What?
- The mead has a vinegar odor (acetic acid, figure). Sensory threshold:
175 ppm [B10].
Acetic acid [B2]:
Why?
- The acétobacter bacteria, naturally found in air, are responsible
for the transformation of alcohol into acetic acid (acetic fermentation)
according to the reaction [V6]:
C2H5OH + O2 -> CH4COOH + H2O
ethanol + oxygen -> acetic acid + water
What to do?
- Not much, except maybe find a book such as "What to do with 5 gallons of vinegar?"
- According to V3, it is possible to dissolve 2 tsp potassium bitartarate
(cream of tartar) in 1 liter (1 qt) of the infected mead then add to the
rest of the batch. If the flavor is not back to normal after a week or
so, try again. After five unsuccessful attempts, bottle your vinegar. This
treatment is at a short term and the mead will have to be drunk quickly.
- If damages are limited and if mead has no other flaw, V6 says it can
be used for blending. J. Recht in V4 does not advise to do this and considers
that the mead is lost.
- If a mead gets infected in a barrel (or any other vessel made of wood),
the vessel is infected and hence can no longer be used.
How to prevent?
- Keep contact with air to a minimum (to avoid introducing bacteria and
providing it with the oxygen it needs).
- Reach an alcohol content of at least 12-14 % (24-28 proof). Concerning
sherry (whose fermentation is partly aerobic), reach an alcohol content
of 14-15 % (28-30 proof) before aerating to form the flor [V6].
- Sulphite [V6].
- A pH lower than 3.2 prevents acetic fermentation [V6] (it is not clear
whether 3.2 is the limit or 3.2 works but a slightly higher pH can be OK too).
Why?
- Transformation of sorbic acid by lactic bacteria [V4, V6].
What to do?
How to prevent?
- Keep sorbic acid doses to a minimum and prevent bacteria from entering
the must/mead (see vinegar odor above).
Why?
- Fungi or molds on the cork [V3].
What to do?
- Immediately check other bottles. Concerning troublesome bottles, clean
the inside of the neck with a clean cloth soaked in a sulphite solution.
Re-cork using new corks [V3].
- Check that the cellar is not too humid. If it is, decrease the humidity
(humidity absorbers that can be purchased anywhere should do the job).
How to prevent?
- Corks can be naturally porous but those split or with holes must not
be used [V3].
- Keep the humidity of the cellar at a medium level.
Why?
What to do?
- Decant for a few hours [V4].
How to prevent?
- Dose sulphite properly.
- Keep a low enough pH so that the amount of sulphite needed is fairly low.
- Use vitamin C along with SO2 to reduce doses.
Why?
- There are yeast cells remaining in the mead.
What to do?
- Age and rack from time to time.
How to prevent?
- This is a natural phenomenon, there is not point trying to prevent it.
May 28th 2002
