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Fermentation in the vegan diet: What are the effects? When you think of fermented food, sauerkraut might come to mind. But you cannot only ferment white cabbage, but also many other vegetables. Additionally, not only vegetables can be fermented. There are many other fermented foods. In this article, you will find out what they are, how fermentation works, and why and how you can try it out when following a vegan diet.
Fermentation is known especially among the health-conscious people on a vegan diet, and many benefits are attributed to fermentation. But what exactly does “fermentation” mean, and are fermented foods really that healthy? Should you include fermentation in your vegan diet?
Definition of Fermentation
Put simply, fermentation creates one food into another – simply by waiting!
More precisely formulated: Fermented foods are “foods or beverages made through controlled microbial growth and enzymatic conversions of major and minor food components” (Marco et al., 2017). Originally, the fermentation process was used to make foods last longer. Today, consumers also appreciate the special taste and changed texture resulting from fermentation. It is often claimed to be important in the vegan diet.
What is Being Fermented?
Most people know that vegetables can be fermented. Many are also familiar with sourdough fermentation with the associated lactic acid bacteria.
When fermenting vegetables, the lactic acid fermentation lowers the pH value and the fresh vegetables become a longer-lasting product with a different taste and texture. You will learn more about why this is the case later.
Bread is also made with the help of microorganisms, the yeasts, by generating the leavening of the dough. They produce the gas carbon dioxide in the dough ripening or fermentation process, which makes the dough “rise.” In the case of sourdough, in addition to improved baking properties, as in the case of fermented vegetables, desirable aromatic substances are formed, digestibility is improved, and the growth of undesirable organisms is inhibited by lowering the pH. By the way, the aroma differs depending on the ratio of acids formed (mainly from acetic acid: lactic acid) (Marco et al., 2017; Elmadfa and Ebermann, 2011).
But did you know that besides these two well-known products, many other foods are produced by fermentation? Both plant foods and products of animal origin are among them.
Vegetables that are well suited for fermentation:
- white cabbage
- chinese cabbage
- carrots
- tomatoes
- cucumbers
Other plant foods produced by fermentation:
- sourdough bread
- soy sauce
- tempeh
- miso
- natto
- vinegar (not always vegan)
- partly plant-based jogurt, “feta”
- herbs (e.g. vanilla)
Fermented products of animal origin:
- sour milk, sour cream, kefir
- joghurt
- cheese (e.g. blue cheese, but also hard cheeses)
- sausages (raw sausages, e.g. salami)
Fermented drinks:
- beer
- wine (not always vegan)
- kombucha
- coffee
- kakao
- tea
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The term fermentation (fermentum, Latin for “fermentation”) goes back to the French biochemist Louis Pasteur, who described the fermentation of organic material (food) into acid, gases or alcohol. Generally speaking, the process of fermentation is a natural biochemical process that takes place with the help of microorganisms (bacteria, molds or yeasts) under low-oxygen conditions. These microorganisms, for example lactic acid bacteria, process the carbohydrates of the food into low molecular weight fractions (Farnworth, 2008).
A distinction is made between two different fermentation processes:
- spontaneous fermentation: the microorganisms are present in the raw food or arise during the process (e.g. sauerkraut, kimchi)
- starter culture-dependent fermentation: the microorganisms are added externally in the form of starter cultures (ferments) (e.g. for kombucha, tempeh). Defined starter cultures can be used to standardize the properties of the end product.
The type and quantity of microorganisms present in the fermented food and the associated effect depend on the ingredients, temperature, and fermentation time, among other factors (Zabat et al., 2018; Dimidi et al., 2019).
The microorganisms convert organic substances of plant or animal origin into metabolic intermediates (i.e. intermediate products, such as sugar, lactic acid and carbon dioxide) by means of metabolic enzymes in a low-oxygen environment. This acidity lowers the pH (< 4) of the surrounding environment, which suppresses the growth of undesirable bacteria or fungi; the reason why fermentation has been used as a preservation method for centuries. On the one hand, the addition of salt to the vegetable removes the breeding ground for undesirable microorganisms, while the lactic acid bacteria tolerate the salty environment. On the other hand, easily fermentable carbohydrates are transported out of the cell by the hygroscopic salt; two factors that promote preservation (Sabersky, 2017).
