It looks like I’m about half to a full gallon short of filling my barrel. My thought was to just open a few beers of similar style and add them to the barrel. Is there any issue with doing this?
Are you talking about a bourbon/whiskey barrel? If so, don’t worry about the head space. I just kegged a RIS that was in the barrel for 11 months and no ill effects on the beer. I put 25 gallons in (25 gallon barrel) and with evaporation I had 21 1/2 left. Now with being said, I would not barrel age a beer under 7% abv for anymore than 2 months and checking it often.
The headspace can get moldy particularly if the barrel’s last use was not bourbon or other distilled alcohol and oxidation increases the more the headspace. So I top off initially and repeatedly. Part of the repeated topping off relates to when you have a group of people putting beer into a barrel, you want everyone to get their fair share at the end - the last person to get beer out shouldn’t get shortchanged. I suppose there could be more than 1 right answer here.
Rotate your barrel regularly to avoid the moldy headspace… and to keep those staves wet and properly swelled up.
I don’t agree that you need to rotate the barrel. You don’t want any sediment to keep churning back into the beer. I have barrel aged with 3 different barrels and used them all with 2 different beers for extended time frames. I haven’t had any mold whatsoever or at least what i could see with the naked eye. The barrel is going to be tight and oxygen ingress is micro.
Thanks for the feedback. I think that the best thing to do here for myself is to do nothing and let it ride. I think that I have a higher chance of oxidation if I add a couple of beers than I do with leaving the barrel with the additional head space.