Mash pH and roasty flavors

[siwelwerd]

In this month's BYO, one of the articles on stouts mentions the following: "Dark malts tend to really acidify the mash pH, and when that happens you start to support roasty and bitter flavors." I have noticed this as well in my limited experience; supplementing my moderate carbonate water with a little more carbonate has kept my brown porter from being overly roasty/acrid. I just flipped through Daniels, Noonan, and Fix, and none of them mention anything like this. In fact, none of them seem to say much at all about the impact of mash pH on the flavor of the beer. They seem mostly focused on attaining proper pH to ensure adequate conversion. Is this the only flavor impact that the pH will have on the beer? I'm a little confused as to why I haven't seen this fact referenced anywhere else in the literature I read; am I just reading the wrong books?

[siwelwerd]

Anyone?

[ajdelange]

I guess I can comment that dark malts don't seem, in my brewing, to lower pH as much as all that. I have water with an RA of about 40 and when I brew a stout with it (untreated) using 10% roast barley the pH goes to about 5.5. This is the upper end of the acceptable range for me largely because when I control mash pH to this level or lower the beer is better in several ways. Lagers faster (I know we are talking stouts here but I'm primarily a lager brewer), clears faster and drops brighter, tastes better, is more stable in the long term and is, in a word, much better beer than what I gor before I became meticulous about mash pH. Notice I've said nothing about conversion. That may be improved too but I really don't care much about that.

Intrigued by the numerous posts I read here in which people are adding teaspoonfulls of chalk to their brews I tried to find out how much roast barley it would take to push deionized water (RA = 2.5, call it 0) to a pH of 5.2, the lower limit of the range I shoot for. It was 30%.

As for the statement that acidity "supports" roasty and acidic flavors, I'd say it is very likely that the extraction of the substances responsible for these flavors depends on pH as almost all biochemical processes do. If you delve into the professional literature (JASBC, MBAA Technical Quarterly...) or look into some of the brewing texts I'm sure you will find some information on this.

The one data point I can give you is that my Irish stout with 10% roast barley and mash pH of 5.5 is not, IMO, overly roasty, ashy or bitter. It's just about where I want it to be.