Sauerkraut, kimchi, or fermented cucumbers have one thing in common: lactic acid bacteria play a central role in their production. This form of fermentation is known as lacto-fermentation or lactic acid fermentation.
The term might sound like it relates to milk or lactose at first. In reality, however, lacto-fermentation does not automatically have anything to do with dairy products. Vegetables, fruit, and other plant-based foods can also be fermented with the help of lactic acid bacteria.
But what exactly happens during lactic acid fermentation? What role do lactobacilli play? And why does this process make vegetables sour and give them a longer shelf life?
What is lacto-fermentation?
Lacto-fermentation is a form of fermentation in which lactic acid bacteria convert carbohydrates into lactic acid and other metabolic products.
Among other things, the lactic acid lowers the pH value of the food. This creates the characteristic sour aroma of many fermented foods and simultaneously creates an environment in which many undesirable microorganisms struggle to multiply.
Lactic acid fermentation has therefore been used for centuries to produce and preserve food.
Typical examples are:
- Sauerkraut
- Kimchi
- fermented cucumbers
- fermented carrots
- Yogurt
- Kefir
- Sourdough
For fermented vegetables, fermentation often occurs spontaneously due to microorganisms naturally present on the vegetables. In professional food production, specifically selected starter cultures can also be used.
Why is it called lacto-fermentation?
The term “lacto” is often mistakenly associated with lactose or milk.
What is meant, however, is lactic acid.
Vegetables also contain carbohydrates that certain microorganisms can utilize during fermentation. This process produces substances including lactic acid.
Therefore, entirely plant-based foods can also be lacto-fermented.
Lacto-fermentation therefore does not mean that milk or lactose must be present.
What are lactic acid bacteria?
Lactic acid bacteria are a group of bacteria that metabolize carbohydrates and primarily produce lactic acid in the process.
They play an important role in food production. They are used in the fermentation of vegetables, dairy products, sourdough, and other foods, among others.
In fermented vegetables, lactic acid bacteria are often among the microorganisms that multiply particularly strongly during the fermentation process and shape its progression.
This does not refer to a single type of bacteria. The term lactic acid bacteria encompasses various genera and species.
What are lactobacilli?
Lactobacilli are among the best-known lactic acid bacteria.
The term “lactobacilli” was long used for bacteria of the genus Lactobacillus. Due to a scientific reorganization, numerous species have since been distributed among various new genera.
In common parlance, however, they are still frequently referred to as lactobacilli.
Various representatives of this group occur naturally on plants or food products and can be involved in lactic acid fermentation.
It is important to note: not every lactic acid bacterium is a lactobacillus, and not every lactobacillus automatically meets the criteria of a probiotic.
How does lactic acid fermentation work?
In simple terms, lacto-fermentation can be explained in several steps.
1. Microorganisms are present on the food
Fresh vegetables are not sterile. Various microorganisms are present on their surface.
These can also include lactic acid bacteria.
2. The vegetables are prepared
For vegetable fermentation, the vegetables are, for example, sliced, grated, or processed whole.
Salt is then often added, or the vegetables are placed in a brine.
The salt influences the microbial environment and helps create conditions under which certain microorganisms can develop better than others.
3. Oxygen is reduced as much as possible
The vegetables are kept completely submerged in the liquid or brine.
This creates low-oxygen conditions that are important for many forms of vegetable fermentation.
4. Lactic acid bacteria multiply
The lactic acid bacteria use existing carbohydrates as an energy source.
This produces various metabolic products, in particular lactic acid.
5. The pH value drops
As more lactic acid is produced, the food becomes more acidic.
This changes the taste, aroma, and microbiological conditions.
Many undesirable microorganisms struggle to multiply in this acidic environment. This is precisely why lactic acid fermentation was historically an important way to make food last longer.
What exactly happens during lactic acid fermentation?
Lactic acid fermentation is a complex microbial process.
The microorganisms involved do not just change the acidity of the food; aroma, texture, and composition can also change.
Which microorganisms dominate during fermentation depends on, among other things:
- the raw food product
- salt concentration
- temperature
- fermentation duration
- oxygen availability
- natural microbial composition
- any starter cultures used
Especially with spontaneously fermented vegetables, the microbial community changes over the course of the fermentation. Different microorganisms can dominate in succession.
What is lacto-fermented vegetable?
The term lacto-fermented vegetable refers to vegetables that have been fermented predominantly with the help of lactic acid bacteria.
Well-known examples include:
- Sauerkraut
- Kimchi
- fermented cucumbers
- carrots
- radish
- beetroot
- cauliflower
- cabbage
- bell peppers
In principle, many types of vegetables can be fermented.
