Primary fermentation is done when yeast has consumed most of the available sugars and your gravity readings hold steady over two or three days. For most ales, that takes 5 to 14 days. For wine, the active primary phase typically wraps up in three to five days, though full fermentation continues longer. The only reliable way to confirm it’s finished is with a hydrometer or refractometer, not by watching your airlock.
Why Airlock Activity Isn’t Enough
A slowing airlock is tempting to read as a finish line, and it does loosely track what’s happening inside your fermenter. During peak activity (usually days two and three), you’ll see a thick foam layer called krausen on beer, and your airlock will bubble constantly. By day five, that foam often collapses and bubbling slows to a few times per hour. But airlock activity only tells you there’s positive pressure in the vessel. Temperature changes, a poor seal, or dissolved CO2 slowly escaping can all create bubbles long after fermentation ends, or stop them while fermentation is still going. Treat a quiet airlock as a hint, not proof.
The Hydrometer Test
A hydrometer measures the density of your liquid relative to water. Sugar makes liquid denser, so as yeast converts sugar to alcohol, the reading drops. Take a reading, wait two to three days, and take another. If the number hasn’t changed, fermentation is done. For beer, you’re comparing against the expected final gravity for your recipe. For wine, “dry” is anything below a specific gravity of 0.995, which actually reads as a negative number on the Brix scale (around -1.0) because alcohol is less dense than water.
If you forgot to take an original gravity reading before pitching your yeast, you can still use this method. Two identical readings spaced a few days apart confirm stability regardless of where you started. You won’t know your exact alcohol content, but you’ll know fermentation is complete.
Typical Timelines by Beverage
Ales ferment fast. Many reach their final gravity within five days at room temperature, though most brewers leave them in primary for one to two weeks to let the yeast clean up byproducts. Lagers work at cooler temperatures (around 50°F) and move more slowly, often needing two to four weeks of primary fermentation plus additional conditioning time.
Wine’s active primary phase is short, typically three to five days at 70 to 75°F, but that’s just the most vigorous stage. The slower tail end of fermentation continues for one to three weeks as yeast works through the remaining sugars. Most winemakers transfer to a secondary vessel once the aggressive bubbling subsides, then monitor gravity until it drops below 0.995.
Mead behaves more like wine but can be slower, sometimes taking two to four weeks in primary depending on honey content and yeast strain. The same gravity-stability test applies: two matching readings a week apart means you’re safe to rack.
Kombucha is different from all of these because there’s no single “done” point. Primary fermentation runs anywhere from 7 to 21 days, and the target is a flavor you like. A finished kombucha generally falls between pH 2.5 and 3.5. If it still tastes too sweet, let it go longer and taste every few days until the balance of sweet and tart suits you.
What the Yeast Is Actually Doing
During primary fermentation, yeast cells multiply rapidly, consuming simple sugars and producing alcohol and CO2. As sugars run low, the cells begin to clump together and settle out of suspension, a process called flocculation. In bottom-fermenting lager yeast, this shift is triggered by dropping sugar levels in the liquid. In top-fermenting ale yeast, rising alcohol concentration plays a bigger role in signaling the cells to group up and drop. Either way, once most of the yeast settles to the bottom of your fermenter, active fermentation is effectively over.
Stuck Fermentation vs. Finished
Sometimes fermentation stalls before the yeast finishes the job. The airlock goes quiet and the gravity stops dropping, but the reading is higher than your recipe’s target. This is a stuck fermentation, and it’s different from a completed one. Common causes include temperatures that are too cold, not enough yeast pitched initially, or a must or wort with very high sugar content that pushed the alcohol level past what the yeast can tolerate.
If you suspect a stall, try gently rocking or swirling your fermenter every 12 hours for about five days to rouse the settled yeast back into suspension. Check the gravity two days later. If it hasn’t budged, the yeast has likely done all it can. At that point, you can pitch a fresh, more alcohol-tolerant yeast strain, or accept the slightly sweeter result.
A more precise diagnostic is a forced fermentation test. You pull a small sample, add a large dose of fresh yeast, keep it warm, and let it ferment out completely. The gravity that sample reaches is the lowest your batch can go. If your main batch matches it, fermentation is truly done. If there’s a gap, you have fermentable sugar left and a stuck fermentation to address.
Cleanup Time Before You Transfer
Reaching final gravity doesn’t mean you should immediately rack or bottle. Yeast produces byproducts during fermentation that it then reabsorbs during the tail end of the process. One of the most noticeable is diacetyl, which tastes like artificial butter. In ales, the yeast handles this naturally at fermentation temperature. In lagers, brewers often raise the temperature to 60 to 65°F for two to three days near the end of fermentation, a step called a diacetyl rest, before dropping to near-freezing for cold conditioning.
For beer in general, leaving the batch on the yeast cake for a few extra days after gravity stabilizes gives the yeast time to finish this cleanup. Rushing to secondary or bottling too early can lock in off-flavors that would have resolved on their own with a little patience. A week or two of total time in primary is a reasonable minimum for most ales. For wine and mead, racking off the heavy sediment after two to three weeks and then allowing the quieter secondary phase to continue is standard practice.