What is Lactic Acid Fermentation? | Giovanni Ceccarelli
Fermentation Techniques

What is Lactic Acid Fermentation?


In the first two generic articles on fermentation we talked about the principles behind these metabolic processes and the basic tools needed to produce fermented foods. As we have seen, there are different types of fermentation and in this article we will investigate the basis of lactic fermentation.

What is Lactic Fermentation

Lactic Fermentation is a type of fermentation found mainly in LAB – Lactic Acid Bacteria.

It is important to remember that the term Lactic Acid Bacteria has no official status in taxonomy and that it is actually just a general term of convenience used to describe a group of functionally and genetically related bacteria, belonging to 12 different genera.

During fermentation, the LABs mainly produce Lactic Acid, which is the name given to fermentation. Lactic acid is not the only compound that is produced during food processing, but there are a number of secondary products that give our ingredients a sharp and complex taste, with a good level of acidity (due precisely to the presence of lactic acid).

Lactic Acid Bacteria

In general, we have two “metabolic” types of bacteria in lactic fermentations:

  • Homofermentative: produces almost exclusively lactic acid; the sugars present are transformed to 90% in this acid;
  • Heterofermentative: here the sugars are metabolized to 50% in lactic acid while the remaining percentage of fermentation products is represented by ethanol, acetic acid and CO2.

Often, at the beginning of lactic fermentation, heterofermentative LABs are more active. This is also visually understandable because the fermentation is tumultuous, producing a lot of gas. When the homofermentive ones are more present, fermentation is less visible.

LABs, by lowering the pH and producing particular compounds such as bacteriocins, make the environment more and more inhospitable to unwanted bacteria and molds, and potentially create the ideal conditions for the proliferation of other LABs, in a succession of different species that make the food more interesting and unique.

For example, in lacto-fermented vegetables they often proliferate in the following order:

Leuconostoc mesenteroides, a salt-tolerant organism, with a relatively short latent phase and a high growth rate at low temperatures (from 15°C to 18°C), contributes quickly to the accumulation of acids and to the lowering of the pH. Beyond a certain threshold, these changes are limiting for its own growth (after the first 4-6 days of fermentation usually they aren’t present anymore), but optimal to let proliferate Lactobacillus plantarum, another lactic acid acidophilic and facultative heterofermentative species (that is that they have the metabolic capacity to ferment different sugars through homo or heterofermentative pathways and which prefers acidic conditions). These bacteria contribute to double the acid content and further lower the pH to 3.4-3.6 within 4-8 weeks.

Remember that acid taste and pH are not exactly the same thing, Giovanni wrote about this issue on Bartales, on page 92 (Italian language). Obviously, in addition to acids, fermentation produces a series of other compounds that modify the flavor of food.

How to create the selective environment

Also for lactic fermentation it is possible to follow two ways: the use of starters, that is inoculating a good quantity of lactobacilli or creating advantageous conditions (a selective environment) so that the LABs wil take over the other microorganisms present.

In this article we will focus on wild lactic fermentation, i.e. without the use of a starter, in order to deepen the use of specific starters in other articles.

As we know, to obtain the wild fermentation we desire, it is necessary to create a selective environment favorable only to the desired microorganisms. If you want to review this concept, read the article on the basis of fermentation here.

The environmental parameters that we can modify most to create selective environments are:

  • Oxygen: harmful for lactic fermentation; it is important to create conditions of anaerobiosis (absence of oxygen), even simply by submersing the food in water.
  • Salinity: sodium chloride (salt) used in certain percentages, creates the ideal environment for some LAB and inhospitable for other unwanted microorganisms. Here, in the article on fermentation tools and ingredients, we talk more in detail about salt. To start, I advise you not to go below 2.5% to avoid the proliferation of unwanted microorganisms, then gradually you will be able to go under this threshold, while you can easily raise. Salting can be done “dry”, i.e. adding salt to food, which will then release enough liquid to keep everything submersed, or by submerging the ingredients in a brine (water and salt to the desired concentration).
  • Temperature: this also creates favorable conditions for certain LABs rather than others. For example, as seen above, bacteria in lacto-fermented vegetables prefer a lower temperature, while LABs used in the production of yogurt, work at higher temperatures, above 40°C.
  • Sugar: Usually the sugar naturally present in the foods to be fermented is sufficient, but if you want to obtain different results you can use different sugars, playing on different flavors with different types. Read here Giovanni’s article on sugars.

Understanding which bacteria we need is the beginning of our decision-making process, which will lead us to study these species and understand the ideal conditions to favor their proliferation.

This is possible thanks to the great bibliographic resource available today. Another approach, much simpler, is to ferment the same food at different temperatures or salinity levels and find out which result we prefer rather than another: the important thing is to always write the starting conditions and the result obtained in order to make all as replicable as possible.

Finally, remember that temperature and salinity often can affect each other: for example if the temperature is high in summer, fermentations risk to be much too fast and uncontrolled, so it may be a good idea to slightly increase the salinity to better control fermentation and vice versa in winter.

The addition of salt is certainly a very simple and effective way to start lactic fermentation, however it is possible to obtain lactofermented foods even using starters or ingredients that already naturally have a good salt content.

The Lactic Fermentation in Mixology

Basically, you can ferment any vegetable or fruit, starting from the famous sauerkraut and lacto-fermented lemons (sometimes called “Moroccan”) up to ferment ingredients that you would never think of, like mint. These ferments can represent the final ingredient in your preparations as well as a starting point for producing a syrup, a shrub or a premix used in drinks, in a broader concept of Home Made, which is so dear to us.

Lately, in Drink Factory we are creating very special recipes where fermentations have added a further step to our creations: the fermented ingredient is the basis of a Home Made preparation that will be the detail that makes a “Twist on classic” unique. A sometimes long path that requires a lot of study, but that can really make the difference. When you see one of your clients with their eyes open wide and exclaim: “I do not know if I like it yet, but I’ve never tasted a drink like this before”, it means that you have done something new: I leave satisfied a bar either when I drank something I already knew, but done with great care, or when I drank something totally new. Lately, you can often hear this phrase also in Drink Factory, when we experiment behind closed doors.

Good fermentation to all!

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