Originally, fermentation was defined as a completely anaerobic process, that means without any supply of oxygen. Nowadays, however, some fermentation processes are also carried out under the influence of oxygen (aerobic), for example vinegar production.
Cultural Aspects
A well-known example of the cultural use of fermented foods is the Southeast Asian region; India is considered the country of origin of fermentation, where traditional dishes such as idli, a small cake fermented from beans and rice, are still consumed today (Durgadevi and Shetty, 2012). In Korea, dishes made from fermented foods or ingredients are popular (Shin and Jeong, 2015). China has always enjoyed fermented foods, such as those made from soy or also vegetables (Chen et al., 2016).
African populations also benefit from fermented foods, and not just from a health perspective: Culturally and socioeconomically, fermented foods and beverages are important in Namibia, for example (Misihairabgwi and Cheikhyoussef, 2017).
Use of Fermented Foods
The fermentation process already has a very long tradition and is now carried out biotechnologically in industrialized countries. But it is also becoming increasingly popular in private households.
Fermentation was introduced into society’s preparation methods at a very early stage, and is the oldest preservation strategy after the drying of food. Maybe your grandma had many jars of pickled fermented vegetables in the cellar? People quickly realized that this not only preserved food, but also brought about sensory changes (Farnworth, 2008).
In Pasteur’s time in the 19th century, knowledge of this “fermentation process” was expanded and the technological as well as nutritional benefits for the consumer were spread. It started with traditional beer and wine production; vegetables, cereals, legumes were gradually fermented and the addition of selected microorganisms to milk revolutionized the dairy or cheese industry.
Nowadays, probiotic cultures, which are microorganisms that are useful for the human intestinal environment, are added to certain foods, which can positively influence the microflora of the colon. In addition, fermentation is used not only in the food and luxury food sector, but also biotechnologically by the pharmaceutical industry or in biogas production.
In summary, food fermentation is used mainly for the following reasons:
- for preservation (conservation)
- for altered taste due to emerging aromas
- for a change in texture
- for nutritional reasons due to the production of organic acids, microorganisms, vitamins
- for possible probiotic effects on intestinal health
(Zabat et al., 2018).
Fermented Food: Importance
Preservation
Economically speaking, the preservation of food plays an enormously important role. This is usually done by shock freezing, drying or by adding sugar, salt or acid. These methods remove the breeding ground for microorganisms that contribute to the rotting of food. During fermentation, the microorganisms present produce certain metabolic products (acids, gases or alcohol) from the organic material, which create a nutrient medium that is unfavorable for the undesirable microorganisms, so that they cannot multiply, and the food therefore spoils less quickly (Berghofer and Zunabovic, 2016).
Lactic acid fermented foods do not require any energy input compared to other preservation methods (freezing, heating, irradiation), so production usually requires more time but otherwise few resources.
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Health Effects
In general, the fermentation process is associated with low nutrient losses, which can make it easier to meet nutritional needs, especially in the (raw) vegan diet.
The studies on the health benefits of fermented plant foods are inconclusive. Among other things, this is due to the small number of human studies and the different preparation methods. The latter influence the composition of the ingredients and microorganisms of the fermented product, and thus possible effects. Therefore, it is also impossible to say what quantities of a fermented food you need to eat to achieve certain effects.
Promising indications of mechanisms of action come mainly from in vitro studies, but so far these have either not been demonstrated in humans or have not been (sufficiently) investigated. These include antioxidant, antimicrobial, blood lipid and gut health effects (Dimidi et al., 2019). What consequences fermented products have on gastrointestinal health also depends on what the composition of the microbiome currently looks like. In studies, individual responses to the same fermented food often differ.
