How to Ferment Homemade Kombucha

Homemade kombucha is a lightly sour, fizzy probiotic drink made by fermenting sweetened tea with a gelatinous culture called a SCOBY (symbiotic culture of bacteria and yeast). The basic process is simple: cool brewed, sweetened black or green tea, add the SCOBY and a little prepared kombucha, and leave it in a jar covered with cloth at room temperature for 7–14 days. During this time, leave the jar untouched in a quiet spot out of direct sunlight.

How Do You Feed a SCOBY and Keep It Alive?
The SCOBY consumes the sugar in each fermentation as food; that is why preparing fresh, sweetened tea for each new batch keeps the culture alive and active. When not in use, the SCOBY can be stored at room temperature in a “hotel” jar containing its own kombucha liquid; this liquid is both a food source and an acidic environment that protects against harmful microorganisms. Refresh the liquid in the hotel jar every few weeks.

What Determines the Fermentation Time?
A seven-day fermentation produces a sweeter, mildly sour result, while a fermentation closer to fourteen days produces a sharper, vinegar-like flavor; the time is adjusted largely according to personal taste. Room temperature during fermentation also affects the timing: 24–27°C / 75–80°F is ideal, and fermentation slows noticeably in colder conditions. Regularly tasting it with a spoon is the most reliable way to stop the process once it reaches the desired sourness.

What Is the Second Fermentation, and Why Do It?
After the first fermentation is complete, the liquid can be strained, combined with fruit or spices, and left in capped bottles for a few more days; this step is called the second fermentation, and it naturally carbonates the drink. At this stage, use only pressure-rated bottles made for carbonated drinks and seal them tightly; because excessive carbonation can cause a bottle to burst, briefly open the bottles once a day to check the pressure. Using plastic bottles instead of glass also makes it easier to feel the pressure by hand.

What Should You Do If Mold Forms on the SCOBY?
If a dry, fuzzy layer of mold, usually green, blue, or black, forms on the surface of the SCOBY, neither the culture nor its liquid can be consumed safely; discard both immediately. This usually results from dirty equipment or an insufficiently acidic environment; start over with a new SCOBY or a culture made from prepared kombucha. Brown, stringy fibers or yeast sediment are not mold and are a normal appearance.

Who Should Avoid Kombucha?
Because kombucha may contain a small amount of alcohol and can affect gut flora, pregnant or breastfeeding people, people with weakened immune systems, and young children should consult a specialist before consuming it. Since the fermentation time and acidity of homemade kombucha vary more than those of commercially prepared products, it is recommended to start with small amounts when trying it for the first time; the amount can be increased gradually after observing the body’s response.

Brief Summary
Homemade kombucha is made by fermenting sweetened tea with a SCOBY for 7–14 days; time and temperature determine how sharp the flavor becomes. Feed the SCOBY regularly with fresh sweetened tea, and if signs of mold appear, discard the culture without consuming it.