DEPARTMENT OF AGRICULTURE 57

 CURING FLUE-CURED TOBACCO
 Flue-cured tobacco derives its name from the manner in
which it is cured. The employment of the flues, or pipes, to
transport or circulate the heat within the barn gave rise to
the name flue-cured tobacco.
 The old wood furnace and flue method of curing is gradu-
ally being replaced by other methods of curing-fuel oil and
gas heaters are now being used more frequently for curing
tobacco. The old clay mortared pole barn, figure 40, has been
replaced by sawed boards and concrete block. Adequate ventila-
tion is necessary regardless of barn construction. This is very
important because a green or fresh leaf of tobacco will contain
over 80 per cent by weight of moisture, most of which is
removed during the curing process.
 Most of the billion pounds of flue-cured tobacco that is
cured each year is cured by the empirical process, which
briefly defined is without due regard to science. Therefore, it
is easy to see why exact or pre-determined schedules cannot
be employed in curing tobacco.
 The degree of tobacco ripeness or maturity may be influenced
greatly by environmental and cultural practices and for this
reason wide leaf quality differences are exhibited at harvest
time and these factors have to be considered by the curing
operator.
 Curing tobacco, with regulated heat, is a very important
phase of the production process, because in the curing process
one is attempting to develop the best expression of all the
important factors which were employed in the production of
the plant. There are definite reasons why curing tobacco is
broken down in several stages, for each stage brings about
additional chemical changes in the leaf.
 The removal of moisture is done by a gradual process
beginning with the yellowing stage when the temperature may
vary from 900 to 120 F. It is during this stage that approxi-
mately 25 to 30 per cent of the water is removed. It may take
30 to 48 hours during this stage.
 For leaf drying, 1350 to 1450 several additional hours will
 be required. When the leaf drying stage is completed a total
 of 65 to 70 per cent of the water is removed. During this