Potential health benefits from fermentation or probiotics can come in a variety of ways:
- directly by the microorganisms in the food
- by metabolites formed in the gastrointestinal tract
- through the transformation of certain compounds into biologically active metabolites
- through components in fermented foods such as prebiotics and vitamins
- through reduction of toxins and antinutritive substances, improved digestibility.
More specifically, some, but not all, of the microorganisms in fermented foods can reach the gastrointestinal tract and have a direct potentially beneficial effect there. People who eat more fermented foods often have higher concentrations of the microorganisms they contain in their gut. Higher bacterial diversity in the gut is generally associated with better health, and the health-promoting organisms can outcompete pathogenic bacteria.
Metabolites produced by the microorganisms in fermented foods that may provide health benefits include various bioactive peptides and polyamines. These could potentially promote cardiovascular, metabolic and immune health. Lactic acid bacteria, for example, can convert phenolic compounds into bioactive metabolites that can potentially trigger antioxidant processes.
Fermentation can reduce the content of antinutritive substances, for example by increasing phytase activity in legumes and cereals. Among other things, the phytic acid reduced by phytase inhibits the availability of various micronutrients (for example, zinc and iron). Therefore, fermentation in a vegan diet can help with the absorption of these potentially critical nutrients. During sourdough fermentation, the content of so-called FODMAPs, fermentable carbohydrates, can be reduced. These can cause digestive discomfort in sensitive individuals; sourdough bread is therefore often better tolerated (Dimidi et al., 2019; Marco et al., 2017). The effects of individual strains of bacteria vary, so it is not possible to generalize about the effects of all fermented foods.
Effects Observed in Humans
In the few existing human studies, positive changes on skin health, hypertension, and bone health have been observed with kimchi, fermented soy products, and kefir (Nozue et al., 2017; Tu et al., 2015; Zabat et al., 2018).
The effects on human gut health have only been studied of kefir, sauerkraut, natto and sourdough bread, according to a 2019 paper by Dimidi and colleagues. In this study, sauerkraut was not shown to have a positive effect on IBS attributable to fermentation, natto and miso soup together led to changes in the microbiome composition of the stool in a study of 8 subjects, and different kimchi vegetables were observed to cause different changes in the bacterial abundance of the gut microbiome. The ultimate consequences of this are unclear. In contrast, no conclusive human studies (randomized control trials) exist on gastrointestinal effects of kombucha, miso, kimchi, and tempeh (Dimidi et al., 2019).
In the case of sourdough bread, it is also clear that the method of preparation has a decisive influence on the composition of the end product. However, due to the effect of temperature during baking, the content of microorganisms in the bread seems to be low, and the positive health effects are mainly because of the above-mentioned improved digestibility due to changed carbohydrate composition.
Overall, therefore, there is little evidence of relevant effects on intestinal health from fermented foods.
Fermented Foods and Probiotics
Some microorganisms in fermented foods are so-called probiotics, for example the lactic acid bacteria (lactobacilli). The term comes from the Greek and means something like “for life”. According to the definition, these are living microorganisms which – if administered in sufficient quantities – have a positive effect on human health (FAO, 2006).
Regular consumption of products containing microorganisms can support the intestinal microbiota. The prerequisite is that they survive the intestinal passage in sufficient numbers and reach the gastrointestinal tract alive. This is usually the case with products that have been specially mixed with probiotics. At best, the amount added and contained in the food is defined (Dimidi et al., 2019; Marco et al., 2017).
This means that not all fermented foods have a probiotic effect. Pasteurized foods, for example, do not contain any living microorganisms due to the heating process. Other foods that do contain living organisms also do not have a probiotic effect because these do not survive the passage through the stomach. Whether a fermented food can have a probiotic effect depends on several factors, including the food matrix and the manufacturing process, as well as the type and amount of microorganisms (Marco et al., 2017).
