This is a comprehensive guide to safely using salt in vegetable fermentation. Find out how much salt you should use to ferment any type of vegetable at home, how to calculate salt concentration, and what to do for low-salt options in fermentation.
Fermenting with Salt
In order to provide the microbes present on raw vegetables with an exact concentration of salt, you must use units of mass to measure your salt. There are two mathematical methods we use to create an exact total salt concentration (please note that I am NOT referring to salinity. Here we are discussing total salt concentration, aka % composition of salt), and the desired approximate salt concentration varies by type of vegetable (see chart below). Here I will use 2.5% as an example.
Using the metric system is much easier because 1 mL of water weighs 1 gram. So there is no mathematical conversion between mL and gram measurements of water in the metric system.
Fermenting Brine Ratio
I do not teach brine ratios, because total salt concentration is better. Total salt concentration accounts for the weight of vegetables and water. Let’s look at 2.5% total salt. The exact, analytical way to create a 2.5% total salt concentration is as follows:
Place a bowl on a scale and tare/zero the scale. Add 2.5 grams of salt to the bowl, then add your produce and any water into that same bowl up to 100 grams. That’s a 2.5% total salt concentration.
What we do is slightly different, easier, and very safe: We weigh all of our produce and water, multiply that weight by 2.5%, and add the number we get in salt. This results in an approximate 2.5% salt concentration that is perfectly safe and optimal for fermentation.
Fermentation Salt Calculator
If we have 100 grams of produce and water, we multiply by 2.5%. So 100 x 0.025 (you have to move the decimal because you are multiplying by a percentage) = 2.5. So we add 2.5 grams of salt. This ends up being a 2.44% total salt concentration.
In order to calculate the total percent salt concentration of the mixture, you divide the grams of salt added by the total grams of the entire mixture: 2.5 grams of salt / 102.5 grams (of salt + water + produce) = 0.02439.
Move the decimal to make it a percent and you get 2.44% And guess what? With this method, we end up with 2.44% salt, no matter the weight of vegetables or water… if we add 2.5% salt, the resulting total salt concentration will always be 2.44%
For example, If we have 756 grams of cabbage and water, we multiply that by 2.5%. That equals 18.9. So we add 18.9 grams of salt.
18.9 / (756+18.9) = 0.02439
Yep. That’s 2.44%
The only way you will get a consistent salt concentration throughout different batches of fermentation is by weighing the produce and water, doing math, and then weighing out your salt.
Salt to Water Ratio for Brine
The salt to water ratio for brine, also needs to include the water inside the vegetables.
Common Questions About Measuring Salt in Vegetable Fermentation:
- Why weigh the vegetables? All vegetables are about 98% water, so you have to account for that water weight. Because of osmosis and concentration gradients, the total salt concentration includes the water found in the vegetables. Since we’re calculating a total (w/w) salt concentration (not salinity) the mass of vegetable matter added to the mixture has to be accounted for.
- They didn’t need math to ferment 2000 years ago. “They” also lived in a less toxic world where agriculture was different, salt was different, microbes were different and antibiotic-resistant bacteria didn’t thrive in an industrialized food system. No, people didn’t always use science to ferment… but they have used weight measurements for recipes, trade, and calculations for a LONG time. A long time meaning since around 1200 BC at least. People of the Eastern world used mass and ratios (aka math) to make fermented vegetables for thousands of years. Not American tablespoons. Traditionally, in the eastern world, fermented vegetables are made with high salt concentrations between 5% and 20%.
Now, I do list recommended total salt concentrations below. These are the total salt concentrations that have yielded the best microbial compositions when fermenting different vegetables, in my recipe development tests and studies. This chart is not to say that you cannot achieve an acceptable quality fermented vegetable using different salt concentrations.
The takeaway here is that no matter what salt concentration you use, the total concentration of salt in vegetable fermentation can ONLY be accurately measured using the mass of the salt, and the mass of the total mixture. There is no possible way to achieve the desired salt concentration by using arbitrary amounts like a head of cabbage and a tablespoon of salt… and you definitely cannot estimate a salt concentration by salting to taste. Taste is arbitrary and salt perception is vastly different for each person depending on diet and lifestyle.
