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This is one of the frequently asked questions about vegetable fermentation. It comes from the idea that salt is unhealthy. Although there are many studies regarding salt in our diets the debate regarding its effect on human health is still not decided but when it comes to lacto fermentation it is a necessary ingredient which helps improve the final product.
SaIt prevents spoilage bacteria from growing on the vegetables in the container which cause off flavors, removes some of the water from the vegetable which keeps them crisp and enhances the flavor of the final product.
Without salt, vegetable fermentations would be dicy to eat, mushy and bland. Not something you would want to put into your mouth.
How salt prevents the growth of spoilage bacteria
Salt has been used to preserve food for centuries. Its properties help to reduce the growth of microorganisms in food in several different ways.
Reduces the amount of freely available water
For microorganisms to grow they need freely available water. Water helps to maintain proper chemical concentrations within the cell and is used in many biologically important processes. Without water there would be no life on earth.
With the addition of salt to a vegetable fermentation the amount of freely available water is reduced. The salt dissolves into the water and reacts with it making some if it unavailable to the various microorganisms found in the fermentation.
Lactic acid bacteria are more salt tolerant than the spoilage bacteria which are found on the vegetables and therefore have the upper hand in the culture, easily out competing the unwanted microbes.
Disrupts the membrane of microorganisms
With a high enough salt concentration salt can cause the membranes of a cell to rupture. This is caused by crystallization of the salt within the cell. Once the cell has solid salt particles in and around the cell’s membrane the sharp edges of the crystal causes damage to the cell which hinders its growth or destroys the cell.
Some species of lactic acid bacteria have been found which have special genes which are activated when they are in a salty environment. These genes help the lactic acid bacteria to alter their makeup to be more salt tolerant quickly. Some species have been found which can survive in a 15% brine solution which is five times the recommended salt concentration used for vegetable fermentations.
Reduces the amount of oxygen available
When the salt fully dissolves into the liquid brine which the vegetables are submerged in, the salt draws out water from the vegetables into the brine. As this happens any bubbles which are trapped are dispelled. This leaves less available oxygen for the aerobic microorganisms and further hinders their growth.
Since lactic acid bacteria are anaerobic, meaning they grow best without oxygen they can out compete the spoilage bacteria in this type of environment.
Forces the living cell to expend energy dispelling salt
Having too much salt within the cell prevents normal biological reactions. Although microorganisms have the ability to remove the salt, this activity takes energy. The more energy the unwanted cells have to expend on removing unwanted salt the less energy is left for growth.
How salt improves the texture of fermented vegetables
Nobody likes a mushy pickle or soft sauerkraut. Salt is the ingredient which most influences the texture of a vegetable fermentation. There are other techniques which help to improve the texture like adding tannins from oak leaves, tea or grape leaves but without the addition of salt these improvements would be too little and too late to make any noticeable difference.
Reducing the sugar content within the vegetable
As the water in the cell is drawn out of the cell, sugar which is dissolved into the water also comes out of the vegetables. The sugar content in the vegetable drops leading to less microbial action within the vegetable. Since lactic acid bacteria cannot convert starch into energy but need simple sugars less respiration happens within the vegetable.
The products of respiration of lactic acid bacteria are lactic acid and CO2. The main culprit of mushy vegetables is the CO2 which is produced within the vegetable. This gas expands within the vegetable and breaks down the structure which holds the vegetable together. The result is a softer pickle or mushy sauerkraut.
With less sugar within the vegetable less CO2 is produced in the vegetable itself which makes for a firmer crisper end product.
Lowering the amount of available oxygen under the brine
Most spoilage microbes are aerobic meaning they need oxygen to live. These spoilage microbes produce flavors within the fermentation which are unpleasant, making the fermentation inedible.
At the beginning of a fermentation culture these microbes grow with the lactic acid bacteria if they have access to oxygen. This is why you want to keep the vegetables under the brine (especially at the beginning) but even if you keep the vegetables under the brine salt is necessary to ensure spoilage does not happen.
The salt draws out water from within the vegetable dislodging any small bubbles which cling to the sides of the vegetables and get trapped within crevasses. This happens faster than the lactic acid bacteria can acidify the environment which improves the final flavor of the fermentation.
Dehydrating the vegetable within the salt solution
As mentioned previously the salt draws out liquid from the vegetable essentially dehydrating the vegetable. As the water content of the vegetable goes down the texture of it improves. With less water in the vegetable it becomes crunchier.
How salt improves the flavor of fermented vegetables
Salt is the most popular flavor enhancer in the world. It is added to almost everything we eat from sweet treats to savory dishes. It is even a major ingredient of condiments which are added to food to adjust it for flavor.
There are many theories as to why we have a strong attachment to salty foods which range from past uses of salt for food preservation to our biological need for salt. Recently several studies have been done which focus on how salt affects our taste.
Attaches to bitter flavors
When salt is dissolved in water it breaks down into its component parts and reacts with other chemicals found in its vicinity. When salt is added to a food with a bitter taste it reacts with these components causing the food to taste less bitter. As the bitterness is eliminated the sweet flavors are left making the food taste sweeter.
Intensifies umami flavor
With the addition of more salt the sweet flavors are also masked and the umami flavor is enhanced. This is the flavor we find so appealing in soy sauce and miso. These two foods are highly salted but are very popular for their unique flavor and interest they add to our food.
How to reduce the amount of salt safely in fermented vegetables
Lower the temperature
Temperature control is a major part of lacto fermentation. Most vegetable fermentations taste better, have better texture and color when fermented in temperatures between 60℉/15℃ and 65℉/18℃ . If you ferment your vegetables at the lower end of the temperature range you can reduce the amount of salt you use to the lower range. Since the recommended salt concentration for lacto fermentation is between 2%-3% fermenting at 60℉/15.5℃ will allow you to reduce the salt to 2% by weight.
This reduction is due to the lack of mold growth at lower temperatures. Mold grows poorly at temperatures below 70℉/21℃ so keeping your fermentation cool eliminates the damage done from these types of spoilage microorganisms.
inoculate the fermentation
One of the main reasons why salt is added to a fermentation is to prevent the growth of spoilage bacteria while the lactic acid bacteria grow to high enough numbers to dominate the culture. This can also be accomplished by inoculating the vegetables with an active culture. This gives the wanted bacterial cultures a head start and can dominate the culture quicker.
To do this just add some brine from a previous batch of lacto fermented vegetables. The active culture in the brine will quickly dominate the environment and prevent the growth of spoilage microorganisms.
Acidify the vegetables
One of the main reasons why spoilage microorganisms do not grow well in lacto fermented cultures is because of the low pH in the container. It is the lactic acid bacteria which produce lactic acid in these types of fermentations but it takes some time for the bacteria to grow and produce enough lactic acid to help.
The salt is added to help hinder spoilage microorganisms while the lactic acid increase in population. If you want to lower the amount of salt you use you can add some acidity to the vegetables when you pack them into the jar.
You can either use vinegar, acetic acid powder or lactic acid powder if you can find it. Be sure not to use very much to prevent making an overly acidic fermentation.
