The fermentation of food by a range of specific microorganisms has been used by humans for millennia to help preserve or transform foods. There is strong evidence that people were fermenting beverages in Babylon circa 5000 BC, ancient Egypt circa 3000 BC, pre-Hispanic Mexico circa 2000 BC, and Sudan circa 1500 BC. There is also evidence of leavened bread in ancient Egypt circa 1500 BC and of milk fermentation in Babylon circa 3000 BC. The Chinese were probably the first to develop vegetable fermentation.
In ancient times, fermentation was considered as a way of both preserving food and retaining its nutritional value. It was probably accidentally discovered in ancient Egypt when dough, made from ground-up wheat and rye, was left for a period of time before cooking. In contrast to dough that was immediately cooked, it was observed that the aged dough expanded in size and, when cooked, produced tastier, lighter bread.
The process was not completely reproducible: sometimes the uncooked dough yielded good bread and at other times it did not. However, if small amounts of good dough were added to the next batch, the bread was again tasty. The Romans went on to improve and perfect this process and popularised this sort of bread throughout the European continent.
The discovery of fermentation in Egypt also led to the first production of wine and alcohol. All these discoveries were largely phenomenological and it would be another 3000 years before the exact cause of fermentation was uncovered. It was Louis Pasteur, in 1857, who was able to demonstrate that alcohol can be produced by yeast when grown in particular conditions. This discovery revolutionised the modern food industry: for the first time the agent of fermentation was identified and could be used commercially.
In general, fermentation stabilises food by making it more acidic or alcoholic, so that undesirable microorganisms find it difficult to grow. Fermented products are often further protected from oxidation and infection by microorganisms by using air-tight containers, heat and possibly smoking. For instance, if wine is not protected from air, aerobic fermentation by Acetobacter will convert the alcohol into ethanoic acid (the principal component of vinegar).
- aids the preservation of vitamin C and actually produces vitamins B and K
- makes food more digestible - particularly some hard-to-digest starches
- can reduce the levels of some toxic compounds - such as hydrocyanic acid, oxalic acid, some aflatoxins and ochratoxin - in certain foods.
Fermentation is used to make many ethnic foods such as sauerkraut and miso. Soy sauce is produced by Aspergillus oryzae, a fungus, growing on soy beans. Erwinia dissolvens, another type of bacteria, is essential for coffee bean production; it is used to soften and remove the outer husk of beans. Finally, fermentation of milk produces many dairy products. Table 6.1 shows examples of several foods that are produced through fermentation.
Table 6.1 Some examples of foods which use fermentation in their production
|Food||Raw material||Fermenting microorganisms|
|Pickles||Cucumber||Leuconostoc mesenteroides, Lactobacillus|
|Chocolate||Cacao bean||Saccharomyces cerevisiae, Candida rugosa, Kluyveromyces marxianus|
|Coffee||Coffee bean||Erwinia dissolvens|
|Soy sauce||Soya bean||Aspergillus oryzae|