Food Preservation

How Fermenting Works

There are three main types of fermentation, producing an industry of fermented products: alcohol (wine, beer), acetic acid (vinegar, kombucha), and lacto-acid (sauerkraut, kimchi, yogurt).

Lacto-fermentation

Of the many groups of fermenting bacteria, those from the lactic acid family are the most important in vegetable fermentation — specifically Leuconostoc, Lactobacillus, and Pediococcus species. This process is unrelated to lactose (sugar) found in milk. 

In an anaerobic (oxygen-free) environment, the specific microorganisms naturally present on the surface of all fruits and vegetables break down the produce's natural sugars into lactic acid. The natural acids and other antimicrobial compounds produced by the fermenting bacteria act as a preservative and 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.

This production of acid during the lacto-fermentation process lowers the pH of the food and creates fermented foods' characteristic, tangy flavor.

Keep in mind that not all fermented foods you buy in the store will contain live probiotics. Check the label for “Live Active Cultures.”

Fermentation Process

Fermented products process best at temperatures between 68 to 72 F. That process takes between three to four weeks to complete under ideal conditions. If the temperature is too high, spoilage bacteria may take over, ruin the product, or produce a less flavorful result. If the temperature is too low, the process may take six weeks or longer.

After fermentation is complete, store products in the refrigerator; store products in a cool, dry place if it has been safely canned. Shelf life for frozen and refrigerated fermented foods depends on the food and based on quality. For canned foods, most products canned properly are of the best quality for up to one year.

Salt used in fermentation should contain no additives. Canning or pickling salt is recommended since it contains no impurities and has a consistent granular size and weight.

Functions of Salt in Fermentation Process

• Pulls needed water and sugars from vegetables.
• Aids in the growth of fermenting bacteria over spoilage bacteria, yeasts, and molds.
• Allows for crispier vegetables by hardening the plant pectin and decreases the activity of pectinase, an enzyme that makes vegetables mushy.
• Slows the fermentation process, allows longer fermentation times, and decreases the chance of undesirable mold growth.
• Gives flavor to the final product.

Prevent Spoilage

Exposure to oxygen can encourage and allow for both mold and yeast to grow, so it is critical for vegetables to remain submerged during the fermentation process to prevent spoilage. Fermenting products should be kept 1 to 2 inches below the surface of the brine. If the fermented product is slimy or smells spoiled or rotten, discard it. Clean and sanitize the container thoroughly and try again.

• 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.

Storing Product

Watch for helpful signs to know when your product is ready to move into cold storage. Once fermentation is completed, store the finished product either in the refrigerator or in a cool, dry location if the product has been safely canned. 

• 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.