Fermentation is the process where alcohol (ethanol), carbon dioxide, and/or organic acids (e.g., acetate, propionate, butyrate and lactate) are produced from foods (primarily from carbohydrates, but also some proteins) by yeast, bacteria or fungi – mostly under anaerobic (oxygen-free) conditions. The accumulation of alcohols and organic acids and the associated decrease in pH (i.e., increased acidity) inhibits the growth of competing microorganisms and the activity of enzymes in the food, reducing the rate of spoilage and consequently extending the products shelf-life. Due in part to their acidity, fermented foods tend to be sour tasting, but they can be very complex in flavour which adds to their culinary appeal.
In the case of alcoholic beverages (e.g., beer, cider and wine), yeast is used to ferment sugars from grains or fruit into alcohol, whereas in yoghurt bacterial cultures are used to ferment the sugar lactose from milk into lactic acid. Fungi can also be used to ferment foods, such as the Japanese filamentous fungi Aspergillus oryzae called koji used to make miso from soybeans. Sourdough bread is another example of a fermented food using wild yeasts in a sourdough culture. The ripening of cheeses involves the introduction of microbes (e.g., bacteria) that develop flavour from breakdown products of proteins and fatty acids in milk, and moulds are sometimes introduced such as in blue-vein cheese.
Common fermented foods and beverages
It has recently been estimated that there are more than 5000 different kinds of fermented foods consumed by people living in different parts of the world. Here are some more common varieties that you may have heard of or even tried:
- Sauerkraut – fermented cabbage
- Kim chee – Korean sauerkraut with added chilli
- Tempeh – fermented soybean cake, similar to tofu but with a beanier, lumpier texture
- Miso – fermented soybean paste used as a soup base and marinade
- Yoghurt – cultured milk using a variety of lactobacillus strains
- Kefir – milk drink cultured with bacteria and yeasts – the bacteria is different to yoghurt
- Surströmming – lightly salted, fermented Baltic Sea herring traditional to Sweden
- Salami – a cured sausage consisting of fermented and air-dried meat, typically pork
- Kombucha – an effervescent fermented tea
What are the benefits?
The primary benefits of food fermentation are food safety and extended shelf-life; however, fermented foods have become increasingly associated with certain health benefits as well.
Fermented foods may be more easily digested than their unfermented counterparts due to partial protein digestion during fermentation, reduction in lactose content (when present), and they can also be enriched in certain vitamins (e.g., B12 and biotin ) and antioxidants.
Clinical trials and observational studies indicate that there are potentially many health benefits, although the quality and strength of the evidence is generally not high. Studies have found:
- Associations between consumption of fermented dairy products and weight management.
- Consumption of yoghurt associated with reduced risk of cardiovascular disease, type 2 diabetes, and mortality (death).
- Enhanced glucose metabolism and reduced muscle soreness following acute resistance exercise as a consequence of consuming fermented milk.
- Anti-diabetic and anti-obesity effects when regularly consuming kimchi.
- Alterations in mood and brain activity and in the gut microbiome (i.e., brain-gut axis).
However, systematic reviews have identified a lack of sufficient clinical trials, variation in the different fermented foods being investigated, and inconsistencies among ethnic groups, suggesting that more research needs to be undertaken in order to confirm the potential health benefits of consuming fermented foods and beverages.
- Leeuwendaal and colleagues. Fermented Foods, Health and the Gut Microbiome. Nutrients. 2022