Alcohol production is the consumption of sugars by yeast. Tobacco fermentation has to do with nicotine reduction. Found this on victoryseeds.com.
After fresh tobacco has been harvested and cured (by air, flue or fire curing), it must be further processed in order to make it a premium product. This applies to the leaf used for all parts of a cigar - filler, binder, and wrapper.
The process is known as fermentation and must be carefully monitored at all times. Essentially, the bales of cured (and dried) leaf are received, moistened, and laid up into large piles called "bulks." The centers of the bulks generate heat and are monitored so that they are not allowed to exceed 115 to 130 degrees F.
The leaves in the bulk are rotated out from center to outside and the heat allowed to build up again. This process is repeated, as necessary, from four to eight cycles until the generation of heat levels off. Each cycle or rotation is know as a "sweat." The "sweating" or fermentation process releases nitrogen and other chemical compounds. It also reduces the nicotine content.
After fermentation has been completed and the leaves re-dried, the tobacco is again restacked into bales or barrels and allowed to age. This aging process helps to enhance the flavors and the burning qualities. It is this step that sets aside premium, high quality cigar manufacturers, an hence their cigars, from the inferior ones.
Common signs that the tobacco leaf has not been fully fermented and aged include:
harshness, bitterness, or a metallic taste on the tongue, lips and in the mouth.
a feeling something like heartburn in the chest cavity.
the cigar keeps going out easily.
One last point, once a cigar is made, the tobacco in it can no longer be fermented. A cigar must be maintained and under the proper storage conditions, may mellow and improve with age. That said, if unfermented or un-aged tobacco is used in the making of a cigar, no amount of time will improve its characteristics.