What is lacto-fermentation? 

The fermentation process results in lactic-acid production from bacteria which are present on the surface of all fruits and vegetables. Lacto-fermentation refers to this process and is unrelated to lactose (sugar) found in milk.

• In an anaerobic (oxygen-free) environment, these bacteria convert sugars into lactic acid, which inhibits harmful bacteria and acts as a preservative. It’s also what gives fermented foods their characteristic sour flavor.
• The natural acids and other antimicrobial compounds produced by the fermenting bacteria inhibit the growth of other harmful bacteria, molds, and yeasts that contribute to spoilage.
• Additionally, the carbon dioxide produced during the fermentation process helps maintain the low-oxygen conditions necessary for the fermenting bacteria to flourish. Carbon dioxide also aids in the stabilization of flavor and color.

Of the many groups of fermenting bacteria, those from the lactic acid bacteria family are the most important in vegetable fermentation – specifically Leuconostoc, Lactobacillus, and Pediococcus species.

Benefits of fermented foods

• Enhanced digestibility due to enzyme action.
• Increased vitamin levels, specifically B vitamins and preservation of vitamins A and C.
• Improved gut health due to presence of probiotics.
• Keep in mind that not all fermented foods you buy in the store will contain live probiotics. Check the label for “Live Active Cultures.”

Salting Methods

Dry Salting

Salt is added directly to the vegetables. After mixing in the salt, leave the mixture for 20 to 30 minutes to allow for natural juice extraction.

Massaging salted vegetables helps to speed up the process and usually takes 10 to 15 minutes to get enough liquid pulled out to cover the vegetables in the fermentation vessel.

Brining

Brining is best for whole or quartered pieces. Mix salt and water to form a brine before adding to the vegetables. This technique can allow for better coverage of the vegetables, lessening the risk of fermentation failure. If there isn’t enough brine to cover the vegetables from dry salting, make additional brine by mixing 1 quart water with 1-½ tablespoons salt.

Brine Concentrations

Shredded vegetables, such as cabbage, use a 3% concentration. Generally, use 5% salt concentrations for large vegetables, such as cucumbers and carrots. Mix water and salt to achieve desired concentration. It is best to weigh salt for accuracy.

• For a 3% solution: mix 1 quart of water 2 tablespoons (1 ounce or 27 grams) of salt
• For a 5% solution: mix 1 quart of water and 3 tablespoons (1.6 ounce or 45 grams) of salt

Preparation

Wash the container, equipment, and food contact surfaces with hot soapy water before you begin. Sanitizing is another crucial step. If chlorine bleach is used, the equipment should be rinsed thoroughly to remove any residues which may inhibit the growth of fermenting bacteria. Boiling containers for 10 minutes is also a safe method for sanitizing.

Tools and equipment

Cutting, chopping, and pounding tools aid in the extraction of the vegetable juices necessary to cover the fermenting mixture. What you will need when it comes to chopping and cutting will depend upon what your desired final product will be.

Kraut boards, food processors, sharp knives, and mandolins all work well. Crushers, pestles, and sauerkraut pounders break the vegetable tissue, allowing more juices to be released.

Clean hands or gloved hands will also get the job done. You may need to massage the shredded vegetables for 10 to 15 minutes until you have extracted enough liquid to cover the vegetables once transferred to your vessel.

Vessels and containers

As a general rule, plan to use a 1-gallon container for every 5 pounds of fresh vegetables.

• Use food-grade containers such as glass or plastic (BPA free).
• Quart-size glass jars with airlock lids are great for small batches.
• High-grade, commercial stainless steel can be used.
• Do not use copper, iron, or galvanized metal containers or lead-glazed crocks.

If the safety of the container is in question, err on the side of caution to avoid harmful materials leaching into your food. Use plastic jar lids since metal lids may degrade under acidic and salty conditions.

Keeping foods submerged

It is critical for vegetables to remain submerged during the fermentation process to prevent spoilage. Fermenting product should be kept 1 to 2 inches below the surface of the brine.

Options for submerging vegetables

• Ceramic or tempered glass weights.
• Food grade bag filled with brine.
• Glass or pie plate in addition to the brine-filled bag.
• Whiskey stones are good for smaller vessels (do not confuse with rocks).
• A cabbage leaf, weighted by a brine-filled bag, can help prevent vegetables from floating.

Controlling mold

Exposure to oxygen can encourage and allow for both mold and yeast to grow. Submerge vegetables 1 to 2 inches below juice/brine mixture to prevent spoilage.

• Use a jar with an airlock lid.
• Keep food submerged below the brine level.
• Control room temperature, keeping it ideally between 68 to 72°F.
• Select fresh, firm vegetables free of spoilage.
• Use the correct amount of salt.
• Clean and sanitize equipment; wash hands and surfaces often.

When in doubt, throw it out

If fermented product is slimy or smells spoiled or rotten, discard it. Clean and sanitize the container thoroughly and try again!

Moving to Cold Storage 

Watch for these helpful signs to know when your product is ready to move into cold storage.

• Bubbling: Fermented products should have bubbles in the brine mixture. This is because lactic acid bacteria produce gases and this shows up in the form of bubbles.
• Aroma: Fermented product should have a pleasant, yet slightly sour, aroma. If it smells spoiled or rotten, discard it.
• Taste: Depending on the type of vegetables used, there will be varying ranges of fermented flavors. Generally, if you want a less sour product, use a shorter fermentation time; allow vegetables to ferment longer for more tang. Expect subtle changes in flavor even during refrigeration as the process slowly continues.

References

• Vegetable Fermentation., Joell A. Eifert, Food Safety Extension Agent, Virginia Cooperative Extension, Renee R. Boyer, Associate Professor
• Food Science and Technology, Virginia Tech, Robert C. Williams, Associate Professor, Food Science and Technology, Susan S. Sumner, Associate Dean Academic Programs, College of Agriculture and Life Sciences
• Breidt, F., McFeeters R. F., Perez-Diaz I., and Lee C. 2013. Food Fermented Vegetables Microbiology: Fundamentals and Frontiers, 4th Ed. Edited by M. P. Doyle and R. L. Buchanan: ASM Press, Washington, D.C.
• USDA. 2009. USDA Complete Guide to Home Canning, Guide 1: Principles of Home Canning. U.S. Department of Agriculture National Institute of Food and Agriculture. Agriculture Information Bulletin No. 539.