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What is fermenting?

Fermentation is an ancient technique for preserving food and drinks that has been practiced since long before the days of refrigeration. Fermented food and drinks are produced via controlled microbial growth and enzyme actions, which convert some of the food’s components into other compounds.

During fermentation, microorganisms like bacteria, yeast or fungi convert organic compounds like sugars and starch into alcohol or acids. These act as natural preservatives and improve the taste and texture of fermented foods, leaving them with a distinctive strong, salty and slightly sour flavour.

There are two main methods of fermentation: natural or spontaneous. Spontaneous fermentation occurs when the micro-organisms naturally present in the food or environment initiate fermentation, or secondly by the addition of a ‘starter culture’. An example of a natural fermentation would be in the production of kimchi or sauerkraut, whereas a starter culture is used to product kefir or natto.

Fermentation is used in many food production methods, including that of yogurt and cheese.

Discover more tips for digestive health and browse our gut-healthy recipes. Want to have a go at making your own ferments? Follow our guides for how to make kombucha, how to make kefir and our quick kimchi recipe. Also check out our health and nutrition page for more recipe inspiration, health benefits guides and advice on special diets.

Nutritional profile of fermented foods

There are many variables involved in fermentation. These include the micro-organisms at work, the nutritional contribution of the ingredients used and the environmental conditions to which they are exposed. What this means is that each of these factors gives rise to thousands of different variations of fermented foods, with associated variability in their nutritional contribution.

Top 5 health benefits of fermenting

1. Source of beneficial lactic acid bacteria

Most fermented foods contribute bacteria that have a potential probiotic effect. This means that these bacteria may help restore the balance of bacteria in your gut, support digestive health and alleviate any digestive issues. Probiotic amounts will vary, however, and the number of bacteria that arrive in the gut, where they can be of benefit, will depend on a number of factors, including the food in which they are delivered, with those supplying fibres referred to as prebiotic being the most beneficial.

2. Easier to digest

As some of the natural sugars and starches have already been broken down, fermented foods are easier to digest. For example, fermentation breaks down the lactose in milk to simpler sugars – glucose and galactose – that, if you are lactose intolerant, may make products like yogurt, kefir and cheese easier to digest.

3. Improves the availability of nutrients

When we ferment certain types of food, we help increase their health potential. This includes making the vitamins and minerals they provide more available for our bodies to absorb. This is because some natural compounds, like phytic acid found in legumes such as soy beans, may inhibit our absorption of nutrients like iron and zinc. However, by fermenting these foods, we remove these ‘anti-nutrients’, making their nutritional content more available to us. The same benefits have been seen with sourdough, with improvements in mineral availability, lower glycaemic responses and a greater break down of proteins all being cited.

Additionally, by boosting the beneficial bacteria in your gut, you may promote their ability to manufacture B vitamins and vitamin K.

4. May improve mood and behaviour

Our understanding of the gut and how it impacts our mood and behaviour is fast evolving, and it would appear that fermented foods may play an important part. Certain strains of probiotic bacteria, including Lactobacillis helveticus and Bifidobacteria longum, commonly found in fermented foods, may improve symptoms of anxiety and depression.

Another strain, Lactobacillis casei Shirota, may also influence the production of cortisol and minimise physical symptoms of stress.

5. May support heart health

Consuming fermented foods as part of a healthy, balanced diet appears to be associated with a lower risk of heart disease. The mechanisms at play may include modest reductions in blood pressure and improvements in cholesterol balance.

Is fermented food safe for everyone?

Fermented foods are safe for the majority of people, but some individuals, such as those with a histamine intolerance, may experience side effects. Furthermore, if fermented foods are new to you or you are not used to a fibre-rich diet, you may experience symptoms such as bloating and flatulence.

Introducing fermented foods to someone who is critically ill or immune-compromised should be done with caution and under the guidance of a GP or healthcare professional.

When making your own fermented foods, always follow recipes and be sure to use sterile equipment, and follow fermentation times and temperatures carefully.

Read more health benefits guides:

Top 5 health benefits of kombucha
The health benefits of kefir
The health benefits of miso
The health benefits of sourdough

This article was updated on 8 November 2021 by Kerry Torrens.

Kerry Torrens is a qualified Nutritionist (MBANT) with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food.


All health content on is provided for general information only, and should not be treated as a substitute for the medical advice of your own doctor or any other health care professional. If you have any concerns about your general health, you should contact your local health care provider. See our website terms and conditions for more information.

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