Why Is My Homebrew Flat? (Instantly Fix The 7 Worst Reasons!)


One of the most common problems that beginner homebrewers encounter is flat homebrew beer. There is simply nothing worse than going through the entire brew process, waiting ages for fermentation, and then weeks for the beer to condition in the bottle only to discover that the beer isn’t carbonated. Today I want to dive deep into the seven most common reasons for this issue and explain how we can prevent them in future batches!

So, why is your homebrew beer flat? The most common reasons for flat homebrew beer are not giving it enough time to condition in the bottle, not using enough priming sugar, keeping the bottles too cold, or problems with the seals. Fortunately, all of these problems can be fixed easily!

I’ve definitely been on the wrong end of several of these reasons in the past and most of the time it’s simply a result of getting in too big of a hurry. After all, homebrew is a hobby that rewards patience and preparation. Let’s dive into the top 7 reasons for flat homebrew and learn how to fix them!

So why is my homebrew beer flat or didn’t carbonate?

As I said, this is one of the most common problems that new homebrewers can expect to encounter (myself included)! That’s because this problem can be caused by both technical mistakes and a lack of patience after bottling – both very common with new brewers!

Fortunately, it’s pretty easy to identify the actual cause of your flat homebrew once you do a little detective work. In most cases, you can even fix your flat homebrew and salvage the batch! Worst case, you’ll at least have the knowledge to prevent it from happening next time.

So, let’s get into it!

Reason #1 – You didn’t give it enough time to condition in the bottle

This is by far the most common issue.

If you haven’t learned already, homebrewing as a hobby requires an above-average amount of patience to get the best results. The fact of the matter is that nature just takes a certain amount of time to do its thing and there really isn’t a good way for us to rush things. If you try, it’s likely to blow up in your face (perhaps literally!)

Homebrew beer primed with corn sugar typically needs to bottle condition for about 2 to 4 weeks before it is fully carbonated and ready to drink. This allows time for all of the priming sugar to ferment, create CO2, and be absorbed into the beer. It also allows time for the overall taste profile to mature.

Now, this is just a general rule.

There are lots of other variables that will determine how long you will need to let your bottles condition, many of which we will talk about in the next sections, but this is a pretty reasonable expectation. In general, you can always assume that the longer you let beer condition in the bottle before you drink it, the better off it will be.

Here’s a trick to use on your next batch to get a better understanding of this process:

  1. Bottle and cap your beer like normal on bottling day
  2. Chill and open a beer at the one week mark and observe the carbonation level and taste
  3. Open another beer at the 2-week mark and observe
  4. 3 weeks
  5. 4 weeks
  6. So on

If you follow this process, don’t expect the first beer or two you open to be the best (or even drinkable). But, it will allow you see how long the carbonation process takes and how the flavor of your beer matures over time. Once you open a beer that tastes good to you then feel free to chill and drink the rest!

Reason #2 – You used the wrong kind of priming sugar or it’s a slowly fermenting sugar

Most beginner recipe kits will include corn sugar or basic white sugar as their priming sugar because they ferment quickly and predictably, mix well, and are cheap.

There is absolutely nothing wrong with using a different kind of sugar for your priming. In fact, some styles of beer require you to use something like honey or other sugars during this process to round out the flavor profile of your beer. Just remember, however, that other kinds of sugar will likely take longer to ferment than simple corn sugar.

If you are using a recipe or kit, be sure to check to see how long they recommend bottle conditioning that particular beer. Odds are, they will tell you to age it longer if they have substituted a different sugar.

Here’s a quick list of the most common corn sugar substitutes:

  • Brown sugar
  • Honey
  • Belgian candy syrup
  • Molasses
  • Maple syrup
  • Tracle
  • Agave nectar
  • Demerara sugar
  • Dry malt extract

Reason #3 – You didn’t use enough priming sugar

Even if you used the easily fermentable corn sugar and exercised monk-level patience while bottle conditioning, your beer might still turn out flat if you don’t use enough of the sweet stuff.

Too little priming sugar will result in little or no carbonation in your beer, no matter how long you let it condition. Too much priming sugar in your beer will result in over-carbonation at best and exploding beer bottles (bottle bombs) at worst.

A good recipe or kit should take care of this for you, but those of you that are ‘free pouring’ or making up your own recipe will need to know what you are doing to ensure you get the right amount. Too much sugar, especially, is a real cause for concern because bottle bombs can be quite dangerous.

Reason #4 – The priming sugar wasn’t mixed thoroughly

What if only some bottles of homebrew are flat?

At first glance, this problem seems a little harder to diagnose, but it likely has a very simple cause.

During the bottling process, most guides will tell you to boil your priming sugar, add it to your fermented beer (or the bottom of your bottling bucket), and then swirl the beer into the bottling bucket as you rack it out of your fermenting vessel to get it nice and mixed. If you do it right, this method should be more than sufficient.

Some people get into trouble, however, because they want to rush the process and not take the necessary time to ensure that the sugar is mixed in. There is no way to see this happening visually, so you have to take care!

Reason #5 – You kept your bottles too cold

Bottle conditioning and carbonation are, at the end of the day, basically just fermentation.

That means that, just like fermentation, temperature is one of the most important variables. All yeast strains have an ideal temperature that they work best in and deviating from that number will lead to deviations in your results.

If your homebrew isn’t carbonating, or it is carbonating very slowly, then you are likely bottle-conditioning at too cold of a temperature. Those of you that condition in a cellar or live in colder climates might struggle with this problem. If so, try moving your brew into a central room of the house or at least one with better climate control. You could even stick a piece of thermometer tape onto one of your beers to see what’s really going on with the temp inside the bottle!

What temperature should I carbonate my beer?

Practically speaking, the same temperature that you should have used for the primary fermentation is the same temperature that you should use for your bottle conditioning. If your recipe called for 68 degrees – keep it there. If your recipe called for 75, keep it there. Obviously, keeping things at ideal temperatures all the time is easier said than done.

In general, anything in the room temperature range (68-80 degrees Fahrenheit) is an acceptable temperature when you are bottling your beer.

Reason #6 – CO2 is escaping from the bottles

This isn’t as common, but it’s still a possibility.

Even if everything else has been taken care of properly (temps, sugars, etc) then you could still have flat homebrew if you have a leak in the seal of your bottles. Essentially, this is a result of a poor job capping the bottles or because you tried to use twist-off bottles instead of pry-off bottles.

One trick that you can use to see if this is your problem is to make a solution of soapy water and dunk the top of your beer into it. Give the bottle a little shake and see if any bubbles come out. If you see some, you have a problem with the caps.

Reason #7 – The yeast have died

This is another less common issue, but something to mention nonetheless.

Just like during the primary fermentation, your yeast buddies are the ones doing the heavy lifting and they are responsible for converting the sugar into sweet, sweet alcoholic goodness. During the bottle-conditioning phase, they should be back in action to clean up the last bit of priming sugar and carbonate your beer for you. If they have somehow gone dormant, or died off completely, there isn’t much you can do about it.

Fortunately, it is rare for all of your yeast to simply die off unless you have done something else wrong. The most common reasons that you would have yeast issues are because you:

  • Tried to condition the bottles cold and the yeast have gone dormant.
  • Used too much sanitizer in your bottles (or left some inside the bottles) and it was enough to kill some or all of your yeast.

Last Thoughts

As you can see, most of the culprits for flat homebrew are pretty easy to diagnose and fix on your next batch. Fixing any of these issues with your brewing process will lead to better beer in your future and less stress as well!

Keep brewing and learning!

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