Microbes and food 3. Food producers
3.2c Other fermented foods
Vinegars photo
Picture 3.2g Vinegar is often used to preserve vegetables.


Vinegar contains acetic acid. It is an excellent food preservative and flavouring although it was originally discovered as a spoilage product of wine. It is made by a two-stage fermentation. First, yeast turns sugars into alcohol and then the alcohol is converted into acetic acid by bacteria. Malt vinegar is made from cereal-based liquor while wine vinegar is made from fruit juice. The Japanese make rice vinegar.

Soy sauce photo
Picture 3.2h Soy sauce is made using moulds acting on soya beans.

Eastern promise

In the Far East and Asia fermented products like tempeh, soy sauce and tofu are all made by the action of moulds on soya beans. Sake (rice wine) is actually a Japanese beer which is made by growing a mould on cooked rice. This mould breaks down the starches into sugars. Yeast is then added which converts the sugars into alcohol.

Chocolate and coffee

Coffee and cocoa beans (which are used to make chocolate) are both seeds which form inside pods on their parent trees. Both types of bean are coated in a slimy layer of plant tissue when they are harvested. Microbes are used to break down this material and prepare the beans for roasting. Bacteria that break down pectin carry out the digestion in coffee, but the fermentation of cocoa beans is more complex and involves acetic acid bacteria and yeasts as well.