how much headspace is too much

I do about equal amounts of wine with raw fruits and concentrates I buy from a supplier. I can control the size of the batch much more easily with raw fruits. Most concentrates are intended to make a specific volume (e.g., 5 gallons).

My last concentrate batch was a Gamay. One 46-ounce can makes 5 gallons. I followed all directions appropriate, first fermenting in a food-grade bucket, etc. etc. then racking to a carboy, which happens to be 6 gallons.

Because of the gases produced during primary fermentation, I am not concerned with the several inches of headspace between the top of the must and either a towel or lid over the bucket, but after the 5-gallon batch goes to the 6-gallon carboy, there's a fair amount of headspace.

I left it in the secondary for 2 months at 5 gallons. Only then did I get worried about headspace causing off flavors, so I topped off to about 6 gallons reducing headspace to just an inch or so in the neck. ...Not thinking at the time that I had just diluted my wine by a gallon.

Real question is: how much headspace is too much for wines in secondary fermentation or conditioning when it's not producing enough gas to help prevent off flavors? Do you think my gamay would have been fine if I hadn't topped off?

You don't want any headspace in secondary, and you definitely have to top up. Lots of winemakers make "extra" wine in a big bottle and use that to top up after racking. Each time you rack, you'll probably lose a bit. You can top up with a similar commercial or homemade wine, and that would be better than water because it wouldn't dilute your wine. For your gamay, you could buy a cheap bottle of gamay and use that to top up.

Some winemakers use sanitized glass marbles, dropping them in the wine to raise the level so they don't have to top up and risk diluting their wine. The only problem with this that I see is you might get some imported marbles that have lead or something, so you have to be very careful on what you buy.

I have a variety of sizes of carboys, so I might use a 5 gallon first then rack to a 3 gallon and 1 gallon and 1 1.5L bottle, if I have alot of lees. Then, I use the smallest bottle to top up each racking and end up with maybe 4 gallons. Kind of a pain, but it works! I of course "sample" any that doesn't fit into one of my selected containers. I bought a selection of bungs and extra airlocks, so I could probably even use a beer bottle for my "top up" wine.

Lorena