What's the downside to going above ~2 qts lb? pH?
I'd think you'd also be driving the enzyme concentration too low
Nope. I know brewers who regularly go over 3 qts/#. Out of curiosity, I thought I'd give it a try. So, I made a few batches of no sparge beer at over 3 qts/#. The grain converted quickly and with
very high efficiencies for no-sparge. It also made delicious beer.
I have very soft water and I made amber and brown beers, which might have helped, but I had absolutely no pH issues or tannin problems. I just finished a run of Lagers, all of which were mashed at 2-2.6 qts/#, and every one is clean, malty and everything I hoped they would be.
Supposedly, a thick mash can help with the low prevalence and poor stability of proteinases during a preotein rest. I think intentionally mashing thick is mostly just a hold-over from the days of under-modified grain and brewers using mash tuns that were too small. I don't know how it ever became seen as "best practice" for starch conversion among homebrewers,