From what I've found at various sources 4.0-4.5 is a good range for ales. I've seen not above 4.0, but every source I've found talks about exceeding whatever limit they consider "ideal" resulting in dull flavors. Lagers are a bit higher and sours lower.
4 is definitely at the low end but some ales and definitely sour beers (Berliner Weiße) drop under it. I had one wheat beer come in at 3.99 but given meter error that could have actually been a bit over 4 (or lower in the 3's).
I don't think high pH is the cause of dull flavors. I think it is a symptom that something or things went wrong in the fermentation and that an incomplete or improper fermentation is the cause of the uninteresting flavors. High mash pH leads to dull flavors even if the fermentation goes well and the beer pH winds up as what we call acceptable. You might prove me wrong by adding a little acid (dilute lactic or phosphoric) to your beer and seeing if that improves the flavor. Gordon Strong mentions doing that in his book and lectures. Check with a pH meter, of course, and do the additions in small increments tasting as you go.
What got me interested in this was an IPA that I brewed (my best beer yet). It scored a 43...each one said there was just something about it that was not quite right. ... measure my beer. It came back at 5.0 pH, so I think I found my culprit.
My mash pH was 5.45, a bit higher than I was shooting for, but still within a good range, I feel.
5.45 is an excellent target. My gut tells me 5.4 is probably ideal but it doubtless varies some with the type of beer.
This was before I started measuring my pH at the end of boil, so I am unsure of that.
Unless you sparged with highly alkaline water (and you say later that you didn't) kettle pH should have dropped down to 5.1 - 5.25 or something like that. Again, this is, AFAIK, just about ideal.
I grew a starter for this and pitched 0.75M cells / mL / °P, estimated. I brew all grain and used almost 94% domestic 2-row, the rest was crystal and a touch of acidulated malt. I feel that due to this my FAN should be sufficient.
Sounds like enough yeast and all grain brewing usually results in sufficient FAN.
I believe I used enough oxygen, even may have over done it. I aerated with pure O2 at 1L/min for 3 minutes through a .5 micron stone (I've since come to find that this may be too much and will be doing an experiment with aeration for my next batch). I believe I pitched the yeast after aeration, but may have pitched it prior (my notes are unclear). My understanding now is that if I pitched first there is a chance that levels reach a toxic level for yeast during the aeration period.
That would be hard to achieve though it is probably possible to do. Not all the oxygen you inject dissolves and of that which does quite a bit comes right back out as the solution tries to stay in equilibrium with the air over it.
I find this as potential problem area #1, but believe I pitched after aeration, which keeps me on the search. I used WLP001 and fermented at 64 F. As I've recently found, the colder the fermentation, generally, the higher the finished beer will be. I'm thinking this may have contributed to my high finishing pH, but am not sure that a few degrees could result in such a high shift.
The problem is that you had wort at pH a little over 5 and the yeast didn't drop the pH below 5. The question is why? The answer is unhealthy yeast or unhealthy conditions for them but it sounds as if you did everything right. Sometimes you get bad yeast i.e. yeast that doesn't perform the way it is supposed to. I have had bad packs/vials from both the major manufacturers. The usual result is disappointing degree of fermentation. How was the ADF (apparent degree of fermentation) on this beer? The yeast may or may not have been the problem but the failure of the yeast to drop pH is a signal that something is wrong. As I don't know what that might be I don't have a fix to offer except to check that you are using good practices throughout i.e. protein rest for FAN (that comment will bring down a cascade of protests that protein rests are not necessary with modern highly modified malts), being sure that sufficient oxygen is supplied, controlling fermentation temperature, being sure that nothing toxic to yeast gets into the wort (iodine from table salt, for example), providing them with trace elements through the use of a yeast nutrient etc. pH at this point (the fermenter) is an indicator rather than a control point. If the yeast don't drop the pH of the wort dramatically in the first few hours of fermentation I don't think you can fix things by adding acid to lower it for them.