Changes in flue cured tobacco as it ages.

[Jitterbugdude]

From a document by Philip Morris titled: "Fermentation and Aging of Cured and Re-Dried Tobacco Leaves", 25 May 1977

I do not have an active link to this document so I will quote a small part of it as it relates to the changes that take place in flue cured tobacco as it ages.


"Aging
The aging of tobacco is comparatively a much milder process than fermentation, although fermented tobacco leaf may continue to "age". The first aging step for cured cigarette tobacco leaves is to subject them to a re-drying process. During aging little self heating takes place. Small amounts of carbon dioxide, acetic acid, formic acid and ammonia are evolved during aging. A chemical study covering a 30 month period of an aging process of several groups of constituents shows there was an increase in moisture and a decrease in sugar, total nitrogen, water soluble nitrogen, amino nitrogen, nicotine, total acids and pH. It is believed that the aging of FLUE CURED tobacco is essentially a chemical process; the main reaction being between sugars and amino compounds with the formation of melanoidins and carbon dioxide"

So this would explain why so many of you have commented on their flu cured tasting better after it ages. I don't smoke flue cured but I always had thought that the high heat of the process stopped the aging process dead in its tracks. Evidently not.

Randy B

 

[leverhead]

Try this,

http://legacy.library.ucsf.edu/tid/bfq38e00

I'll have to read this tonight.

 

[rustycase]

Tnx LH!
I'll review that pdf, also!
Best
rc

 

[deluxestogie]

Randy,
I believe there are two factors that determine the aging of flue-cured tobacco. (In addition, I'll state again that I believe that "fermentation" of tobacco, in the commonly used sense, is entirely a chemical reaction, and does not involve microbes. This is in disagreement with the mythology of tobacco fermentation.)

1. All of the chemical changes that occur in tobacco with time--in the presence of sufficient moisture to facilitate the reaction--will progress with or without the presence of active enzymes. As many of you know, enzymes are defined as biologically created catalysts. Catalysts accelerate a reaction that would otherwise occur even without a catalyst. So the chemical oxidations that occur in aging tobacco leaf can occur without enzymes, but at a much slower rate than in the presence of active enzymes.
2. There are both an oxidase enzyme and a peroxidase enzyme that accelerate the aging processes. The oxidase is far more active than the peroxidase, though both seem to lead to the same chemical endpoint. Some flue-cure regimens take the max temp up to 165ºF. This denatures (destroys) the more active oxidase enzyme (denatures at ~149ºF), while preserving the less active peroxidase enzyme (denatures at ~191ºF). So we would expect leaf that is flue-cured to a "kill" temp of 165ºF to further age at a pace that is more rapid than leaf "killed" at the more radical 200ºF+, a temp which also denatures the peroxidase enzyme. With either flue-cure regimen, the possible oxidation reactions of the leaf constituents will still continue, but at a significantly slower pace.

Bob

 

[BigBonner]

There is one thing to consider about after the flue cure at 165 degrees . The fact of desteming and redrying . The temperatures may be alot higher in the redrying tunnel than the 165 degrees .

Tobacco is destemed and boxed in c-48 cartons at 14% moisture .The c-48 cartons are 48" X 32" X 32" and are pressed to hold 441 LBS of destemed tobacco .Some of the c-48 cartons use plastic liners and some don't .

 

[Jitterbugdude]

(In addition, I'll state again that I believe that "fermentation" of tobacco, in the commonly used sense, is entirely a chemical reaction, and does not involve microbes. This is in disagreement with the mythology of tobacco fermentation.)

Bob, How would this explain the massive population growth of microbes such as bacillus subtilis (sic) and others that occur when tobacco is fermented? Typically the bacteria will increase and the molds and fungi will decrease. Note: I'm not talking about flue cured but air cured cigar leaf.

Randy B

 

[skychaser]

Wow. What an interesting and useful bacterium. If you don't know anything about it, this is worth the read.

http://en.wikipedia.org/wiki/Bacillus_subtilis

snip....
B. subtilis can divide symmetrically to make two daughter cells (binary fission), or asymmetrically, producing a single endospore that can remain viable for decades and is resistant to unfavourable environmental conditions such as drought, salinity, extreme pH, radiation and solvents. The endospore is formed at times of nutritional stress, allowing the organism to persist in the environment until conditions become favourable. .....

