Lactic Acid Fermentation 101

Lactic Acid Fermentation at a glance

Lactic Acid Fermentation is straightforward and can be done by following a few rules of thumb and with little equipment. You can easily make sauerkraut and kimchi at home, but no need to stop there! Most vegetables can be lacto-fermented to unlock great taste and preserve them. However, as for any fermentation, particular attention must be paid to cleanliness of equipment and anything that comes into touch with vegetables.

If you want to learn more about fermenting in general, you can read the article “what is fermentation?”.
If you instead want to skip directly to a recipe, try my Fermented Giardiniera! It is delicious and will change your sandwiches and salads forever!

Keeping that in mind, the rules of thumbs and simple steps mostly adopted to lacto-ferment vegatables are the following:

1. Work with very clean hands and very clean equipment (ideally sanitised);
2. Chop your vegetables if advised in the recipe;
3. Use an amount of salt that is at least 2% of the total weight of vegetables, spices (if using), water (if using);
4. Keep vegetables submerged in liquid at all times, by using some weights. Best also to add a lid (and open it every day to let gases out) or a lid with an airlock (so you won’t need to let the gas out).
5. Wait for the appropriate amount of time indicated on the recipes, although generally (after a few days) it is mainly a matter of taste driving the choice of when to eat/refrigerate your ferments.

That’s it! Simple as that! Clean, chop, salt, submerge, wait! Below, more details on the steps for the curious ones, as well as some equipment and books referrals with amazon links (please notice that if you buy those products on Amazon after clicking the link, I will be paid a small percentage of the revenues).

A bit more details on the steps

I have always been a bit of a scared cat. When I first learned about fermentation, I was reading about it with curiosity, thinking I would never do that myself. “Hey, I do not want to get botulism!” I would say. Fast-forward a few months, and I found myself making sauerkraut, miso, amazake, and other fermented foods. I think that if you are worried but still want to try, the best way is to learn about the process, to understand the steps and the science, so you can be confident enough to go through it. As this is only a brief article, to show you how easy it is to make lacto-fermented products like sauerkraut, I will not discuss at length each single steps, but I would still like to give you hints of why each of them is important.

What is Lactic Acid Fermentation?

Lactic Acid Fermentation is a process through which vegetables are preserved by leveraging on lactic acid bacteria (LAB). Nowadays, it is used by some chefs and home cooks more for flavour development than for preserving, as the microbes and their products have a distinctive funky, complex, sometimes almost fizzy taste.  LAB are found on the skin of vegetables, in relatively small quantities. As soon as vegetables are picked, more nutrients become available for the bacteria, which start to increase in population. Once vegetables are submerged in liquid (and therefore an anaerobic environment is created), LAB start the fermentation process. Initially, over the first few days, some strains of bacteria (L. Mesenteroides) produce lactic acid, as well as carbon dioxide, acetic acid, alchool. Later on, as the PH of the ferment lowers, some other strains of LAB become predominant (Lactobacillus Plantarum). These strains, which are very good at surviving in acid environments, mainly produce lactic acid. Source for this information: “The Art of Fermentation” by Sandor Ellix Katz (if you are interested in learning more, I posted below an amazon link where I refer you to the book).

1 – Clean

Cleaning is mainly done to ensure there are no harmful bacteria or molds on your jars, spoons, or any other equipment that comes into touch with the ferment. While many people are comfortable cleaning the equipment with hot water and soap, it is advised to sanitise equipment to be on the safe side. Sanitising (i.e., killing most microbes) is different from sterilising (i.e., killing all microbes). Sanitising can be done through a hot cycle in the dishwasher, or by steaming/boiling equipment for a few minutes, or alternatively even using products like Starsan or Milton tablets.
It is considered unnecessary to use gloves for LAB fermentation, as long as you clean your hands very well.

2 – Chop

Chopping or grating is mainly for maximising surface area, but it really depends on the recipe. For example, for making sauerkraut, cabbage is shredded and salted so it will pull out so much water to submerge the vegetables without adding any additional liquid. Some other recipes call for fermenting whole vegetables.

