Headspace in fermenters plays a big role in brewing beers and making wines, meads, and ciders.
It’s possible to have too much headspace when fermenting just as it’s possible to have not enough headspace. Moreover, sometimes the wrong headspace can ruin the fermentation and affect the end product, especially the long aging drinks such as wines.
In this article, I’ll explain the role of headspace and answer some common questions regarding it.
How much head space should a fermenter have?
Fermenters come in different shapes and sizes, and we don’t always plan to use their full capacity nor should we.
How much head space should a fermenter have depends on a few factors such as the recipe you are making that either creates active or passive fermentation and the time the brew will remain in the fermenter due to oxygen exposure.
Ideally, you should use the almost full capacity of the fermenter but leave some room in case of aggressive fermentation.
However, it’s possible to use only a part of the whole fermenter capacity as there aren’t hard limits on how much head space can be left in primary fermentation.
When can too much head space be a problem?
When you leave too much head space in a fermenter, there’s more room for oxygen to get trapped which means the odds for oxidations are higher, just as it’s the case with leaving too much headspace when bottling homebrew.
While oxygen is the desired nutrient prior to the fermentation kicking off, adding oxygen during or after the fermentation process can seriously hurt the brew.
Oxidation is among the most usual ways to create off-flavors in beer and off-flavors in ciders, meads, and wines.
However, during primary fermentation, the yeast produces a Co2 layer at the top of the wort/must which creates a membrane that doesn’t allow the oxygen to enter.
This is the reason why it’s possible to do an open fermentation without an airlock, yet if you disturb the fermenter by moving it or shaking it, it’s possible for oxygen to enter, so be careful how you manipulate it.
For best fermentation results, don’t disturb the fermenter nor open the lid unless you have a good reason to, such as adding secondary additions like fruits or hops.
Secondary fermentation and aging
While primary fermentation naturally protects the beer, wine, cider, or mead you are making by creating the Co2 level, secondary fermentation can be a problem.
In a secondary fermenter, there’s either no yeast activity or it’s very minimal and thus the Co2 layer doesn’t exist or it’s too weak to protect against oxidation.
This especially applies when you are long conditioning in any type of container which has plenty of room in it.
Over time, things get worse and the oxygen will penetrate in, so it’s important to either top it to the container’s full capacity and leave no room when conditioning or create a vacuum by removing the oxygen, and purging the container with Co2.
Secondary fermentation is the only time when you should have real concerns regarding leaving too much headspace.
Whenever I am making wines and meads, I pay extra attention to these details that may seem unimportant but actually play a big role.
When you hear stories about people making the finest brews, only to screw up at this step and then 2 years later realize their precious booze turned into vinegar or is oxidated to the bone, you won’t leave room for the errors to happen.
Don’t fully top the primary fermenter
On the other side, too much space taken can result in unwanted problems not related to oxygen.
Ideally, you should always leave some space from the top to reduce the effects of the overflow.
For instance, if the fermenter has a 6-gallon capacity, don’t fill it with more than 5 gallons of liquid.
Some recipes contain certain ingredients that can cause aggressive fermentation and a forming of krausen which can clog the airlock and create a mess around.
In some cases when krausen completely clogs the airlock, it may cause the Co2 to build up inside the fermenter and due to an inability to escape, cause a mini explosion.
Furthermore, if not treated quickly enough, the overflowing can lead to contamination, as the airborne bacteria can find a way into the fermenter.
Sometimes, the overflow may happen even when enough room was left, so you should have a reserve airlock and the means of cleaning the mess.
For the piece of mind, leave 20% headspace of the total fermenter volume to ensure that if the fermentation ends up agressive, you don’t experience an overflow. If you want to take as much space in the fermenter as possible, ensure the overflow doesn’t happen!
Use temperature to your advantage
The warmer the temperature, the higher the yeast activity, and thus the higher the effects of the overflow.
If you are experiencing problems with overflow whether you left some headspace or forgot to, you can always drop the temperature and slow the forming of krausen.
But, don’t do this if the yeast can’t ferment at the temperature you want to drop it to, you can keep it at the lower range of fermenting range for best results.
From my experience, most yeast actually works better at the lower point of its total fermenting range, so I think that this is generally good advice to follow.
Besides increased overflow, the results of fermenting at high temperatures are potential off-flavors such as the creation of too many esters resembling the fruits or the creation of harsh alcohol off-flavors.
Use anti-foam agents
One way to counter the overflow and thus use more of a fermenter is to use the anti-foam agents that counter the production of krausen.
There are stories of homebrewers using olive oil as it has similar properties to anti-foam agents, but I wouldn’t recommend it.
Conclusion
While it’s possible to use just a portion of the volume the fermenter allows, it’s not always the smart idea, just like it’s not always smart to leave too less of space.
In conclusion, don’t worry about leaving too much room in a fermenter when doing primary fermentation because as long as there’s a good co2 membrane, there’s nothing to worry about.
Be careful not to leave too much headspace in a secondary fermenter/aging container due to a lack of protection from Co2 and the fact that the longer you age it, the worse the odds for oxidation.
If you must leave so much headspace in the secondary or aging container, make sure to purge the headspace with Co2!
After all, the long aging of wines and other high-alcohol brews requires perfect conditions to be met.
And finally, when using most of the volume the fermenter allows, be sure to always leave a bit of the headspace just to counter the overflowing effect!