Fermentation is a necessary part of every beer brewing process and while it is necessary to ferment your beer properly there are not many things that can go wrong.
You may have heard that keeping a beer in the primary fermenter for too long may produce off-flavors such as the meaty, sulfur-like taste but in reality, people often pay too much attention to the things that won’t really matter in the overall process of beer brewing.
So, how long can beer really stay in the primary fermenter without going bad?
The beer can stay in the primary fermenter for months without going bad even after it’s finished with fermentation. When fermentation is complete, the yeast simply goes dormant because it has no more sugar to eat, and the beer doesn’t have to be immediately taken out.
As you can see, there is not much to worry about, however, there are still a few important factors that I am going to mention if you are homebrewing your beer. Moreover, the mentioned applies to home brewery fermenters and not to commercial fermenters that store more than 150 gallons of beer because there’s a great difference in pressure which affects autolysis.
It’s better to keep the beer in the primary for longer
When Co2 stops getting out of the airlock and the temperature stabilizes, the beer might still be fermenting in a healthy way and there is no reason to put it out of the fermenter immediately.
Let’s say that the yeast took between 6 to 10 days to fully ferment as stated in the instructions.
The bubbles are not reaching out from the fermenter airlock, the temperature is stable and the beer does not produce any signals any longer, but the yeast may still be active without producing more noticeable levels of Co2.
Due to this reason, I like to leave the beer in the fermenter for a few days longer than what seems to be necessary to achieve a full fermentation.
This is not necessary if you took a gravity reading before the fermentation and if you take one after you think it’s done. However, this is a precautionary measure for all the homebrewers who don’t use hydrometers to take gravity readings.
Moreover, even when I use a hydrometer I like to give the fermentation a couple of days longer because the small difference in gravity readings can not be measured after a day, but often requires from 3 days to a week to be sure.
In conclusion, if you are brewing a simple recipe, low to medium ABV beer (less than 6%) this is not a big deal, but when you brew high ABV beers or meads that reach over 10% ABV, it’s harder to check when the fermentation is truly done and the mentioned applies.
How long is too long for the beer to be kept in the fermenter?
I have heard of stories where brewers kept the beer in a fermenter for weeks and even months without it going bad.
This might not be the planned decision but rather a misconception of the time due to people forgetting about the beer or being busy with other things in life.
Keeping your beer in the fermenter for this long should not be a practice unless you know exactly why you are doing it (you have some idea, a recipe, or a will to experiment).
Every homebrewer knows that the process of brewing a beer at home takes too long already and it should be a priority to finish the process as soon as possible to be able to enjoy the final product as soon as possible.
Thus, the conclusion is that you should follow the procedure and leave it for a couple more days in the fermenter like I usually do to achieve full fermentation but in case you forget about it or are limited with time it won’t go bad if you kept in there even for a couple of weeks.
Is it possible to over-ferment beer and will it become stronger the longer it stays?
It’s impossible to over-ferment a beer because the yeast can only eat as much sugar as there is to convert it into ABV and Co2, then it goes dormant. Once the yeast is dormant, there won’t be any more action from it which can cause fermentation.
Due to the same reason, it’s not possible to get a stronger ABV beer if the beer stays longer in the fermenter. However, when the beer conditions for longer in the bottles or kegs it will get better and stronger in positive beer flavors and aromas.
What bad can happen to the beer left too long in the primary?
Although it’s difficult for something bad to happen to your beer in the primary because it can stay there for quite some time without going bad, keeping it there for too long can have negative effects.
Nothing is permanent, so If the beer is kept for too long in the primary or any other fermenter the yeast can eat itself which is called yeast autolysis. This can produce bad sulfur-like flavors in your beer and spoil it.
Moreover, keeping your beer in a fermenter under bad environmental conditions can hasten the process of yeast autolysis and impact the hops which can also cause similar bad flavors and ruin your beer.
Cases when the beer can go bad while being prolonged in the fermenter
As you can see you shouldn’t really worry about keeping the beer in the fermenter for weeks or even months after the fermentation is done, but there are a few important factors that are correlated with keeping the beer in a fermenter too long that can make your beer go bad.
If the temperature changes
The temperature is a huge factor when it comes to beer brewing and it matters during fermentation it continues to be important in other stages as well.
Small variations in the temperature are not a game-breaker, but huge differences can truly hurt your beer.
During fermentation, the yeast has to find an optimal temperature to work with. Depending on the temperature range you use, yeast will produce different chemical reactions which will result in different flavors.
For this reason, it is important to have good temperature control and if the temperature drastically changes warmer after fermentation is done, it can cause negative chemical reactions when left for more than weeks.
When long is too long
Yeast continues to exist in your beer after fermentation. So, it doesn’t magically disappear unless you kill it or put it in a dormant state.
When fermentation is complete, the yeast might go dormant if there are no sugars it can eat, but it will remain in the fermenter.
Leaving the beer in a fermenter for a long time can cause the yeast to decompose, which will spoil the flavors of the beer.
However, this rarely happens to homebrewers and is more of a danger in commercial breweries. You see, a big factor is pressure, and in small batches, there isn’t much of it, while those big tanks can put a lot of pressure on the yeast below.
Thus, breweries need to quickly transfer the beer, while homebrewers can keep beer in fermenters for months after it’s finished.
Anyways, it is not recommended to keep your beer in a fermenter for too long because the longer it is, the greater the risk of complications. This can be either a big drop in temperature, bugs, and air can get in if the airlock malfunctions and the risk for autolysis is increased as months pass by.
The risk of contamination is higher the longer it stays
This should not happen if you are careful, but sometimes a small piece of object or material may get into the fermenter before you seal it.
10 days or a couple of weeks may not be enough for the object to start degrading and realizing the chemicals, but months may certainly be enough time and then your beer goes bad.
This is a niche problem, and it never happened to me but I am sure people somewhere experienced this problem.
The airlock gets out of the liquid
The liquid in the airlock protects the beer from the oxygen that could otherwise get into the fermenter compromise the beer and allow the Co2 to get out.
After some time (and it may be days) the water may vanish, leaving the fermenter compromised which could make your beer go terribly wrong.
For this reason, I recommend that you use the right liquid in the right amount to fill the airlock.
Always ensure that the airlock is not empty while the beer is found in the fermenter. I am sure there have been cases where people would forget about their fermenter and wouldn’t check their airlock and with only a day the air exposure ruined the batch.
Final take
Let the beer ferment fully and check the progress with a hydrometer by taking gravity readings. After you are sure the beer is fully fermented, you can immediately rack it into a secondary fermenter or proceed to bottle.
However, there’s no need to hurry with these actions as the beer can be kept in a primary fermenter for extra time even when it’s finished fermenting.
If you don’t use a hydrometer, then you should always leave beer in the fermenter for extra days to be sure the fermentation is complete.
Unfinished fermentation can be dangerous as beer will continue to ferment within the bottles and it may cause the bottles to crack.
Besides this, there’s no much more to worry about!