The meat should be allowed to cook for at least 4 hours, but longer if
possible. If, during this long cooking, too much water evaporates, more
should be added to dilute the stock. The salt that is required for
seasoning may be added just a few minutes before the stock is removed
from the kettle. However, it is better to add the salt, together with
the other seasonings, after the stock has been drawn off, for salt, like
heat, has a tendency to harden the tissues of meat and to prevent the
flavor from being readily extracted.

25. Although, as has been explained, flavor is drawn from the fibers of
meat by boiling it slowly for a long time, the cooking of meat for soup
does not extract the nourishment from it to any extent. In reality, the
meat itself largely retains its original nutritive value after it has
been cooked for soup, although a small quantity of protein is drawn out
and much of the fat is removed. This meat should never be wasted;
rather, it should be used carefully with materials that will take the
place of the flavor that has been cooked from it.

26. FLAVORING STOCK.--It is the flavoring of stock that indicates real
skill in soup making, so this is an extremely important part of the
work. In fact, the large number of ingredients found in soup recipes
are, as a rule, the various flavorings, which give the distinctive
flavor and individuality to a soup. However, the housewife whose larder
will not produce all of the many things that may be called for in a
recipe should not feel that she must forego making a particular kind of
soup. Very often certain spices or certain flavoring materials may be
omitted without any appreciable difference, or something that is on hand
may be substituted for an ingredient that is lacking.