Cream Cheese

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Cream cheese is easy to make at home, and many methods and recipes are used. Consistent, reliable, commercial manufacture is more difficult. Normally, protein molecules in milk have a negative surface charge, which keeps milk in a liquid state; the molecules act as surfactants, forming micelles around the particles of fat and keeping them in emulsion. Lactic acid bacteria are added to pasteurized and homogenized milk. During the fermentation around 22 °C (72 °F), the pH of the milk decreases (it becomes more acidic). Amino acids at the surface of the proteins begin losing charge and become neutral, turning the fat micelles from hydrophilic to hydrophobic state and causing the liquid to coagulate. If the bacteria are left in the milk too long, the pH lowers further, the micelles attain a positive charge, and the mixture returns to liquid form. The key, then, is to kill the bacteria by heating the mixture to 52–63 °C (126–145 °F)[citation needed] at the moment the cheese is at the isoelectric point, meaning the state at which half the ionizable surface amino acids of the proteins are positively charged and half are negative.