At the beginning of the cheese making process, the milk is heated to the required temperature to promote the growth of bacteria that ferment lactose into lactic acid. If milk is pasteurized before cheese production, it must be cooled to 32 ° C to promote the growth of the starter culture.
Acidification and coagulation
The production of acid at an optimum rate is essential for the production of quality cheese. Cheese can be roughly divided into yogurt or curd cheese.
Yogurt is made by adding acid directly to milk. Fresh cheese varieties, such as cream cheese, are made in this way. Adding 1.5% – 2% of the starter is a common way to reduce the pH of milk. Historically, adding starter to cheese milk 30-60 minutes before adding rennet was a common practice to reduce the pH of milk and improve the function of rennet.
Bacteria in milk may be wild or added as a starter. Homotypic bacteria only produce lactic acid during fermentation, while heterotypic bacteria produce other compounds, such as alcohols, aldehydes, ketones and carbon dioxide, in addition to lactic acid. Synfermentative bacteria are commonly used in cheeses, such as cheddar, to clean the sour taste. Heterologous fermentation bacteria produce a variety of flavors, including fruit. Typical starter cultures include Lactococcus lactis subsp. Lactic acid streptococcus or salivary streptococcus subspecies. Thermophilic bacteria, Lactobacillus delbrueckii subsp. Lactobacillus bulgaricus and Lactobacillus swiss. Auxiliary cultures can also be added to further enhance flavor and improve texture. These can cause holes in the cheese. Mold spores can also be added to milk when making mature cheese. Some cheese varieties still use starter; However, due to the risk of bacteriophage infection, many people have stopped this practice.
As a mature alternative, milk can be pre acidified directly by adding acids (lactic acid or hydrochloric acid) or acid producing agents (gluconic acid and lactone). Chemical acidification is mainly used for cheese varieties whose texture is more important than flavor. The acidification time ranges from 5-6 hours for cheddar cheese to 10-12 hours for Swiss cheese. The target pH varies depending on the type of cheese being processed. For example, Swiss and blue cheeses require a pH of 6.2 – 6.5.
Coagulation is an important step in cheese formation. If fat is present, it will coagulate casein to form a gel that wraps fat. Most cheese varieties (75%) are produced by coagulating with rennet. Coagulation milk contains rennet, which converts K casein into para-K casein and glycoprotein. Calf chymosin or chymosin produced by microbial processing can be used. Curd acts on milk proteins to form curd. After adding chymosin, the curd will not be disturbed for 30 minutes or more.
The third condensation method is acid/thermal condensation. This method is less common and is used to produce cheese from whey or a mixture of whey and skimmed milk.