s reason green tea
especially should be infused for a very short time and never boiled.
Tannin in foods in large amounts may interfere with the normal digestion
of the protein compounds, because it coagulates the albumin and peptones
after they have become soluble, and thus makes additional work for the
digestive organs.

215. Judging Teas.--Teas are judged according to: (1) the tea as it
appears prepared for market, (2) the infusion, and (3) the out-turn
after infusion. The color should be uniform; if a black tea, it should
be grayish black, not a dead black. The leaves should be uniform in size
or grade. The quality and grade are dependent upon flavor, and, with the
strength of the infusion, are determined by tasting. This work is
rapidly done by the trained tea taster. The out-turn should be of one
color; no bright green leaves should be present; evenness of make is
judged by the out-turn. The flavor of a tea is largely a matter of
personal judgment, but from a physiological point of view black teas are
given the preference.

216. Adulteration of Tea.--A few years ago tea was quite extensively
adulterated, but the strict regulation of the government regarding
imported tea has greatly lessened adulteration. The most common form
was the use of spent leaves, _i.e._ leaves which had been infused.
Leaves of the willow and other plants which resemble tea were also used,
as well as large quantities of tea stems. Facing or coloring is also an
adulteration, since it is done to give poor or damaged tea a brighter
appearance. "Facing consists in treating leaves damaged in manufacture
or which from age are inferior, with a mixture containing Prussian blue,
turmeric, indigo, or plumbago to impart color or gloss, and with a
fraudulent intent. There is no evidence that the facing agents are
deleterious to health in the small quantities used, but as they are used
for purposes of deception, they should be discouraged."[73] Facing and
the addition of stems are the chief adulterations practiced at present.

217. Food Value and Physiological Properties of Tea.--Tea infusion
does not contain sufficient nutrients to entitle it to be classed as a
food. It is with some persons a stimulant. The caffein or theine in tea
is an alkaloid that has characteristic physiological properties. In
doses of from three to five grains, according to the United States
Dispensatory, "it produces peculiar wakefulness." Larger doses produce
intense physical