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Vegetable Fermentation

    It is a food preservation that has been long used to slow down the rottenness of vegetables and fruits and to prolong the shelf life of products for several months without using a refrigerator; as a result, it requires low investment, simple machinery, and low technology. The fermenting process came to exist as a result of demand to keep food out of its season for use or consumption during journey, especially by sea. Apart from extending the shelf life, fermentation also yields desirable flavor and taste.

    It was believed that cucumber was the first fermented vegetable product, produced 4,500 years ago in Mesopotamia . Cleo Pattra believed that consuming fermented cucumbers could make beauty. During the war time, Julius Cesar and Napolien had fermented cucumbers for food. Presently, consumption of fermented vegetables is still popular. In the United States , the highest sales volume is fermented cucumbers. In England , fermented red onions are popularly used in foods and spicy fermented beet roots as a side dish. In China , there are several fermented vegetable products such as radish, cabbage, chili, cucumber, etc. Fermented peach, fermented cucumber, sauerkraut, and fermented radish are popular in Taiwan and daikoon, fermented peach, cauliflower, and Chinese cabbage in Japan . Korea uses cabbages for making sauerkraut. India prefers to ferment mixed vegetables.


Types of Fermented Vegetables
  1. Processed Pickles. It takes several weeks to complete the fermenting process while the crispiness and unique flavor and taste of pickles remain. The concentration of brine solution used for fermenting will be less than 12%, mostly around 4-8% or 1/2 - 1 cup of salt per 1 gallon of water. The concentration of brine solution at this level is high enough to inhibit the growth of microorganisms and suitable for growth of the microorganisms producing lactic acid. The brine solution should be kept at 21 ° C; and vegetables must be submerged in brine solution throughout the whole period of fermenting process. If there is fungi on the surface of brine solution, it must be immediately skimmed off because fungi will decompose lactic acid and build the environment in which the microorganisms causing damage can grow. However, the most proper concentration of brine solution depends on type of vegetables to be fermented. This type of fermentation needs microorganisms, using oxygen for growing, to change from sucrose in vegetables to lactic acid; and are good for cucumber pickles, sauerkraut, fermented radishes, kimchi, etc. The change in these foods during the fermenting process is activated by only lactic acid bacteria or other bacteria as shown in the following Table.





    Nukamiso pickles




    Ginger beer




  2. Unfermented Pickles. It is used for fermenting vegetables with high acid content, such as cucumber, cauliflower, onion, carrot or chili etc., by using salt with high concentration of 20-25%. The purpose of this method of fermentation is to preserve vegetables in brine solution or as a step to eliminate bitter taste in dried vegetable products e.g. myrobalan, etc.
  3. Fermenting in Vinegar Solution. This fermenting method may be used together with brining, either using bacteria or not using bacteria. It may not go through a curing process at all, but vegetables are being submerged in the vinegar solution flavored with seasonings, sugar, and salt. It is considered as the easiest fermentation that the curing process can be completed within 1-2 days. In this process, it is important to use a good quality, clear vinegar that is free from sediment with 5% acetic acid. Home-made vinegar should not be used because it darkens the food.

  4. Fermenting in Oil. In some countries like India and England , fermenting in oil is popular by using turnip, cauliflower or other plants going through or not going through a fermenting process. Then, vegetables are mixed with salt and seasonings, packed in jars, and dried in the sun for 4-8 days. After that oil is added in jars until it is mixed well.


     The fermenting process needs bacteria in the Lactobacteriaceae family to change from sucrose in the vegetables to lactic acid. There are five genera in this family which are:
  1. Streptococcus
  2. Pediococcus
  3. Diplococcus
  4. Leuconostoc
  5. Lactobacillus

     These bacteria are positive gram and cannot build spore. They, therefore, need vitamin B complex and amino acid for growing, but cannot grow in the environment with the presence of acetic acid concentrated higher than 3-6%. The bacteria in these groups can quickly activate the fermenting process by adding the increasing amount of carbon dioxide in the system. These bacteria are divided into two groups. They are given below.

  1. Homofermentative. This group uses 85-95% of sugar in producing only lactic acid. The remaining will be used for generating energy and volatile compound. Streptocooccus faecalis, Pediococcus cerevisiae are examples of this group of bacteria.
  2. Heterofermentative. This group uses 50% of sugar in producing lactic acid. Another 25% is utilized to create acetic acid and ethanol. The remaining percentage of sugar will be used for producing carbon dioxide. Leuconostoc mesenteroides, Leuconostoc fermenti are examples of this group of bacteria.

     Fermented foods have acid to control the growth of microorganisms because each type of microorganisms requires different amount of acid for growing. So, the final products will contain just the bacteria that can survive in high acid. The increasingly high acid condition will later destroy itself; as a result, yeast and fungi that tolerate acid will further grow. Fungi is able to utilize acid while yeast will produce an alkali substance. As a consequence, the acidity will gradually reduce to the level that the bacteria can further work.

     The reaction occurred during the fermenting process will yield texture, appearance, flavor and taste of fermented foods in a way that consumers can accept. Such a reaction may happen as a result of the performance of microorganisms which will use enzymes in their cells to decompose nutrients e.g. carbohydrate, protein, and fat, leading to compounds that give good flavor/taste and new phenomenon to foods. The following are examples of chemical changes of foods caused by microorganisms in the fermenting process.

