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Commercial brewers make sure that beer production is as efficient as possible by providing the best possible conditions for yeast to grow and ferment. For this to happen, the following factors must be carefully controlled:

• temperature
• oxygen supply
• amount of glucose
• unwanted microorganisms must be kept out

The easiest way to make sure that this happens throughout the fermentation is to set up all the conditions at the start, together with the raw materials and then to leave the whole system closed and untouched until the fermentation is complete. This has the disadvantage that production is only possible in batches rather than by a continuous process. A production process like this is called batch processing.

Using bacteria to make cheese and yoghurt

Cheese and yoghurt making are also processes that depend upon microorganisms, in this case bacteria. The souring of milk is a fermentation process, as it takes place when oxygen is absent. Fresh milk contains sugars and some bacteria. The bacteria feed on the sugars in the milk. The main sugar in milk is called lactose. Lactose is converted into lactic acid by bacterial fermentation, the increased acidity sours and thickens the milk.

Bacterial fermentation can be summarized by the following word equation.

Lactose -----------> Lactic Acid

Enzymes in bacteria