I adjust along the way as necessary. Mash pH for hoppy beers is generally targeted at around 5.3 room. I acidify sparge water to 5.4-5.5 and kettle full pH will generally fall around 5.4. Most of the time I leave it there for at least 30 if not 60 (it will fall incrementally on its own throughout the boil) as I have to boil for 90 and I get better DMS reduction at 5.4. Just depends on when I’m adding hops and how much as to when I’ll add acid to lower it.
I haven’t done many experiments testing one vs the other it’s just based on research I’ve done over the last year or so on pH throughout the process. A quote from Shaun Hill sparked my curiosity.
“Every beer I brew. Constant surveillance on brew day throughout production. Especially pre and post boil. “
Got me looking into pH more outside of Mash and Sparge and the effect it has. If mash and sparge fall into spec and you boil for long enough without a ton of hops the pH into the Fermenter will generally be fine. You’re generally going to want below 5.2 for lighter beers at KO and obviously the hot break is maximized at a certain pH. But if you’re adding a ton of hops I’ve found it can get out of whack. I’ve heard Henry from Monkish talk about getting pH as close to 5.0 at KO, I’ve heard Dan Suarez mention it needing to be below 5.2 for hoppy beers. The brew log for Pliney you can find online has mash pH spec at 5.3-5.5, Kettle Full pH at 5.24, and KO pH at 5.07.
Also Nate’s comments on adding plenty of hops in the boil and obviously TH beers have rather low bitterness. Only way to get less bitterness out of hops is to have a lower pH, at least that I know of.
There are supposedly hop oil conversions that happen within a narrow PH band as well, although I need to do more research on this.