Technique: fermenting

Below you’ll find the most important information about the fermentation technique.

Technique: fermenting

Fermentation changes the structure of foods using moulds, yeasts, and bacteria to enhance flavour, to make it more digestible, and to be able to store it for longer. The first descriptions of this process date to 7000-6600 BC and were found in a Neolithic settlement called Jiahu in China. Trial and error played a big part in the development of different methods, but the modern fermentation techniques are still based on these ancient processes. The biggest difference is that modern science and technology enables us to control the microorganisms, temperatures, and humidity. Widely consumed foods that require fermentation include cheese, beer, soya sauce, yoghurt, sourdough bread, coffee, tea, and chocolate.

Equipment required
The materials and equipment required depends on the recipe and the type of fermentation. Mostly, all you need is a bottle or jar, but sometimes you need a few extra things to achieve the right result.

  • Gram scale. For weighing salt, sugar, or starters.
  • Glass jars. For the fermentation and/or storage of vegetables and yoghurt.
  • Plastic bottles. For fermentation processes that produce carbon dioxide. The plastic can withstand the pressure.
  • Fermentation lock. For fermentation processes without oxygen. Ensures that gas produced by the fermentation process can be released without allowing air in. 
  • Bucket with lid. For large amounts. A fermentation lock is often required.
  • Fermentation cabinet. A device in which you can adjust the humidity and the temperature to ensure a controlled process.
  • Thermometer. To control the fermentation temperature. 

“Fermentation is different to cooking. It's a world of its own''


What is fermentation?
Fermentation changes the structure of foods; it alters their taste and texture and preserves it for longer. Even if you follow the storage instructions, all fresh food will eventually spoil due to the activities of microorganisms, moulds, yeasts, and bacteria. Some microorganisms are harmful, yet others are beneficial and these are the ones that are used for fermentation. The good microorganisms prevent the growth of pathogens and microorganisms that cause food to spoil by using up all their resources (sugars, proteins, and fats) and converting these into acids and/or alcohol in which these harmful pathogens and microorganisms cannot survive.


“Safety first” 

Some microorganisms are harmful while others are beneficial. During the fermentation process, good microorganisms hamper the growth of pathogens and spoilage bacteria by using up their resources and by producing certain chemicals. So, it is vital to keep only the good microorganisms. The following factors play an important part in food safety during fermentation.

1) Moisture: Without water there can't be life. Many microorganisms need free water to survive. The more water is bound to proteins, fat, salt, and sugar, the more difficult it becomes for the microorganism to grow. Please note: this does not mean that liquid substances have more free water available. Examples include sugar water, preservation liquid, and soya sauce. These liquids contain relatively little free water as much of it is bound to sugar and salt. Bacteria require more free water than yeasts and moulds. By limiting the amount of free water available, you are able to restrain the growth of one type of microorganism in favour of the other.

2) Temperature: Temperature influences the growth rate of microorganisms. In general, organisms will grow slower if refrigerated than in warmer room temperatures. Few can survive temperatures exceeding 100°C. This temperature factor is often employed in the fermentation of yoghurt. First, raw milk is boiled to kill as many of the microorganism as possible. The milk is then fermented at a temperature of between 30-45°C. The fermentation is later paused by refrigerating the yoghurt.

3) Oxygen: Certain microorganisms require oxygen to function while others do not. Some types can function in both circumstances. By changing the level of oxygen you are able to promote or pause the growth of certain types of microorganisms. Sauerkraut is an example of fermentation without oxygen. Sliced white cabbage is put in a bucket with salt and weighted down. The weight ensures that the cabbage remains submerged in the liquid that is drawn out by the salt and does not come into contact with the air. A lid with a fermentation lock is then placed on the bucket. This releases the fermentation gases from the bucket but does not allow oxygen to enter. Oxygen will cause the sauerkraut to rot instead of ferment.

4) Acid: Fermentation causes food to become more acidic. This acidity has a preserving effect, as it makes it difficult for many types of microorganisms to multiply.

5) Salt: Salt can also impede the growth of certain microorganisms while lactic acid bacteria have a higher tolerance for salt than other types. This means that you can encourage the growth of these bacteria while eliminating the rest. This is what happens in the production of fish sauce. Lactic acid bacteria enable the fermentation process while the salt eliminates many of the other microorganisms.