Perhaps this bacterium can survive the high temperatures of flu curing and re-drying. ??

 

[deluxestogie]

Bacillus subtilis is ubiquitous, and likely present on most tobacco leaf that is brought into the shed. The presence, and even the proliferation of ubiquitous bacteria only on the surface of the leaf, which I believe is the case with B. subtilis, does not suggest that the bacterium participates in any way in the biochemical reactions within the intact laminar cells. (With the pressure-disrupted cells of Perique processing, it's a different story.)

When B. subtilis is sprayed onto living leaf, blossoms, vegetables and fruit, it appears to scavenge the nutrients available on the surface, but is unable to invade the cells. So, Serenade (a suspension of living B. subtilis) requires re-spraying on a weekly schedule, since the bacteria quickly exhaust the surface nutrients, and die off.

I don't really have all the answers on tobacco-bacteria interactions during curing, "fermenting" and aging. But I simply have not seen convincing evidence that would support the definition of a fermentative process that is akin to that of yogurt or cheese or wine or fermented pickles.

Larry points out another variable in the mix. It's all pretty complex. I guess what I'm suggesting is that if you intensely irradiated color-cured leaf (to kill everything), it would nonetheless age in accordance with the concentrations of active enzymes that remain within the dead laminar cells. I'm wide open to data that supports or debunks that understanding.

Bob

 

[Jitterbugdude]

I don't really have all the answers on tobacco-bacteria interactions during curing, "fermenting" and aging.

I'm right there with you on that one Bob. I find it interesting that the literature, clearly into the 1950's was still debating what caused fermentation. I need to keep reading.

Randy B

 

[leverhead]

Thank you gentlemen, this has turned out to be a very interesting thread!

Let me throw this link in

CHANGES IN BIOLOGICAL ACTIVITY DURING ARTIFICIAL FERMENTATION OF FLUE-CURED TOBACCO

http://www.tobaccoscienceonline.org/doi/abs/10.3381/0082-4623-46.1.24

The link to the full text is near the top of the page.

 

[deluxestogie]

leverhead,
Very interesting article. I'm not sure what to make of their methodology. In measuring the "enzymatic activity" of the test and control batches at various intervals, the researchers apparently made no effort to distinguish between enzymatic activity within the cells, and enzymatic activity occurring among the microbial surface contaminants outside the cells. If we make the assumption that the enzymes on the surface penetrate the cell tissue, then their conclusions may be valid. That we can make this assumption is unclear.

The curiosity of their data is that far greater numbers of these microbial contaminants are found on the [non-fermented] control group--the group with wildly active microbial growth, yet the enzymatic activity is notably lower in that group. They point out that the high fermentation temperature (~122ºF) inhibits growth of the contaminants--in fact, killing a high proportion of them, as evidenced by reduced numbers of active organisms, and a sharp increase in spore formation (a survival mechanism induced by inhospitable conditions).

So, we have dramatically falling numbers of surface microorganisms proposed as a possible explanation for the biochemical changes within the leaf tissue during kilning, while the substantially rising numbers of surface microorganisms on the control group apparently have little effect on the internal chemistry of the leaf tissue.

While I can't say that their conclusions are incorrect, I feel that they have left too many questions for their scant data to support their conclusions. To be meaningful, a method for eliminating all microbial surface contamination from a third group [We'll call it the microbe-free group.] would need to be implemented to offer a comparison of internal vs. external enzyme activity. If the leaf analysis of our proposed third group indicated significanly less biochemical change than their kilned test group, then they might make their assertions with more force.

Bob

 

[leverhead]

Bob,

I've been treating most of this stuff as teasers, good food for thought. I'm pretty sure the people doing this research are professionals, for job security reasons they would want to raise enough questions to keep themselves busy. I don't really want to bad mouth them, but their business is answers and questions.

A month or more ago I had a thought to post links to, or the material in useful groups, that I have collected. I didn't get very far, personal and business issues have gotten in the way. This thread bumped me enough to post the link, it's making an interesting thread. My understanding of some of this is very much at a layman's level, so it'll take me a while to respond.

