After curing in the barn, tobacco is still too raw to smoke. Fermentation turns it into usable cigar leaf. Bundles of tobacco leaves, called hands, are stacked into piles called pilones. Moisture, pressure, and natural chemical changes in the leaf make the pile heat up. Workers turn the pile so the inside does not overheat and the outside ferments as well. Ammonia and other harsh compounds escape, and the leaf becomes darker and sweeter.
Ligero is fermented at higher temperatures and for longer than volado. Maduro wrappers often go through more fermentation, or an extra heating stage, than a natural wrapper. This step is essential: without it, the cigar tastes raw and green.
Fermentation happens at the factory. Aging cigars in your own humidor is a smaller, slower process. See how cigars are made.