ground coffee with
water results in a large loss of aromatic principles by steam
distillation, a partial hydrolysis of insoluble portions of the grounds,
and a subsequent extraction of the products thus formed, which give a
bitter flavor to the beverage. Also, the maintenance of a high
temperature by the direct application of heat has a deleterious effect
upon the substances in solution. This is also true in the case of the
pumping percolator, and any other device wherein the solution is caused
to pass directly into steam at the point where heat is applied. Warm and
cold water extract about the same amount of material from coffee; but
with different rates of speed, an increase in temperature decreasing the
time necessary to effect the desired result.

It is a well known fact that re-warming a coffee brew has an undesirable
effect upon it. This is very probably due to the precipitation of some
of the water-soluble proteins when the solution cools, and their
subsequent decomposition when heat is applied directly to them in
reheating the solution. The absorption of air by the solution upon
cooling, with attendant oxidation, which is accentuated by the
application of heat in re-warming, must also be considered. It is
likewise probable that when an extract of coffee cools upon standing,
some of the aromatic principles separate out and are lost by
volatilization.

The method of extracting coffee which gives the most satisfaction is
practised by using a grind just coarse enough to retain the
individualistic flavoring components, retaining the ground coffee in a
fine cloth bag, as in the urn system, or on a filter paper, as in the
Tricolator, and pouring water at boiling temperature over the coffee.
During the extraction, a top should be kept on the device to minimize
volatilization, and the temperature of the extract should be maintained
constant at about 200 deg. F. after being made. Whether a repouring is
necessary or not is dependent upon the speed with which the water passes
through the coffee, which in turn is controlled by the fineness of the
grind and of the filtering medium.

_The Water Extract_

Although many analyses of the whole coffee bean are available, but
little work has been reported upon the aqueous extracts. The total water
extract of roasted coffee varies from 20 to 31 percent in different
kinds of coffee. The following analysis of the extract from a Santos
coffee may be taken as a fair average examp