Kombucha Calculator

Black tea is the traditional choice and produces the most robust, classic kombucha flavor. The tannins and nutrients in black tea feed the SCOBY optimally. Green tea produces a milder, lighter kombucha with a more delicate flavor. A 50/50 blend of black and green tea is popular for balancing flavor and SCOBY health. Herbal teas (without caffeine) should not be used as the sole tea source, as the SCOBY requires the nitrogen, vitamins, and tannins naturally present in Camellia sinensis (true tea) to stay healthy.

During fermentation, yeast in the SCOBY convert sugar into ethanol and CO2 (standard alcoholic fermentation). Simultaneously, acetic acid bacteria convert much of this ethanol into acetic acid (vinegar) and other organic acids. The balance between yeast and bacterial activity determines final alcohol content. Home kombucha typically has 0.5-1.0% ABV after first fermentation. Second fermentation can increase this to 1-3% if bottles are left too long or temperatures are warm. Commercial kombucha in the US must be below 0.5% ABV to avoid alcohol regulations.

The best indicator is taste — sample your kombucha starting around day 7. It should have a pleasant balance of sweet and tart, with the vinegary taste of acetic acid becoming more pronounced as fermentation progresses. Beginners often prefer to stop at 7-9 days for a sweeter result, while experienced brewers may ferment to 12-14 days for a more sour, complex product. You can also measure pH: commercial kombucha is typically pH 2.5-3.5. A pH below 2.5 indicates very acidic, potentially over-fermented kombucha.

Kombucha contains organic acids (acetic, glucuronic, lactic), B vitamins, antioxidants from tea, and potentially beneficial bacteria and yeasts. Laboratory and animal studies suggest antimicrobial, antioxidant, and hepatoprotective effects. However, robust clinical evidence in humans is limited. Probiotic claims for kombucha are controversial — the microorganisms in kombucha do not always survive stomach acid to reach the intestine. That said, moderate consumption appears safe for most healthy adults and can be part of a varied, health-conscious diet.

Yes, when done correctly. The key safety principles are: always use adequate starter liquid (at least 10% of batch volume) to immediately acidify the brew, never use metal containers (acidity corrodes most metals), use clean equipment, brew in a warm spot (68-78°F) away from direct sunlight, cover with breathable cloth to prevent dust and insects from entering, and inspect for contamination (unusual mold colors like black, green, or pink indicate a problem — discard if contaminated). Normal SCOBY and pellicle growth is white to tan/brown and not cause for alarm.

Second fermentation (F2) involves bottling finished kombucha in airtight swing-top bottles with a small amount of additional sugar or 10-15% fruit juice. The remaining yeast and bacteria continue fermenting the added sugar in the sealed bottle, producing CO2 that dissolves into the liquid, creating carbonation. Leave bottles at room temperature for 2-3 days, then refrigerate to stop fermentation and preserve carbonation. Always burp (briefly open) bottles daily during F2 to prevent dangerous over-pressurization, especially in warm environments.

The standard ratio is 50-70 grams of sugar per liter of water for first fermentation. This calculator uses 70g/L. Plain white granulated sugar (sucrose) is most commonly used and provides the best results. The SCOBY consumes a significant portion of this sugar — studies estimate 50-60% is metabolized during a standard 7-14 day fermentation, leaving 30-50% as residual sugar. Do not use artificial sweeteners as they cannot feed the SCOBY and will result in failed fermentation.

Some people with type 2 diabetes report benefits from kombucha, and some animal studies suggest potential hypoglycemic effects of the organic acids and antioxidants in kombucha. However, commercial kombucha can contain 2-7 grams of sugar per 100mL, which contributes to blood glucose load. Home-brewed kombucha fermented for longer periods has lower residual sugar. Anyone with diabetes considering regular kombucha consumption should consult their healthcare provider and monitor blood glucose response carefully, as individual responses vary considerably.

Commercial kombucha is standardized, pasteurized or filtered for consistency and safety, and must meet regulatory alcohol limits. Homemade kombucha is raw (unpasteurized), retaining all live cultures. It has more variability in pH, alcohol content, and flavor between batches. Home brewers have complete control over tea variety, fermentation time, flavoring, and sweetness. The cost of homebrewing is typically 80-90% less per serving compared to commercial kombucha. The main advantage of commercial kombucha is convenience and safety assurance.