Drying of tobacco leaves

Curado: What Happens During the Drying of Tobacco Leaves?

After tobacco leaves are harvested, the green leaves go through the natural process of curado, a desiccation process during which internal chemical changes occur.

During the first part of the procedure, the leaves undergo the ensarte: following certain norms, they are sewn together through their stems and are hung on wooden poles [Span.: cujes] With strict temperature and humidity control, the yellowing of the leaves maintains residual cellular respiration. No longer attached to the plant’s stem, the leaves draw on their reserves, which causes beneficial chemical and biological changes. The changing of color from green to yellow is a result of hydrolysis, oxidization of the chlorophyll pigment, and the emergence of other pigments such as carotenoids.

Over four to six days, the yellowing process leads to the substantial loss of solid matter and a moderate loss of water in the leaves. Later, during the drying of the tissues, no more respiration or evapotranspiration occurs and the biochemical transformation of the cells becomes negligible. Thus, there is a reduction in solid matter loss and the loss of water is accelerated – usually lasting for 20 to 25 days depending on the ambient conditions and priming.

Photo: Simon Lundh

The oxidation of polyphenol produces the typical color changes from yellowish to brownish. Emerging avonoid pigments also complement the colors given by the carotenoids, causing the leaves to turn to a darker shade of brown. Progressing from the leaf edge to the veins, the yellowing has a characteristic view – the leaf tissue is yellowish and the veins remain green.

When needed, the humidity and temperature in the casa del tabaco are controlled by sprinkling water and/or burning charcoal on the floor. Having open doors and windows can regulate ventilation in these wooden barns.

The ultimate coloring of the tissue is attained during the drying of the center veins – the circulatory organs of the plants – which are sturdier than the tissue and thus still contain water. These aqueous residues must be eliminated to complete the drying process. The curado is only terminated when the center vein breaks with a dry cracking noise when the leaf is folded in half. Respiration and hydrolysis lead to the chemical transformation of often complex and irritant substances into simpler molecules in the leaves. Proteins and mainly carbohydrates transform into simple sugars, amino acids, ammonia, carbonic dioxide, water, etc.

In fresh leaves, around 85% of the weight is water and 15% is solid matter. After drying, these proportions are almost exactly inversed. The positions of the cujes are adjusted to encourage air circulation and to evacuate the humidity given off by the leaves.

Finally, during the zafado the leaves of each cuje are detached and then re-attached by their stems with the same linking thread. Two groups of 40 to 60 leaves are formed with the leaves of one single drying cuje. A well-executed drying process ensures good chemical composition and physical properties in the leaves to optimally start the subsequent processes of cigar making: fermentation and classification. The curado is therefore a delicate and crucial stage in cigar production.

This article was published in the Cigar Journal Autumn Edition 2016. Read more


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