curd and a hard curd is the amount of water remaining in the curd. Hard curds have very little water left in them.
Once the curds have sufficiently hardened, salting and shaping begins. In this part of the process, salt is added to the cheese. Salt is added for flavor and to inhibit the growth of undesirable microbes. Large curds are formed as smaller curds are pressed together. This will often involve the use of a cheese press.
The shaped cheese is allowed to ripen or age for various periods of time. During this time, bacteria continue to grow in the cheese and change its chemical composition, resulting in flavor and texture changes in the cheese. The type of bacteria active at this stage in the cheese making process and the length of time the cheese is aged determine the type and quality of cheese being made.
Sometimes an additional microbe is added to a cheese. Blue veined cheeses are inoculated with a Penicillium Roqueforti> spore which creates their aroma, flavor and bluish or greenish veining. Such cheeses are internally moulded and ripen from the inside out. On the other hand, cheeses such as Camembert and Brie have their surfaces treated with a different type of Penicillium spore which creates a downy white mould (known as a bloomy or flowery rind) this makes them surface ripened cheeses.
Many surface ripened cheeses have their surfaces smeared with a bacterial broth. With others the bacteria is in the atmosphere of the curing chambers. These cheeses are called washed rind varieties as they must be washed regularly during their ripening period (longer than for Camembert or Brie) to prevent their interiors drying out. The washings also help promote an even bacterial growth across the surfaces of the cheeses. As this washing can be done with liquids as diverse as salt water and brandy, it also plays a part in the final flavor of the cheese.
The rinds of the cheeses are formed during the ripening process, many quite naturally. Some are created artificially. Rinds may be brushed, washed, oiled, treated with a covering of paraffin wax or simply not touched at all. Traditional Cheddars are wrapped around with a cotton bandage. The rind’s basic function is to protect the interior of the cheese and allow it to ripen harmoniously. Its presence thus affects the final flavor of the cheese. Salting plays an important role in rind formation. Heavily salted cheeses develop a thick, tough outer rind, typified by the Swiss range of cheeses. Cheddar, another natural rind cheese, is less salted than the Swiss varieties, and consequently has a much thinner rind.
I hope this introduction to principles of cheese making has been interesting and informative. As you begin to make home made cheese, I would advise to start with the simple quick cheese recipes. Then, move on to the soft cheeses and finally the hard cheeses. You’ll find that you learn more about the process every time you try a recipe. Your final cheese is affected by many factors. I would advise using a log book in which you can record such factors as starter type and amount, inoculation time, temperature, etc. Each recipe will have different factors you’ll need to look at. The use of a log book will help you reproduce your outstanding cheeses on command, while avoiding the many pitfalls that can ruin your hard work.