A question for you experts out there! One of the things I like to pay attention to as I brew is cost per batch -- mostly as a matter of curiousity (since quality is the major concern to me), but also as a matter of economy. If I can make a batch that is "equivalent" on the most significant measures as to quality but lower in cost, that's something I like to keep in mind.
Along those lines, what is the effect of replacing a portion of one's malt with adjuncts? Say, I'm making a big beer (like an imperial stout), and the recipe calls for 15+ lbs of 2-row pale, plus the adjuncts that typically go in to the impy to get the whole to somewhere around 18 lbs. What percentage of the pale malt could I reasonably replace with some less expensive unmalted grain? As the percentage went up, what factors would I need to counterbalance? Obviously, one of them would be that the unmalted grains contribute no amylase; I'm assuming that is already accounted for by setting a lowerbound on the replacement. (Between 1/2 and 2/3rds of the total grain bill must be malt.)
Any thoughts? Experiences doing this?