What is Lacto-Fermentation? Why and how to do it?


What is lacto-fermentation?

Lacto-fermentation can also just be called “fermentation.” For example, we say certain foods like sauerkraut, kimchi, and sour pickles are “fermented.” The term lacto-fermentation is simply a way of specifying the type of fermentation we are talking about, because there are various types and classifications of fermentation.

In lacto-fermentation, lactic acid is produced over time, which preserves foods due to its acidity (i.e. low pH). Incidentally, this type of fermenting can also be called “pickling” and is part of the definition of pickling. Pickling refers to a broad practice of preserving foods through use of a low pH medium, such as in vinegar pickling, which is not a type of fermentation (although vinegar itself is the result of a two-step fermentation process).

Some of the most widespread fermentations are yeast-based, such as in the production of alcohol and bread. Some ferments, such as milk kefir and kombucha, rely on the use of a type of organic matter called a SCOBY, which is a “symbiotic combination of bacteria and yeast,” to produce the specific ferment.

What all of these have in common is that some living organism (or enzymatic catalyst), such as bacteria, yeast, fungus, or a combination, converts sugars and nutrients in other organic matter into acids, alcohol, and CO2 (producing the bubbly and fizzy effect we see in different stages of most ferments). 

Unlike the other ferments mentioned, lacto-fermentation is a bacterial-based fermentation. The title “lacto” refers to the specific type of bacteria – lactobacillus, which is a broad genus of bacteria with hundreds of species and subspecies – and also the type of acid it produces, lactic acid.

Many of these bacteria are considered probiotic – that is, they are normally beneficial bacteria for the body.

The name “lacto-fermentation” can be confusing because it sounds like there is some connection to lactose or lactate, i.e. that milk or dairy is somehow involved. Some people even go so far as to put dairy-based starter cultures (such as yogurt cultures or whey) into their ferments, thinking it is a necessity for a truly lacto ferment. This is a major misnomer.

While some of the bacteria in the lactobacillus family are indeed responsible for culturing yogurt (most famously, lactobacillus acidophilus), a different variety of these bacteria are normally responsible for lacto-fermenting fruits and veggies, and under different conditions.

In short, when any normal fruits and veggies are placed in an anaerobic (i.e. oxygen-free) environment within a suitable temperature range, lacto-bacillus will begin to thrive while harmful bacteria deteriorate. (An exception could be fruits or veggies which were irradiated, as could be done for export purposes, or exposed to extreme heat, in which case the lactobacillus, as well as any other bacteria, could all be dead or too depleted for a normal ferment.)

When high enough concentrations of salt are added to this scenario, the environment becomes very inhospitable to pathogenic bacteria. Meanwhile, lactobacillus thrives in this salty, anaerobic environment. (Note that if the environment is too salty and/or acidic, then it too will have a harder time.)

This environment is best produced today in a sealed container with a salty storage medium (usually a saltwater “brine,” typically with a 2-5% salinity, although the liquid could also come from the fruits and veggies themselves by applying a similar percent of salt based on the weight of the produce). In either case, no matter how effective the storage device, produce must be completely submerged under the brine to ensure a successful end product. Contact with air poses mold and other risks.

Ideal temperatures

The ideal ambient temperature range for most lacto-fermentation is 65-72 degrees Fahrenheit. That said, 55-75 degrees normally has reasonably good results. Lower temperatures slow the rate of fermentation and higher temperatures speed it up. When using recipes which suggest specific lengths of fermenting, therefore, it means doing so within this temperature range and possibly modifying the timespan of this ferment based on extremes on the lower or upper side. In other words, if a recipe calls for a weeklong ferment but your house is in the upper 50s, it can take a bit more time to achieve the same flavor and texture profile. The ferment itself may not appear as vigorous, though in fact everything is likely doing just fine.

I normally discourage recipes which call for placing ferments directly in the fridge (for reasons I won’t get into here). It is also worth noting that while a number of ferments can be fine above 75, it frequently has a softening effect on the produce. Cucumber pickles, for example, don’t do well at these temps and can turn soft or hollow out.

