How many airlock bubbles per minute is normal?

During vigorous fermentation a typical 5-gallon ale can bubble 30–60+ times per minute. Early lag and late decline phases produce only a few bubbles per minute, and a finished or stuck batch produces none.

Can I tell if fermentation is done from the airlock?

No — the airlock only shows CO2 activity, not sugar content. Bubbling can slow or stop while fermentation continues, or continue from CO2 off-gassing after it ends. Always confirm with a stable hydrometer reading over two to three days.

My airlock isn't bubbling, is fermentation stuck?

Not necessarily. A loose lid, a leaky grommet, or a large headspace can let CO2 escape without bubbling. Check the seal and take a gravity reading before assuming the yeast has stalled.

Why does bubble rate vary so much between batches?

Bubble rate depends on vessel headspace, seal quality, temperature, batch size, and yeast strain — not just fermentation vigour. That is why the same true fermentation rate can look very different across two fermenters.

When should I take a gravity reading?

When the bubble rate has dropped to a few per minute or stopped, give it a day or two then measure gravity. If the reading is stable across two to three days, fermentation is complete.

Fermentation CO2 Airlock Bubble Rate Interpreter

The Fermentation CO2 Airlock Bubble Rate Interpreter turns a quick bubble count into an estimate of where your fermentation is in its life cycle, so you know whether to wait, hold temperature, or grab the hydrometer. It is built for homebrewers reading their fermenter at a glance.

How it works

As yeast consume sugar they release carbon dioxide, which escapes through the airlock as bubbles. The bubble rate is a rough proxy for the rate of CO2 evolution, which rises and falls with the fermentation phase. The calculator converts your count to a per-minute rate:

bubbles per minute = (bubbles counted ÷ seconds) × 60

It then maps that rate to a likely phase. Zero bubbles means fermentation has not started, has finished, is stuck, or the seal is leaking. A few per minute points to the lag phase at the start or the decline/conditioning phase at the end. Tens of bubbles per minute indicate the exponential phase, and 30–60+ per minute is high krausen — peak activity.

The important caveat

Bubble rate depends on much more than fermentation vigour: vessel headspace, seal quality, temperature, batch size, and yeast strain all change how fast the airlock bubbles. Two fermenters at the same true fermentation rate can bubble very differently. Crucially, the airlock shows activity, never gravity — it cannot tell you fermentation is finished.

Tips and notes

Use the bubble rate to decide when to measure, not to decide that fermentation is done. Once bubbling slows to a few per minute or stops, wait a day or two and take a hydrometer reading; if gravity is stable over two to three days, the beer is finished. If a fresh batch isn’t bubbling within 24–72 hours, check the lid and grommet for leaks before assuming a stuck fermentation.