of astringency is caused when tannins bond to
proteins in our saliva, which normally provide
lubrication and help food particles slide
smoothly along the mouth surfaces. Tannins
cause the proteins to clump together and stick
to particles and surfaces, increasing the
friction between them. Tannins are another of
the plant kingdom’s chemical defenses. They
counteract bacteria and fungi by interfering
with their surface proteins, and deter plant-
eating animals by their astringency and by
interfering with digestive enzymes. Tannins
are most often found in immature fruit (to
prevent their consumption before the seeds
are viable), in the skins of nuts, and in plant
parts strongly pigmented with anthocyanins,
phenolic molecules that turn out to be the
right size to cross-link proteins. Red-leaf
lettuces, for example, are noticeably more
astringent than green.
Leaves and Fruits Shaped Our Vision