Originally Posted by kingwood-kid
I've seen this same idea mentioned a lot. Without specifically saying it's 100% false, I feel obligated to point out that apple and grape juices each have a pH below 3.4, and ale yeasts seem to chew through those easily. Whatever off-flavors you get from stressed yeast at a pH of 3-3.5 will probably be covered up by that same pH anyway.
Good point. Maybe the issue is a combination of pH and sugar profile? Much easier for yeast to ferment the simple sugars in juice than the more complex sugars in wort?
What do you mean by off flavors being covered up by the pH? Lactic acid really doesn't do much to hide off flavors. A friend did a pre-pitched Lacto ferment and ended up with some pretty bad (phenolic) off flavors.
Here is a quote from "The Effect of pH on Yeast (Saccharomyces cerivisae) Alcohol Production in Beer" that looked at the fermentation in various buffered solutions:
"At pH 3, the average alcohol by weight (ABW) percentage was 3.788% ± 0.026% (±SEM, N=5); at pH 5, the average ABW percentage was 4.370% ± 0.026% (±SEM, N=5); at pH 6, the average ABW percentage was 3.761% ± 0.026% (±SEM, N=5); at pH 8, the average ABW percentage was 3.141% ± 0.058% (±SEM, N=5)."
So lower attenuation at a low pH. Sadly, the more standard final pH of ~4 was not included.