Brewing Kombucha in a 5-Gallon Carboy

You can brew a full 5-gallon batch of kombucha in a glass carboy. It works. But a full carboy holds about 42 lb (19 kg) of liquid, its narrow neck makes it hard to add a SCOBY and fit a cover, and some brewers report that very large vessels take longer and shift the flavor. Most beginners do better starting with a 1-gallon jar. If you’re going big, the steps below are the ones to follow.

What 5 gallons looks like

5 US gallons is 640 US fluid ounces, or about 18.9 L.
That’s about 53 bottles of 12 oz, or 40 bottles of 16 oz, before any losses in transfer or sediment.
Because most kitchen pots can’t hold that much tea, you’ll brew it in several smaller batches.

Ingredients for a 5-gallon batch

Scale the quantities from common one-gallon recipes:

Sugar: about 1 cup per gallon, so about 5 cups (roughly 1 kg) for the batch.
Tea: 4 to 8 tea bags per gallon, so about 20 to 40 bags. Black or green tea works well. Herbal tea doesn’t.
Starter: 1 to 2 cups of mature kombucha per gallon, so about 5 to 10 cups, plus a SCOBY.
Water: clean drinking water. Many recipes suggest filtered water.

Equipment

A glass carboy, food-grade, clean and free of residue.
A cover that fits the carboy’s opening. A cloth and rubber band can slip on a narrow neck. What to cover your kombucha with covers suitable options.
Pots for brewing the tea in batches.
A food-grade siphon hose for drawing off the finished brew.
Swing-top bottles for the second fermentation. See best bottles for kombucha.
A plastic bottle as a carbonation gauge.
Optionally, pH strips to check that the brew has turned acidic.

Why carboys are awkward

The narrow neck. A wide-mouth vessel is easier to add a SCOBY to, cover, and lift the SCOBY out of. Food52’s guide recommends a wide-mouth jar for air circulation and easier SCOBY removal.
The weight. A full carboy holds about 42 lb (19 kg) of liquid. Set it on a stable surface before you fill it, and avoid lifting it once it’s full. Move the liquid out with a siphon instead.
Tasting. You can’t easily reach the bottom. Use a clean straw or a long spoon.
No airlock. Don’t seal the top with a stopper or airlock. The surface needs air exchange during the first fermentation.
Glass breaks. Keep the carboy on a sturdy surface, away from edges.

Step by step

Clean. Rinse the carboy and tools thoroughly.
Brew the tea in batches. For each gallon, heat about half the water, steep 4 to 8 tea bags for about 10 to 20 minutes, remove the bags, and dissolve the sugar in the hot tea.
Cool. Top up with cold water until the whole batch is at room temperature. Food52’s guide advises the tea be below 90 °F (32 °C) before the SCOBY goes in.
Pour into the carboy. Leave some room at the top.
Add the SCOBY and starter. Use 1 to 2 cups of starter per gallon.
Cover. Secure the cloth with a band or bungee cord.
Ferment. Keep it out of direct sun, somewhere with a steady temperature. Guides typically say 7 to 14 days, and a big batch in a cool room can take longer.
Taste from about day 7. Use a clean straw. Stop when it tastes right to you.
Harvest and keep some back. Siphon off the finished kombucha. Leave the SCOBY and at least 1 to 2 cups of brew per gallon in the carboy to start the next batch.

Bottling 5 gallons

Plan for about 53 bottles of 12 oz, or 40 of 16 oz, minus losses. Use swing-top bottles, fill them nearly to the top, and seal. Leave them in a closed cabinet or cooler without ice while they carbonate, then refrigerate them. A gauge bottle helps you judge when they’re ready. Best bottles for kombucha covers the safety steps.

Common problems with big batches

Slow fermentation in a cool room. Keep the batch warm and steady. Do you need a heating pad for kombucha? covers options.
Flavor shifts on long ferments. Taste often and stop when it’s right, before it turns vinegary.
Flies getting in around a loose cover. Check the cover every time you taste.
Mold. Fuzzy green, blue, gray, black or brown growth means discarding the batch and cleaning the carboy.
Spills and lifting injuries. Move the liquid with a siphon instead of lifting the carboy.

Start with a 1-gallon batch

A 1-gallon batch lets you learn your room’s temperature, your cover and your bottling routine before you commit to 5 gallons. Once you’re confident, scaling up is a matter of multiplying the quantities by five.

Why it’s called a carboy

The word is generally traced back to the Persian qarābah, meaning a large flask or bottle. Glass carboys have long been used to hold large volumes of liquid, including wine.

Is kombucha good for pH levels?

Kombucha is acidic. Finished kombucha is often about pH 3 or lower, and home brewers sometimes use pH strips to confirm that a brew has turned acidic, as described in is homemade kombucha safe to drink? That acidity is part of why a healthy brew resists mold.

Body pH is a different question. Your blood’s pH is tightly controlled within a narrow range, roughly 7.35 to 7.45, whatever you eat or drink. Kombucha doesn’t change that. Claims that it “alkalizes” or “balances” your body’s pH aren’t supported by good evidence.