How to brew kombucha at home
A full first-fermentation walkthrough for home kombucha, with sugar ratios, temperature targets, day-by-day visual cues, and what each stage should look and taste like.
What you'll need
- A healthy SCOBY with starter tea One SCOBY plus 1 cup of liquid from a previous batch. Buy one or get a piece from a friend who brews. Skip dehydrated SCOBYs; they often fail to revive cleanly.
- A 1-gallon wide-mouth glass jar Wide mouth so the SCOBY has surface area to grow across. Glass only; metal corrodes in the acidic brew and plastic can leach during long contact.
- Loose-leaf or bagged black or green tea 8 bags or 8 grams of loose leaf per gallon. Plain tea only. Earl Grey, herbal blends, and flavored teas contain oils that damage the SCOBY.
- Plain cane sugar 1 cup per gallon. Organic preferred. Honey, maple, and most sugar substitutes will not feed the SCOBY correctly.
- A breathable cover with rubber band A tea towel, coffee filter, or paper towel held with a rubber band. Cheesecloth has weave gaps large enough for fruit flies. No solid lid during fermentation.
- pH strips reading 2.5–4.5 Optional but useful. Lets you confirm safety without tasting on day-one batches. Replace after 6 months; strips degrade.
TL;DR
A standard 1-gallon batch is 8 bags of black tea, 1 cup of cane sugar, water to fill, 1 cup of starter tea, and a healthy SCOBY. Cover with a breathable cloth, leave it at 72–80°F for 7 to 14 days, and taste from day 5 onward. When it tastes balanced sweet-tart with the tea flavor receding, first fermentation is done. Bottle for second fermentation if you want carbonation and flavor, or refrigerate as-is.
Two non-negotiables: plain ingredients only (no flavored tea, no honey, no sugar substitutes) during the first fermentation, and never seal the jar until you intentionally start the second fermentation. The rest is taste.
What kombucha actually is
Kombucha is sweet tea fermented by a symbiotic culture of bacteria and yeast, the SCOBY. The yeast converts sugar into alcohol; the bacteria convert that alcohol into organic acids, primarily acetic acid (the vinegar tang) and gluconic acid. As fermentation proceeds, pH drops from neutral starting tea down to roughly 2.8 to 3.5, which is where finished kombucha sits.
That pH drop is the thing keeping the brew safe. Pathogens cannot establish in an acidic, alcoholic environment with active microbes already filling the niche. A healthy first fermentation is one of the safer home ferments because the starter tea is already acidic on day zero; there is no high-risk early window the way there is with vegetable lacto-ferments.
The byproduct of all this is two layers of value: the liquid, which is the kombucha you drink, and the new SCOBY layer that grows on the surface, which is the seed for the next batch.
The conditions
Three variables matter, in order:
- Sugar: 1 cup of plain cane sugar per gallon of finished brew, roughly 7% by weight. Less and the SCOBY runs out of food early, producing thin and overly sour kombucha. More and the brew stays too sweet without enough acidity to be safe by traditional standards. Stick with 1 cup until you have ten batches under your belt and a reason to deviate.
- Temperature: 72 to 80°F. Below 68°F, fermentation slows so much that mold has a window to take hold; above 85°F, the yeast component starts to dominate and the brew tastes harsh and yeasty. Most kitchens fall in the sweet spot most of the year. In a cold house, a seedling mat or the top of a refrigerator (warm from the compressor) works well.
- Tea: plain black, plain green, or a mix. 8 bags or roughly 8 grams of loose leaf per gallon. Tannins from the tea feed the bacterial component of the SCOBY directly; without them, brews get progressively weaker over many batches.
Vessel choice is the other quiet variable. A wide-mouth gallon jar gives the SCOBY room to grow flat and full. Tall narrow jars produce thick, lumpy SCOBYs and less consistent fermentation. Glass only; metal corrodes in acid and plastic can leach during 1- to 2-week contact.
Step by step
1. Brew the sweet tea
Bring a quart of water to a near-boil. Steep 8 bags or 8 grams of loose-leaf tea for 5 to 7 minutes, then remove the tea. Stir in 1 cup of plain cane sugar until fully dissolved. Add cold water to bring the total to roughly 3 quarts. The result should be lukewarm.
The exact volume is not critical. Aim for total liquid plus starter tea to fill the jar to about an inch below the rim, leaving headspace for the SCOBY and any pellicle growth.
