Approachable Tobacco Leaf Science

[deluxestogie]

Leffingwell has made available on-line, for free, an interesting book chapter that discusses tobacco leaf chemistry, and its changes during curing and aging.

To gain the most from this article, you need some background in chemistry. However, sprinkled throughout this 20 page document are easily understood graphs and tables, as well as very clear, simple statements, such as:
"The major Amadori compounds present tend to
show a gradual increase peaking at about 2 years and
then a decrease. During the same period, the amino
acid content of the tobaccos shows decreasing values
each year. Of course, it is also known that the flavor of
Virginia tobacco improves with aging, it rarely being
used for cigarettes prior to 12 to 14 months aging, and
preferably 18 to 24 months, which interestingly corresponds
quite well to these graphs. Amadori compounds
are also known to generate a number of
flavorful pyrazines and pyrroles on pyrolysis."
[emphasis mine]

Chapter 8
leaf Chemistry
Basic Chemical Constituents of Tobacco Leaf and Differences among Tobacco Types
J.C. Leffingwell, Leffingwell and Associates, Canton, Georgia, USA
http://www.leffingwell.com/download/Leffingwell - Tobacco production chemistry and technology.pdf

Some other graph highlights. You don't even need to know what they're talking about, but can just look at the time scale of the changes. They should be vaguely familiar.

Of course, the graphs on aging do not consider the changes from one month of kilning.

Bob

 

[Chris A]

Oh my God I had a college flashback there. Cold sweats & all. I was told there would be no tests when I signed up....

 

[leverhead]

Bob, that's a great find! After just reading the first couple of pages, there's something here for everybody. It's a right click and save for me, thank you.

 

[deluxestogie]

The key information in that book chapter is:

• there are good things that increase with time (to a peak)
• there are bad things that decrease with time (to a plateau)
• there are significant chemical differences in different classes of tobacco
• don't smoke-up your home flue-cured leaf before it has a chance to age--it will get better and better (but you already knew that)

If you are curing and finishing your own tobacco (regardless of class), the time graphs can clarify the duration of the processes.

Bob

 

[Gdaddy]

I read that a while ago and became very interested in this...



"the pH of smoke plays an exceedingly important role on the sensory impression imparted."

"Accordingly, the increased alkalinity of straight air-cured cigarettes renders them virtually unacceptable to nearly all smokers as the high smoke pH imparts an alkaloid harshness with a flavor distortion which can be unpleasant."


"Conversely, many American blend cigarette smokers find the 'acidic' smoke of straight Virginia cigarettes to be unbalanced"

 

[deluxestogie]

I would read "nearly all smokers" to mean nearly all regular purchasers of commercial cigarettes. There is also the confusion of terms. By "straight air-cured cigarettes," do they mean cigarettes of "air-cured" varieties, or air-cured leaf from flue-cure varieties? That would make a big difference. Flue-cure varieties seem to maintain a lower pH (more acidic) than air-cure varieties, even when both have been entirely air-cured and kilned (or aged).

Bob

 

[Bex]

You don't even need to know what they're talking about,

Thank goodness you put that caveat in there. I've downloaded it as well, and will study it. The further I get into this plant and process, the more I wonder....has there ever been so much study and investigation done on any other plant ever? I find it doubtful, and am constantly amazed at the amount of scientific analysis that has gone into this....all so that modern politicians can attempt to instill the idea that this is now socially unacceptable behavior. Thanks for the link (and yes, for the university flashback, as well....)

 

[Bex]

I took an Evelyn Woods speed reading class when I was in school (not really), and have just finished (trying to) trawl through this. Ah, I am happy to learn that there are actually plant sterols in tobacco. I can now stop drinking Benecol and taking my cholesterol medicine, and just smoke more. Cool......
It's good to know that the tobacco will improve over time - he specifies that it should be stored at about 12% humidity, as well.....And, funnily enough, also admits that there has been no other plant on earth that has been the subject of such intensive research.

 

[DonH]

I would read "nearly all smokers" to mean nearly all regular purchasers of commercial cigarettes. There is also the confusion of terms. By "straight air-cured cigarettes," do they mean cigarettes of "air-cured" varieties, or air-cured leaf from flue-cure varieties? That would make a big difference. Flue-cure varieties seem to maintain a lower pH (more acidic) than air-cure varieties, even when both have been entirely air-cured and kilned (or aged).

Bob

I'm pretty sure by air cured they mean Burley, Dark Air, etc., not flue cured varieties that were air cured. I know for a fact that most smokers I've done research on (by having them try my cigarettes) really like air cured flue cured types blended in the right proportion with true air cured types. Air cured flue cured varieties definitely are lower pH than Burleys.

 

[leverhead]

...he specifies that it should be stored at about 12% humidity...

I'm just picking nits..... It's 12% moisture content, if the RH was 12%, it would age very slowly.

 

[DGBAMA]

I'm just picking nits..... It's 12% moisture content, if the RH was 12%, it would age very slowly.

A small but good point, rh and leaf moisture content are two VERY different things.

 

[Bex]

I'm just picking nits..... It's 12% moisture content, if the RH was 12%, it would age very slowly.

Ah, thanks for pointing that out - of course, this now opens the door for the next question - how do you measure the moisture content of the leaf??

 

[leverhead]

Ah, thanks for pointing that out - of course, this now opens the door for the next question - how do you measure the moisture content of the leaf??

That's a good question! There are meters to check it, but I've never used one. I haven't really researched it, but I'm under the impression that they are neither cheap or very handy. I've tried the old fashioned way of weighing before and after heating with a desiccant, it's time consuming.

 

[DGBAMA]

Found a chart for Tea Leaves, temp vs rh vs moisture content. I imagine baccy would be similar.

 

[deluxestogie]

I would not count on tobacco behaving like tea leaves. Even from one tobacco variety to the next, the hygroscopic character varies. I've seen bags of the same priming of the same variety, kilned for the same duration, in which some leaves remain moist, while others dry--even when allowed to equilibrate for a couple of weeks.

Also, while %moisture content is a weight measurement comparison, %RH is a relative air saturation measurement that is dependent on temperature. All very messy.

Bob

 

[Bex]

I have just learned to click on the 'settings' menu, to show me what threads I've asked questions on....lucky y'all...Of course, I don't get the above chart at all - tea leaves at all those different temps having the same moisture content and ERH (which I assume means estimated RH). Thank goodness we are told that maybe this wouldn't work. I'm getting an unsightly frown line in between my eyebrows from concentrating on all this information and trying to understand it all.
So, I googled this - you can apparently do this with some dielectric something or other, or spend $500 on this

:
http://www.globalw.com/products/lw100.html#Options

 

[Alhefner]

Ah, thanks for pointing that out - of course, this now opens the door for the next question - how do you measure the moisture content of the leaf??

For $14, you can get a meter that's "good enough for government work" that will keep you in the ballpark. there are better ones out there for a few dollars more.

http://www.harborfreight.com/catalogsearch/result?q=moisture+meter

 

[Jitterbugdude]

Ebay is loaded with them too. I bought one a year ago, came via China. I think I paid $14.00 for it. It works well, no complaints.