The Curing (Fermentation) of Tobacco.


Anyone who has read the comments on my recent post called ‘Weeds in my garden’ will have observed some discussion about ‘the curing’ of tobacco. ‘Rose’ and ‘Mummy’ kindly point out to me certain sources on the internet. I have not looked at them all as yet, but I have looked at a couple and also done a little investigating of my own.

We are by no means in a definitive position yet, but the matter of ‘curing’ is beginning to lose its opaqueness.

Where to start and how to describe? What I’ll do is quote some quotes from here and there, and, if I can remember, reference the quotes at the end. OK?

Let’s start with a simple and direct quote from British American Tobacco:

“”The harvested tobacco leaf is then cured. This is a carefully controlled process used to achieve the texture, colour and overall quality of a specific tobacco type. During the cure, leaf starch is converted into sugar, the green colour vanishes and the tobacco goes through colour changes from light yellow to orange to brown like tree leaves in autumn.

There are four common curing methods:

  • Air-cured tobacco is hung in unheated, ventilated barns to dry naturally.
  • Flue-cured tobacco is produced when heat is introduced into a barn via pipes from an exterior furnace.
  • Sun-cured tobacco leaf is strung out on racks and exposed to the sun.
  • Fire-cured tobacco is produced when brushwood is burnt under the tobacco leaf.

There are three main types of tobacco used in cigarettes:

  • Virginia is flue-cured and yellow/orange in colour – aromatic, but with a mild flavour.
  • Burley turns brown when it is air-cured and has a slightly bitter cigar-like taste.
  • Oriental is the smallest and hardiest of the three tobacco types. It is grown in hot countries and sun-cured, giving it a highly aromatic flavour.”

It is easy, when reading these things, for one’s eyes to skip important points, and so I will point them out:

  1. “…used in cigarettes”. Virginia, Burley and Oriental are the tobacco types (but there are variations within them)
  2. Virginia is flue-cured, Burley is air-cured and Oriental is sun-cured. (However, we will see later that there may be ‘traditional’ reasons for using different methods)
  3. Fire-cured is not used for cigarettes. (I believe that fire-curing has a niche following, especially in the USA)
  4. There is no mention of humidity. No mention of introducing special moisturisation into the process. Certainly, I cannot see how moisturisation plays any part in sun-curing or air-curing

By way of light relief, and a better understanding, I will point you now to a Utube video about the harvesting of tobacco leaves. It is only 5 minutes and so I would watch it now. Points to note while watching:

  • The colour of the collected leaves.
  • The careful way in which the leaves are stacked on the trailer.
  • The lock-up, permanent nature of the ‘container’ in which they are stored. Question: why are they stored on site rather than being transported immediately to the tobacco manufacturer? how long are they stored for? Storage must be important since the production of cigarettes must be phased over the whole year. 

  We will now move to another source (but again from Brit American) which is similar but has a bit more info:

“”One tobacco plant can produce several grades of leaf.  The sensory, physical, chemical and visual properties of a tobacco grade are generally determined by the leaf position on the plant.  For example, the leaves at the top of the plant are more exposed to the sun than the ones at the bottom and typically contain higher levels of nicotine and other alkaloids.”” 

A tobacco leaf with the percentages of nicotine & sugar on the leaves from top to bottom.

 Now isn’t that interesting! The higher up the plant that the leaves are, the greater the nicotine content, whilest sugars are highest in the middle and least at top and bottom. That suggests to me that it would be as well to ‘bunch’ your leaves in groups as you pick them so that you can ‘blend’ them later.

Looking at the matter from a slightly different point of view:

A study from 1925 (!).

 This study was intended to find out what fermentation does to tobacco, but it is very technical. I will quote only a few, small passages:

“”THE decomposition of nicotine during the so-called fermentation process which takes place in the tobacco leaf is one of the most important reactions concerned in this complicated process, as a result of which the raw or dried tobacco becomes converted, in the fermentation stores, into the valuable product of commerce. According to the statements in the literature, decomposition of nicotine also occurs in green tobacco before drying. It is our intention to study the processes taking place during the fermentation, especially to find out the enzymic constituents of the cells of the tobacco leaf which take part in the fermentation.””  (Excuse the weird fonts – that is how it copied)

The decomposition of nicotine’! What’s that? ‘….the enzymic constituents…! What are they? OK, we will take ‘enzymes’ to mean internal, genetic, chemical interactions, shall we? That is, not microbes or bacteria.

A bit more:

“”On the other hand, many investigators to-day suggest that the process of fermentation here concerned depends upon bacterial action. The question is still open and has to be investigated whether or not bacteria, either directly or indirectly, limit the actual fermentation process.”

So, a further intention of that study was to verify or falsify bacterial action. And here is the conclusion:

 “”Since the solutions, kept in the thermostat for 2 hours at 37 degrees, showed no change in appearance under the conditions we employed, there can be no possibility of bacterial action.””

So the whole business of ‘curing’ (fermentation) is about internal, chemical reactions! No outside influences are involved – other than oxygen and nitrogen in the atmosphere and, possibly, sunlight and moisture. But there are queries about those influences as well. Look at this pics:


That is a picture of ‘sun-cured’ tobacco from Iran.  Looking closely, does it look as though any particular leaf will get much sun, oxygen or nitrogen – or, indeed, any signs of extra moisturisation? (A much bigger picture can be seen by clicking the Wikipedia link below)

We need to look further, but it seems to me that the ‘curing process’ is a natural thing. Special treatments merely speed up the process. As a small-scale grower, I see no reason that I should not blend various methods. For example, I have in mind to make some simple racks (similar to clothes racks) and suspend the leaves on the racks. Normally, they will reside in the garage, but in sunny weather, I will put them outside during the day. I could even make some simple covers so that, in settled warm weather, I could leave them out overnight. 

So my plan, as things stand at the moment, is this:

Over the winter, a few leaves –

  • Strung up in garden shed.
  • Strung up in garage.
  • Strung up in loft.
  • On home-made racks.

It seems to me that the change in colour is the thing to look out for. If leaves over-dry, rehydration can be done.

After curing, the question of storage arises – but that can wait.

The Utube harvesting video:

The ‘curing’ methods:

The ‘nicotine and sugars’ content:

the 1925 paper:

The picture from Iran (scroll down – pic on right – click to enlarge a lot):

For some reason, the words in the last bit are all spread out. I do not know yet how to correct that, but it seems to make no difference so I will leave it alone!




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