Carbonation and exploding bottles
A live drink in a sealed bottle keeps making gas. Where it comes from, why some bottles burst, and the rules for getting bubbles without surprises.
6 min read Getting good Reviewed October 26, 2026 33 facts, each with its source
Where the fizz comes from
Yeasts turn sugar into alcohol and carbon dioxide1. In an open jar, the gas escapes. In a sealed bottle it stays inside, and the drink carbonates until the gas itself slows fermentation down2. This is the second fermentation, the one that gives bubbles to kombucha, water kefir and ginger beer.
A strained drink is still alive. In kombucha, bits of SCOBY stay behind and keep fermenting3, and the sugar left in it, plus the sugar from fruit or juice, feeds that second fermentation4. More sugar and more heat mean more gas.
Why bottles explode
Kombucha sealed airtight builds up gas and can explode if nobody keeps an eye on it5. Without a fridge, some kombucha and jun explode6: the cap can come off or the bottle can break, and that can hurt someone7.
It happens with commercial products too:
- In Australia, a kombucha was recalled because the pressure could pop the cap off8 and injure someone9.
- In Canada, a ginger beer was recalled in 2015 because its bottles were bursting10.
- In Singapore, a sriracha sauce that kept fermenting was recalled: the pressure could make the bottles explode on opening11.
Jun is fizzier than kombucha and calls for extra care when bottling and opening12. Vegetable jars make gas too, and they have to let it out so they don't burst13: with an airlock, or by loosening the lid now and then14.
Which bottles work
BCCDC, British Columbia's public health agency, asks for bottles that resist acid and pressure15. Fervida only uses bottles made for carbonated drinks: PET soda bottles, crown-capped beer bottles or swing-top glass bottles. Never jars, or bottles for wine, oil or still water. That's a house rule, and the app won't let you bottle in a jar.
The University of Reading school guide goes further: it allows no glass at all, because the gas makes it explode16. Fervida allows glass made for carbonation, but always with a PET test bottle alongside. Fill it with the same drink and squeeze it every 12 hours: when it's as hard as an unopened soda, everything goes in the fridge. That's a house rule too, because PET can be felt firming up before glass reaches its limit.
Leave 3–5 cm (1–2 inches) of air at the top of each bottle17.
Before you bottle
- A base that's already acidic. Flavor goes in once the first fermentation is done: kombucha and jun with the pH below 4.218; water kefir at 4.6 or lower19. With the fruit in, measure again: the pH has to stay below 4.2 and above 2.520.
- No added sugar. Don't add sugar to finished kombucha21. Fruit and juice bring sugar too, and with it, more alcohol or more vinegar22. Fervida warns you above 10 g of added sugar per liter, counting the fruit's: that's a house rule.
- Juice, pasteurized and store-bought23.
How long out of the fridge
The sources don't agree, and none gives hours for homemade kombucha:
| Source | What it says |
|---|---|
| BCCDC, for jun | 1 to 3 days at 20–26 °C (68–79 °F), then the fridge24 |
| BCCDC, for water kefir | The second fermentation with fruit, in the fridge, for at least 24 hours25 |
| University of Reading, for ginger beer | No more than 48 hours at about 21 °C (70 °F)26 |
BCCDC also asks to avoid long second fermentations when it's warm27. Fervida sets the limit at 48 hours and 25 °C (77 °F), and that's a house rule; past 72 hours, it doesn't allow it for any drink. If your home is above 25 °C (77 °F), do the second fermentation in the fridge: it's slower and makes less gas.
The fridge, and opening the bottle
When it's done, into the fridge, at 4 °C (40 °F) or below: the cold stops fermentation28. Flavored, it's drunk within 2 days29. Even cold, the pressure can push the liquid out all at once30.
Open it after a few hours in the fridge, without shaking it: BCCDC recommends bottles carry the label "Do not shake. Contents under pressure"31. Do it slowly, over the sink, with a towel over the top and away from your face. That's a house rule.