How much salt for lacto fermentation?
Here is a page from our lesson two workbook in the fermented foods semester online course that can help you understand what amount of salt to use for different types of vegetables:
What About options for Low Salt in Vegetable Fermentation
The concentration of salt in vegetable fermentation greatly influences the microbial composition of fermented vegetables. Even the type of salt used can have a profound effect on which types of microbes populate fermented vegetables.
A critical safety step in the fermentation of vegetables is the accumulation of lactic acid produced by lactic acid bacteria. This acid accumulation is what creates a preserved and safe fermented vegetable product.
Acid production, and the resulting pH in vegetable fermentations, is affected by the use of different salt concentrations, because the use of different salt concentrations influences which microbes thrive and how fast they can thrive.
Essentially, salt encourages the growth of desirable heterolactic and homolactic microorganisms, like Leuconstoc and Lactobacillus. So the microbial community, the production of acid, and thus food safety are all a result of the initial salt concentration in fermented vegetables. (5)(12)(11)
The lowest salt concentration I’ve found, that claims to be safe without using a starter culture is about 1.3% (2). However, in the paper referenced (2) initial levels of pathogenic yeasts, fungi, Gram-negative organisms, S. aureus, L. monocytogenes, and E. coli were not monitored, measured, or reported. No data was collected on biogenic amine levels or aflatoxin presence. Thus, this paper lacks some data on the safety of the vegetables fermented at 1.3% salt concentration and drew conclusions based solely on the sensory acceptability of the kimchi. Also, it should be noted that this low of salt concentration is conducive to fungi growth.
A more thorough study indicates that a 2.5% salt concentration is ideal. The result of their microbiological analysis showed that the population of LAB in 2.5% salted sauerkraut is significantly higher than that in samples with lower salt concentrations. Correspondingly, the speed of decrease in pH and accumulation of acids were the highest in 2.5% salted sauerkraut (12). The quicker the lactic acid accumulates, the safer the product.
It should be noted that most research indicates that lower salt concentrations result in undesirable and possibly pathogenic bacteria and fungi thriving in certain stages of fermentation (6)(5), which can cause food poisoning, unpleasant textures, and vegetable softening (10). Generally, as salt concentration is lowered below 2%, wild fermentation is no longer an option and starter cultures, preservatives, calcium chloride, mineral salts, and/or potassium chloride must be added to account for reduced salt content and to ensure safety(4)(5).
In commercial pickle fermentation, something called bloating can occur if an inadequate salt concentration is used, because lower salt concentrations allow for carbon dioxide and acetic acid-producing Lueconostoc bacteria to thrive for a longer time, discouraging a swift transition to homolactic Lactobacillus. With regular safe salt levels, Leuconostoc only thrives for a short time before producing enough acid to encourage homolactic (lactic acid-producing) Lactobacillus spp. to take over the fermentation(3). This shift to Lactobacillus is vital to controlling the levels of biogenic amines produced in fermented foods, as Lactobacillus can consume and degrade biogenic amines.
For at-home fermenters, I advise using the salt concentrations in the chart above. If you’d like to experiment with salt concentration levels as low as 1% I highly suggest buying some pH strips to ensure your at-home fermentation project has achieved a safe pH level of around 3 to 4 pH. Also, you still need to weigh the salt in order to verify that you’re actually using a specific % salt concentration. By using extremely low salt concentrations, your fermentation projects can be contaminated with Shiga toxin-producing E. coli, acid-tolerant S. aureus, acid-tolerant pathogenic fungi, C. botulinum, and/or become undesirable in flavor and texture(6)(7). This is because a low salt concentration can allow for secondary fermentation by yeasts. Some yeasts have the ability to deacidify, raising the pH and increasing the chances of pathogen growth. It’s also important to note that salt concentrations greater than 10% are sometimes inhibitory to fermentation.