The one thing I can say for sure that I have taken away from this is that flue-cured leaf is far from finished when the leaves are brought back into order. You don't smoke cigarettes, but you should try some of that leaf I sent you, now and in a few months. Next year I'm thinking about trying Gold Dollar to see what that does.

Steve

 

[deluxestogie]

...flue-cured leaf is far from finished when the leaves are brought back into order.

I agree. That's a valid point. Unfortunately, the research protocol in that article did not clarify the flue-cure regimen that was used on their tobacco, but instead, stated that it was "standard."

My first (failed) flue-cure attempt did yield some yellow leaf, but the process was halted before the temp was raised to 149ºF. During the following month, that leaf rapidly aged to a darker color. This darkening did not occur in the leaf from the second batch, which reached a kill of 165º. But I do expect the 165º leaf to gradually age further.

What is unclear is the extent to which flue-cured leaf would age if the kill were taken to 200ºF+ (i.e. all the leaf enzymes are toast). If such leaf changed dramatically following a month of post-flue-cure kilning, then I would have to lean more toward the microbial explanation put forward by the Chinese researchers.

This evening, I will place some of your beautiful, lemon yellow flue-cured leaf into a kiln, and see what differences I find in a month.

Bob

 

[leverhead]

Kilning might make a cool experiment, I age mine at 80-95 degrees. A bit off topic, I've been thinking lately about when I was sun-curing the Orientals what the leaf temperature might have gotten to in the morning when the sun got on them with a high moisture content from the overnight. Kind of a cyclical kilning/airing out. So many questions to try to answer. Your point a while back about UV exposure (another thread) was a good one! It's a bit beyond me, but if UV selectively denatured some enzymes similar to the 165 degree temperature point in flue-curing..... You get my drift? It's not a fully formed thought, I can't get it to lead anywhere yet.

I got my Bitlis seed a week or so ago, it is of high enough interest to me to try side by side flue-cure and sun-cure next year. I think it would be fun/interesting to compare and contrast the two cure methods. Chemical analysis is another story, I could probably get close to the PH and figure out a stab at reducing sugars. The rest, I wouldn't have a clue to cost or even where to get it done.

This is such an interesting hobby, I need to be careful how far I let drag me in.

Steve

 

[leverhead]

"What is unclear is the extent to which flue-cured leaf would age if the kill were taken to 200ºF+"

Bob,

Next year I could make a sample to fit that, I might need to be reminded. Do you know of a good lab I could talk to?

Steve

 

[deluxestogie]

Steve,
I have no lab connections.

Bob

 

[leverhead]

I might ask smokestack, he might know.

 

[deluxestogie]

leverhead's flue-curred Southern Beauty does change with subsequent kilning. In the image below, the color change after 1 month in the kiln is clear. While it still retains the unique aroma of flue-cured leaf, it is milder, smoother, and the pH (to my taste) is a bit higher.

My conclusion is that flue-cured tobacco definitely ages--based on kiln results, although the change is not as marked as would be seen with air-cured leaf.

I used one strip of the kilned flue-cured leaf as a cigar wrapper, and found it to be flavorful and interesting. I also rolled another using the kilned flue-cured leaf as wrapper, over a truly rare, intact strip of FmGrowit's Perique-processed leaf (which usually is pretty tattered when separated from the compressed mass) as binder. Since this flue-cured wrapped, Perique bound cigar did not knock me to the ground with nicotine, I assume that there's still some acidity remaining in the kilned flue-cured leaf.

Bob

 

[leverhead]

That's fascinating! I wouldn't have recognized the kilned leaf. Is that red? I'm going to have to try this and sample it each week. A new twist to an old process, doesn't happen every day. Thank you for being an adventurous soul! This has made my day!

Steve

 

[Matty]

I have noticed that the flue cured I got from WLT changes continuously as it ages. I ordered some on three seperate occasions over the year, all three times the leaf was slightly different in smell, taste, color and texrure. They all aged differently. One batch I believe lost it's acidity, another developed distinct spicy smells like potpourri and another darkened several shades and is almost not yellow anymore. All my leaf I store nearly dry just below a low case and at room temperature.