I started aging my wine in a 1 gallon glass carboy. I plan on aging it about 2 to 3 months. How high should I top it up to? Right now I have it little under two inches from the top as shown in the image.
Like GreenEnvy22 says, you really want no air space in the carboy. Fill it up inside the neck with the smallest of space between the surface of the wine and the bottom of the bung.
You have to allow for expansion of the liquid if the temperature or even air pressure changes. I normally fill to somewhere close to the upper point where the 'handle" attaches.
If the tip of your airlock touches the liquid - I'd call that too full.
Yep like Scooter said, I don't go closer than in inch to the rubber bung, as the level will rise/fall based on temp and I don't want the wine touching the rubber bung.