6) Poison: Alcohol is a poison and many microorganisms can't function in alcohol. But brewer's yeast is an exception to this. By producing alcohol, other microorganisms can't grow, which results in a longer shelf life.


“The heros of fermentation”

Types of fermentation
Fermentation is a complex process that can be performed by different microorganisms which can roughly be divided into bacteria and fungi.

1) Fermenting with bacteria
Fermentation with bacteria predominantly relies on three types of bacteria: lactic acid bacteria, acetic acid bacteria, and bacillus bacteria.

  • Lactic acid bacteria: Lactic acid fermentation produces cheese, yoghurt, sauerkraut, dried sausage, and gherkins and uses lactic acid bacteria to start the fermentation process. These bacteria use up the carbohydrates and produce mostly lactic acid and can also produce carbon dioxide, other acids, and alcohol.
  • Acetic acid bacteria: Acetic acid fermentation is a process used for producing sourdough bread and vinegar and is started by acetic acid bacteria. These bacteria convert alcohol into acetic acid and water and often work together with yeasts, such as is the case with sourdough bread. Here, the yeasts convert sugar into alcohol which is then converted into acid by the acetic acid bacteria.
  • Bacillus bacteria: Fermentation with bacillus bacteria is called alkaline fermentation. This method is applied to high-protein products such as soya beans, nuts, and certain types of seeds. These microorganisms convert proteins into ammonia and make foods more basic instead of overly acidic. This process is used to make nattō, a traditional Japanese food product.

2) Fermenting with fungi
The fungi group can be separated into yeasts and moulds. Yeasts are single-celled organisms while fungi are multicellular organisms.

  • Yeasts: Products like beer, wine, and bread are made using fermentation. The yeasts used in most yeast fermentation processes are disaccharide yeasts, which break down sugars and convert them into alcohol in the absence of oxygen or into carbon dioxide if oxygen is present.

  • Moulds: Mould fermentation is used to make soya sauce, tempeh, miso, white and blue cheeses, and sausage. Amongst the moulds, many different types are used for fermentation, but they are all excellent at breaking down complex carbohydrates such as starch and cellulose. During this process they produce different types of flavours and antibiotics which protects against other microorganisms. They are also good at breaking down proteins and make previously acidified foods less acidic. This also contributes to the structure of food, as demonstrated by the creaminess of camembert, which is produced by a combination of lactic acid fermentation (acidifying) and mould fermentation.


“Fermentation keeps”   





Most important agent

Lactic acid bacteria

Acetic acid bacteria

Bacillus bacteria



Mostly yeasts and bacteria

What's it called?

Lactic acid fermentation

Acetic acid fermentation

Alkaline fermentation


Mould fermentation

The different types of fermentation are usually listed separately

What do they eat?





Complex carbohydrates, proteins

Sugars and alcohol

What do they produce?

Lactic acid

Acetic acid


Alcohol, carbon dioxide, water, acid

Mostly flavour-enhancing enzymes. antibiotics, ammonia

All of the above

Is oxygen needed?

Yes and no They prefer no oxygen but they can tolerate it.



Yes, e.g. bread

No, e.g. beer


Yes and no

What foods do they produce?

Vegetables, cheese, salami, sauerkraut

Vinegar, sourdough bread

Nattō, soya bean paste

Wine, beer, bread

Cheese, some wines, miso, tempeh

Sourdough bread, kombucha, ginger beer, kefir            

“Start at the beginning”

Scobys and starters: Nearly every form of fermentation is an interplay of multiple types of microorganisms. When making vinegar, the fermentation process converts sugars into alcohol which is used by acetic acid bacteria to produce acetic acid. A scoby or starter is a somewhat slimy-looking mass made up of a symbiotic culture of bacteria and yeasts used to start or speed up the fermentation process. These include yoghurt cultures, kefir bulbs, ginger beer plants, and kombucha mushrooms. You won't need to use a scoby or a starter. Certain products like unwashed ginger, have sufficient amounts of the right microorganisms on the skin that can be used for fermentation.

