Lactic Acid Fermentation

Lactic Acid Fermentation

A half-gallon jar of fermented salsa verde.

What is Fermentation?

​Fermentation is the anaerobic (without oxygen) breakdown of substances such as sugars and carbohydrates into other substances often acid or alcohol via microorganisms such as bacteria and yeast (1, 2). Microorganisms ferment to make energy, while acid, carbon dioxide, and ethanol (alcohol) are side products that we utilize (1). For food purposes, two different types of fermentation are most often used: ethanol and lactic acid fermentation (also known as lacto-fermentation). Yeast, specifically certain wine and beer strains or bread strains of Saccharomyces cerevisiae, which you can purchase, is generally used to make alcohol or bread, respectively (1). Carbon dioxide is released which is what causes bread to rise or it is off-gassed in the case of ethanol fermentation (1). In contrast, wild lactic acid bacteria, particularly certain strains of Lactobacillus, Leuconostoc, and Streptococcus, generally perform lacto-fermentation, although other bacteria may also play a role (1). Lacto-fermentation is used to make many common food products such as sauerkraut, kimchi, pickles, hot sauces, cheese, yogurt, and more (1, 2). A third type of fermentation sometimes performed at home uses acetic acid bacteria which are used to make vinegar and kombucha (2).

Various fermented hot sauces and one of my favorite ways to use hot sauce, over eggs!

Why Ferment?

​Fermentation is a form of food preservation. Before refrigeration, freezers, and safe canning equipment existed, fermentation was used to preserve the harvest and make food safer to store. Fermentation can also make food more nutritious and more digestible (2). Most cultures have food preservation techniques based on lacto-fermentation, ethanol fermentation, or both. I ferment not only to preserve the produce I grow but also because I like the taste. Fermented hot sauces and pickles taste different than a typical vinegar-based hot sauce or pickle. I am also prone to acid reflux and find that fermented foods are easier on my stomach than the typical vinegar-type pickle (although I love vinegar as well!).

Fermented kimchi, one of my favorite ferments!

How to Ferment

​Fermentation is a very safe method of food preservation assuming you start with enough salt. A good rule of thumb is to use at a minimum 2% salt, although some vegetables require more. For example, cucumbers consist of a lot of water therefore, up to 5% salt is better to prevent mold formation. For a good chart on how much salt to use and more information on how to make up the salt solution, I like this website. Because fermentation is one of the safest ways to preserve food, I am often willing to follow random internet recipes for fermentation (unlike canning where I only follow safe, tested recipes) because generally if a fermentation goes bad, you know. Just double-check how much salt to add to that vegetable for any fermentation recipe. If your fermentation turns slimy or moldy (anything fuzzy), throw it out! What is commonly called Kahm yeast (a white coating on top of the ferment that is not fuzzy) is safe to eat but can give the food an off flavor.

A mustard ferment with an Easy Fermenter lid.

​The key to successful fermentation is to keep everything below the brine and eliminate as much oxygen as possible at the top of the ferment. Anaerobic lactic acid bacteria grow without the presence of oxygen however mold contamination always occurs at the top of the ferment as it requires oxygen to grow. Once the fermentation gets started enough carbon dioxide is produced to push out excess oxygen and the risk of mold contamination is reduced. To keep oxygen from re-entering ferments I like wide-mouth mason jars (quart or half-gallon sizes are great), with glass weights to hold everything below the liquid brine and a lid to keep the air out. I often use the Easy Fermenter Lids or simple airlocks used for alcohol fermentation as they self-burp, so you do not need to keep opening the lids. If you use an actual lid you will need to release the gas produced often enough to keep the jar from exploding but you also run the risk of incorporating oxygen into the top of your ferment every time you crack the lid which can allow mold to grow. For larger ferments, you will likely want a fermentation crock. I like the water seal fermentation crocks with a lid in a moat at the top that holds water, forming an airlock. A small hole in the lid allows the gas to escape but the hole is covered by water to keep oxygen from entering the crock. 

A 3 gallon water sealed fermentation crock from Ohio Stoneware. The top moat is filled with water and the hole in the lid that allows gas to escape is visible in the second picture. Most fermentation crocks also come with stone weights to hold the vegetables below the brine.

​For a basic fermentation, you make up your salt solution (some things like sauerkraut are traditionally brined dry, meaning you add salt directly to the vegetables and the salt pulls liquid out) and pour it over your prepped vegetables. Make sure all the vegetables are covered, add your weight to keep the vegetables submerged, and attach the lid. Most ferments such as hot sauce go at least 30 days but commercially made Tabasco is generally aged 3 years, sauerkraut generally takes 6-8 weeks, and cucumbers are usually much shorter, 5-7 days although you can go longer if you want a sourer pickle. I tend to do shorter cucumber ferments to reduce the risk of mold formation and because I like crunchier pickles. In general, the longer the ferment the softer the vegetable will become.

Resources

For sauerkraut and cucumber-fermented pickles, I follow Ball (one of the safe canning resources) recipes. Their online website only has a fermented tomato salsa recipe, but other fermentation recipes such as sauerkraut, pickles, hot sauces, and Worcestershire sauce are available in several of their books. See my Canning post for more information on the Ball books that are currently available. Pickles are more likely to mold in my experience, so I like the Ball recipe because it uses a little vinegar at the beginning of the ferment to help reduce the risk of contamination before the fermentation gets started. However, there isn’t enough vinegar added to inhibit fermentation.
For fermentation resources other than Ball, I like the Insane in the Brine website, particularly for his hot sauce recipes. The author has also written a couple of books, which feature even more of his recipes than are available online. Other books I recommend include “The Noma Guide to Fermentation” by Rene Redzepi and David Zilber, “The Art of Fermentation” and “Wild Fermentation” by Sandor Ellix Katz, “Fermented Vegetables” and “Fiery Ferments” by Kirsten and Christopher Shockey, and “The Kimchi Cookbook” by Lauryn Chun.

References

1. Madigan, M. T., et al. Brock Biology of Microorganisms. 12th Edition. Pearson Benjamin Cummings, 2006.
2. Redzepi, R. and Zilber, D. The Noma Guide to Fermentation.  Artisan. 2018.