Kombucha Brewing Calculator

This calculator uses 5 bags per liter for green tea versus 4 for black tea. Green tea leaves are generally lighter and less densely packed per bag than black tea, so a slightly higher count is needed to extract comparable strength and nutrients for the SCOBY to feed on. The rate is a fixed lookup by tea type, not something you can fine-tune directly.

Starter liquid is calculated as a straight percentage of total batch volume, and the calculator's own minimum is 5%. Below roughly 10%, the batch takes longer to acidify, leaving a window in the first 24–48 hours where the pH hasn't dropped enough to reliably keep mold and unwanted bacteria out. The remainder of the batch volume is always filled with water, so a lower starter percentage directly means more water, not a smaller total batch.

The calculator returns a flat 7 days for black tea and 6 for green tea, reflecting green tea's typically quicker fermentation. This is a starting estimate, not a fixed rule — actual time depends heavily on ambient temperature, how established your SCOBY is, and how tart you like the final product, so many brewers taste-test starting a day or two before the estimate and let it run longer if it's still too sweet.

Not directly — sugar in this calculator is food for the SCOBY, not a sweetener for you. The culture consumes most of it during fermentation, converting it into acids and trace alcohol. A higher sugar-per-liter setting gives the SCOBY more fuel and can support a longer or more vigorous ferment, but the finished tartness is driven more by fermentation time than by how much sugar you started with.