OK ... filling in for Slim, here's a bit of copy and paste re: Maduro tobacco
Maduro tobacco begins its journey the same as other tobacco, in the harvest fields. After weeks of growth, workers harvest certain tobacco leaves, otherwise known as priming. These leaves are bundled according to size and texture and hung in curing barns for anywhere from 3 – 8 weeks. This whole process from seedling planting to total priming, takes some 4 months time, with workers involved In a high labor practice of checking each plant one by one at least 1 – 2 times a day. As these leaves are hung in curing barns, their leaf color changes from green to brown. After curing, they are separated and grouped once again, whereby they stack them together in large bundles about 3 feet high, to begin the fascinating process known as fermentation. This is the time when leaves are transformed from mere vegetation, to your favorite smokes. These large stacks of fermenting tobacco emit tremendous heat, upwards to 120 degrees, having to be monitored frequently over a period of 1 – 3 months. It is at this point , were maduro tobacco is altered, by manipulating the fermentation temperature to even higher levels, for much longer periods of time. Maduro leaves, may take as long as 6 months to reach their peek shades of dark color.