Why Is My Kombucha Not Carbonating Troubleshooting Fermentation Fizz Issues

Homebrewed kombucha should be tangy, slightly sweet, and effervescent. When your batch comes out flat, it’s frustrating—especially after days or weeks of careful fermentation. Carbonation is one of the most anticipated qualities of a successful brew, yet it's also one of the trickiest to master. If your kombucha isn’t fizzing as expected, you're not alone. Many home fermenters face this issue, often due to subtle missteps in temperature, timing, sugar use, or bottling technique.

Carbonation in kombucha occurs during a secondary fermentation phase when yeast consumes residual sugars and produces carbon dioxide (CO₂) in a sealed environment. Without the right conditions, this process stalls. The good news? Most fizz failures are fixable with adjustments to your method. This guide breaks down the science behind kombucha carbonation, identifies common causes of flat brews, and provides actionable solutions so you can consistently produce bubbly, refreshing kombucha.

Understanding How Kombucha Gets Its Fizz

Kombucha’s carbonation doesn’t happen during the primary fermentation—it develops in the second fermentation (often called “second ferment” or “bottle ferment”). During the first stage, SCOBY (Symbiotic Culture Of Bacteria and Yeast) converts sweet tea into acids, trace alcohol, and minimal CO₂, which mostly escapes into the air. It’s only when the liquid is transferred to airtight bottles with added sugar that pressure builds and carbonation forms.

The yeast in your kombucha—mainly species like Saccharomyces cerevisiae and Zygosaccharomyces bailii—consume simple sugars (glucose, fructose, sucrose) and produce ethanol and CO₂. In a sealed bottle, the CO₂ has nowhere to go, so it dissolves into the liquid, creating bubbles. This process typically takes 2–7 days at room temperature.

Several factors influence whether this gas production happens efficiently: sugar type and quantity, temperature, yeast health, oxygen exposure, and container integrity. Missing any one element can result in flat kombucha.

Tip: Always leave at least 1–2 inches of headspace in your bottles before sealing to allow room for gas buildup without risk of explosion.

Common Causes of Flat Kombucha and How to Fix Them

Flat kombucha rarely stems from a single mistake. More often, it’s a combination of small oversights that prevent proper carbonation. Below are the top reasons why your brew might lack fizz—and how to correct them.

1. Insufficient Sugar in the Second Ferment

Sugar is fuel for yeast. If there’s not enough sugar available during the second ferment, CO₂ production drops dramatically. While some brewers skip adding extra sugar to reduce sweetness, this often sacrifices carbonation.

Solution: Add 1/4 to 1/2 teaspoon of sugar per 16 oz (500ml) bottle. Use easily fermentable sugars like white sugar, coconut sugar, fruit juice, or chopped fruit (e.g., ginger, berries). Avoid artificial sweeteners—they won’t work.

2. Bottles Aren’t Airtight

If CO₂ leaks out, it can’t dissolve into the drink. Swing-top bottles (like Grolsch-style) are ideal because they create a reliable seal. Plastic soda bottles can work but degrade over time. Screw caps with plastic lids often fail to seal properly unless the lid has an intact gasket.

Solution: Test your bottles by filling one with water, sealing it, and shaking it upside down. If it leaks, replace the cap or switch bottles entirely.

3. Temperature Is Too Low

Yeast activity slows significantly below 68°F (20°C). If your bottles sit in a cold basement or near a drafty window, fermentation may stall completely.

Solution: Keep second ferment bottles in a warm spot—ideally between 72–78°F (22–26°C). A kitchen cabinet away from drafts is usually sufficient. You can place bottles on top of the refrigerator, where heat rises, or use a seedling mat set to low if needed.

4. Over-Fermenting the First Brew

If your primary fermentation runs too long, the yeast consumes nearly all the sugar, leaving little for the second ferment. An overly sour kombucha may taste strong, but it lacks the fuel needed for fizz.

Solution: Taste your kombucha daily after day 6 of primary fermentation. When it’s pleasantly tart with a hint of sweetness (usually 7–10 days), it’s ready to bottle. pH testing helps: aim for 2.5–3.0 at bottling.

5. Using Pasteurized or Heat-Treated Ingredients

Pasteurized fruit juice or heat-treated flavorings can kill active yeast and bacteria. Even boiling ginger before adding it to bottles can sterilize it and halt fermentation.

Solution: Add raw, unpasteurized ingredients. Grate fresh ginger directly into bottles. Use frozen fruit (thawed) or raw juice. Never heat anything above 120°F (49°C) before adding it to kombucha.

“The key to consistent carbonation is maintaining viable yeast populations through both fermentation stages. Interrupting their activity—even briefly with heat or chemicals—can derail the entire process.” — Dr. Laura Chen, Microbiologist & Fermentation Scientist

Step-by-Step Guide to Achieving Perfect Carbonation

Follow this structured approach to maximize your chances of a fizzy batch every time.

