Home Fermentation Guide: How to Make Sauerkraut, Kimchi and Kombucha Safely

Fermenting vegetables and tea at home does not require special cultures in most cases: naturally occurring lactic acid bacteria on cabbage, or a SCOBY (symbiotic culture of bacteria and yeast) added to sweet tea, do the work. According to the University of Georgia's National Center for Home Food Preservation (NCHFP), the process depends on salt concentration and acidity to favor beneficial microorganisms while suppressing the ones that cause spoilage or illness.

Sauerkraut: the baseline fermentation

The Clemson University Home & Garden Information Center (HGIC) recommends shredding cabbage to about a quarter-inch thickness and layering it with salt in a stoneware crock, glass jar or food-grade plastic container — never aluminum, copper, brass, galvanized metal or iron, which react with the acid and salt and can discolor the ferment. The target salt concentration is 2.25% to 2.5% of the cabbage's weight, which HGIC translates to roughly 3 tablespoons of salt per 5 pounds of cabbage.

Once packed, the cabbage must stay submerged under its own brine by 1 to 2 inches, using a weight if needed; if there isn't enough liquid, HGIC advises adding a brine of 1½ tablespoons of salt per quart of water. NCHFP notes that regular dill pickles and sauerkraut take about three weeks to ferment fully, and that salt must never be reduced below tested amounts, since adequate salt is essential for both safety and texture, inhibiting undesirable bacteria while favoring the lactic acid bacteria that produce the sour flavor.

HGIC lists optimal fermentation temperature as 60°F to 70°F (about 15–21°C): at 60–65°F the kraut needs five to six weeks, while at 70–75°F it finishes in three to four weeks but develops more acidity and less complex flavor. Below 60°F fermentation may stall, and above 75°F the cabbage can turn soft. Surface scum should be skimmed off during fermentation, and HGIC states the finished product should reach a pH of 4.6 or below to be considered safely acidified.

Kimchi: higher salt, shorter brining

Kimchi starts with a more concentrated brine than sauerkraut. According to Korean cooking site Kimchimari, the traditional standard for salting napa cabbage is a 13% to 15% salt solution, though many home cooks now use a lighter 10–12% brine, which shortens brining time. Halved cabbages soak in this brine for two to three hours until the leaves soften, and salt is also worked by hand between individual leaves, focusing on the thicker white stem sections.

The cabbages then go back into the brine for an additional 10 to 12 hours, traditionally overnight, and are rotated periodically for even salting. Afterward they are rinsed three times before being seasoned with the chili-paste mixture and other ingredients. Kimchimari notes that in the final product the salinity of properly made kimchi settles to roughly 3–3.5%, since much of the surface salt is rinsed away before seasoning.

Kombucha: a sweet-tea ferment with two stages

Kombucha fermentation is built around the SCOBY, described by the American Homebrewers Association as a culture containing Acetobacter bacteria and Saccharomyces yeasts that convert sweetened tea into a tart, lightly carbonated drink. For a 4-liter batch, the association's recipe uses about 20 grams of black or green tea leaves, 200 grams of table sugar (sucrose) and chlorine-free filtered water, plus about 2 cups of starter liquid from a previous batch (or ¼ to ½ cup of distilled vinegar) to acidify the mixture and protect it from contamination.

The brewing vessel should be covered with cloth or a coffee filter secured with a rubber band — not an airtight lid — to let in air while keeping out fruit flies. The recommended fermentation temperature is 70–80°F (21–27°C); below 68°F fermentation slows or halts, and above 85°F the risk of mold or harmful bacteria increases, per the association's guidance.

A first fermentation of at least seven days converts about 65% of the sugar into ethanol, carbon dioxide and other compounds, with extended fermentation up to 21 days metabolizing roughly 80% of the sugar. Many brewers then bottle the liquid for a second fermentation of three to seven days in sealed, pressure-rated bottles to build carbonation, often adding fruit or flavorings at this stage. The association recommends keeping the brew's pH below 4.5 early on, aiming for about 3.6 in the finished product.

Shared safety rules

Across all three ferments, the sources agree on several non-negotiable safety points. NCHFP states that acidity level is as important to safety as it is to taste, and that home fermenters should never alter tested salt or liquid ratios. Clean equipment — washed with soap and water or run through a dishwasher — is sufficient; full sterilization used for canning is not required, but cleanliness matters because, as the Homebrewers Association puts it regarding mold-contaminated kombucha, 'the best and safest course of action is to throw out the whole thing (SCOBY included), sterilize your equipment, and start over.'

Keeping vegetables fully submerged under brine, avoiding reactive metal containers, and monitoring temperature are consistent requirements across the NCHFP and Clemson guidance.

• Use non-reactive containers: glass, food-grade plastic or stoneware, never aluminum, copper, brass, galvanized metal or iron (NCHFP, HGIC).
• Keep vegetables fully submerged under brine with a weight to limit air exposure (NCHFP).
• Do not reduce tested salt amounts; salt controls which microorganisms can grow (NCHFP).
• Watch fermentation temperature closely — too cold stalls the process, too warm risks mold or soft texture (HGIC, Homebrewers Association).
• Discard any batch that develops mold rather than trying to scrape it off, since mold spores are hard to eliminate once established (Homebrewers Association).