Kombucha is made from four core ingredients: tea, sugar, water, and a live culture of bacteria and yeast. That’s it for the base recipe. But the fermentation process transforms these simple inputs into a more complex drink containing organic acids, B vitamins, a small amount of caffeine, trace alcohol, and carbon dioxide. Store-bought versions often add fruit juices, herbs, and supplemental probiotics on top of that.
The Four Base Ingredients
Every batch of kombucha starts with brewed tea, sugar, water, and a rubbery disc of living microorganisms called a SCOBY (symbiotic colony of bacteria and yeast). Black or green tea provides the caffeine and polyphenols that feed the culture. White sugar, typically plain cane sugar, is the fuel source for fermentation. The SCOBY floats on top of the sweetened tea and slowly converts the sugar into acids, CO2, and trace amounts of alcohol over one to two weeks.
The sugar isn’t there for sweetness in the final drink. It’s food for the microbes. Traditional kombucha starts with 60 to 80 grams of sugar per liter, but the bacteria and yeast consume a significant portion during fermentation. A standard brew finishes with roughly 15 to 40 grams per liter of residual sugar. Batches fermented longer can drop to nearly zero.
What Lives Inside the SCOBY
The SCOBY looks like a single organism, but it’s a dense community of bacteria and yeast species working together. A 2021 study analyzing commercial SCOBY cultures across North America found two dominant groups. On the yeast side, a genus called Brettanomyces made up the vast majority, with one species alone accounting for about 77% of the fungal population. On the bacterial side, acetic acid-producing bacteria from the genus Komagataeibacter represented roughly 71% of the bacterial community, followed by smaller populations of related acid-producing microbes.
These aren’t random. The yeast breaks down sugar into alcohol, and the bacteria convert that alcohol into acetic acid, which gives kombucha its signature tartness. This back-and-forth between yeast and bacteria is the engine of the entire fermentation process.
What Fermentation Creates
The finished drink is chemically different from the sweetened tea it started as. Fermentation produces acetic acid (the same acid in vinegar, responsible for the sour tang), along with other organic acids. The process also generates carbon dioxide, which gives kombucha its natural fizz, and small amounts of alcohol.
B vitamins appear during fermentation as a byproduct of microbial metabolism. Studies have detected vitamins B1, B6, and B12 in kombucha, though concentrations vary widely depending on the brew. Vitamin C has been measured at anywhere from 25 to 151 milligrams per liter, again depending on fermentation time and conditions. Antioxidant activity peaks around seven days of fermentation, then slightly decreases as the brew continues to acidify.
Caffeine
Because kombucha is brewed from real tea, it contains caffeine. The fermentation process reduces caffeine levels to roughly one-third of what was in the original brewed tea. If you started with a tea that had 45 milligrams of caffeine per cup, the finished kombucha would contain around 15 milligrams per equivalent serving. That’s less than a cup of green tea and far less than coffee.
Alcohol
All kombucha contains some alcohol as a natural byproduct of yeast activity. The Alcohol and Tobacco Tax and Trade Bureau sets the legal dividing line at 0.5% alcohol by volume. Below that threshold, kombucha is sold as a non-alcoholic beverage. Above it, the product falls under federal alcohol regulations and must carry a health warning label. Fermentation can continue inside the bottle after packaging, especially if the kombucha isn’t pasteurized, which means alcohol levels can creep up during storage.
Acidity
The pH of safe, finished kombucha falls between 2.5 and 4.2, according to New York State food safety guidelines. That’s roughly as acidic as orange juice or apple cider vinegar. Kombucha that drops below 2.5 is considered too acidic for consumption.
Flavoring Ingredients in the Second Fermentation
Most kombucha goes through a second fermentation after the base brew is finished. This is where flavoring happens. The kombucha is bottled with added fruit, juice, herbs, or spices in a sealed container. Residual yeast feeds on the new sugars, producing extra carbonation and infusing the drink with flavor.
Common additions include:
- Fresh fruit and juices: ginger, lemon, mango, raspberry, strawberry, pineapple, blood orange, watermelon, cherry
- Herbs and botanicals: fresh mint, rosemary, thyme, lavender, hibiscus flowers
- Spices: cinnamon, turmeric, whole ginger root
- Floral waters: rosewater, orange blossom water
A typical ratio is about a quarter to a third of a cup of juice or puree per 16-ounce bottle. Some of the added sweetness gets consumed by the yeast during this second fermentation, so the final flavor is less sweet than the ingredients suggest.
Extra Ingredients in Store-Bought Brands
Commercial kombucha often goes beyond the traditional recipe. A survey of commercial products published in the journal Nutrients found that many brands add supplemental probiotic bacteria on top of the microbes already present from fermentation. The most common addition is Bacillus coagulans, a heat-resistant probiotic that survives bottling and shelf storage. Some brands also add Bacillus subtilis, Saccharomyces boulardii (a probiotic yeast), or Lactobacillus strains. In some products, these added probiotics actually outnumber the original fermentation microbes in the final bottle.
Beyond probiotics, commercial labels frequently list supplemental vitamin B12, fruit juice concentrates (white grape and apple juice are popular bases for flavored varieties), alternative sweeteners like monk fruit extract, stevia, or allulose syrup, and green coffee bean extract for added caffeine. “Natural flavors” is another common line item, a catch-all term for flavoring compounds derived from plant or animal sources.
Reading the label on a store-bought kombucha, you might see something like: kombucha culture, green tea, black tea, cane sugar, ginger juice, lemon juice, Bacillus coagulans, and vitamin B12. The simplest brands stick close to the original four ingredients plus fruit. Others read more like a supplement label. If you want kombucha with nothing extra, look for short ingredient lists that name only tea, sugar, culture, and whatever fruit or herb provides the flavor.