I think it’s possible, but I’ve never done it. I’d go with 1 gallon of water and 1/2 oz of magnum or something big. Add some DME with 5 minutes left to reach the same OG as your other brew. Ferment it out and then blend in to taste.
It’s unlikely that you’ll be able to achieve over 100 IBUs in this 1G batch, and I think hop utilization is going to be lower than you find in regular 6 gallon boils. Tinseth method of calculating IBUs gives 200 IBUs for 1/2 oz of 14%AA at 60 minutes with no sugars. This might end up giving you around 100 IBUs, which would mean you could add 20 IBUs to the beer (as long as things are as simple in reality as they are in the math). Adding the sugars at the end will help with utilization, and since you don’t know how much bitterness you’ll have there, Don’t just blend it all. Taste the 1G batch post-fermentation to make sure it’s not totally nasty or infected, or way too harsh, then use eye droppers or something to do some trial blends in a glass before scaling up to the whole batch.
Most of what I’ve heard about blending batches is that if you make a beer that’s bad, you’re better off pouring it out than trying to save it by blending. Other than the lack of bitterness, is the first beer good?