The lactic acid fermentation of cabbage is particularly well known. For classic sauerkraut, white cabbage is shredded, salted, and fermented with the substantial exclusion of oxygen.
During this process, various lactic acid bacteria gradually take over the fermentation.
Fermented vegetables and pickled vegetables: what is the difference?
Fermenting and pickling are not the same thing.
With classic pickling, vinegar, for example, is added to a food. The acid is added from the outside.
In lactic acid fermentation, by contrast, the acid is created through the metabolic activity of microorganisms.
A pickled gherkin is therefore not automatically fermented.
Fermented cucumbers, on the other hand, turn sour with the help of microorganisms and usually a brine.
The difference lies primarily in how the acid is created:
Pickled: Acid is added.
Lacto-fermented: Lactic acid is created during fermentation by microorganisms.
What role does salt play in lacto-fermentation?
Salt is an important ingredient in many vegetable fermentations.
It serves several functions:
- It draws water out of the vegetables.
- This allows a natural brine to form.
- It influences the activity of different microorganisms.
- It can inhibit undesirable microorganisms.
- It influences taste and texture.
The correct salt concentration is therefore an important factor for controlled fermentation.
Too little or too much salt can alter the course of the fermentation.
Why must fermented vegetables stay under the brine?
In many vegetable fermentations, the vegetables should remain completely covered by liquid.
This reduces contact with oxygen.
This supports the conditions under which the desired fermentation processes can occur and can simultaneously make it harder for certain undesirable microorganisms to grow on the surface.
For this reason, weights are often used during fermentation to keep the vegetables under the brine.
Are lactic acid bacteria naturally present on vegetables?
Yes. Fresh vegetables carry a diverse community of microorganisms on their surface.
Lactic acid bacteria often represent only a small part of this microflora initially. Under suitable fermentation conditions, however, they can multiply strongly and eventually dominate the process.
This is precisely what makes spontaneous vegetable fermentation possible.
Alternatively, manufacturers can specifically add selected lactic acid bacteria as starter cultures to make the fermentation process more controlled and reproducible.
Spontaneous fermentation or starter culture: what is the difference?
In spontaneous fermentation, no special microorganisms are added.
Instead, one uses the microorganisms that are naturally present on the food and in its environment.
In a fermentation with a starter culture, on the other hand, specifically selected microorganisms are added.
This can help make the fermentation process more controlled and achieve a more reproducible result.
In modern food production, specifically selected starter cultures are therefore often used.
Does lacto-fermented vegetable contain living lactic acid bacteria?
That depends on further processing.
Fresh, unpasteurized lacto-fermented vegetables can still contain living lactic acid bacteria when consumed.
If the product is heated or pasteurized after fermentation, however, many of the microorganisms are inactivated.
Therefore, the following also applies here:
Lacto-fermented does not automatically mean that living cultures are still contained in the finished product.
Production, processing, and storage are the deciding factors.
Are lactic acid bacteria automatically probiotics?
No.
Lactic acid bacteria and probiotics are not synonyms.
For microorganisms to be designated as probiotics, certain scientific prerequisites must be met. Among other things, specific microorganisms must be defined and provide a proven health benefit in sufficient quantities.
In spontaneous vegetable fermentation, by contrast, numerous different microorganisms can be involved.
Therefore, one cannot automatically infer that a fermented vegetable is probiotic just because it contains lactic acid bacteria.
Is lacto-fermentation healthy?
Fermented vegetables are the subject of numerous scientific studies.
These studies investigate, among other things, how fermentation affects:
- microbial composition
- nutrient content
- plant-based compounds
- taste and aroma
- shelf life
Lactic acid fermentation can change the composition of plant-based foods. Depending on the food, microorganisms, and fermentation conditions, different metabolic products can be created.
Nevertheless, the blanket statement “lacto-fermentation makes food healthy” would be too broad.
The health profile of a fermented food always depends on the specific product, its composition, processing, and the quantity consumed.
What changes when fermenting vegetables?
The fermentation process can change vegetables in several areas.
-
Taste:
Lactic acid provides the typical sour taste. -
Aroma:
Numerous other metabolic products that influence the aroma are created during fermentation. -
Texture:
Depending on the food and fermentation duration, vegetables can become firmer, softer, or more tender. -
Shelf life:
The increasing acidity can create conditions under which many spoilage organisms struggle to grow. -
Plant-based compounds:
Microorganisms can convert various components of the vegetables during fermentation. Exactly which changes occur depends heavily on the raw material and the microorganisms.
