Do I need to completely fill my keg?

Question

I'd like to make some smaller batches in order to test recipes, but without the hassle of bottling multiple different beers. The whole process of sanitizing and cleaning bottles takes too long if I'm going to be frequently brewing small test batches. So this brings me to my question:

If I were going to force carbonate 1 gallon of beer in a 5 gallon corny keg, what do I need to know?

What's the best way to expel the air that would be in the keg? CO2 has a higher density than air, correct? Could I just fill the keg with CO2, open the lid, pour in my beer and then increase the pressure to the appropriate level?

Would there be an increased chance of infection? Would it age poorly? Is there any adverse effect of having a large amount of CO2 head space in a keg?

Answer 1

After sanitizing everything, you could connect the CO2 line from the tank to the keg, only connect to the downspout side rather than the normal gas inlet side. With the lid removed, slowly fill the keg with CO2 - it will fill from the bottom, pushing the air out. You can use a lighter to test to see when it's full of CO2. (Lower a long fireplace lighter down just inside the mouth of the keg - if it immediately extinguishes, you're good.)

Once you've done this, you can fill your purged keg with beer. (Don't forget to swap your lines back!)

There are no unusual risks associated with lower levels of liquid, and as long as you properly sanitize and purge, the risks of infection and oxidation are minimal.

Answer 2

My batches often dont reach 5 gallons. All I do is hook up the co2 to the normal line, then pull on the release valve. Since the co2 sinks to the bottom, the stuff that gets pushed out first is the normal air. I do this a few times since it takes a moment for the co2 to settle out.