Kombucha Brewing Calculator
Calculate ingredients for homebrewed kombucha from batch size and fermentation preferences. Enter values for instant results with step-by-step formulas.
Calculator
Adjust values & calculateFermentation Estimates
Formula
Use one cup of sugar per gallon, tea bags based on tea type strength (black: 8, green: 6, oolong: 7, white: 5 per gallon), and ten percent of total volume as starter liquid from a previous batch. Fermentation duration determines sugar consumption and final tartness.
Last reviewed: December 2025
Worked Examples
Example 1: Standard 1-Gallon Batch with Black Tea
Example 2: Large 5-Gallon Continuous Brew
Background & Theory
The Kombucha Brewing Calculator applies the following established principles and formulas. Cooking and food preparation involve a surprisingly rich set of mathematical relationships that govern texture, flavour, nutrition, and safety. Recipe scaling is perhaps the most immediately practical: to adjust a recipe serving 4 to serve 10, every ingredient quantity is multiplied by the ratio 10/4 = 2.5. This works straightforwardly for most ingredients, but leavening agents, salt, and strong spices often need more conservative scaling because their effects are not strictly linear at larger volumes. Baker's percentage is a professional notation system in which every ingredient is expressed as a percentage of total flour weight. If a dough uses 1000 g flour and 650 g water, the hydration is 65%. This system makes formulas portable across batch sizes and allows bakers to adjust hydration, enrichment, or fermentation characteristics with precision. Temperature conversion between Fahrenheit and Celsius (°C = (°F − 32) × 5/9) is essential when following recipes written for a different regional audience. The Maillard reaction, responsible for browning and the development of complex flavour compounds in bread crusts, roasted meats, and caramelised vegetables, occurs most rapidly above approximately 140°C (285°F) and accelerates with temperature. Yeast activity is highly temperature-sensitive: active dry yeast proofs optimally between 38°C and 43°C (100°F–110°F), and temperatures above 60°C are lethal to yeast cells. Volume-to-weight conversions in cooking rely on ingredient density, which varies significantly: a cup of all-purpose flour weighs approximately 120–130 g, while a cup of honey weighs around 340 g. Relying on volume for dense or variable-density ingredients introduces meaningful measurement error. The pH of a batter determines how leavening agents behave: baking soda (sodium bicarbonate) requires an acid such as buttermilk or vinegar to activate, while baking powder contains its own acidic component and works in neutral batters. Nutritional density calculations, expressed as kilocalories per 100 g, allow comparison of foods on a consistent basis, supporting dietary planning and labelling compliance.
History
The history behind the Kombucha Brewing Calculator traces back through the following developments. The culinary arts have ancient roots spanning every human civilisation, but the formalisation of cooking as a measurable, teachable discipline emerged gradually over centuries. Ancient Egyptian, Greek, and Roman texts contain references to food preparation, and medieval European monasteries developed sophisticated brewing and baking traditions that implicitly encoded ratios and techniques passed through apprenticeship. The most transformative figure in modern professional cooking was Auguste Escoffier, whose systematisation of classical French cuisine in the late 19th and early 20th centuries created a codified brigade system and a catalogue of standardised preparations that became the foundation of professional culinary training worldwide. His work, particularly Le Guide Culinaire published in 1903, treated cooking as a discipline with repeatable, transmissible formulas rather than purely intuitive craft. Home economics emerged as a formal academic discipline in the 19th century, partly in response to industrialisation and urbanisation. Figures such as Catharine Beecher and later Ellen Richards in the United States worked to apply scientific principles to domestic cooking and nutrition, eventually institutionalising the subject in schools and universities. Standardised recipe development became central to the food industry in the 20th century as mass food manufacturing required consistent, scalable formulas. The USDA introduced its first food pyramid in 1992 as a public health tool to communicate recommended nutritional ratios to a general audience, though the model has been revised multiple times since. MyPlate replaced the pyramid in 2011 with a simpler visual. Molecular gastronomy, pioneered in the 1990s by chefs such as Ferran Adria at elBulli and Heston Blumenthal at The Fat Duck, brought laboratory techniques and rigorous scientific analysis to high-end cooking, exploring the chemistry of gels, foams, emulsifications, and temperature-controlled preparations. Food calorie labelling laws, mandated on packaged foods in the United States since 1990 under the Nutrition Labeling and Education Act, formalised the expectation that consumers would engage with nutritional arithmetic as part of daily food choices.
Frequently Asked Questions
Formula
Sugar (cups) = Batch Size (gal) x 1 | Tea Bags = Batch Size x Rate/Gallon | Starter = Batch x 10%
Use one cup of sugar per gallon, tea bags based on tea type strength (black: 8, green: 6, oolong: 7, white: 5 per gallon), and ten percent of total volume as starter liquid from a previous batch. Fermentation duration determines sugar consumption and final tartness.
Worked Examples
Example 1: Standard 1-Gallon Batch with Black Tea
Problem: Brew a 1-gallon batch of kombucha using black tea, fermenting for 10 days with a 15% ginger-lemon second fermentation.
