A kombucha starter is the live culture and acidic liquid you use to turn sweet tea into kombucha. It has two parts: a SCOBY and starter tea. Together they start the fermentation and make the brew acidic early on, which helps keep mold and harmful microbes from taking hold while the culture gets going.
The two parts of a starter
The SCOBY stands for symbiotic culture of bacteria and yeast. It’s a rubbery, flat, cellulose-based disc that floats on the surface of the brew. People sometimes call it a “mother” or “tea fungus,” but it isn’t a mushroom. A healthy SCOBY is usually whitish or tan and may have strands and dark spots, which are normal. Each batch usually adds a thin new layer on top.
Starter tea is mature, unflavored kombucha from a previous batch or from a commercial culture. It carries live cultures and acid. Adding it to fresh sweet tea lowers the pH straight away.
Why the starter matters
Pouring acidic starter tea into sweet tea immediately lowers the pH, which makes the environment harder for mold and harmful bacteria. Meanwhile, the live yeasts and bacteria in the SCOBY and the starter liquid use up the sugar and produce acids and some carbon dioxide. The carbon dioxide is what gives you fizz later, during the second fermentation in sealed bottles.
Where to get one
- Buy a culture. Live or dried starter cultures and SCOBY kits are sold online. Ask how the seller handles heat, since cultures don’t do well when hot.
- Ask a brewer. A friend who brews kombucha often has a spare SCOBY and some extra starter tea. This is the classic way to start.
- Use plain store-bought kombucha. A bottle of plain, unflavored, raw kombucha with live cultures can work as starter liquid. Pasteurized kombucha has no live culture, so it won’t work. Flavored bottles contain juices and flavorings that change the brew, so choose a plain one.
- Grow your own. Sweet tea covered with a cloth, with a bottle of raw kombucha added, can grow a new SCOBY over a few weeks. Some guides say it can take up to about two months. The SCOBY is ready when it’s thick and opaque, roughly a quarter inch (6 mm) thick.
How much starter to use
For a gallon of tea, use a SCOBY and 1 to 2 cups of starter liquid. Scale the amounts up or down by the gallon.
Checking a SCOBY
- Healthy: thick, whitish or tan, and it may have strands and dark spots, which are normal. A sour, vinegary smell is also normal.
- Mold: fuzzy growth in green, blue, gray, black or brown. Mold looks like the fuzzy growth on bread or cheese, not brown strands. If you see it, discard the SCOBY and the kombucha, and clean the vessel. Mold or a healthy SCOBY? goes into more detail.
- Off smells: a rotten or putrid smell is a reason to throw the batch away.
Storing a starter between batches
Keep the SCOBY in a clean jar with enough kombucha to cover it, and cover the jar with cloth. One guide says you can keep it at room temperature for up to a month before it needs fresh sweet tea. Keeping a SCOBY in the fridge slows it down, and it may take a few extra cycles to get back to full strength. For longer breaks, see how long a SCOBY can sit in starter liquid.
Common starter mistakes
- Adding it to warm tea. Let the tea cool to room temperature first. Food52’s guide advises below 90 °F (32 °C).
- Covering the jar with cheesecloth. Fruit flies can get through it. Use a tight-weave cloth instead.
- Using pasteurized or flavored bottles as starter liquid.
- Sealing the jar. The culture needs air.
- Using a SCOBY that shows mold.
For covers, see what to cover your kombucha with. For the full set of basics, see best kombucha starter kits.