Free Kombucha Brewing & Sugar Calculator
Calculate precise sweet tea sugar ratios, acidic SCOBY starter volume, primary fermentation time, and F2 bottle carbonation priming sugar.
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📊 Recipe Weights & F2 Priming
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The Biochemistry of Kombucha Fermentation
Kombucha is a fermented sparkling tea produced by a symbiotic culture of bacteria and yeast (SCOBY). During the First Fermentation (F1), yeasts split sucrose into glucose and fructose, converting sugars into ethanol and carbon dioxide. Acetic acid bacteria (such as Komagataeibacter xylinus) consume the ethanol and oxygen to produce healthy organic acids (acetic, gluconic, and glucuronic acids) and synthesize the cellulose pellicle mat.
1. Why Plain Cane Sugar Is Mandatory
Never use artificial sweeteners, stevia, xylitol, or raw honey (for standard kombucha). Yeasts cannot metabolize artificial polyols. Pure granulated white cane sugar is the cleanest fuel for kombucha yeast, leaving zero harsh sulfur or off-flavor byproducts.
2. Second Fermentation (F2) & Bottle Carbonation
Once F1 achieves the desired balance of crisp tartness and sweetness (typically 7-10 days at 75-80°F), the liquid is bottled into pressure-rated glass bottles with a tight seal. Yeasts consume the remaining or added priming sugar in the absence of oxygen, saturating the liquid with effervescent carbon dioxide bubbles.
Frequently Asked Questions
How do I prevent glass bottles from exploding during F2?
Never use decorative or craft-store glass jars. Use heavy pressure-rated swing-top flip bottles (Grolsch style) or beer bottles. Keep F2 priming sugar under 5 grams per 16 oz bottle, ferment F2 at room temperature for only 2 to 4 days, and immediately transfer bottles to the refrigerator once carbonated to put yeast into dormancy.
Can I brew kombucha with green tea instead of black tea?
Yes! Green tea produces a lighter, floral kombucha (often called Jun style when brewed with green tea and raw honey). A 50/50 blend of black and green tea is widely considered optimal, providing the nitrogen and tannins from black tea with the light antioxidants of green tea.
Do I need the physical floating rubbery disc (pellicle) to start a batch?
No! The floating rubbery cellulose pancake is merely a byproduct of bacterial activity. Over 90% of the active living yeasts and bacteria reside suspended in the liquid starter tea. A cup of strong, unpasteurized plain kombucha will successfully brew a new batch and grow its own fresh pellicle within 10 days.
What is the ideal temperature range for brewing kombucha?
The sweet spot is 75°F to 80°F (24°C to 27°C). Below 70°F, fermentation slows dramatically, favoring yeast over bacteria and increasing mold risk. Above 85°F, yeasts ferment too aggressively, producing an overpowering vinegar taste in only 4 days.