On Food and Cooking

Tomato Enzymes and Consistency The final
consistency of a tomato puree depends not
just on how much water has been removed,
but also on how long the puree spends at
either moderate or high temperatures. Ripe
tomatoes have very active enzymes whose job
is to break down pectin and cellulose
molecules in the fruit cell walls, and so give
the fruit its soft, fragile texture. When the
tomatoes are firstcrushed, the enzymes and
their target molecules are thoroughly mixed
together, and the enzymes start breaking down
the cell-wall structures. If the raw puree is
held at room temperature for a while, or
heated to a temperature below the
denaturation temperature of the pectin
enzymes, around 180ºF/80ºC, then the
enzymes will break down a lot of the cell-wall
reinforcements, and these liberated molecules
will give a noticeably thicker consistency to
the puree.
However, when the puree is then heated to