A thin veil or a few strands inside the bottle are SCOBY growing back, because the drink is alive32. Fuzz or colored spots are mold: throw out the whole bottle33.
Where every number comes from
Every number in the text leads to its figure: the exact sentence from the official guide it comes from, in its own language.
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1
Yeasts turn sugar into alcohol and gas
“Starter culture microbes include yeasts that convert sugars to alcohol and carbon dioxide”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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2
In a sealed container it carbonates until the gas slows fermentation
“Sealing in containers often creates carbonation (fizziness) until carbon dioxide slows fermentation by creating anaerobic conditions.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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3
Without the SCOBY, kombucha keeps fermenting from the bits left behind
“Your kombucha will continue to ferment after the SCOBY is removed because tiny fragments of the SCOBY will remain in the beverage.”
Virginia Cooperative Extension (Virginia Tech) · What do I need to know to sell KOMBUCHA at the farmers market? (FST-297, last reviewed November 2025) · read on October 20, 2026
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4
Leftover sugar and flavorings cause a second fermentation
“Flavourings and residual sugars may cause secondary fermentation.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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5
In an airtight container, gas builds up and can explode
“Storing kombucha in airtight containers can cause the accumulation of CO2 (carbonation), potentially leading to an explosion if not regularly monitored.”
National Center for Home Food Preservation (USDA, University of Georgia) · Kombucha Tea · read on October 20, 2026
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6
Without a fridge, some kombucha and jun explode
“Some jun and kombucha products can explode if not refrigerated.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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7
Caps can come off or containers break, with a risk of injury
“If fermentation is not properly controlled, the container lids may come off under extreme pressure or containers may break. This poses a potential risk of injury.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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8
A kombucha recalled because the pressure could pop the cap
“The recall is due to high levels of pressure which may result in the cap to pop open.”
NSW Food Authority · Recall: LoBros Lemon Lime and Bitters Kombucha, high pressure, cap may pop off (27 Feb 2019) · read on October 25, 2026
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9
The cap could pop off and injure
“This product may cause injury due to cap popping off.”
NSW Food Authority · Recall: LoBros Lemon Lime and Bitters Kombucha, high pressure, cap may pop off (27 Feb 2019) · read on October 25, 2026
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10
Canada recalled a ginger beer in 2015 for bursting bottles
“A fermented ginger beer product, also made in the U.S., was recalled in Canada in 2015 for bursting bottles presumed due to extreme pressure.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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11
A sriracha sauce recalled because its bottles could explode on opening
“The build-up of pressure in the bottles may cause them to explode upon opening.”
Singapore Food Agency · Recall of “Huy Fong Sriracha Hot Chilli Sauce” (media release, 27 December 2019, updated) · read on October 25, 2026
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12
Jun is fizzier than kombucha: take extra care bottling and opening
“Jun tends to be more carbonated than kombucha so extra caution is needed when bottling and opening.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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13
Vegetable jars have to let gas out so they don't burst
“During the fermentation, containers should allow gas to vent to avoid containers exploding.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.1: Fermented Vegetables (August 2024, updated December 2024) · read on October 25, 2026
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14
Without an airlock, loosen the lid now and then
“If a one-way valve is not used, the gases will need to be released manually by loosening the lid occasionally.”
K-State Research and Extension (Kansas State University) · Taking a New Look at Fermented Foods (MF3491, June 2020) · read on October 20, 2026
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15
Bottles that resist acid and pressure
“Glass bottles, cans or kegs should be resistant to acid leaching and pressure build-up.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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16
The University of Reading school guide allows no glass at all
“Glass bottles must NEVER be used, as the gas produced will cause them to explode.”
