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Fermentation is any process where microorganisms use an external food source for energy. This process is done in a fermenter, conditions are controlled by mixing, water jacket.


Below is a diagram of a simple fermenter. In industry, these would be very large and would have lots of different pipes and tubes coming out of it for various functions.

diagram of a fermenter

PaddlesInside the fermenter, they are rotated to evenly distribute the mixture.
Water JacketCold water is pumped through this to reduce and maintain the temperature. Respiration by microorganisms heats it up.
Data loggerMeasures a range of conditions (temperature, pH, oxygen concentration); measurements can be used to adjust the conditions in the fermenter.
ProductsProducts are removed, all at once in batch culture or bit by bit in continuous.
Air supplyProvides oxygen for respiration. Must be sterilised so no extra microorganisms contaminate the fermenter.

Yogurt Production

A fermentation process is used to make yogurt. Milk contains the sugar lactose; and some bacteria will ferment lactose to produce lactic acid.

Yogurt is produced by batch culture, where pasteurised milk has the bacteria Lactobacillus bulgaricus and Streptococcus thermophilus added. The mixture is maintained at a temperature of around 40°C. The bacteria will produce lactic acid by respiration, and this lowers the pH. When it reaches a target the product is harversed.