Making Cheese To make cheese you need milk, milk clotting enzyme (rennet), bacterial cultures and salt. Rennet causes the milk proteins (caseins) to clump.

Presentation on theme: "Making Cheese To make cheese you need milk, milk clotting enzyme (rennet), bacterial cultures and salt. Rennet causes the milk proteins (caseins) to clump."— Presentation transcript:

1 Making Cheese To make cheese you need milk, milk clotting enzyme (rennet), bacterial cultures and salt. Rennet causes the milk proteins (caseins) to clump together and they change the liquid milk into a semi-firm gel. When this gel is cut into small pieces (curds), the whey (mostly water and lactose) begins to separate from the curds. Many combinations of bacteria, enzymes, aging processes, moisture and humidity are controlled in the cheese making process.   Most cheeses found in the supermarket are made using rennet and a combination of different bacteria.

2 Making Cheese Effect of pH: Lowering the pH increases the enzyme activity and therefore coagulation (clotting) takes place more quickly at a lower pH. Effect of Calcium: Calcium is needed to help to clump the casein. Almost instant coagulation can occur by adding sufficient calcium chloride. Effect of temperature: The optimum coagulation temperature for most cheese is 30-32°C, the exception is Swiss which is set at 37°C. At temperature less than 30°C the gel is weak and difficult to cut and at temperatures less than 20°C coagulation does not occur. Effects of heat treatments: Mild heat treatment such as pasteurization decreases the rate of coagulation. During heat treatment calcium becomes less soluble so there is less calcium available to assist with coagulation. Heat treatment of milk in excess of pasteurization temperature (UHT) results in an increased clotting time and a weak gel. High heat treatments cause absorption of whey proteins onto the casein particles. The casein particles are then unable to form a strong gel.

3 Making Cheese Coagulating Enzymes
The traditional enzyme is rennet (chymosin) which comes from the stomach of milk fed calves. The practice of cheese making probably began when somebody discovered that milk stored in bags made from calf stomachs formed a sweet curd. Other protease enzymes which have been used for cheese making include: Pepsins from pigs cows and chickens Proteases from fungi – e.g. rennilase/fromase Synthetic chymosin made by recombinant DNA techniques using strains of Klyveromyces lactis as the host organism. The transferred genetic material exists in a plasmid inside the host cell. It is used to produce an enzyme identical to chymosin.

4 Making Cheese Altering pH:
1 cm³ of 1 mol dm-3 hydrochloric acid added to 10 cm³ of milk plus enzyme results in a pH of about pH 1 1 cm³ of 1 mol dm-3 citric acid added to 10 cm³ of milk plus enzyme results in a pH of about pH 5 1 mol dm-3 sodium hydrogen carbonate added to 10 cm³ of milk plus enzyme results in a pH of about pH 8 1 mol dm-3 sodium hydroxide added to 10 cm³ of milk plus enzyme results in a pH of about pH 14 distilled water added to 10 cm³ of milk plus enzyme results in a pH of about pH 7 Calcium chloride concentration The following concentrations are suggested: 0.02% calcium chloride; 0.05% calcium chloride; 0.1% calcium chloride; 0.5% calcium chloride: