When new homebrewers start out, they often only have a few pieces of equipment. The volume of alcohol in fermentation can vary based on the recipe, the type of alcohol, and the fermentation conditions. The amount of head space you should leave may vary greatly, depending on who you ask.
What is Head Space in Home Brewing?
Head space, simply put, is the amount of air between the top of your fermenting liquid and your airlock. To make the matter less simple though, many will say you need enough head space to allow your brew to bubble without overflowing the airlock, but not so much that all that extra oxygen degrades the liquid.
Oxygen sitting on top of your brew can cause off-flavors. When oxidation occurs, the ethanol (alcohol) in your brew can get be converted into acetaldehyde – which is what can cause a wine to taste vinegary. However, according to BeerandBrewing.com, DISSOLVED oxygen in your brew helps support a healthy, active yeast colony.
In a rather scientific study, this homebrewer with the HomebrewAssociation.org found that blind taste testers were actually able to tell the difference between two identical recipe beers with different head space.
How Much Head Space Should You Have?
How much head space you leave in your brew will depend on what type of alcohol you’re fermenting, the volume, and the size of your fermenter.
The actual amount of head space recommended isn’t well defined. However, a general rule of thumb suggests no more than 20% of your total volume of fermenting liquid should be left as headspace. For example, if you have a five-gallon wort, 20% of five gallons is one gallon. So, you should choose a 6-gallon fermenter.
What if you have too little headspace? You might see your fermenting liquid bubble up or foam up so much that the foam pushes out through the airlock. Make sure you clean this up with sanitizer as soon as you notice it to help minimize the chance of contamination.
How to Manage Head Space
Here are a couple of options to consider if your fermenter has too much room in it:
- Split your homebrew into two separate fermenters, each with the right amount of head space.
- Fill your fermenter with a sanitized filler – such as marbles – to reduce the amount of headspace.
- Spray in a wine preserver, such as this one from Wine Enthusiast.
- Not recommended (since you’re wasting precious homebrew!) – pour off a bit to fit in a smaller vessel.
I hope this post helps clarify how much headspace you should have. Check out my video on making a Pinot Noir, where I definitely leave too much headspace!