Beer tastes or smells like green apple or fresh latex paint
lowAcetaldehyde is an intermediate in normal yeast metabolism. Healthy yeast reabsorbs it; bottling too early traps it in the beer.
Likely causes
| Cause | Process article | Ingredient | Notes |
|---|---|---|---|
| Bottled or packaged before yeast finished cleaning up | Fermentation control — temperature, schedule, packaging | — | Confirm FG with three stable gravity readings over 3 days before packaging. |
| Underpitched yeast couldn't fully process intermediates | Fermentation basics | Fermentis SafAle US-05 | Two sachets for ≥1.060 OG; check pitch rate against your starting gravity. |
| Oxidation post-fermentation | Fermentation control — temperature, schedule, packaging | — | Minimise transfers; use CO₂ purge if available. |
How it tastes
Acetaldehyde is a bright, sharp note reminiscent of cutting into a green apple or freshly-opened latex paint. Unlike diacetyl (which is creamy and rich), acetaldehyde is sharp and astringent on the tongue.
Will it age out?
Yes — if there’s still live yeast in the bottle. Acetaldehyde mellows during the same conditioning period that produces full carbonation. Wait three to four weeks after bottling before judging. Many homebrewers diagnose acetaldehyde in week one and dump beer that would have been clean in week four.
Fix in the brewer
For future batches:
- Confirm fermentation truly finished — three identical gravity readings, 72 hours apart
- Pitch the right amount of yeast for your gravity
- Hold post-primary at fermentation temperature for an extra 2-3 days before cold-crashing
Related learn articles
- Off-flavours — what they are and where they come fromA quick reference for the most common off-flavours in homebrew, what they taste like, and what causes them.
- Fermentation control — temperature, schedule, packagingWhy fermentation temperature is the single most important brew-day variable, and how to manage it on a homebrew budget.