Noise.

[Chippy_Tea]

I have read many posts here about beer brewers finding their airlocks don't bubble (there is one active now), one of my FV's (a cheap one) has never bubbled without my assistance but after 2 days i can hear fermentation is taking place (if i put my ear to the side), i assume beer fermentation is as vigorous as that of wine so is this not a better method of finding out if fermentation is taking place as opening the FV is generally frowned on.

 

[stevie123]

Im going to try it right now!

 

[sponge_]

Throw out the airlocks and just use gladwrap (held down with the O-ring from the lid). Did that on my 3rd brew and never looked back.

One less item that needs cleaning, and you can easily see inside the FV. It also reduces the height of the FV so you can get away with a smaller fermenting fridge. You'll see condensation on the gladwrap and the krausen forming on the wort for signs of fermentation. Otherwise a hydrometer reading will show you if fermentation has kicked off.

Airlocks should not be relied upon for fermentation activity IMO.

 

[JapanBrew]

You don't need air locks. Just make sure it's not open to outside air. I do however use air locks just because my FV have these lids with a pour hole that is exactly the size of a bung. And they seal too tight to let the air out.

 

[Godfather50]

I sniff for CO2. The end of fermentation produces very little CO2, bubbles can be so infrequent that they are not a good indicator. But you can take the lock out, press down the lid and smell the CO2.

 

[MickDundee]

My airlock didn't bubble at all last brew. I had thought it was because my airlock is currently sharing its hole with my Inkbird sensor, but Saturday's brew shot off like a rocket and my airlock was bubbling this morning so I think it might also have been that my last yeast was a low attenuator.