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How do I tell if my beer fermented properly?

how to tell if beer fermented

How do I tell if my beer fermented properly?

Fermentation is the name of the game when making beer. It you don't have fermentation taking place, you simply don't have beer.

You have just have a 23 litre bucket of watery malt.

Home brewers can face fermentation stage issues and a common problem is that fermentation has not begun. A typical sign is that there is no bubbles coming through the airlock.

Is no bubbles in the airlock really a sign of a lack of fermentation?


The first thing to bear in mind is that it can take at least 15 hours of your Earth time before the CO2 bubbles start gurgling through the airlock. 

So don't go drowning your sorrows just yet if the bubbles haven't started. If you think that your beer hasn't started brewing there's some problem solving you can do. 

If you are using a glass fermenter you can look for a dark scum that rings around the water level mark. You can probably see it through the standard white fermenter drum as well.

Or check for signs of foam. Give it 20 - 48 hours before you start to worry.

If using a plastic drum you might be able to see through to check for the scum. Another trick is to take out the air lock and try and peek through the whole to identify scum or foam.

You could also check the gravity by using a hydrometer.

I'll assume you know how to use one.  The beer has usually finished fermenting if the final gravity reading is is 1/3 to 1/4 of the original gravity. This of course means you took an original reading when you first prepared your beer.

If you have the same reading 24 hours apart - that's your final reading and an indication that the fermentation is finished. 

Don't bottle your beer just yet, let it mellow for a bit longer. The longer the better your brew will probably be. If you are a beginner brewer, trust me on this. Let you brew rest up just a little bit longer than you may have the patience for. Brewing is a game of patience, and those who wait are rewarded with good tasting, clear beer

So why wasn't there any bubbles in the airlock? 

That's a fair question to ask. It could be that there was a leak that allows the CO2 to escape (to teach you to suck rotten eggs, those bubbles in the air lock are carbon dioxide gas, the bi-product of fermentation).

You may have not tightened the drum enough or possible not screwed in the tap properly. It's a good idea to check this is the case before you worry too much


  • If you didn't see any signs of fermentation it could be that it's too cold to brew.
  • Is your batch of beer in a warm enough place?
  • If your brewing during summer months, it's probably not too cold.


If you've left your beer in a cold place in the shed, then it may be too cold. If it's too cold to brew in your 'man shed' - say it's the middle of winter, you might want to bring your brew inside the house.

You could consider wrapping it in blankets. This is a handy trick and will help to keep the chill of your beer. I think this trick works best if the beer is already warm enough to brew. 

Maybe leave it in the laundry if it's a warm place?

When I brew in winter I will often leave the fermenter in the warm kitchen or living room at least overnight so that the fermentation process has a decent chance to start. 

Some brewers like to use heat pads or panels to keep the beer at a consistent warm temperature. If you do wish to use a pad, you'll need to be able to store your brew close to a power socket so the heat pad can operate.

Yeast issues?

Another more serious reason for beer failing to ferment is yeast failure.

This may occur if the yeast has become dry. This is why you will hear a constant refrain from expert beer users to only use fresh ingredients.

In the case of a beer kit brewer, this means to not purchase old stock as the yeast could be too old (I do suspect however this is a bit of a housewives tale - as stock should rotate fairly we. 

However, in our experience we haven't had this problem from a beer kit yet. 

A key trick is to add the yeast at the appropriate temperature - if using a beer kit follow the instructions - you especially do not want to add the yeast if the solution is too cold as it may be hard for the yeast to get traction - and what ever you do, don't add yeast to boiling water (if that's what you are using to mix everything together) - as that will almost certainly kill the yeast and ruin any chance of your beer successfully fermenting.

So in summary here's some problem solving tips:
  • Check for leaks that allow the CO2 to escape - tighten the drum
  • Look for foamy residue
  • Look for scum residue
  • Make sure the temperature is appropriate to the kind of beer you are making
  • Consider using a heat pad to ensure a consistent temperature
Image credit to Quinn Dombrowski via Creative Commons Licence

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