For example, lactobacilli could strengthen an intact intestinal barrier, which could be associated with reduced invasion of unwanted bacteria into the blood system. This could theoretically counteract gastrointestinal as well as inflammatory diseases (Hemarajata and Versalovic, 2013). However, there is also evidence of negative effects from probiotics or fermented foods, and not all probiotic foods on the market help all consumers (Lee and Bak, 2011; Dimidi et al., 2019).
Factors that determine whether a probiotic food has an effect: sufficient quantity of living organisms, bacterial species, duration of intake, individual factors (for example, original composition of the intestinal flora). Evidence of health benefits from probiotics exists for only a few disease conditions (Sharifi-Rad et al., 2020). Thus, a general recommendation for the intake of probiotic products cannot be made.
Nutritional Relevance
The microorganisms can enzymatically break down substances that are difficult to digest. On the one hand, this can improve digestibility, as already described for sourdough bread, and on the other hand, it can increase the bioavailability of some nutrients. Also, the degradation of antinutritive substances already mentioned ensures that some micronutrients become better available due to fermentation. This may improve the nutritional status, especially in vegan diets (Englert and Siebert, 2020).
Some of the bacterial strains are also able to synthesize nutritionally relevant substances for the human host, such as amino acids and vitamins. At the same time, they can break down value-reducing substances such as mycotoxins in grains or enzyme inhibitors in legumes, and produce a number of B vitamins such as riboflavin, folic acid or vitamin B12. However, consumption of fermented foods is not enough to meet vitamin B12 requirements on a vegan diet (Gibson et al., 2006; Thakur et al., 2016; LeBlanc et al., 2011; Englert and Siebert, 2020).
Enjoyment Factor
Compared to other preservation methods, the fermentative process produces sensory desirable substances. On the one hand, the flavor changes, but also the consistency of the food. The aroma substances are produced, for example, when the microorganisms break down fatty acids from triglycerides.
This can increase the enjoyment factor of the food for the consumer; a good example is the fermented vegetable white cabbage, aka sauerkraut, which is less chewy and more aromatic than the raw product (Sabersky, 2017).
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Fermenting Vegetables
In the supermarket, the selection of fermented foods is rather limited. But fermenting vegetables is not difficult. The only thing you need besides the vegetables is salt and some patience. If the theory has whetted your appetite to try it out for yourself, here is a quick guide.
- Clean vegetables well and cut into small pieces, mash firm varieties (carrots, beet, celery, cauliflower, etc.) a little.
- Mix with 1–2 % salt and place covered in the refrigerator.
- Fill a suitable container*with no more than two-thirds, squeezing again slightly. If the vegetables are not covered with liquid, fill up with brine (water with about 3–5 % salt), weigh down the food if necessary and close the lid loosely.
- Allow to ferment at cool room temperature for about 7 days, carefully opening the lid daily if necessary to allow the gases to escape.
- Then place in the refrigerator for another week or two. The longer you let it ferment, the more acidic the vegetables will taste and the longer they will keep.
*There are special fermentation vessels. However, most containers made of glass, ceramic or wood are also suitable. They should only be airtight, and of course, have an appropriate size. Particularly good are canning jars or jars with rubber rings because there the air does not get in, but the resulting carbon dioxide can escape. Otherwise, you have to open the lid briefly daily as described.
Conclusion: Fermentation in a Vegan Diet
Whether it is sour pickled vegetables, the production of bread, fermented soy products or even beverages and luxury foods: the well-known fermentation process is used in the processing of many of our foods. Fermentation can enrich your vegan diet in many ways: taste, texture and nutrient composition are changed compared to non-fermented products. In particular, specific effects on gut health have not yet been proven, but if the special flavor ensures that more vegetables and legumes are consumed, this is definitely a benefit. Also, the altered nutrient profile may expand nutrient intake. Especially in vegan diets, the degrading effect of antinutritional ingredients is an advantage, as it can increase the bioavailability of important nutrients.
Our advice: If you have acquired a taste for fermenting vegetables, you can find instructions on how to prepare tempeh in our article on tempeh as a fermented product that needs starter cultures.
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