How to fix 'flat' homebrew beer

Wednesday, March 3, 2021
Ah, there can be no greater disappointment as a home brewer to flick a beer opener onto the top of a bottle to crack the brew and you hear the sound of... silence.

You have a flat beer. 

It’s actually an experience sadder than most Simon and Garfunkle songs.

Flat beer means something has gone wrong in the brewing or bottling process and you will need to trouble shoot it to figure out what went wrong - there is a fix or two!

Why is my home brew beer flat? Can I fix it? 

What is this flat beer and how can I fix it?

It means your beer has not carbonated in the bottle and hence your brew has no fizz, sparkle or pop.

So, the first thing one can do is check if this was a single instance of a dud by opening a second bottle.

If you hear that fizz of C02 escaping, you know that first bottle was just a dud. 

This was probably due to user error when bottling the beer. 

Did you properly cap it it? Y

ou’ve got to make sure your capper really makes a firm seal. Other wise your beer will carbonate but the CO2 can escape and no pressure builds.

Sometimes this has happened to me, mistakes will happen to the best of us right?

So the fix in this example is to mix the flat beer with a properly carbonated beer - this way, I don’t have to dump the flat beer and I get to drink two beers.

Two beers!  

I call that #winning.

But, if you opened two beers and they bptj were flat, then you’ve got a problem and you're back to:

...hello darkness, my old friend.

What's the play to fix this?

Consider first:

Did your beer ferment in the first instance?

  • Were there bubbles coming out of the airlock for two to four days at least?
  • Was there some thick gunky residue at the water level where the wort sat inside the drum - this is a strong sign fermentation has occurred properly
  • Did you take readings of your beer using a hydrometer - did you see a change in readings and obtain a final gravity?

If you did observe any of that, you probably achieved primary fermentation. This is good as it means your flat beer will have alcohol in it.

So what might be happening here is that secondary fermentation has not occurred.

Beers need to condition properly at the right temperature for secondary fermentation to start.

If a bottled beer is too cold, then the yeast will go to sleep and not eat the sugars in the beer - and thus you’ve got no bubbles.

So, if you are certain primary fermentation has occurred and that you properly capped your beers, then ask yourself, was your beer stored in a suitably warm place?

This has totally happened to me once before - I left a crate of beers to condition in my outside shed in the middle of winter - and sure enough, it was too cold for the yeast. The solution was to bring the beers inside and leave for another week. Sure enough, the yeast warmed up, started fermentation and my flat beer became bubbly beer in a week.

It’s clear then that when you bottle, your beer needs to be warm - so the yeast can activate and commence secondary fermentation. 

It’s OK to place it in a cooler place later (but don’t make it an extremely cold environment!) - so to give your beer its best chance of fermenting - let your bottles condition for three or 4 days in a warm place.

They can then be conditioned for another few weeks elsewhere.

But what if primary fermentation did not occur? Why could this be?

You know the cliche of when your computer goes bung and won’t turn on and you call the helpline and they say, is it plugged in Sir? 

And you feel like a real jackass because your laptop was not plugged in?

Not pitching your yeast into the wort is the equivalent.

So ask yourself, did you add your yeast to the fermenter?

So you did them. Fine. Let's move on.   

A secondary question, did you pitch the yeast at the right time?

If you add the yeast when the brew is freshly boiled, the hot wort will kill the yeast and you will not have fermentation occur.

If you have realized you’ve done this before bottling, you can add some new yeast to your now properly cooled wort and see if it will rejuvenate it - there should still be plenty of sugars for the yeast to eat

It just means you’ve delayed your brewing schedule!

If you’ve already bottled, you may want to dump your beer or open them all up, dump them in a fermenter, pitch a new yeast and try your luck. If you go this route, try and introduce as little oxygen into your new mix as possible as beer hates oxygen past primary fermentation.

Not enough sugar?

Sugar content is intrinsic to the success of your beer

Another reason why your beer may be flat is that you under primmed the sugar.

If you put too little sugar in your bottled beer, then not enough bubbles will be produced as there’s not enough food for your yeast.

Batch priming your wort with sugar is an easy way to get sugar into your beer (as opposed to individually adding it to each bottle) and it saves time - but make sure you add enough sugar!

If you are trying to make a low calorie beer, then you need to reduce sugars at the primary fermentation stage, not during bottling.

Corn sugar, cane sugar, and dried malt extract (DME) work best for priming beer.

If you used old yeast or primary fermentation did not occur, a bit of a hack to fix is to open up each bottle by hand and add a few grains of yeast to each one. 

Do not add too much as the yeast may over fermenting, leading to gushers. Accordingly, your results may vary with this trick!


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