Being a newbie, a friend and I were discussing the instructions for most of NB’s Extract Kits, which are premised on the idea that you boil 2.5 gallons, add the extract to that boil, and then dump that into the remaining 2.5 galls to meet your 5 gallon total volume.
After doing my first batch of Irish Red Ale that way, I switched over to doing full 5 gallon boils in a large brew kettle. In boiling a full 5 gallons, plus extract, I noticed a lot of boil off evaporation, such that I was left with less than 5 gallons at the end of the boil. That led to a yield on my second batch (of Irish Red Ale) of only 1.5 cases of 12 fl. oz. bottles, about 10 beers less than the first batch. I had some inconsistencies in the brew process, so the taste of the second batch didn’t really match the first.
Since then, I’ve brewed a couple more batches (Irish Stout and Dawson’s Red Ale) and have noticed the same loss through boil off evaporation. The former is in 22 oz. bottles, conditioning, and the latter is in the Big Mouth fermenting.
So, my question is, after I do the full 5 gallon boil, if I notice that total volume is less than 5 gallons, should I top the wort off with unboiled water to reach 5 gallons and aerate/mix that with the wort before pitching the yeast to increase yield? Or, is the risk too great that I’ll introduce bacteria or wild yeasts by so doing?
My gut tells me that I can top off, since NB’s extract kits instruct a partial brew and pour into 2.5 gallons of unboiled water, but I’d love some direction from the experts. Thanks!
ps-I use Kroger Drinking Water for brewing. Our tap water tastes odd and I don’t trust it for brewing.