Microbes and food 3. Food producers
3.2a Lactic acid fermentations
Lactic acid bacteria convert sugars to lactic acid. Flavours are produced as well and the increased acidity of the product helps to prevent the growth of unwanted spoilage bacteria and pathogens. Changes in texture may also occur.
Lactic acid bacteria photomicrograph
Picture 3.2b Lactic acid bacteria.

Dairy products

Cheese, yoghurt and fermented milk drinks are made using cultures that can produce acid from the milk sugar lactose, break down milk proteins and add flavour compounds and sometimes gas.

Yoghurt is a thickened, fermented milk made using a mixture of bacteria which work together to produce the desired acid and flavours. The microbes are only killed if the product is pasteurised to extend its shelf life. Many people believe that eating live yoghurt bacteria is good for their health.

Cheese manufacture depends on microbial activities at several stages to produce the required flavour, texture and appearance. There are many different types of cheeses. Blue cheese is made by inoculating the whole cheeses with a fungus which gives the typical taste and appearance.

Olives photo
Picture 3.2c Olives are made by lactic acid fermentation.

Fermented meats

Products like salami and chorizo rely on a combination of lactic acid fermentation with curing salts and drying for their keeping quality, safety and colour. Yeasts and moulds may also contribute to the flavour of these products.

Fermented vegetables

Sauerkraut, olives and gherkins are made by lactic fermentation of the brine-soaked food. A succession of different lactic acid bacteria is involved, sometimes together with certain yeasts and moulds.

Fermented doughs

Lactic acid bacteria work alongside baker’s yeast in some doughs to improve the structure, flavour and storage life of French bread and similar products.


Some of the flavours in wine are partly due to fermentations by bacteria which break down malic acid in the fruit juice to lactic acid and carbon dioxide gas.