For ferments like hot peppers which will be used for hot sauce, the softening associated with higher temps doesn’t necessarily pose a problem, as it will be blended anyway. However, getting into the 80’s and above always carry greater risks for mold (and therefore using a higher salt concentration and keeping in a dark area is advised if this will be an issue for you).

Lastly, maintaining a consistent temperature is also ideal, but of course outside the realm of possibility for many people. Cucumber pickles, for example, do best (texture wise) when temperatures can remain steady (or as steady as possible).

Why are lacto-fermented foods healthy?

There are several reasons why lacto-fermented foods are healthy. First of all, as stated, harmful bacteria that might have been present on the food is eliminated. This means the harmful bacteria will not enter the digestive system, but meanwhile healthy bacteria – lactobacillus – is introduced to the digestive system in a much larger concentration. There, it will continue to consume unhealthy bacteria in the gut and otherwise keep it at bay.

Furthermore, fermented foods are similar to many cooked foods in that the vitamins and minerals become more bioavailable – that is, they are more easily absorbed and digested by our bodies.       

Fermented foods, as stated, contain lactic acid as a product of the activity of lactobacillus bacteria. Lactic acid itself gets a bad rap as what causes muscle soreness after rigorous exercise (although modern studies have shown this to likely be untrue), and is also part of what gives rancid milk its sour flavor & smell.

But in lacto-fermentation, lactic acid is produced under a different set of conditions and winds up in our gut, not muscles. Lactic acid brought into the body this way is not painful to muscles and actually some preliminary studies suggest it has a healthy effect on our body. Like the lactobacillus bacteria which produce lactic acid, the lactic acid itself also creates an inhospitable environment for pathogenic bacteria to survive.

Another positive aspect of fermented foods is that they will keep for very long periods, or potentially indefinitely. So you’re not going to waste food, and older food which has been fermented doesn’t pose a health risk (assuming it has been stored properly, kept submerged under the brine).

Perhaps to your surprise, the salt used in lacto-fermentation also can have certain health benefits. Salt is typically over-used and over-consumed in our society, but this is also refined salt often with additives such as “anti-caking agents.” Natural, unrefined salts, however, retain their trace minerals which are sources of electrolytes like magnesium, potassium, and calcium. These are the salts often suggested in lacto-fermentation, such as Himalayan Pink Salt, Celtic Sea Salt, Redmond Real Salt and others. Although there may be a valid argument that these are overpriced “luxury” salts, at minimum, additive-free and iodine-free salt should be used in lacto-fermentation to ensure the natural fermentation process isn’t disrupted.

While everyone’s health and dietary needs are unique, healthy individuals who use these natural salts in moderation (and tend to avoid processed salts) are arguably making a better dietary choice, one which aligns more closely with our evolutionary nutritional needs.  

Lastly, there is emerging evidence that the act of fermenting itself reduces anxiety. Could a reason for this be because it connects us to our ancient practices of food preparation and conservation we have evolved doing over millennia? Or maybe just because it is fun and rewarding?  

What type of equipment to use?

First off, for detailed info on product recommendations, go to my post on suggested products. The following is a discussion of the essentials to get started.

First and foremost, clean vessels for fermentation are needed. Common household vessels today include glass mason jars, ceramic crocks, foodgrade buckets, and much more.

In order to consistently ferment fruits and vegetables successfully, they also need to be in an anaerobic (oxygen-free) environment. A common approach is to completely submerge organic matter in a saltwater solution, providing the necessary conditions for a safe, mold-free ferment. Since many fruits and veggies are naturally buoyant and can easily rise above the brine, “fermentation weights” or items that can be used to serve this purpose are of extreme importance and usefulness. Although not every type of lacto-ferment necessarily involves a brine, such as kimchi, it is common practice. Therefore, the weights are a critical piece of equipment.

Although they are often touted as of paramount importance in fermenting, airlocks are an excellent piece of equipment but I’d argue not to the extent that weights are. That’s because even produce in an airlocked jar can rot and mold if anything is above the brine.

