casein becomes entangled in it, and if the coagulated skin is rejected,
these food substances, in addition to the albumin, are lost. Another
change that results from boiling is in the fat globules that remain, for
these separate and exist no longer in the form of cream.

57. When milk that is not perfectly fresh is cooked with other materials
or soups, sauces, and puddings it sometimes curdles. To prevent
curdling, the milk should be heated as rapidly as possible before it is
used with the other ingredients. While the separate heating of the milk
involves a little more work, time may be gained by heating the milk
while the remaining ingredients are being prepared. The curdling of
comparatively fresh milk is often caused by the addition of salt,
especially if the salt is added when the milk is hot. However, if a
pinch of bicarbonate of soda is added to the milk before it is heated,
it will not be likely to curdle even though it is not absolutely fresh.
When tomato is to be used in soup that contains milk or cream, curdling
can be prevented if the milk or the cream to be used is thickened with
flour or corn starch or a little soda is added to the tomato before the
two are mixed. The mixing is accomplished by pouring the _tomato into
the milk_ instead of the milk into the tomato. When acid fruit juices
are to be added to milk or cream and the mixture then frozen, curdling
can be prevented by thoroughly chilling the milk or cream in the freezer
can before combining it with the juices.

58. As has already been learned, great care must be taken in the heating
of milk, because the solids that it contains adhere quickly to the
bottom of the pan and cause the milk to scorch. For this reason, milk
should never be heated directly over the flame unless the intention is
to boil it, and even if it must be boiled every precaution should be
taken to prevent it from burning. It should be remembered, too, that a