I normally make 5 gallon wine kits. I purchase a 1 gallon kit and I have 6 gallon fermentor. Will this hurt the wine using the same fermentor? Do I need to get smaller fermentor for small batches?
My initial thought was that you should get a smaller vessel, but thinking it through likely the CO2 would drive out any excess oxygen or the yeast would consume it. I think you should be OK.
I would personally get a second smaller fermenter as it allows you to make a small and a large batch in parallel, which isn't a bad thing :-)
If you have smaller bottles you use as secondary fermenters, you can use those to free up your large fermenter. Either way, it doesn't matter as long as you have an airlock, which will prevent oxygen from seeping back into the fermenter.