1. End primary fermentation at the right time: After 7–10 days, taste test. Stop when balanced between sweet and sour. Over-souring depletes sugar reserves.
2. Prepare flavorings and sugar: Measure 1/4 tsp cane sugar or 1 tbsp fruit/fruit juice per 16 oz bottle. Use raw, unheated ingredients.
3. Use proper bottles: Clean, inspect, and confirm seals on swing-top glass bottles. Discard cracked or worn bottles.
4. Bottle carefully: Pour kombucha into bottles, leaving 1–2 inches of headspace. Add flavorings and sugar just before sealing.
5. Store at optimal temperature: Place bottles in a warm, dark location (72–78°F / 22–26°C). Avoid refrigeration at this stage.
6. Ferment 2–5 days: Check daily after day 2. Gently open one bottle to test fizz. If soft, reseal and wait longer.
7. Refrigerate to stop fermentation: Once carbonated, chill bottles immediately to preserve fizz and prevent over-pressurization.

Tip: Burp bottles gently every 2–3 days during warm weather to release excess pressure and avoid explosions.

Troubleshooting Checklist: Why Is My Kombucha Flat?

Use this checklist to diagnose and correct flat kombucha:

• ✅ Did I add sugar or fruit to each bottle for the second ferment?
• ✅ Are my bottles airtight? Have I tested the seals recently?
• ✅ Is the room temperature between 72–78°F (22–26°C)?
• ✅ Did I over-ferment the first stage? Was the kombucha extremely sour?
• ✅ Did I use pasteurized juice or boiled flavorings that could kill yeast?
• ✅ Am I opening bottles too early? Has it been at least 3 days?
• ✅ Did I store bottles in a cold area like a garage or basement?
• ✅ Is my SCOBY healthy and active? Have previous batches worked?

Do’s and Don’ts of Kombucha Carbonation

Do’s	Don’ts
Add 1/4–1/2 tsp sugar per bottle to feed yeast	Assume no added sugar means healthier kombucha—without sugar, no fizz
Use fresh, raw fruit or juice for flavor and fermentables	Boil or heat ingredients before adding to bottles
Keep bottles in a warm, stable environment (72–78°F)	Store bottles in cold garages, basements, or near AC units
Leave 1–2 inches of headspace in each bottle	Fill bottles to the brim—no room for gas buildup
Refrigerate after 2–7 days to lock in carbonation	Leave bottles at room temperature indefinitely—risk of over-pressurization

Real Example: Sarah’s Flat Kombucha Breakthrough

Sarah had brewed kombucha for six months with inconsistent results. Her first few batches were mildly fizzy, but then she switched to using homemade ginger syrup—boiled with honey and stored in the fridge. From then on, every batch was flat.

After researching, she realized two mistakes: she was boiling the ginger (killing beneficial microbes) and using honey, which contains antibacterial properties that inhibit yeast. She adjusted her method—grating raw ginger into bottles and adding a pinch of cane sugar instead. Within three days, her next batch was bubbling vigorously. Now, she enjoys reliably fizzy kombucha every time.

Sarah’s experience highlights how small ingredient choices can have major impacts on microbial activity. Even “natural” additives can interfere with fermentation if not used correctly.

Frequently Asked Questions

Can I re-carbonate flat kombucha?

Yes. Open the bottles, add 1/4 tsp sugar or a small piece of fruit per bottle, reseal, and return to a warm spot for 2–4 days. Monitor closely and refrigerate once fizz returns.

Why is my kombucha fizzy at first but goes flat after opening?

This is normal. Once opened, CO₂ escapes quickly. To preserve bubbles, pour quickly and keep the remainder tightly sealed and chilled. Never leave an open bottle at room temperature.

Is it safe to drink flat kombucha?

Absolutely. Lack of carbonation doesn’t mean spoilage. As long as the smell is vinegary (not moldy), the taste is tart, and there’s no visible mold, flat kombucha is safe to consume. It may just be less enjoyable.

Final Tips for Consistent, Bubbly Success

Perfect carbonation isn’t magic—it’s a balance of biology and technique. Start by ensuring your SCOBY is healthy and active. Then focus on the second ferment: feed the yeast, seal the bottles, maintain warmth, and monitor time. Keep a brewing journal to track variables like temperature, sugar type, and fermentation length. Over time, you’ll recognize patterns and refine your process.

Remember, even experienced brewers have off batches. What matters is learning from each one. Adjust one variable at a time to isolate what works best for your environment and preferences.

💬 Got a fizz failure story or a winning tip? Share your experience in the comments and help fellow brewers troubleshoot their way to better bubbles!