3 – Salt

Salt is very important and helps to considerably reduce the probability of harmful bacteria growing in the ferment. It is generally advised to ferment with at least 2% salt (2% of the total weight of water and vegetables).
2% is considered enough to prevent Clostridium Botulinum (the bacteria causing botulism disease, which you would never want to get) from reproducing and generating toxins before the PH becomes low enough to prevent it from doing that (low PH means acidity). C. Botulinum can be found on the surface of many vegetables, especially root vegetables, as it is easily found on soil. However, it is not harmful until it is in anaerobic environment, where it can thrive and produce spores and toxins. Two things C. Botulinum does not like: salt (a concentration above 5% would considerably hinder its growth) and acidity (PH lower than 4.6). Even though the 2% mentioned above is lower than 5%, it is considered enough to inhibit the growth of the bacteria, while LAB thrive and produce lactic acid, which will lower the PH of the ferment. If the PH is lower than 5 within a couple of days, and lower than 4.6 when ready to eat, the ferment can be expected to be safe. Source for this information: “The Noma Guide to Fermentation” by Rene Redzepi and David Zilber (if you are interested in learning more, I posted below an amazon link where I refer you to the book).

Mind that Sandor Katz, in “The Art of Fermentation”, lists salt as a step that is not strictly necessary to fermentation. He would harness it mainly for a matter of taste. However, I prefer to stay on the safe side when fermenting, and make the environment more “selective”. LAB won’t be bothered by 2% to 7% salt, so they will thrive while other bacteria that might be harmful will be inhibited. I do admit having a bit of a Botulinum-phobia, but this is also the approach followed by “The Noma Guide to Fermentation”.

4 – Keep submerged

The reason for keeping vegetables submerged is to avoid the development of molds or yeasts that might need air to thrive and could develop on the surface of the floating vegetables. Veggies tend to float, so you will most likely have to use a weight to weigh them down. Sometimes you will have to push the weight down again after a few days: I can assure you that sauerkraut can be so lively and bubbly to slowly lift some weights!

5 – Wait

You should wait at least a 2-3 days, to give time to the ferment to reach the “safe” acidity level (see paragraph 3 above), but the timing can also depend on temperature. Once past the “right acidity” point, it is a matter of taste. “Younger” LAB ferments will have more texture. “Older” LAB ferments will be more mushy and possibly with a funkier flavour. Both will taste funky enough to make all your sandwiches great again!
Once done, you can jar the ferment and move it to the refrigerator, where fermentation will continue but at a slower pace.

Equipment and Books Recommendations

When it comes to equipment, you will not need much. On the minimalist end of the spectrum, a wide mouth mason jar with a small freezing bag full of water to be used a “weight” will be enough, as long as you are willing to “burp” (i.e., open the lid to let gases out) the jar once a day, at least on the first days where carbon dioxide production is strong.
There are however several types of jars and crocks available on the market. Some of them come with an an “airlock”, which is a small tool that lets the air and gases out of the jar but prevents air from going into the jar.

On my side, I tend two have two setups, that I use depending on the amount of vegetables I want to ferment (I generally do a large batch).

Please notice that if you buy any of these products after clicking on the link, I will get a percentage of the revenues. However, these are my genuine recommendation, you can see how often I use these products through my recipes.

• • For large batches: a 3L Kilner jar with airlock and weights. This works great for sauerkraut, or my fermented giardiniera.
    
  • For small batches: wide mouth Ball mason jars + Masontops Pickle Pipes (a bit expensive, but SO convenient to use).

   

Below, books about fermentation that I consider great. They are simply amazing, rich with information (scientific and non) and historical references. Even if you do not want to ferment, but you are interested in fermented products, these books are incredibly interesting. The first two (The Noma Guide to Fermentation and The Art of Fermentation) are all rounders, where you can find so much about LAB and any other fermentation. The other two (Koji Alchemy and The Book of Miso) are more focused on Koji-based fermentation and miso, to which I dedicate and entire section of the blog.