At NHC 2017, Annie Johnson said that her PU recipe shot for a 4.7 to 4.9 mash pH.
I had to triple take that... Why would you do that?
That would render enzymatic activity nearly useless (alpha for sure), beta seriously slow. You would have a crap effciency, and a poor fermentation. Is that thought because you want to the beer to finisher higher? If thats the case you could just mash super high, and leave the beer to finish at 1.015 or so. But its not the same beer. PU is sweet, sweet like unfermented sugar sweet, not high dextrines blah (to me thats neither dry or sweet, just blah..).
To get the proper PU mouthfeel, mash for a 1.010 beer, and halt fermentation by chilling with about 4-5 points remaining. Simple as that! You get the syrupy sweetness and if you pitched low cell counts, probably most of the diacetyl.
Here are the lab results of PU:
OG 1.047
FG 1.014
RDF 58.5
ABV 4.41
IBU 31.6
Color 6.2
pH 4.66
Diacetyl 113ppb (taste threshold 40ppb)
PU is just a showcase of what poorly fermented beer tastes like when you are good at it! That being said, I'll drink it.