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taste. However, once the grapes are fermented, the acidity in the resulting
wine will begin to break these bonds, rendering the phenols volatile once
again. “Blending away” smoke-tainted wine with unaffected wine is not productive,
as relatively low levels are still detectable. So why ruin sound wine?
Some practices such as whole-cluster pressing (where there is no crushing
of the grapes on the stems first) and use of gentle pressing and isolating freerun
juice from press juice can minimize the amount of phenols that escape
into the grape juice. Certain yeasts have also been isolated that emphasize
fruit, while adding oak chips or tannin can mask it to a degree. But use of oak
can backfire, creating a wine that is both oaky and smoky.
Other scientific methods of removing “unpleasant” odours or flavours
from wine, such as reverse osmosis, do not help. Smoke taint will come
back in the bottle in a couple of months, or even worse, may come back
while you are consuming it. The enzymes in your mouth are able to break
down any glycosides that remain, and the undesirable aromas can be vaporized
as you taste, so that the wine might smell fine, but then taste off. From
a personal perspective, the thought that a wine will spoil in the act of consuming
it ranks as the most depressing of experiences.
Australian research has identified a handful of the many volatile phenols in
smoke primarily responsible for taint. They are guaiacol, 4-methylguaiacol, o-
Cresol, p-Cresol and m-Cresol. More are being discovered as time passes.
Much of the research has been aimed at determining the stage of development
at which the grape is most susceptible, what difference an interface
fire (as opposed to generalized smoke) may make, and the effect of ash settling
on the leaves and berries.
Researchers have concluded that the nearer the fruit is to harvest, the
higher the risk associated with smoke exposure. Dr. Usher is not convinced
that ash plays much of a role unless it is carried on the grapes and any stems
or leaves (what the industry calls MOTS-material other than grapes) that
end up mixed in bins of grapes from poor harvesting practices through to
fermentation. This can be controlled with hand harvesting and sorting,
rather than machine harvesting.
The threshold for detection is not known:
Though we know high levels of these compounds will indicate smoke taint,
there is no threshold level that will definitely signal that. “It is really difficult
to predict smoke taint from volatile phenol levels in the grapes … it
depends how much of this gets released during winemaking,” said Anita
Oberholster an enology specialist at UC Davis. “Additionally … sometimes
smoke taint or smoky characters are identified in the wine even though all
the individual compounds are below their odor-threshold levels. This suggests
a synergistic effect and that there are potentially additional compounds
contributing to the character that we still need to identify.”