Dried out cigars/ cigar tobacco

[Ben Brand]

I hear a lot of stories about dried out cigars that's lost its oils etc and can be binned. Looking at my tobacco hanging in my shed, all dried out and ready for fermentation (after its been rehydrated ) and there are a few pipe tobacco farmers in S.A. that's doing the same thing with their tobaccos.
Now I was thinking, my tobacco is dry, realy dry, here in S.A. at the moment there is 0% humidity, what's happening to those oils. How does the rest of the world dry their tobacco? Are the rest of the world's tobacco less dry than ours, and if not, where does the oils go to?

 

[deluxestogie]

Here's my understanding of the evaporative loss of oils from tobacco leaf.

Evaporation of any volatile (water or oil) is a play between the vapor pressure of the volatile at the evaporative surface (e.g. the surface of a tobacco leaf) and the concentration of that specific volatile already in the ambient air.

Water loss from the leaf is highly dependent on relative humidity. That is, the rate of evaporation from the leaf surface relates to the vapor pressure of water in the leaf, compared to the concentration of water molecules already in the air. At identical air temperatures, the weather pattern dictates how much water is already in the air. If the weather gives you very dry air, then water evaporation will increase from the leaf.

Volatile oils pass from the leaf surface into the air (which contains nearly no oil molecules). Weather patterns have virtually no impact on the concentration of oils in the air. The sole determinant of surface oil evaporation (in an open environment) is the temperature. So the oils in tobacco leaf will evaporate at a rate that is independent of the relative humidity (which is only a statement of water content). Here, I'm talking about tobacco leaf, or a cigar, exposed to the open air--the warmer the environment, the greater the rate of evaporative loss of volatile oils. On the other hand, a cigar, say, in a closed container, will evaporate less oil, since its ambient air will have a measurable concentration of trapped oil molecules.

CONCLUSION: Evaporative loss of oils from tobacco hanging in a shed at a given temperature will be the same, whether the relative humidity is high or low.

Bob

 

[MarcL]

That was nice Bob. Don't we have to burn oil to vaporize it?

 

[deluxestogie]

With oils and most other hydrocarbons, the higher the molecular weight, the lower the vapor pressure. [Increased vapor pressure indicates a greater likelihood of evaporation.] This is complicated by the extent and complexity of molecular branching, as well as by other attached components. But, in general, the lightest hydrocarbons are a gas at room temperature (and pressure), with various oils being liquid at room temp, but increasingly evaporating as the temp rises. The really big hydrocarbon molecules (waxes) are solid at room temp. If you can smell an oil, then some of it is evaporating.

To add another bit of confusion, some of what we conveniently call "oils" in tobacco consists of alcohols, aldehydes and aromatic (ringed like benzene) components. But the basic idea is the same. Their evaporation is temp dependent, rather than dependent on the water content (relative humidity) of the ambient air.

Bob