19. SUGAR, another important form of carbohydrate, is mainly of
vegetable origin, except that which is found in milk and called
_lactose_. This, together with the fat found in milk, supplies the child
with energy before it is able to digest a variety of foods. The sap of
various plants contains such large quantities of sugar that it can be
crystalized out and secured in dry form. The liquid that remains is
valuable as food, for, by boiling it down, it forms molasses. Sugar is
also present in considerable amounts in all fruits, and much of it is in
a form that can be assimilated, or taken up by the body, quickly. A
sugar very similar to this natural fruit sugar is made from the starch
of corn and is called _glucose_. Much of the carbohydrate found in
vegetables, especially young, tender vegetables, is in the form of
sugar, which, as the vegetables grow older, changes to starch.
Sugar melts upon the application of heat or, if it is in a melted
condition, as sirup or molasses, it boils down and gives off water. When
all the water has boiled away, the sugar begins to caramelize or become
brown, and develops a characteristic flavor. If the cooking is continued
too long, a dark-brown color and a bitter taste are developed. Because
the sugar in fruits and vegetables is in solution, some of it is lost
when they are boiled, unless, of course, the water in which they are
cooked is utilized.
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