I know this is probably a dumb question, but is there any reason I shouldn’t use my five gallon kit to brew one gallon test batches? Would all the extra air in the fermenting bucket cause some sort of unforeseen issues? I’m new to home brewing and just put my first batch in the fermentor this morning, so right now I’m most definitely still learning.
I would personally prefer a smaller fermentor. Small jugs can be bought for cheap. You can also get smaller food grade buckets from bakeries. They usually throw them out.
You certainly can ferment a 1 gal test batch in your 5 gal set up. There are a few drawbacks though.
First, don’t worry about the extra air. The fermentation will put off a lot of CO2 and force all the O2 out. That will be fine.
Second, one thing you may want to consider is with the increased surface area of your container and the larger distribution of sediment you may run into a larger part of your batch that you lose to dead space and trub. That larger amount of wasted beer may be enough to cause you to reconsider.
Last thing I can come up with off the top of my head is the simple fact that if you’ve got your 5 gal tied up with a 1 gallon you can’t brew another batch!! That may be the biggest reason not to use that set up 
Enjoy the obsession!
I guess it just makes more sense to get a couple small containers for one gallon batches. I’m not sure why, but I was thinking I have to get a bunch more equipment. Guess that’s my inner tight wad taking over. Thanks for the help guys! I’m excited about getting into this new hobby/lifestyle and experiencing my own homebrew!
Whenever I need gallon jugs I find my way to the wine isle of the grocery store and pick up a gallon of the Carlo Rosi, between the wife and I we can make sure we polish it off in time to use it for fermentation 
