With many wines, laying them down for a long period improves them
and this is a factor in good wines becoming great wines. However, sometimes
wines go off and develop a bad smell. New research reveals why.
Sometimes a wine has been in storage, with the expectation that the
bottle of vino, when opened, will produce something special to the palate and
to the nose. To create the delightful bouquet, within wine there are volatile
and non-volatile compounds that contribute to the makeup of a wine's aroma.
Occasionally a bottle is removed from the cellar and, when opened,
there is a highly unpleasant smell. The main cause of this off-odor is hydrogen sulphide, which
delivers to the affected wine an aroma of sewage or rotten eggs.
Hydrogen sulfide
Sulfate-reducing microorganisms can be
traced back to 3.5 billion years ago and are considered to be among the oldest
forms of microbes, having contributed to the sulfur cycle soon after life
emerged on Earth.
Why wine goes off?
Although the chemical that causes off-wine has been established, the
specific causes have always been uncertain. Now, with hydrogen sulphide,
scientists have identified some potential sources of this stinky compound.
According to Laboratory Manager magazine, hydrogen sulphide is
produced naturally during fermentation. However, the bulk of the gas disappears
or is removed in subsequent winemaking steps. Why it sometimes re-emerges after
bottling has been a puzzle.
One theory, with a touch of irony, is that it might derive from
polysulfanes and other sulfur byproducts created during the actual act of
hydrogen sulphide removal.
Research process
For the study, the scientists
developed a model wine that was composed of a mixture of polysulfanes. Taking
this wine, the researchers treated it with antioxidants like sulfur dioxide and
ascorbic acid. These additives are introduced to many wines as preservatives
during bottling.
Once this was prepared, the researchers identified and calculated
the concentration of a several sulfur compounds in the wine after six months of
storage. It was discovered that polysulfanes containing four or more linked
sulfur atoms per molecule were most likely to decompose during wine storage.
This reaction correlated with elevated levels of hydrogen sulphide.
The inference from this discovery is that wines with polysulfane
additives are most likely to experience re-emergent hydrogen sulphide. This
finding is set to be tested out on a bigger scale.
The study was funded by Wine Australia and the Australian
government.
Research paper
Posted by Dr. Tim Sandle, Pharmaceutical Microbiology
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