Do you mean boiling x amount of AG wort down and then diluting it with an amount of water to increase the batch size? Like topping off in an extract w/grains batch?
Yeah, I have been experimenting with something like that this winter on my stove- top. I've only talked about it a little on here, and haven't given much details, 'cause I've wanted to try a few different beer styles and see what works and what doesn't.
And then write something more formal up.
So far I've done a wit (twice), a vienna lager, an Ipa, a Red ale, and a Cream ale. And the Vienna actually won honorable mention in a bjcp contest last year.
Basically what I've been doing is doing a fairly high grain mash for a preboil volume of between 3.5 and 4 gallons (which is the max my stove can handle) to boil down to 2.5 gallons.
To be topped off to 5 gallons.
I use beersmiths dilution calculator to see what the the final gravity will be when it's diluted to 5 gallons.
I take lots of refractometer readings during this, use an ibu/bg chart and constantly tweek my beersmith as I go along.
To compensate for hop utilization I up the hops in my recipe by 18%. But I am also figuring stuff out on the fly.
All the beers that I have tasted (which is half of those I have brewed, the rest are still fermenting or bottle conditioning) and they've turned out good. I have had the best luck with low IBU beers- like the wit and the vienna lager, and with the ipa.
The hopping on the former is really conservative so it's not over hopped. And the Ipa is really hoppy, but it's an ipa and even if it were overly bitter, It's still a good thing since I like hops.
Hope this helps.