Step-by-step kombucha:

  • 1 kombucha mushroom
  • 1l water
  • 5-7g black or green tea
  • 2 tbsp vinegar
  • 75g sugar

Preparation method

  • Bring the water to the boil. Dissolve the sugar in the boiling water and infuse the tea until the water is dark.
  • Remove the tea and pour into a glass jar and set aside to cool to room temperature.
  • Add the kombucha mushroom and the vinegar.
  • Place a cloth over the glass jar and secure with an elastic band or piece of string.
  • Store the jar in a dark place at room temperature for one to three weeks. Don't worry about the slightly sour smell.
  • Remove the kombucha mushroom, strain the tea through a cloth and store the kombucha in plastic bottles at room temperature for a few days until bubbles start to form.
  • Store the carbonated kombucha in the fridge to stop the fermentation process.

Step-by-step kimchi:

  • 1kg Chinese cabbage
  • 4 spring onions
  • 3 carrots
  • 10g ginger
  • ½ white radish
  • 3 cloves garlic, pressed
  • 15g paprika powder
  • 5g chili powder
  • 1 tsp fish sauce
  • 5g sugar
  • 22.5g sea salt

Preparation method

  • Chop the cabbage into coarse slices.
  • Finely chop or grate the remaining vegetables.
  • Mix all the ingredients until moisture is released.
  • Place the mixture in a fermentation pot, preserving jar, or bucket with fermentation lock.
  • Store at room temperature for two to three weeks.
  • Store the kimchi in the refrigerator to stop the fermentation process.

Step-by-step sauerkraut:

  • 1kg white cabbage, cleaned and core removed
  • 5g mustard seeds
  • 4g juniper berries
  • 1 bay leaf
  • 22.5g sea salt, fine

Preparation method

  • Finely slice the cabbage with a mandolin or meat slicer.
  • Mix the cabbage with the salt and bruise until it becomes translucent and releases liquid.
  • Rest for a few minutes, and repeat the process.
  • Mix the cabbage with the remaining ingredients and place everything in a fermentation pot, preserving jar, or bucket. Place a weight on the cabbage in the pot/bucket. The weight ensures that the cabbage remains submerged in the liquid and does not come into contact with air.
  • Place a lid with a fermentation lock on the pot/bucket. This will allow the fermentation gases to escape but not allow oxygen to enter. Oxygen will cause the sauerkraut to rot instead of ferment.
  • You can also pull vacuum all the ingredients together after the bruising process for them to ferment without air. Just ensure the gas from the fermentation process doesn't break the bag.
  • Ferment at room temperature. After approximately two to three weeks the sauerkraut is ready.
  • Store the sauerkraut in the refrigerator to stop the fermentation process.

Step-by-step white wine vinegar:

  • 4l white wine, dry
  • mother of vinegar or unpasteurised vinegar

Preparation method

  • Let the sulphite-containing wine stand open (cap/cork removed) for a week. This allows the sulphite to escape and prevent it from hampering the activity of acetic acid bacteria.
  • Heat the wine for ten minutes to no more than 60°C to kill any harmful microorganisms. Please note: if you exceed 60°C, the alcohol that is needed for the fermentation process will evaporate.
  • Allow the wine to cool back down to 30°C.
  • For every half litre of wine, add 50ml unpasteurised vinegar or follow the instructions on the mother of vinegar packaging.
  • Pour into a large glass jar and cover with a cloth.
  • Store the jar at 30°C (in a warming cabinet) for a week.
  • After one week, add 1 litre of the pasteurised wine.
  • After another week, add 2.5 litres of the pasteurised wine.
  • After two months at 30°C the vinegar will start to clarify and signals the end of the acetic acid fermentation process. Filter the vinegar, pour into sterilised bottles, and store in a cool place.



“Would you like to know more?”


Fermentation is an incredibly extensive and complex technique. This has provided a brief overview of the most important basic elements of the process. Before experimenting with fermentation we recommend that you read more about it. Interesting manuals and recipes can be found in the following books:

  • The Art of Fermentation by Sandor Katz.
  • Fermentation, a practical approach by L.M. Harvey.

Here you can find all the Gastronomix components for the fermenting technique.