Sucrose + Streptococcus spp. Lactic acid (yogurt, fermented fruit)
Sucrose + Saccharomyces spp. (yeast) Alcohol + gas (wine)
Alcohol + oxygen + Acetobacter spp. Acetic acid + water (vinegar)

     Factors affecting the fermentation are pH balance, quantity of oxygen, temperature, quantity of salt, and starting agent. When these factors are in the proper environment, the microorganisms can fully grow and produce the sufficient amount of enzymes for activating the chemical reaction with foods. As a consequence, the fermenting can speedily carry on until the fermented foods reach the quality that is accepted by the consumers.


     It is very important for the fermenting process to kill yeast, mold, and bacteria that make the products deteriorate or inhibit enzymes to work on color and flavor/taste of fermented vegetables . The fermenting process will differ depending on the raw material used for fermenting. Generally, the steps of fermenting process are as follows:

Fermenting process

Baby Cucumber Pickling Process

Making Sauerkraut

Making Fermented Asparagus

Making Fermented Cabbage

Making 3-Flavor Fermented Radish
Making Sweet Radish

Making Sweet-Sour Fermented Ginger

Making Fermented Garlic

Making Kimchi

Making Spicy Pickled Cabbage

Making Mixed Vegetable and Fruit Pickles

Making Mixed Vegetable Pickles
  1. Vegetables used for fermenting should be firm, fresh, clean, free from bruises and fungi, and right size. They also should not be waxed because the pickling solution cannot penetrate the wax; as a result, the fermented vegetables will not be crisp. If necessary, vegetables should be cut into pieces before fermenting. For highest quality, fermentation should start within 24 hours after vegetables have been harvested and stored in a cold room or in a cold place with good ventilation.
  2. For the selecting process, vegetables that are rotten, broken or too soft should be taken out. Then, select the proper size.
  3. Cleaning is done to eliminate soils on the surface of vegetables. These soils are the source of bacteria causing undesirable texture.
  4. After being cleaned, some vegetables need to be cut in a desirable form before fermentation takes place. In case of wanting fermented vegetables to be unusually crisp, the vegetables must be wet before soaking in a lime-water solution (1/4-1/2 cup of food-grade lime/1 gallon of water) overnight (for cucumbers). After that the vegetables are washed and soaked in clean water for one hour. Repeat the rinsing and soaking steps twice more to remove excess lime absorbed by fruits. Failure to remove lime adequately may increase the risk of botulism.
  5. Vegetables can be fermented in a large stoneware crocks, large glass jar or food-grade sterilized plastic containers. Do not use aluminum, copper, brass, galvanized or iron containers for fermenting vegetables because these materials can react with acid or sodium, yielding undesirable color of the finished products. Generally speaking, a one-gallon container is needed for each 5 pounds of fresh vegetables. So, it should not be over packed because the pickling solution will over flow during sterilization. The stain of the pickling solution will stay on the rim of a jar, resulting in the jar not being closed tightly. If the jar is loosely packed, then, the air is still in the jar.
  6. Pour pickling solution in the bottle. The ingredients of pickling solution are as follows:
    6.1 Salt: It should not be iodized salt because iodine will inhibit bacteria to work on the fermenting process.
    6.2 Sugar: It may be cane or beet sugars. It should be white sugar, giving a product a lighter color. If it is brown sugar, the color of the product will be darker and its smell and taste stronger. Honey can be used as a sweetener, but should be ? less than the sugar called for.
    6.3 Spices: Use fresh whole spices for the best quality and flavor in pickles by tying whole spices loosely in a clean white cloth or cheesecloth bag and then remove the bag from the product before packing the jars. Powered spices may cause the product to darken and become cloudy.
    6.4 Water: Use clean water without the presence of any compound, particularly iron because it gives the product a dark color.
    6.5 Alum: It is used to firm fermented vegetables. For good result, use 1/8 teaspoon alum per quart jar.
    6.6 Others such as citric acid, preservative like sodium benzoate .
         Pickling solution should be clear without any sediment and boiled at the approximate temperature of 76-82.2 ° C. Let it warm before pouring it over vegetables 1-2 inches high. Stir inside the jar with a plastic spatula to expel air. Clean the rim of the jar with clean cloth. Then, tightly close the jar with a cork cap or lid.
  7. The products are stored. Fermentation will gradually go on throughout the storing period. The proper length of fermenting depends on type of vegetable, including the demand of consumers' taste.
  8. After being fully fermented, the products must be pasteurized to stop the fermenting process and destroy bacteria that may spoil the products since the products contain high acid. In doing so, jars must be place in a canner half filled with warm water(48-60 ° C). Add hot water to a level of 1 inch above jars. Then heat the water to 82-85 ? C and start timer. Process for 30 minutes and then immediately remove jars from canner at the end of processing time.
         Heating fermented vegetables before packing is called hot pack. Another method, raw pack, is giving heat to fermented vegetables after packing. The processing time is given below.

Recommended Processing Time

Style of Pack

Jar Size

Processing Time

Hot pack






Raw pack





Thailand Institute of Scientific and Technological Research (TISTR)
Food Technology Department
35 Technopolis, Klong 5, Klong Luang, Pathumthani 10120 Thailland
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