I have a 10 gallon cooler for a mash tun. Holds temp well so I want to try and do a step mash for a pilsner recipe. My steps would be at 122/145/155 and then mash out at 168. The calculators I've been consulting basically say to add a bunch of boiling water to adjust the mash temp. If I start off with my mash thickness at 1.25 qts/lb, will adding all (around 10 more qts or so) of boiling water mess with my numbers? I can't see how I should be able to hit my OG with all that added water. Anyone?
I do this all the time. Usually I fudge a little and start off with 1.1 qts/lb to make it a little easier. For a five gallon batch I'm usually adding ~2 gals of boiling water for the first step and a touch less for step three. To do a mash out (total of four steps) will be pushing it . . . the workaround is to drain a gallon or two and boil it, essentially a decoction and yes that works. I let Beersmith calculate the grav and it's within a point or two. The extra water is not a problem, you'll end up using less sparge water. BS does tend to understate the amount of boiling water needed, either tweak the setting and/or keep some extra boiling water handy.
I do decoctions for certain brews. Fill in initial infusions then rests/infusions. This will get you close. I usually boil a little more then it says. http://www.brewersfriend.com/mash/
