86 CIRCULAR 249, U. S. DEPARTMENT OF AGRICULTURE 
CURING 
A. During the initial stages of curing the leaf remains alive but 
undergoes a slow process of starvation. At first the leaf is rich in 
starch. The starch is converted into sugar, some of which is respired 
during this and succeeding stages, in the forms of carbon dioxide and 
water. Green chlorophyll disappears, leaving the leaf yellow or 
greenish yellow. Changes occur in the nitrogenous compounds 
present. 
B. The leaf dies. The consumption of starch and sugar is checked. 
Products of the changes in nitrogenous compounds which occurred 
while the leaf remained alive are further broken down. Ammonia is 
formed and there is a considerable loss of nicotine. The color changes 
to brown as a result of oxidation processes. Throughout the curing 
the leaf undergoes gradual drying, finally losing most of its water, 
and there is also a considerable loss of dry matter. After the curing 
is complete and the tobacco has come into order the leaf is tied in 
bundles and transferred to specially constructed buildings for fermen- 
tation. At this time the tobacco is raw, rather bitter, lacking in 
aroma, and relatively high in nicotine. 
FERMENTATION 
The changes that occur during fermentation are complex and not 
fully understood. It is known, however, that there is a further loss 
of nicotine—10 to 15 percent in shade-grown, as much as a third in 
cigar filler. The nicotine lost by volatilization is that portion of the 
total nicotine content which is in a relatively free state (7, &, 9, 10). 
Volatilization as well as decomposition of nicotine takes place through- 
out the curing, fermentation, and aging of tobacco, but most rapidly 
during those stages of fermentation when the temperature in the 
bulk or bale is highest. The reduction of nicotine has an important 
relationship to the smoking quality of the tobacco, that is, its freedom 
from pungent, biting, unpleasant taste and aroma. 
Other changes occur during fermentation, including further loss in 
weight, and some changes in color. Tobacco tinged with green 
usually loses its greenish cast; colors tend to darken and to become 
more uniform. ‘The texture of the tobacco changes. In the case of 
shade-grown wrapper tobacco discussed above, the leaves become 
more pliable and elastic—necessary attributes for wrapper purposes. 
Tobaccos that are by nature gummy previous to packing, of which 
the fire-cured types are the extreme examples, lose most of their 
gumminess. Sometimes the physical changes are adverse, as when 
the tobacco has been packed in too high order and has fermented too 
much or sweated too hard. Then the tobacco is apt to be harsh and 
rough to the touch, or in extreme cases to show evidence of mold, 
must, or rot. 
SUMMARY OF Losses IN WEIGHT 
From the foregoing discussion it is clear that losses in weight occur 
from the time tobacco has been cured until it is exported or is used in 
manufacturing processes; that these losses are attributable to several 
different factors; and that they vary in extent for different types of 
tobacco. Tables 23 and 24, excerpted from an earlier circular on the 
subject (22), summarize the losses in weight of different types of 
tobacco. 
