(2) The completion of the “yellowing” process and the fixing of the desired color.
(3) The preservation of the juices, etc., which give the characteristic flavor and aroma.
(4) To give the necessary toughness and suppleness to the leaf.
The first part of the curing is done by the grower in curing sheds on the farm immediately after the cutting of the crop; the final part, or the fermentation part is usually done by the leaf dealer or manufacturer in special buildings called leaf-houses.
There are three methods of curing in use by the growers, i. e., sun curing, air curing, and artificial heat curing. In the case of the tobacco known as Perique the curing process is more or less peculiar to itself. “Sun” and “air” curing are much slower processes than the curing by artificial heat.
All cigar leaf tobacco is sun-cured, and as a general rule pipe smoking and chewing tobacco are cured by artificial heat.
For the purpose of drying and curing by artificial heat, the leaf is hung up in specially constructed curing houses or sheds. It is found that after the exposure to the sun for the first process of “yellowing” tobacco leaf still contains 1 lb. of water approximately in each plant. The first part of the process of curing consists in drawing off this superfluous moisture. Dry heat is applied at a temperature of 90° F. to 120° F. for about 16 to 30 hours to effect this. A further exposure of about 48 hours at a temperature of 125° or so is necessary to complete the curing, and fix the color.
The stems and stalks being thicker take a longer time and generally require 9 to 10 hours further exposure and a temperature which may range as high as 175° F. before they are fully cured, the temperature being graded hourly until the maximum necessary is reached.
The process of curing varies considerably in different states. Some growers prefer to put the tobacco into the sheds immediately after cutting, and allow very little exposure in the fields. The temperature is usually kept steady at about 90° F. Again the process is different according to the quality of tobacco required. For the heavy type of leaf which is intended for the export trade, the curing in the sheds is done by an open fire, the fuel being usually hardwood logs. The smoky, creosotic flavor is absorbed by the leaf, and, although this flavor is not relished by the smokers of the U. S., it is much liked in Europe. The curing in such cases may last for 4 or even 5 days. The tobacco is suspended on poles by the stalks and the fires are built on the floor immediately under them so that the carbonaceous products are easily absorbed by the open pores of the leaf.
The chewing and pipe smoking tobacco, as well as cigarette tobaccos including all the bright yellow tobaccos used in the U. S. are usually cured by Flue curing. In this case the heat comes from pipes which run around the curing houses and are fed from a furnace in an adjoining chamber or in a cellar. The temperature can be easily regulated. “Flue” curing is generally completed in about 4 days. “Flue” curing does not clog up the pores of the leaf which therefore remain more absorbent than in the open fire cured tobacco. This is an important matter for the manufacturers because the flue cured leaf will absorb twice as much of the flavoring sauces (which are added to certain kinds of tobacco) than tobacco leaf cured by open fires.