What foods are created through lactic acid fermentation?
Lactic acid fermentation is not limited to vegetables.
Lactic acid bacteria also play an important role in other foods.
These include, among others:
-
Sauerkraut:
Fermented white cabbage. -
Kimchi:
Traditionally Korean fermented vegetables. -
Yogurt:
Lactic acid bacteria convert part of the lactose into lactic acid. -
Kefir:
Various bacteria and yeasts work together here. -
Sourdough:
Lactic acid bacteria and yeasts work together to influence the aroma, structure, and acidity of the dough.
Lactic acid bacteria are therefore an important component of a wide variety of traditional food cultures.
Lacto-fermentation, alcoholic fermentation, and acetic acid fermentation: what is the difference?
Not all fermentation processes occur in the same way.
In lactic acid fermentation, lactic acid bacteria primarily produce organic acids, especially lactic acid.
In alcoholic fermentation, yeasts mainly convert sugar into alcohol and carbon dioxide.
In processes involving acetic acid bacteria, alcohol can be converted into acetic acid under the influence of oxygen.
In many fermented foods, several microorganisms even work together. Traditional fermentations are therefore often more complex than a single chemical reaction.
Can you lacto-ferment vegetables at home?
In principle, vegetables can also be fermented at home.
However, it is important to work cleanly, use appropriate salt concentrations, maintain suitable temperatures, and avoid unwanted contamination.
Typically, vegetables are:
- washed and prepared,
- salted or covered with brine,
- kept completely submerged under the liquid,
- fermented at a suitable temperature,
- subsequently stored in a cool place.
If there is an unusual smell, noticeable mold, severe discoloration, or other signs of food spoilage, the product should not be consumed.
Anyone fermenting at home should therefore follow proven recipes and hygienic working methods.
Frequently asked questions about lacto-fermentation
What is lacto-fermentation?
Lacto-fermentation is a form of fermentation in which lactic acid bacteria utilize carbohydrates and produce, among other things, lactic acid. This lowers the pH level and can alter the taste, aroma, and shelf life of the food.
Does lacto-fermentation have anything to do with lactose?
No. In this context, “lacto” refers to lactic acid and does not mean that milk or lactose must be present. Vegetables can also be lacto-fermented as a completely plant-based process.
What are lactic acid bacteria?
Lactic acid bacteria are various bacteria that can ferment carbohydrates and primarily produce lactic acid in the process. They play an important role in the production of many fermented foods.
What are lactobacilli?
Lactobacilli are a well-known group of lactic acid bacteria. Many species that were previously classified under the genus Lactobacillus have since been scientifically assigned to new genera.
Which vegetables can be fermented?
Many types of vegetables are generally suitable for lactic acid fermentation. Particularly well-known examples are white cabbage, napa cabbage, cucumbers, carrots, radishes, beetroot, or cauliflower.
Is fermented vegetable always lacto-fermented?
No. While lactic acid fermentation is one of the most common forms of fermentation for vegetables, other microorganisms and fermentation processes can also be involved in principle.
Is lacto-fermented vegetable probiotic?
Not automatically. Lacto-fermented vegetables may contain live lactic acid bacteria if they have not been heated after fermentation. However, the presence of live bacteria alone is not enough to scientifically classify a food as probiotic.
Is sauerkraut lacto-fermented?
Traditionally produced sauerkraut is made through lactic acid fermentation and is thus a classic example of lacto-fermented vegetables.
Is kimchi lacto-fermented?
Yes. Lactic acid bacteria play an important role in traditional kimchi production. The exact microbial composition changes during fermentation.
Why does fermented vegetable turn sour?
During fermentation, organic acids, especially lactic acid, are produced. This lowers the pH of the food and creates the typical sour taste.
Conclusion: Lacto-fermentation is fermentation with lactic acid bacteria
Lacto-fermentation, or lactic acid fermentation, is a traditional form of food production in which lactic acid bacteria convert carbohydrates.
Among other things, this produces lactic acid. It provides the typical sour taste and contributes to changing the microbial conditions within the food.
The method is particularly well known through lacto-fermented vegetables such as sauerkraut, kimchi, or fermented cucumbers.
The term “lacto” has nothing to do with the need for milk to be present. The crucial factors are the lactic acid bacteria involved.
It is also worth making a precise distinction with terms like lactobacilli, live cultures, or probiotics: not every lactic acid bacterium is a lactobacillus, and not every fermented food with live lactic acid bacteria is automatically probiotic.
These very microbial processes make lacto-fermentation one of the most versatile forms of traditional food production.