Can apple cider ferment on its own?
Fresh apple cider (unfermented juice) can start fermenting on its own, because yeasts are naturally present on the fruit and equipment. It turns fizzy and slightly alcoholic, and sealed containers can build pressure. Pasteurisation, preservatives and cold storage slow this down. If a fizzy juice worries you, don't drink it.
Updated
Why fresh cider can ferment
- Wild yeast. BJCP 2025 says cider yeast "may be either natural (occurring on the fruit itself or present in the milling and pressing equipment) or cultured". [1]
- Sugar. Apple juice contains the sugar that yeast turns into alcohol and carbon dioxide. Fermentation in cider making is complete at a specific gravity of about 1.0 or lower. [2]
- Unpasteurised juice. FDA says most juice sold in the US is pasteurised, but some cider mills and farmers' markets sell untreated cider. [3]
What happens when it ferments?
The juice becomes fizzy, less sweet and slightly alcoholic. This is the starting point of hard cider, and the guide on how cider is made explains the process. Cider makers control it with cultured yeast, because "results are often variable" with wild yeasts. [2] An uncontrolled ferment in a kitchen is not a reliable way to make cider; see how to make cider at home and the glossary entry for wild fermentation.
What safety points do sources raise?
- Pressure. Carbon dioxide builds up in closed containers. PNW 621 warns that the pressure from carbonation in bottles is potentially explosive, and that fermentation restarting in the bottle can make it explode. [2]
- Untreated juice. FDA requires a warning on packaged untreated juice because it may contain harmful bacteria. [3]
- Changes you don't expect. If the juice smells or looks wrong, don't drink it. For finished cider, see can cider go bad.
How is fermentation slowed down?
Commercial juice is often pasteurised, and cider makers may add sorbate at bottling; BJCP lists sorbate among the additions allowed in cider. [1] [3] Temperature matters too: PNW 621 notes that cider ferments in as little as 5 days at 70°F (21°C), against 10 days to 4 weeks at 60°F (16°C) or lower, so warmth speeds yeast up and cold slows it down. [2] More on US fresh cider is in what sweet cider is.
Related answers: what sweet cider is · can cider go bad
Related on Cider Radar
Cider, perry, calvados and pommeau are alcoholic drinks. Enjoy responsibly and follow the legal drinking age where you live.
We don't give health advice. For questions about your health, talk to a doctor or pharmacist.
Questions
Is fizzy apple cider safe to drink?
We can't judge a specific bottle. FDA warns that untreated juice can contain harmful bacteria and that packaged untreated juice must carry a warning label. [3] If in doubt, throw it out and ask your food safety authority.
Does fermented apple cider turn into vinegar?
It can. Vinegar is made in a second fermentation, when bacteria turn the alcohol into acetic acid. [4] See how apple cider vinegar is made, and for spoiled cider can cider go bad.
Why does cider in the fridge get fizzy?
Fermentation produces carbon dioxide. Cold slows yeast down but does not necessarily stop it; cider makers deliberately ferment at 16°C (60°F) or lower, and it still takes days to weeks. [2]
Sources
- 2025 BJCP Cider Style Guidelines (Introduction) — Beer Judge Certification Program (BJCP)
- Hard Cider Production & Orchard Management in the Pacific Northwest (PNW 621) — Washington State University, Oregon State University and University of Idaho Extension
- What You Need to Know About Juice Safety — FDA
- Vinegar FAQs — The Vinegar Institute