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All grain partial boil

I do 10 gal batches but I am considering brewing 15 gal of my cream ale. My cream ale recipe produces 10 gal of 1.045 wort post-boil.

I basically want to scale up the grain bill to get 10 gal of 1.068 wort then top off with water to get to 15 gal of 1.047 wort.

My kettle only fits 15.5 gal so my thinking is:

Near the end the of the boil, I could add 2 gal of water (since boil off has made “more” room in the kettle). I would add 1 gal of preboiled/chilled water to 3 carboys. I would then distribute the wort as evenly as I could between the 3 carboys. Each carboy would be filled with 4 gal of wort After topping off with water, the OG should be around 1.047.

I use a mix-stir attached to a power drill to aerate so the wort and water would be thoroughly mixed before yeast is introduced.

I’ve adjusted the hops to compensate for the concentrated wort and water addition. I’ve also adjusted salts for the mash and all of the water (including top off) would be treated with campden tablets for dechlorinating (if such word exist).

Other than having a much thicker mash, has anyone done something similar? Any advice / lessons learned? Am I missing anything?


I wouldn’t add water to your brew pot near the end of the boil. I would just boil as much as possible, split it into your 3 fermentors and top off with purified or filtered water.

I would go this route ^^^

I have done the same with an 8 gallon pot… brew as high volume as possible, fill up fermenters rather than boil. Split into appropriate batch size.

I top up whenever my boil reduces my wort below 5 gallons/10 gallons as desired and I have had no problems. I think that is what the macro brewers pretty much do, although they may be adding it post fermentation with specially treated water (nitrogen infused deoxygenated water to prevent oxidation). Add it anytime preferment and you should be good to go.


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