But let’s not underestimate their usefulness either. They allow gases to escape a ferment continuously, helping to avoid excessive gas buildup which can lead to brine overflow and other problems. They also (when working properly) prohibit air from entering the fermentation vessel. Although the saltwater brine in the vessel provides a barrier, air circulating into the vessel through a faulty lid (or use of makeshift covers) makes fermented goods more prone to spoilage.

On the other hand, a simple lid can achieve the same protection at a much cheaper cost. That said, a jar with a regular lid will need to be “burped” by hand to release gases, whereas an airlock makes this process automatic. Hence, with an airlock you can “set it and forget it.” Regular lids require daily burping in the initial days and often weeks of a ferment.

Salt Guidelines (adapted from Fermentation Basics, 2nd ed.)

Types of Salt:

As noted, an unrefined salt with all its minerals intact is a good choice. These salts can be pink or grey in color and this is normal; this doesn’t carry a risk to your health or the ferment. If using a refined salt, choose one that is pure salt and does not contain any additives or anti-caking agents. I tend to just use the more economical Morton Canning & Pickling Salt, and have had consistently good results.

It is possible to create low sodium ferments (like this pickle recipe), but there is more risk of spoilage, the vegetables can get mushy, and the shelf life will be shortened. Proper salinity helps keep vegetables crisp and encourages the growth of beneficial bacteria. If you choose a natural, unrefined salt you will also be ingesting necessary trace minerals.

Mixing a Salt Brine:

Vegetables are normally cured in brines from 1.5% to 5%. There are several bacteria that work together to ferment vegetables and they all have a different optimum salinity. A brine of 2% to 3% will tend to achieve the best flavor profile for most things. Brines higher than 5% will curtail bacterial activity, however it is possible until about 10% salinity. Beyond that point, the bacteria cannot live long enough to reduce the pH to shelf-stable levels.

Cucumber pickles should be fermented in a brine of 4-5%. Half sours for 3-4 days, full sours for 6-7 days. If the ambient temperature is warmer (e.g. upper-70s or higher), the ferment time should be slightly decreased to obtain similar results.

Peppers or hot peppers (for hot sauces) tend to do best in a higher salinity, 3.5-5%, as they are more prone to mold issues. 

The following are instructions for mixing brines. Real Salt brand fine grind (table salt) was used to get these measurements. Measure salt and stir into cool water until dissolved.

For 1 quart of water (4 cups)

  • 2% = 19g or 1 tablespoon
  • 2.5% = 24g or 1 tablespoon + 1 teaspoon
  • 3.5% = 33g or 2 tablespoons
  • 5% = 48g or 3 tablespoons

Dry-Salting Vegetables:

Dry-salting means you mix salt with sliced or grated vegetables to draw liquid out so they create their own brine. This is the method used for sauerkraut, many kimchis, and sauerruben. Measure salt as a percentage of the weight of the vegetables. Again, a range of salinity will work. These measurements are for a salinity of 2%, which works well for dry brining and won’t be too salty for most palates. Real Salt fine grind was used to calculate these measurements.

Vegetables (pounds) to salt (grams) (for a 2% salinity)

  • 1/2 lb. : 5g or 1 teaspoon
  • 1 lb. : 9g or 2 teaspoons
  • 2 lb. : 18g or 1 scant tablespoon
  • 2.5 lb. : 23g or 1 rounded tablespoon
  • 3 lb. : 27g or 1 tablespoon + 2 teaspoons
  • 3.5 lb. : 2 scant tablespoons
  • 4 lb. : 36g or 2 tablespoons
  • 5 lb. : 45g or 3 tablespoons
  • 10 lb. : 91g or 5 tablespoons


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  2. Joseph Tomko

    It gets into the high nineties in my house now and I noticed my fermenting peppers would bubble like a boil for three days and stop. When the house was cooler I would ferment for three or four weeks. When the bubbles stop, is it done fermenting? Thanks for this cool page.

    • Bubbles stopping isn’t a sign fermentation is over per se, just that the most active phase is complete. It is truly done fermenting when pH no longer drops, which is usually when it hits 3.2, though it could get even lower. SO, it could still be dropping in pH without obvious signs of bubbling. But anyway, yes, this process will definitely happen more rapidly in hotter temps.


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