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Dan McFeeley
01-16-2004, 12:22 PM
I've been meaning to post this information for awhile but haven't gotten to it yet -- apologies!

Not so long ago I did some experimentation on measuring acid levels in mead using the standard acid testing kits used by home winemakers. They're simple and easy to use, about $6.00, and have been used by meadmakers as well. There is a problem, however, in using them for checking TA levels in mead. There is a chemical reaction that occurs in honey when titrating for acid levels in honey and mead that skews the results of any standard titration method. Here's a brief description.

The primary acid in honey, and of course, mead, is gluconic acid. Gluconic acid co-exists with its lactone, gluconolactone, in a pH dependent relationship as part of the process by which honeybees change flower nectar into honey. Bees secrete several enzymes which work on the sucrose sugar in the nectar, first changing the sucrose into glucose, and then into gluconolactone. The gluconolactone then spontaneously hydrolizes into gluconic acid, thus raising pH and acidity levels that help to preserve the now ripened honey. Not all of the gluconolactone will hydrolize into gluconic acid. A certain amount remains behind, and acts as an acid reservoir of sorts. Here's where the pH dependent relationship between the two comes in. Whenever the acid level of the honey is neutralized, the pH will rise. The rising pH triggers the reaction, causing the gluconolactone remaining in the honey to change to gluconic acid, thus lowering the pH again and restoring the acid level of the honey.

Now, picture this process going on during the titration process used in standard acid testing kits. Sodium hydroxide is titrated, raising the pH. All the while this is going on, gluconolactone is changing to *more* acid, making it necessary to add even more sodium hydroxide in order to reach the endpoint. This reaction is *extremely* fast, too fast to see without a pH meter and impossible to detect using the simple titration method. The result is that all TA measurements in mead resulted with a standard acid testing kit are inaccurate.

This is actually a well known reaction, first identified by John W. White jr. in 1958. It had been known for some time that it was impossible to obtain accurate TA readings in honey, but up until then no one knew the cause. White was able to isolate the lactone/acid reaction as the reason for the unstable endpoint problem, and devised a new method of measuring TA in honey that bypassed the reaction.

I did a simple experiment, duplicating White's 1958 experiments but using mead instead of honey. Sure enough, the lactone/acid reaction persists in mead. I got the same results as White. This was published in Bee Culture magazine, and also given attention in Ken Schramm's book, _The Compleat Meadmaker_.

The bottom line here is that using an acid testing kit to measure TA is not reliable. It's far better to ferment the honey must to completion, taste the mead and adjust according to taste.

Oskaar
08-24-2004, 11:51 AM
This is excellent information. I was always getting inconsistant TA values using titration so I switched to a handheld pH meter. I generally end up using my tastebuds because the numbers generally don't bear out what I am shooting for.

Oskaar

WikdWaze
08-24-2004, 04:10 PM
Well, now I know I have no need to buy those Ph strips at my local supplier.

Is there any way to determine how much "acid" is held in store?

Oskaar
08-25-2004, 04:36 AM
The strips would help to give you and overall idea, mouthfeel would be your measure though. If the pH from the strips, and the mouthfeel jive, then you can proceed to add more acid, or bring it more to the basic end of the spectrum with some Calcium or Potassium Carbonate.

Oskaar

WikdWaze
08-25-2004, 05:07 PM
The strips would help to give you and overall idea, mouthfeel would be your measure though. If the pH from the strips, and the mouthfeel jive, then you can proceed to add more acid, or bring it more to the basic end of the spectrum with some Calcium or Potassium Carbonate.

Oskaar
Are those carbonates the ones that produce a salty taste when overdosed?

Oskaar
08-26-2004, 01:40 AM
I would say, chalky, drywally, sodiumy.

Oskaar

WikdWaze
08-26-2004, 02:07 AM
I would say, chalky, drywally, sodiumy.

Oskaar
Mmmmmmmm, drywall.... :P