2. Check the temperature before adding starter
The sweet tea must be at or below 85°F before adding the SCOBY and starter tea. Hot tea kills the culture. If in doubt, leave it longer; cool tea is safe, hot is not.
A 30-second test on the side of the jar by hand is usually enough. If it feels warm but not unpleasantly hot, it is fine. If it feels actively hot, wait.
3. Add starter tea and SCOBY
Pour 1 cup of starter tea (the liquid that came with your SCOBY) into the cooled sweet tea. The starter does two jobs: it drops the pH below 4.6 immediately, putting the brew in safe territory from day zero, and it inoculates the new batch with the microbes from the previous one. Always add at least 1 cup per gallon. More is fine; less is risky.
Slide the SCOBY in last. It will probably sink; that is normal. It will rise as fermentation produces CO2, usually within 24 to 72 hours. A SCOBY that sits at the bottom for the entire ferment is not dead, just buoyancy-shy, and the brew will fill out around it.
4. Cover and wait
Cover the mouth of the jar with a tea towel, coffee filter, or doubled-up paper towel. Hold it in place with a rubber band. The cover must be breathable so CO2 can escape, and tight enough that fruit flies cannot get in. Cheesecloth has gaps large enough for fruit flies and is a frequent source of contamination issues; use something tighter.
Place the jar somewhere with stable temperature, out of direct sunlight, and where it will not get jostled. Tops of kitchen cabinets work. The back corner of a countertop works. Refrigerators are too cold.
5. Taste from day 5
For the first 4 days, leave the jar alone. The brew is doing its work and disturbing it serves no purpose.
Starting day 5, slip a clean spoon or a long pipette in along the edge of the SCOBY (not through it) and pull out a small sample. Taste:
- Still strongly sweet, very mild tang. Not done. Wait two more days and taste again.
- Balanced sweet and tart, tea flavor receding, slight vinegar note. Done. Bottle or refrigerate.
- No sweetness left, dominant vinegar tang. Slightly past the target window. Still drinkable, but more vinegar-forward than most people prefer. Bottle for second fermentation if you want to carbonate it; otherwise refrigerate and use in salad dressings.
- Harsh, yeasty, or off-tasting. Something is wrong; see the troubleshooting section below.
Most batches finish between day 7 and day 14. A warm spring kitchen at 78°F regularly finishes by day 7. A 70°F basement may need the full 14.
What you might see along the way
A pellicle forming on top. A thin tan or off-white film appears within the first few days. This thickens into a new SCOBY layer over the rest of the fermentation. Expected and good.
Brown stringy bits hanging from the SCOBY. Yeast strands. They look unappetizing and are completely normal. Filter them out at bottling if you find them visually objectionable; they do not affect safety or flavor meaningfully.
Air bubbles trapped under the SCOBY. CO2 trying to escape. The SCOBY may tilt or float at an angle. Normal.
The original SCOBY sinks and stays sunk. The new pellicle still forms at the surface. Both will be viable for the next batch.
A small spot of fuzzy growth on the surface. Stop. This is the one critical visual cue. See kahm yeast vs mold before doing anything else. True mold means discarding the whole batch including the SCOBY. Kahm yeast (a flat, smooth white film) is harmless and can be skimmed off.
Common mistakes
Adding the SCOBY to hot tea. The single most-common batch-killing mistake. Always confirm the sweet tea is at or below 85°F before introducing the culture. A killed SCOBY produces a brew that smells faintly bready or rotten rather than tart, and the pH never drops.
Sealing the jar during first fermentation. Pressure builds. Glass jars can crack or worse. Always use a breathable cover during the first fermentation. Seal only when you intentionally start the second fermentation, with the understanding that you will need to burp the bottles to release pressure.
Skipping starter tea. New brewers sometimes think the SCOBY alone is enough. It is not. The starter tea is what makes day zero safe, and without it, the brew sits at neutral pH long enough that mold can take hold before fermentation drops the pH. Always add at least 1 cup of starter per gallon.
Using flavored or scented tea. Earl Grey, jasmine, peppermint, fruit-blended teas. The oils that give them their character also damage the SCOBY over repeated batches. Flavor during the second fermentation by adding fruit, juice, or ginger to bottles; the first fermentation uses plain tea only.
Brewing in metal. Stainless steel, aluminum, copper, all bad. The acid in even a fresh batch is enough to react with most metals over a week-long contact. Glass only.
