Does wort PH have any effect on the beer´s diacetyl content? What´s the mechanism?
Thanks in advance,
High beer pH doesn't cause high diacetyl levels, although the two are often seen together. Rather than one causing the other, they are usually both symptomatic of a microbial contamination...
Some yeast strains are noted for producing higher diacetyl levels under normal conditions (mostly English ale strains such as Ringwood) but these beers usually have what most would consider normal pH's.
Diacetyl is a bi-product of the iso-leucene/ valine biosynthetic pathway, and happens in every fermentation.
Allow for proper time and temperature control during fermentation, and the yeast will further metabolize diacetyl producing 2-3 butanedione which has a much more favorable flavor threshhold.
Let your yeast attenuate, and don't knock down fermentation temp until the diacetyl is gone. You may even increase the ferm temp about six to seven days into fermentation, expediting the process.