Any foodstuff can be fermented, particularly meat, milk, cereals, fruit and vegetables. The ferments in the raw material feed by converting sugar and protein into alcohol, acid and carbon dioxide. These different products change the ambient conditions and can thus prevent undesirable microorganisms from multiplying. We are familiar with the food resulting from these fermentation processes and it is regularly found on our tables. Yoghurt is made from fermented milk. The lactic acid produced when bacteria transform lactose coagulates the casein to form a gel. This is lactic fermentation. When cheese is made, the action of rennet, an enzyme extracted from the abomasum of young ruminants, is added to the lactic acid fermentation.
Wine can be made from any fruit. The yeasts that are naturally present on their surface come into contact with their sugary juice during pressing and convert the sugar into alcohol, releasing CO2. This is alcoholic fermentation.
Vinegar is made from fruit juice using a double fermentation process: first alcoholic, then acetic. Acetic acid bacteria develop quickly on the surface of the fruit juice and form a film called the mother of vinegar. They then convert the alcohol produced by the fermentation of the fruit juice into acetic acid.
Bread is prepared from dough made from flour, water and salt to which the baker adds ferments in the form of leaven or yeast. In the case of leavened bread, there are two simultaneous fermentation processes, alcoholic and lactic.