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:
- Add water to the wine. We would only recommend doing this if you only need to add a glass or two of water because too much water will start watering down the wine. No one likes a wine that is very low in body and flavor.
- You can use a wine similar in style to the wine that you are making to fill the gap. For example, if you are making a merlot wine, then buy a store version of merlot. Don’t go out and buy a $100 bottle of merlot thinking the rest of your wine will turn out tasting like it. Your wine won’t, because the store bought wine will be broken down and its flavors will blend with the wine that you are making. We do suggest buying a wine that you like though, because you will likely have some left over, and someone will have to drink it.
- Displace the wine using glass marbles, or anything glass that is small enough to fit in the neck of the carboy, but large enough that it won’t end up becoming a part of the wine. Why glass? Because it is easy to sanitize because glass is a hard surface. Plastic marbles won’t work because they are easy to scratch, which can be a haven for bacteria. Always sanitize the marbles before using them. The marbles will displace the wine, causing the gap to shrink.
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.