Solution: Batch size = 1 gallon = 128 oz\nBlack tea bags = 8 bags (or 5 tbsp loose)\nSugar = 1 cup (200g)\nStarter liquid = 128 x 0.10 = 13 oz (1.6 cups)\nWater = 128 - 13 = 115 oz (14 cups)\nSugar consumed after 10 days = 50% = 100g remaining\nResidual sugar per 8oz serving = 6.3g\nEstimated ABV = 0.3%\nFlavor addition = 128 x 0.15 = 19 oz juice/ginger\nBottles needed = 8 (16oz) or 11 (12oz)
Result: 8 tea bags | 1 cup sugar | 13 oz starter | 8 bottles (16oz)
Example 2: Large 5-Gallon Continuous Brew
Problem: Set up a 5-gallon continuous brew with green tea, fermenting for 14 days, with 20% fruit flavoring for second fermentation.
Solution: Batch size = 5 gallons = 640 oz\nGreen tea bags = 5 x 6 = 30 bags (or 20 tbsp loose)\nSugar = 5 cups (1000g)\nStarter liquid = 640 x 0.10 = 64 oz (8 cups)\nWater = 640 - 64 = 576 oz (72 cups)\nSugar consumed after 14 days = 70% = 300g remaining\nResidual sugar per 8oz serving = 3.8g\nEstimated ABV = 0.9%\nFlavor addition = 640 x 0.20 = 128 oz\nBottles needed = 40 (16oz) or 54 (12oz)
Result: 30 tea bags | 5 cups sugar | 64 oz starter | 40 bottles (16oz)
Frequently Asked Questions
How much sugar do I need for kombucha brewing?
The standard ratio is one cup of white granulated sugar per gallon of kombucha, which equals approximately 200 grams. This sugar feeds the SCOBY culture during fermentation and is largely consumed by the bacteria and yeast, so most of it does not remain in the finished product. After a typical seven-to-fourteen-day primary fermentation, about fifty to eighty percent of the sugar is converted into organic acids and a small amount of alcohol. Do not substitute artificial sweeteners, as the SCOBY requires real sugar to ferment properly. Raw cane sugar, white sugar, and evaporated cane juice all work well, while honey and maple syrup can be used but may alter fermentation speed.
How long should I ferment my kombucha?
Primary fermentation typically takes seven to fourteen days at room temperature, though the exact duration depends on temperature, SCOBY health, and your taste preference. Shorter fermentation times around seven days produce a sweeter, milder kombucha with more residual sugar. Longer fermentation of twelve to fourteen days creates a more tart and vinegary flavor with lower sugar content. The ideal temperature range is seventy-five to eighty-five degrees Fahrenheit. Below seventy degrees, fermentation slows dramatically, and above ninety degrees, you risk killing beneficial organisms. Taste your kombucha daily starting around day five to find your preferred balance of sweet and tart. Second fermentation in sealed bottles adds two to four additional days.
How do I carbonate my kombucha naturally?
Natural carbonation happens during second fermentation when you seal the kombucha in airtight bottles with a small amount of additional sugar or fruit juice. The residual yeast consumes the added sugar and produces carbon dioxide, which becomes trapped in the sealed bottle and dissolves into the liquid. Add one to two teaspoons of sugar or one to three tablespoons of fruit juice per sixteen-ounce bottle. Seal tightly and leave at room temperature for two to four days, then refrigerate to stop fermentation and retain carbonation. Burp the bottles once daily by briefly opening the cap to release excess pressure and prevent explosions. Flip-top glass bottles designed for fermentation work best for safety.
What temperature is best for kombucha fermentation?
The optimal fermentation temperature for kombucha is between seventy-five and eighty-five degrees Fahrenheit, with seventy-eight to eighty degrees being the sweet spot for most brewers. At these temperatures, the SCOBY is most active and produces a well-balanced flavor in seven to ten days. Below seventy degrees, fermentation slows significantly and may take three to four weeks, increasing the risk of mold growth due to the extended timeline. Above ninety degrees, heat-sensitive beneficial bacteria begin to die off, producing an imbalanced and overly yeasty brew. During winter months, use a heating mat or seedling heat pad wrapped around the brewing vessel to maintain consistent temperature. A stick-on thermometer strip on the jar makes monitoring easy.
Can I use different types of tea for kombucha?
Black tea is the traditional and most reliable choice for kombucha, providing the nitrogen and minerals that the SCOBY needs to thrive. Green tea produces a lighter, more delicate kombucha with slightly less robust SCOBY growth. Oolong tea offers a middle ground between black and green, creating complex flavors. White tea makes a very mild kombucha but may result in slower SCOBY development over many batches. You can also blend teas for custom flavor profiles. Avoid teas with added oils like Earl Grey or flavored teas, as the essential oils can inhibit SCOBY growth and potentially damage the culture. Herbal teas alone lack the caffeine and tannins the SCOBY requires, but can be used as a partial blend up to twenty-five percent of the total tea.
How do I know if my kombucha has gone bad or has mold?
Mold on kombucha appears as fuzzy, circular patches on the surface of the SCOBY and is typically blue, green, black, or white with a dry, fuzzy texture. Mold always grows on top of the SCOBY where it contacts air, never beneath the liquid surface. If you see mold, discard the entire batch and the SCOBY, and thoroughly sanitize all equipment before starting fresh. Normal SCOBY variations that are not mold include brown stringy yeast strands, white bumpy new SCOBY growth, and dark spots from tea particles. A healthy batch smells pleasantly tart and vinegary, while a contaminated batch may smell putrid or cheesy. Maintaining proper starter liquid ratio and temperature is the best prevention against contamination.
References
Reviewed by Daniel Agrici, Founder & Lead Developer · Editorial policy