Unit C3-8 Food Science

Problem Area 3 Agricultural Processing Systems

Lesson 8 Making Cheese

Student Learning Objectives 1. Explain the effects of microorganisms in the cheese-making process. 2. Explain how/why milk curdles and describe the conditions at which milk will curdle. 3. Describe what happens to cheese during the ripening process.

Terms Casein Curd Hydrolyze Lactose pH Pasteurization Proteolytic enzymes Rennet Ripening Whey

What are the effects of microorganisms in the cheese- making process? A. Bacteria and fungus cultures are added to milk to initiate the fermentation process through enzymatic action. These starter cultures ferment lactose, or milk sugar, into lactic acid and other products. B. Lactic cultures are non-spore-forming bacteria and are harmless, except in very high populations. The lactic acid will destroy or inhibit food-borne pathogens and spoilage microorganisms by lowering the pH of the milk.

 1. The degree of acidity or alkalinity of a substance is known as the pH. On the pH scale from 0 to 14, 7 is neutral, anything lower than 7 is acidic and anything higher than 7 is alkaline, or basic. C. Lactic acid bacteria improve the flavor and texture of dairy products, along with increasing the absorption of calcium and the utilization of Vitamin D. Molds are added along with bacteria cultures to produce special cheeses, such as Swiss or Blue Cheese.

How and why does milk curdle and what are the conditions at which milk will curdle? Milk must curdle, or begin to ferment, to produce cheese. Most cheese products require the same basic curdling process. A. Milk contains 3.5% protein, of which about 80% is casein. Caesin is a phosphoprotein that is one of the chief constituents of milk and the basis for all cheese. Cheese is a food product derived from separating the curd, or soft, semi-solid substance made mostly of casein, from the whey, or watery liquid that is separated from the curd after coagulation. Caesin is formed into curds by the acid buildup created by bacteria.

B. Most proteolytic enzymes, proteins produced by living cells to speed up the transformation of milk casein into curd, will cause milk to coagulate. These enzymes hydrolyze, or break down, milk proteins and place them in an unstable state where curds begin to form at a pH of 4.6. The coagulation is brought about by lactose fermentation, which lowers the pH enough to begin curd formation. Coagulation occurs because milk proteins are being linked together.  1. Coagulation can be increased by an increase in temperature and acidity. Likewise, coagulation can be decreased by a higher milk fat content. The enzyme rennet is commonly used to aid in the coagulation of milk proteins in the fermentation process.

What happens to cheese during the ripening process and why does this happen? Cheeses must be allowed to ripen to enhance their flavor and texture. A. Cheese is a safe food product for consumers because the lactic acid and other end products inhibit the growth of food-poisoning organisms. Pasteurization, or the heating of milk to a temperature that kills microorganisms, also makes food poisoning by bacteria unlikely.

B. The type of cheese produced depends on the emphasis placed on specific steps in the cheese making process, environmental conditions during ripening, and microorganisms added for fermentation. Ripening, or the time allowed for cheese enzymes to breakdown fats, carbohydrates, and proteins, varies for each type of cheese being made. Some cheeses are ripened up to one year to enhance their flavor and texture. The ripening enzymes are released when the starter bacteria begin to break down.

Review/Summary What are the effects of microorganisms in the cheese-making process? How and why does milk curdle and what are the conditions at which milk will curdle? What happens to cheese during the ripening process and why does this happen?