What head space do I need in my secondary when making wine?
You’ve got your wine transferred and are ready to add the metabisulphite to your wine. Head space becomes important after you have added the metabisulphite because you are killing the yeast. Up until now, your wine has been fermenting and that creates a CO2 layer over the wine. This CO2 layer protects the wine from oxidizing, and can help prevent bacteria from floating into the wine. CO2 isn’t much help from protecting the wine from bacteria, but it does help a little. Once you add metabisulphite the yeast starts to be killed off and you lose your CO2 layer.
Now your wine is unprotected from oxidizing.
You do want a small amount of air to contact the wine because this is what is going to help age the wine. A small amount of air will allow the wine to slowly oxidize, but it will also help the alcohol to mellow and the flavors to blend better. Wine makers get in trouble because they leave a large air gap during this stage, and all of a sudden they end up with a prune juice tasting wine. Not very appealing for most people.
Proper Spacing The proper amount of head space is vital to having your wine turn out. Being off a little bit won’t hurt anything, but being off a lot can ruin your wine. For proper head space, you want to have a gap of 2-3” from the bottom of the stopper to the top of the wine. Anything below that and you are starting to add too much air to the wine that will make the wine start to oxidize too quickly.
Gap Suggestions So what happens when you have a gap of a ½ gallon or so? You need to fill up that gap somehow, and here are a few suggestions on how to do that:
A little extra care on the head space is all you need to do. Any gap prior to the addition of metabisulphite is fine because the CO2 will protect the wine. You can ferment a 2 gallon batch of wine in an 8 gallon container without having to worry about oxidation. But, once you add the metabisulphite, you need a container small enough so that there is only a 2-3” air gap. Or, a lot of store bought wine to make up the difference.
Hint: Some wine makers are using a product like Private Preserve at this stage as well. Private Preserve is made up of argon and CO2. It comes in a can that you spray into your carboy. You add a little of this gas and it pushes the air out of the carboy, and the heavier gas stays in the carboy, which helps preserve the wine better. This is just a little extra protection against wine oxidation.