Agriculture Reference
In-Depth Information
The ability of tannins to precipitate proteins has important
implications for the aging of wines and beers. Precipitation
refers to the dissolved tannins combining with dissolved
proteins to form a compound that can't be dissolved. This
compound, once formed, slowly sinks to the bottom of the
vessel. When this happens, the astringent or bitter flavors
imparted by the tannin are lessened and the haziness imparted
by the protein is diminished.
Tannins are also chelators. That is, they combine with the
ions (positively charged atoms) of metals in order to make
them non-reactive. A major effect of tannins is that they
combine with iron in such a way as to make it biologically
useless to living things. Pathogenic bacteria love iron. They
love iron so much that they invade the human body to get
it.
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One of the reasons why red wines keep so much better
than others is because the tannins have tied up the iron,
making the environment unattractive for pathogenic bacteria.
Tannins also chelate magnesium, copper, and other metals,
but do so without making the metals unavailable. This alters
the taste by altering the nature of the compounds.
Ingredients other than grapes can have more or less tannin
content, and that content will vary based upon the amount of
time the whole fruit is left in the primary fermenter as well.
Unfortunately, because tannins encompass such a vast array
of compounds, assessing the tannin content of a must is a
devilishly complex exercise in experimental chemistry. If you
are curious, please see New Tannin Assay for Winemakers by
Moris L. Silber and John K. Fellman for the most accurate
method using protein dye markers or the older (and more
controversial) precipitation technique published by Hagerman
