On food and cooking the science and lore of the kitchen ( PDFDrive ) 379
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an unpleasant muddy aroma. It’s most often
encounteredinbottom-feedingfish,especially
catfish and carp that are raised in ponds dug
directlyintheearth.Thechemicalculpritsare
two compounds that are produced by bluegreen algae, especially in warm weather
(geosmin and methylisoborneol). These
chemicals appear to concentrate in the skin
and the dark muscle tissue, which can be cut
away to make the fish more palatable.
Geosmin breaks down in acid conditions, so
thereisagoodchemicalreasonfortraditional
recipes that include vinegar and other acidic
ingredients.
Fishiness The moment fish are caught and
killed, other aromas begin to develop. The
strong smell that we readily identify as
“fishy” is largely due to the saltwaterbalancing compound TMAO (p. 188), which
bacteria on the fish surfaces slowly break
down to smelly TMA. Freshwater fish
generally don’t accumulate TMAO, and
crustaceans accumulate relatively little, so
they don’t get as fishy as ocean fish. In
addition, the unsaturated fats and freshsmelling fragments (aldehydes) produced
from them slowly react to produce other
moleculeswithstale,cheesycharacters,some
of which accentuate the fishiness of TMA.
And during frozen storage, the fish’s own
enzymes also convert some TMA to DMA
(dimethylamine), which smells weakly of
ammonia.
Fortunately,thefishinessoffishpastits
primecanbegreatlyreducedacoupleof
simpletreatments.TMAonthesurfacecanbe
rinsedoffwithtapwater.Andacidic
ingredients—lemonjuice,vinegar,tomatoes
—helpintwoways.Theyencouragethestale
fragmentstoreactwithwaterandbecomeless
volatile;andtheycontributeahydrogenionto
TMAandDMA,whichtherebytakeona
positiveelectricalcharge,bondwithwater
