Kombucha Calculator

Kombucha is a fermented tea beverage produced by symbiotic culture of bacteria and yeast (SCOBY) feeding on sugar dissolved in tea. The fermentation process converts the sugar into organic acids, carbon dioxide, trace amounts of alcohol, and beneficial probiotics. The result is a mildly fizzy, slightly tart drink that has been consumed for centuries across Asia and is now one of the fastest-growing segments in the functional beverage market.

The fermentation happens in two stages. First fermentation (F1) is the primary brewing phase where the SCOBY metabolizes sugar over 7-14 days, producing the characteristic tangy flavor and developing the culture. Second fermentation (F2) is an optional bottling phase where fruit juice, herbs, or ginger are added to create natural carbonation and flavor variations. During F2, residual sugars and the added flavorings continue feeding the bacteria, building pressure in sealed bottles.

Getting the ratios right is essential for consistent, safe kombucha. Too little sugar starves the SCOBY and produces weak kombucha. Too much sugar overwhelms the culture and results in overly sweet, under-fermented tea. The right balance of tea, sugar, starter liquid, and water depends on your batch size, flavor preferences, and desired fermentation strength.

Standard kombucha brewing follows well-established ratios that have been refined by home brewers over decades. These ratios scale linearly with batch size, making it straightforward to calculate ingredients for any volume.

These ratios adjust based on your desired fermentation strength. Mild kombucha uses about 75% of the standard sugar ratio and ferments for 5-7 days. Standard strength uses the full ratio and ferments for 7-10 days. Strong kombucha increases sugar by 25% and ferments for 10-14 days, resulting in a more vinegary, less sweet beverage.

Tea provides the nitrogen, minerals, and micronutrients that the SCOBY needs to thrive. Not all teas are equally suitable. Black tea is the traditional choice and produces the most robust fermentation. Its higher caffeine and nitrogen content gives the SCOBY optimal nutrition, and the resulting kombucha has the classic slightly malty, tangy flavor profile.

Green tea produces a lighter, more delicate kombucha with grassy notes. It works well blended with black tea (a 50/50 blend is popular) for a balanced flavor. Oolong tea falls between black and green, offering a more complex, floral character. White tea is the most delicate and requires slightly more leaves per cup (1.5 tsp instead of 1 tsp) to provide adequate nutrition.

Herbal teas should never be used alone because they lack the caffeine and specific nitrogen compounds the SCOBY requires. However, herbs like ginger, mint, and fruit can be added during second fermentation for flavor. Avoid teas with oils, artificial flavors, or heavy bergamot (such as Earl Grey), as these can inhibit SCOBY growth.

Calculate your perfect kombucha recipe in five steps:

1. Set your batch size: Enter the volume and choose gallons, liters, or quarts. The calculator converts everything to gallons for the ratio calculations.
2. Select your tea type: Choose from black, green, oolong, white, or a black/green blend. Each affects flavor and nutrition.
3. Choose your sweetener: Standard white sugar is traditional. Honey creates Jun kombucha. Raw sugar and coconut sugar offer subtle flavor variations.
4. Set fermentation strength: Mild, standard, or strong determines the sugar ratio and fermentation timeline.
5. Decide on second fermentation: If planning F2, the calculator includes bottle counts and flavoring amounts.

The results display exact measurements for tea, sugar, starter liquid, and water, along with fermentation time ranges and temperature guidelines.

Temperature is the single most important variable in kombucha fermentation speed and flavor. The optimal range is 75-80°F (24-27°C), where the SCOBY is most active. Below 68°F (20°C), fermentation slows dramatically and may stall. Above 85°F (29°C), the culture works too fast, producing excess acetic acid and a harsh, vinegar-like taste. Consistency matters more than perfection — stable temperatures produce more predictable results than fluctuating ones.

The starter tea serves a critical safety function by lowering the pH of the fresh tea-sugar mixture to below 4.6, which prevents harmful bacteria from establishing before the SCOBY can dominate. Always save 10-15% of your finished kombucha as starter liquid for the next batch. This maintains a continuous chain of healthy culture and consistent results over many generations of brewing.