How Tobacco Drying Works
When drying tobacco, various factors must be taken into account, including a slow drying process. But why exactly? Learn more about drying methods and related aspects.
From the Field to the Drying House
Right after harvesting the tobacco leaves from the field, the green leaves are taken to so-called drying houses or drying barns. They are transported in baskets or wheelbarrows to prevent damage to the leaves.
The leaves are then threaded in pairs or in slightly larger bunches onto strings and hung from poles. A specific type of twine, known as tobacco twine, is used for this purpose. This is a relatively strong three-ply flax twine, as most other cellulose-based strings are unsuitable; they can rot and eventually break due to prolonged moisture at the threading points. Plastic strings are also not recommended, as they tend to cut into the leaf midrib over time.
Each string holds between 30 and 50 leaves. There must be enough space between the leaves to allow air to circulate, preventing mold from forming where the leaves touch. Depending on the intended use, whether wrapper or binder, they may be hung in greater numbers or, for high-quality leaves, even individually.
Curado – The Drying Process
The drying of the leaves is referred to as "curado" in Spanish. This word translates to "mature," "ripened," or even "cured" in English. In this case, "cured" best describes the process as it applies to tobacco leaves.
The drying process (curado) is a dehydrogenation process – essentially, the drying of leaves while involving certain chemical processes within the leaves themselves.
Why Should Tobacco Be Dried Slowly?
These chemical reactions within the leaves are more intensive than those in later fermentation.
Cellular life within the leaves must be maintained for a certain period after harvest to allow residual cellular respiration to trigger advantageous chemical and biological transformations.
Most conversion processes occur during the wilting phase in the first week after hanging. During this phase, natural plant compounds start to break down stored nutrients such as proteins, sugars, and starches, as well as leaf pigments. At this time, the tobacco must dry slowly to allow these breakdown processes to occur in the living leaves.
If, however, the cellular life within the leaves is maintained for too long after harvest, the existing nutrients would be depleted too quickly, leading to excessive chemical transformation processes. This would result in a loss of leaf substance and significantly reduce flavor quality.
Thus, the drying process cannot be completed within hours or a few days; it requires up to six weeks. During this period, temperature and humidity must be strictly controlled.
Freshly harvested tobacco leaves contain 80 to 90 percent water, with the rest being the solid matter of the leaves. After a week, the leaves lose approximately half of their weight through water evaporation. By the end of the drying process, the water-to-solid matter ratio is reversed, with 15 to 25 percent water and 75 to 85 percent solid matter.
Drying Methods
There are different methods for drying tobacco:
- Natural Methods: Air-Curing and Sun-Curing
- Artificial Methods: Flue-Curing and Fire-Curing
One unique method is known as Kalfrisa. This drying method was developed in Cuba as an alternative to air-curing.
Unlike traditional air-curing, drying barns are sealed airtight. Inside, specially designed climate channels control humidity and temperature. This hermetic sealing allows for a higher internal temperature of up to 34 degrees Celsius. The advantage of this method is that it reduces the drying time to 25 days instead of the usual 45 to 60 days. Traditionalists among tobacco growers view this method with skepticism, believing that quality tobacco requires time.
Tobacco Drying Barns or Curing Sheds
In tobacco drying barns or curing sheds, tobacco is dried using the air-curing method. These buildings have windows or other ventilation openings to allow dry air to be regulated within the barn. These ventilation openings also allow sunlight to enter, contributing to the browning of the leaves. Simple functionality and an unusual interior structure characterize these tobacco barns.
These buildings still exist in Germany today, such as in Hamburg's Speicherstadt and, notably, in the southern Palatinate. However, they no longer serve their original purpose; some are under heritage protection and repurposed by local communities.
