I have heard that some all grain brewers prefer to steep roasted barely during prior to the boil, because it would otherwise lower the pH of the mash.
In addition to this, what purpose would an all grain brewer have when they steep grains?
Well you don't steep any grain "during the boil". But to avoid upsetting mash pH you can steep all your non mash required grains in the wort during runoff in the kettle before you start the boil. I routinely add my roasted and crystal malts to a grain bag and steep them this way when I make stouts.
Another application of steeping malts is to actually make two beers. If the base malt of two recipes is the same I have mashed in to make 12 gallons of base wort. Then steeped malts in 6 gallon portions to make a Pale ale with half and a Porter in the other.
There really is no magic to mashing the specialty grains when doing all grain. Its basically the same thing as diluting out extract and steeping grains like many of us did when we started with extracts.
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