glpease said:
A: There are two things of interest here, namely "casing" and "top flavouring." They are two distinctly different approaches to altering a blend's flavor. Some tobaccos employ both.
Casing requires that the tobacco be soaked in or sprayed with a "sauce" that may contain sugar, molasses, liquorice, alcohols like rum or whiskey, and various flavourings, natural or otherwise, depending on the manufacturer. Once the tobacco "drinks" the sauce, it's conditioned in large cylinders that dry it back to the desired moisture level, generally between 12% (on the dry side) and 22% (very moist). Optimal moisture for smoking depends on the smoker, but it's generally in the 13-16% range. The aromas and flavours imparted by casing will remain in the tobacco pretty tenaciously, and will affect the smoke throughout the bowl.
Top-flavouring is added by spraying the finished blend with scents and flavourings. This is usually a much lighter application, and doesn't alter the moisture content of the leaf dramatically. Sometimes called "top-notes," this can be quite ephemeral. Because of the volatile nature of many of the commonly used components, a tobacco left to "air out" may lose a lot of the perfume that's applied this way.
topping = sprayed, a light application
casing = soaked or sprayed, a heavy application
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