7 Reasons Why Your Homebrew Is Not Fermenting (And What To Do!)


If you have gone through all of the work on brew day only to worry because your homebrew is not fermenting then you are probably freaking out a little bit right now. Since I’ve definitely been in your shoes before, I thought it would be best to look at the reasons why your fermentation might have failed, what to do about it, and remind you that you might be overreacting!

Homebrew fermentation can fail if you didn’t use enough yeast, the yeast wasn’t healthy, the temperature of the wort is too low. Sometimes, a fermentation that appears to have failed could just be starting off slowly or became stuck for a variety of reasons.

To determine whether or not you have a failed fermentation or simply a slow and/or stuck one we will need to take a look at these 7 possible culprits. Read on to find out more about the reasons why your fermentation isn’t going perfectly.

What do you do if your homebrew isn’t fermenting?

First, calm down.

It’s pretty common for homebrewers, especially new ones, to freak out if they don’t see a lot of activity in their fermenter within 12 hours. While it’s definitely possible to have signs of a healthy, active fermentation within that time period, it certainly isn’t a given.

In fact, it could take up to 36 hours or so for signs of active fermentation to appear depending on variables such as yeast health, quantity, etc.

Let’s take a look at what I’ve found to be the seven most common reasons that your homebrew is fermenting slowly or not fermenting at all.

If you have considered these potential issues and it’s been longer than 36 hours, then it might be time to worry. Worst case scenario, you will just need to make an emergency trip to your homebrew store to pick up some new yeast. Plus, you’ll probably start picking up a couple of packets of dry yeast to have on hand in case it happens again!

You didn’t pitch enough yeast

This one is more common than you think.

Many beginner recipes simply come with a packet of dry brewer’s yeast and instruct you to simply throw it into the fermenter after the wort has been cooled. While this will usually get the job done, the yeast will definitely take much longer to get going because they have been in an inactive state for so long. They will need to absorb nutrients, water, and oxygen to prepare themselves for the fermentation process.

If you are in this boat, check the time. Your fermentation might not be active for the first 12 hours or so because of this delay.

You might also want to check your recipe here. Bigger beers, such as strong ales and barleywines benefit from a hefty amount of initial yeast being pitched because they have so much more fermentable material in the mix.

You didn’t make a yeast starter

Similar to the last reason, not making a yeast starter can cause a slow or failed fermentation. That’s because the two primary benefits of making a yeast starter are:

  • You know the yeast is alive and working because you will see activity in the starter
  • The yeast will have a headstart with oxygen, water, nutrients, and multiplication to tackle fermentation at a faster rate. Basically, you have healthier and more active yeast from the start

Not making a starter is not the end of the world, but without one, you might have to consider the fact that the yeast you used were no good. If they died, maybe during transportation if you ordered online, then you will waste a lot of time waiting for fermentation to start that was doomed from the beginning.

Hopefully, the lack of a starter just means things have been delayed. Continue to wait until the 36-hour mark.

After that point, you might want to run to the homebrew store and pick up some more yeast.

The temperature is too low

Depending on where you live and where you are storing your fermenter, this could be a HUGE factor in your fermentation.

Basically, different yeast strains work best within a specific temperature range. Typically, this is between 68-72°F. Check the packaging of the particular yeast that you used for your batch to see the recommended temperature range.

If you have sat your fermenter somewhere that is especially cold then you could be dramatically slowing down the pace of your fermentation or stalling it out altogether.

Importantly, some beers and yeast strains are actually meant to be kept at lower temperatures. Lager yeast, in general, actually like much cooler temperatures compared to ale yeasts. While most people are familiar with the word ‘lager’ to describe a kind of beer, the word ‘lagering’ actually describes the process of letting a beer mature at or near-freezing temperatures for an extended period of time.

Still, it’s likely that beginner brewers are going to make a basic ale for their first few recipes and you’ll need to make sure that the temperature is high enough for your yeast!

There is not a good seal on your fermenter

Since most people are looking for bubbles in the airlock as the primary sign that their beer has begun active fermentation, not having a seal on your fermenter could make the situation very misleading.

Air bubbles escape from the airlock because the yeast are busy eating the sugar inside your wort and creating CO2 and ethanol as a result. As the pressure builds inside the fermenter, the CO2 will start escaping through the only exit – the airlock. If you are using a plastic fermenting bucket and there isn’t a good seal around the lip then it becomes the path of least resistance for the CO2 which will slowly vent out, bypassing the airlock completely.

I’ve actually seen this personally even with a carboy fermenter because I didn’t have the rubber stopper firmly sealed into the opening. The batch before that one had such a violent explosion that I tried to err on the side of caution and barely push it in. The result was that all of the CO2 just came out around the rubber stopped, leading me to believe that I had a bad start to my fermentation. Once I unwrapped the carboy and took a closer look, I realized what had happened!

If you have an opaque fermenter and you are relying on the airlock to monitor fermentation, consider removing the lid of the fermenter to check for other signs of fermentation.

It’s just starting slowly

I’ve mentioned this indirectly a few times, but really this general reason is usually the culprit for new brewers.

On the first few batches, most people have a tendency to constantly want to check things out and make sure they are progressing. This can make 12 hours feel like an eternity and 36 hours feel like forever.

Check your time and be prepared to exercise patience. If, after 36 hours, you still don’t see any signs of fermentation then you can start to worry.

The fermentation is stuck

Let’s just say that you saw a decent amount of activity inside your fermenter shortly after pitching. There were bubbles, you saw yeast, it was all great.

Then, everything seemed to stop a little quicker than usual. You take a couple of readings and your gravity readings are nowhere near where they are supposed to be. In this scenario, it’s possible that you actually have a stuck fermentation. This can happen for the same reasons that it fails to start or slowly starts in the first place.

Typically, your biggest culprit here is temperature.

Since we boil the wort to get it ready for fermentation, we are supposed to then cool it back down before we pitch our yeast. If we pitch the yeast when the wort is a little hot, you could see some pretty intense activity quickly. If you place that fermenter in a cold place, however, that too-warm wort can quickly turn into too-cool wort and the fermentation will slow down or even stop if it gets cold enough.

If you think this is the problem, move your fermenter to a warmer place inside your house and you could even consider wrapping it up in a towel or purchasing a carboy jacket or heater.

There was a catastrophic problem with your brewing process

This is the last thing on the list because, honestly, it’s not a very likely reason that your beer isn’t fermenting correctly.

The only time that the brewing process could be the culprit is if you were doing an all-grain brew and managed to not get any fermentable material into your wort. Luckily, extract-only recipe kits are guaranteed to have fermentable sugar and if you took an original gravity reading before pitching your yeast then you should have noticed if the reading was way lower than expected.

Still, it is possible to mess up the brewing process so badly that you are literally unable to ferment the beer!

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