Science in School (EIROforum), Dean Madden, National Centre for Biotechnology Education, University of Reading · Ginger beer: a traditional fermented low-alcohol drink (Issue 8, Spring 2008) · read on October 25, 2026
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17
Leave 1–2 inches of air at the top
“leaving a 3–5 cm air gap at the top”
Science in School (EIROforum), Dean Madden, National Centre for Biotechnology Education, University of Reading · Ginger beer: a traditional fermented low-alcohol drink (Issue 8, Spring 2008) · read on October 25, 2026
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18
Flavor goes in with the pH already below 4.2
“Flavouring agents should be added after initial fermentation, when the pH has dropped below 4.2.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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19
Water kefir at pH 4.6 or lower
“Ensure the pH of final product is 4.6 or less, but not lower than pH of 2.5.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
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20
With the flavor in, measure again: between 2.5 and 4.2
“After juice or other flavouring agents have been added, the pH must again be tested to ensure the pH of the finished product is less than 4.2 but above 2.5.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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21
Don't add sugar to finished kombucha
“Don’t add more sugar to your kombucha to make it sweeter after it’s done fermenting.”
UGA Extension Forsyth County · Relax, Unwind, and Safely Make Your Own Flavored Kombucha at Home (11-jul-2025) · read on October 20, 2026
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22
Juice and flavorings bring sugar too: more alcohol or more vinegar
“Additional ingredients like juice or other flavorings could also contain sugar and allow for further fermentation, producing even more alcohol or vinegar.”
Virginia Cooperative Extension (Virginia Tech) · What do I need to know to sell KOMBUCHA at the farmers market? (FST-297, last reviewed November 2025) · read on October 20, 2026
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23
If you use juice, pasteurized and store-bought
“If juice is added for flavouring after the fermentation step, a pasteurized, commercially produced juice is recommended.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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24
Jun, 1 to 3 days at 68–79 °F before the fridge
“Secondary fermentation occurs in anaerobic environment and lasts 1 to 3 days at ambient temperature (20°C to 26°C) before refrigeration.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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25
BCCDC does water kefir's second fermentation in the fridge, for at least 24 hours
“occur after grain removal and should be performed in the refrigerator for at least 24 hrs.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
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26
Ginger beer, no more than 48 hours at about 70 °F
“Allow the beer to ferment at room temperature (~21 °C) for no more than 48 h, then place the bottles in a fridge.”
Science in School (EIROforum), Dean Madden, National Centre for Biotechnology Education, University of Reading · Ginger beer: a traditional fermented low-alcohol drink (Issue 8, Spring 2008) · read on October 25, 2026
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27
In warm weather, no long second fermentations
“A prolonged second fermentation period when temperatures are warm should be avoided.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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28
Into the fridge at 40 °F or below to stop fermentation
“Once fermentation is completed, kombucha and jun should be bottled and refrigerated to 4°C or lower to stop further fermentation”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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29
Flavored, it goes in the fridge and is drunk within 2 days
“Once flavors have been added kombucha should be stored under refrigeration and consumed within 2 days.”
University of Georgia Cooperative Extension (National Center for Home Food Preservation) · Crafting Kombucha at Home: Frequently Asked Questions (2026) · read on October 20, 2026
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30
Pressure pushes the liquid out
“Excess pressure can build-up from carbon dioxide, causing fluids to leak out.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.12: Kefir, milk and water (December 2024) · read on October 25, 2026
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31
Recommended label: “Do not shake. Contents under pressure”
“Precautionary statement labels on bottles are recommended to advise consumers “Do not shake. Contents under pressure.””
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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32
A new SCOBY can grow in the bottle
“Even after filtration, as the culture is live, there is a possibility for regrowth of SCOBY after bottling.”
BC Centre for Disease Control, Environmental Health Services · Safety of Fermented Foods, Section 3.11: Kombucha and Jun (September 2023, updated December 2024) · read on October 25, 2026
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33
If there's mold, it goes
“If you confirm mold growth on any part of a ferment, it should be immediately discarded.”
UC Davis, Department of Food Science and Technology · Common issues with fermented fruits and vegetables (v1.0, 15-mar-2022) · read on October 20, 2026