Sugar, Tea, and Ratio Basics for Consistent Brews

Kombucha is a fermentation, and fermentations are governed by ratios. Change the ratio of tea to sugar to water to starter and you change the rate, the final acidity, the flavour balance and how reliably the next batch turns out. Most people who describe kombucha as unpredictable are in fact varying their ratios without noticing.

This guide sets out what each input actually does, gives workable starting ratios, and explains how to scale them without losing the balance.

The four inputs, and what each one does

Notice that three of these four are food or environment for the culture, and one — starter liquid — is the culture itself. That is why starter proportion is the most powerful lever you have and the one most often skimped on.

Workable starting ratios

The table below is per litre and per US gallon so you can work at either scale. These are ranges used widely in home brewing, not a single correct answer.

Per litre, that gives roughly 45–68 g of sugar and 1.3–1.7 g of leaf tea. The sugar figure is the more important of the two to get right; the tea can be adjusted to taste within a reasonable range.

Sugar: how much, and which kind

Sugar is the substrate for the entire fermentation. The yeast breaks sucrose into glucose and fructose, ferments those into ethanol and carbon dioxide, and the acetic acid bacteria then convert the ethanol into acetic acid. Almost all of the sugar is consumed in the process, which is why a brew that started sweet finishes tart.

Which sugar to use matters less than you might expect. Plain white cane or beet sugar is the standard because it is pure sucrose, cheap, and ferments predictably. Beyond that:

• White cane or beet sugar — the default. Neutral and predictable.
• Raw or turbanned sugar — works, and carries a little molasses that adds colour and a slight caramel note. Ferments slightly less predictably because the sugar composition varies.
• Honey — works but varies a great deal between batches and can suppress the culture at higher proportions. Better used as a flavouring in the second fermentation.
• Coconut sugar, palm sugar, agave — all work to varying degrees, but each changes the flavour profile and ferments differently. Fine for experimentation, less good for a baseline.
• Artificial sweeteners — never. The yeast cannot ferment them, so you get sweetness with no fermentation and, in a sealed bottle, no carbonation.

Tea: type, strength and steep time

The tea must come from Camellia sinensis — black, green, white, oolong or pu-erh. The culture needs the nitrogen and micronutrients those leaves provide, and it uses the tannins as part of building a healthy pellicle.

Steep for 8 to 12 minutes. Longer extraction pulls out harsh, bitter compounds that fermentation does not mellow. This is one of the few places in kombucha brewing where more is genuinely worse.

Starter liquid: the ratio that matters most

Starter liquid is finished kombucha, and it is the difference between a batch that starts safely and one that spends its first two days vulnerable. The usual range is 7 to 10 percent of the total volume.

If you are brewing in a cool kitchen, restarting after a failed batch, or using a culture that has been stored for a while, go to the top of the range or a little beyond. There is essentially no downside to using more starter — it acidifies the batch faster and provides a larger population of the organisms you want.

The one constraint is that starter liquid is also finished kombucha, so using more of it means carrying over more of the previous batch's character. If your last batch was strongly flavoured, take the starter from before you added the flavouring.

Water

Water makes up the vast majority of the batch, so its quality matters. Most tap water is fine. Two things to watch for:

• Chlorine and chloramine. Both can suppress the culture, and chloramine does not dissipate by standing the way chlorine does. If your water is heavily treated, filter it or use bottled water for the first batch or two and see whether fermentation improves.
• Very hard or heavily mineralised water. Can affect flavour and, at extremes, the fermentation. If your water tastes strongly of minerals, consider filtered water as a baseline.

Do not use distilled or reverse-osmosis water as your only water source. It lacks the minerals the culture needs, and fermentation in pure water is noticeably sluggish. If you use RO water, blend it with a portion of tap water or add a mineral supplement intended for brewing.

Scaling without losing the balance

Ratios scale linearly, with one important exception: starter liquid. Larger batches are more thermally stable and more microbially resilient, so they can safely use the lower end of the starter range. Smaller batches are the opposite — they change temperature faster and have less buffering capacity, so they do better at the upper end.

When scaling up, change one thing at a time. Going from one gallon to five involves a different vessel geometry, a different thermal mass and a different surface-to-volume ratio, and the fermentation will behave differently even with identical ratios.

Recording ratios is the whole technique

Every experienced home brewer has, in effect, a personal ratio table — one built from their own notes. The information worth recording for every batch is short:

• Date started and date bottled
• Batch volume
• Tea type and weight
• Sugar type and weight
• Starter liquid volume and its source
• Fermentation temperature (and how much it varied)
• pH at the start and at bottling
• A one-line tasting note

With three or four batches of that data you can reproduce the one you liked. Without it, every batch is an experiment you cannot repeat.