Troubleshooting
The SCOBY looks completely different from when you bought it. SCOBYs change with each batch. The new layer that grows is the freshest, healthiest part; the original layer may darken, develop a bumpier texture, or get holes in it. None of these affect performance. As long as a new pellicle is forming on top and the brew tastes tart by week two, the culture is fine.
The brew is taking longer than 14 days. Most often a temperature issue. Check whether the spot has cooled, especially if seasons changed. Move the jar to a warmer location and give it another week. If still not progressing, the starter tea may have been too dilute or too cold when added; finish the batch and start fresh with more starter next time.
The brew tastes harsh and yeasty. Yeast dominance, usually from heat (over 85°F) or from using a sugar substitute that the yeast can metabolize but the bacteria struggle with. Drop the temperature for the next batch and switch back to plain cane sugar.
Fruit flies have appeared. The cover has a gap somewhere or the weave is too loose. Replace the cover with a tighter fabric. The current batch is usually still fine; fruit flies on the cover have not contaminated the brew unless they have actually reached the surface of the liquid.
The pH never drops below 4.6. Either the SCOBY is dead (rare; see “adding to hot tea” above) or no fermentation is happening because the temperature is too low. Pour a small sample into a glass and warm it in your hands for a minute; if there is still no fizz or smell change, the culture is not active. Start a fresh batch with new starter and a new SCOBY.
For bottling, flavoring, and carbonation, see kombucha second fermentation. A ginger bug runs on the same bottle-carbonation mechanics if you want to try a wild soda next.
Frequently asked
How long does kombucha take to brew?
Most home batches finish in 7 to 14 days during the first fermentation. Warmer rooms (75–80°F) finish closer to 7; cooler rooms (68–72°F) closer to 14. If you live somewhere that drops below 65°F, brewing slows dramatically and you may need a seedling mat or warmer spot. The most reliable signal that a batch is done is taste, not the calendar.
What kind of tea works best?
Plain black tea is the most reliable; the SCOBY thrives on the tannins. Green tea works but produces a paler, lighter-tasting kombucha. White and oolong work in a pinch but tend to produce weaker SCOBYs over time. Avoid Earl Grey (bergamot oil), herbal blends, decaf (chemical residues), and any flavored or scented tea during the first fermentation. Flavor in the second fermentation, not the first.
Can I use honey instead of sugar?
Not for standard kombucha. Honey has antibacterial compounds that suppress the SCOBY's bacterial component and shift the brew toward a yeast-dominant ferment. A specific variant called jun is made with honey and green tea, but it uses a different culture adapted to honey. For standard kombucha, plain cane sugar gives the most predictable result.
Why isn't my kombucha bubbly?
First fermentation rarely produces visible carbonation. The CO2 escapes through the breathable cover. Carbonation develops during the second fermentation, when sealed bottles trap the gas. If your bottled kombucha is also flat after 3–7 days at room temperature, the most common cause is not enough residual sugar at bottling time; brew the first fermentation for fewer days so more sugar remains.
How do I know when first fermentation is done?
Two signals to watch for. Start with taste; pour a small sample around day 5 and again every day or two. When the sweetness has dropped to a balanced sweet-tart and the tea flavor has thinned out, it is done. The second signal is pH. A finished first fermentation typically reads 2.8 to 3.5. Above 4.0 means more time. Below 2.5 means it has gone past kombucha into vinegar territory, still safe but sharp.
Is the new layer that grew on top a new SCOBY?
Yes. Each batch grows a fresh SCOBY layer on the surface, which you can peel off and use for a new jar, share with friends, or keep in a SCOBY hotel. The original SCOBY does not weaken from this; both layers remain viable for many cycles. A sluggish brew is more often a temperature or tea-quality issue than a tired SCOBY.
Is it safe to brew kombucha at home?
Yes, with the standard precautions. The combination of low pH (under 4.6), starter tea acidity from day one, and a breathable cover that allows CO2 out but blocks contaminants in makes kombucha one of the safer home ferments. Mold is the only meaningful risk, and it is rare and visually obvious. See the kahm yeast vs mold guide for what to look for. Never use metal vessels, never seal during first fermentation, and start each batch with at least 1 cup of starter tea per gallon.
How long does finished kombucha last?
In the refrigerator, finished kombucha keeps for several months. The flavor continues to develop slowly, becoming more vinegar-like over time. Unrefrigerated kombucha in a sealed bottle keeps fermenting and can become over-carbonated; burp bottles every few days or refrigerate within 3–7 days of bottling.