I'm going to be doing some small batch brewing (1 gallon) to refine some recipes. So I recently picked up some 1 gallon glass carboys. Upon filling them to measure where 1 gallon of liquid fills to, I noticed there is not much space left for CO2.https://goo.gl/photos/T6et1bwxx5osxm656
As you can see, there is a small amount of space left. This measures to approximately 1 cup of liquid. sorry for the link. I'm having issues embedding the image here.
My questions are:
Is this enough space for fermentation? I'm assuming not. If not, would using a blow off tube make it work?
How much space should there be left?
Any input/suggestions here would be appreciated.