Through five years of commercial fermentation recipe development research, I’ve found that success in fermentation comes from using exact and adequate salt concentrations. The chart I created above contains the salt concentrations that have encouraged the quickest drop in pH, the best progression of microbial populations, as well as the best food sensory outcomes in my recipe development tests. Experiment at your own risk!
Another option for those on low sodium diets is to ferment with the salt concentrations listed in the chart above. Once fermentation is complete, you can remove half of the liquid and replace the liquid removed with raw apple cider vinegar before placing it in the fridge. This results in a vastly different flavor, but I enjoy it and it cuts the salt content almost in half without compromising food safety and sensory qualities.
A Valid Experiment on Salt in Vegetable Fermentation?
If you want to read a thesis on various salt concentration effects on fermentation CLICK HERE. This is someone’s master’s degree thesis, and I think it was executed wonderfully. Overall, they found that 1% to 2.5% salt concentrations didn’t differ much on the outcome of safe pH levels and end-product control of pathogens. Salt concentrations of 2.0% and 2.5% resulted in the most lactic acid formation. Their results also indicate that 2.0% NaCl resulted in the highest final levels of lactic acid bacteria. However, they did not differentiate between the population development of heterofermentative Leuconostoc spp. vs homofermentative Lactobacillus spp. across the different salt concentrations. This differentiation is important because, as stated previously, lower salt concentrations can discourage the transition to a desired homofermentative Lactobacillus predominate population. This microbial population transition is vital and impacts acidity, gas production, biogenic amine content, potential pathogen growth, sensory qualities, and glucose levels. A transition to a Lactobacillus predominate population results in a population of bacteria that are verified probiotics. Also, Lactobacillus spp. are the specific bacteria involved in fermentation that exhibit the enzymatic activities that biotransform phenolic compounds into health-promoting substances (8). Essentially, fermented vegetables contain more verified probiotic bacteria and health-promoting compounds when a salt concentration of about 2.5% is used and vegetables are fermented for at least 14 days (12).
In conclusion, more studies are needed to validate and ensure the safety of fermented foods produced with extremely low salt concentrations. For thousands of years, traditional fermented vegetables have been made with high salt concentrations ranging from 5% to 20% (9). Before we can change and disregard thousands of years of fermentation recipes and traditions… Before anyone culturally appropriates these historical recipes to meet the low-sodium needs of the American diet, we must fully study and validate the safety and repercussions of these changes.
A note on traditional fermentation practices
Natural fermentation precedes human history, I know. Since ancient times, humans have exploited the fermentation process. I think it’s only reasonable that, in our modern times, we allow ourselves the space to respect and learn about the microbes of fermentation. We should choose to understand microbes to harness fermentation in the healthiest way possible. Also, let’s not irresponsibly culturally appropriate recipes and instead bring pride and respect to the long-standing culture of fermented foods by understanding the process fully.
Some traditional fermented foods, like Baechu Korean kimchi and Dưa Chua Vietnamese fermented vegetables have a swift fermentation time. This is thanks to specific ingredients, adequate salt content, and traditional methods.
Dưa Chua, for instance, is made by drying vegetables in the sun then submerging them in a brine that includes salt and sugar. Dưa Chua is usually fermented for about 4 days at 80-95° F.
Baechu Korean kimchi is made by soaking nappa cabbage in a high salt concentration for 12 hours before it is rinsed and rubbed with a paste made of salted shrimp, fish paste, gochugaru, sugar, ginger, garlic, and scallions. Then it is packed into an air-tight fermentation crock and enjoyed after only three days of fermentation.
In both of these examples, the ingredients, salt content, methods, and temperature are very important factors influencing the fermentation outcomes. If you want to make traditional fermentation recipes from other cultures, some of which have quick fermentation times, find a teacher from that culture who provides recipes (there are so many) and follow EVERY step, method, temperature, time, and ingredient. These types of recipes are time-tested and perfected over thousands of years.
(8) Frias, Juana & Martinez-Villaluenga, Cristina & Peñas, Elena. (2016). Fermented Foods in Health and Disease Prevention.