Jmattioli said:
For comments by Dan, Chuck and anyone else that wishes to particpate in dialog,
The statement by Action & Duncan in Making Mead that " Where a must is deficient in acid, certain peculiarly flavored substances are produced during fermentation and these spoil the finished mead."
Is that still considered true by modern standards? And if so, What is the standard measurement and quantity that makes a must considered deficient in acid before fermentation?
Acton & Duncan's _Making Mead_ is an old book, put out about 38 years ago and there's no doubt that much of the advice is dated. They weren't the only ones saying this, however, and you can still find other sources saying things like "yeast needs an acidic environment" in order to ferment well.
You'll find this idea expressed in a lot of old sources on meadmaking -- that honey is deficient in acidity and needs supplementation. Totally untrue. Prior to John W. White's research in 1958, there was no reliable method to measure total acidity in honey using standard titration methods. White eventually developed an alternate method which he used in his landmark study of 490 U.S. honeys in the early 1960's. The source of reports in meadmaking that honey is deficient in acidity all stem from this period prior to White's work when the measurements of acidity in honey were unreliable and inaccurate.
More accurately, yeast do not need acid in order to ferment sugars -- they produce various organic acids themselves during the process of metabolizing the sugars. What is important to the yeast is the pH of the honeymust which itself is a product of acidity. It doesn't have to be especially acidic. The late Roger Morse found a pH window within which the yeast would do quite well -- from pH 3.7 to 4.6. A pH above or below this range would cause a sluggish or stalled out fermentation.
From my own observations, all of my honey musts start out at about pH 4.0. That's just about right, no need for acid to lower the pH any further. Other people I've talked with have found similar values. The organic acids naturally secreted by the yeasts will lower the pH of the honeymust even further. This is an excellent adaptive mechanism -- the acids secreted by the yeasts will lower the pH to the point where it will inhibit bacterial growth, allowing them to dominate the environment. This is an important factor in keeping out infection -- getting the fermentation off to a quick and vigorous start.
In meadmaking, adding even more acid in addition to the acids secreted by the fermenting yeasts will drop the pH much too low. This has often been a cause for sluggish fermentations lasting months or longer -- adding acid at the start of the fermentation.
-- Dan M.
