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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11 Responses to “The Curing (Fermentation) of Tobacco.”

  1. Pat Nurse Says:

    Excellent article which I’ll bookmark for future reference.

  2. Rose Says:

    More reading matter, Junican

    Decomposition of nicotine.

    “Nicotine is formed primarily in the roots of the tobacco plant and subsequently transported to the leaves, where it is stored.
    The nicotine molecule is comprised of two heterocyclic rings, a pyridine moiety and a pyrrolidine moity, each of which is derived from a seperate biochemical pathway.

    The pyridine moiety of nicotine is derived from nicotinic acid.
    The pyrrolidine moiety of nicotine is provided through a pathway leading from putrescene to N-methylputrescene and then to N-methylpyrroline.”;jsessionid=DC0EE03FFA63A329517CD121BEEBF25C?tid=wfb29e00&page=2

    Trust me, you don’t want to know anything about the Putrescene, you just have to get rid off it or your tobacco will smell like a rotting fish.

    An experiment I did by accident, putting dried tobacco in a box.

    “Niacin was first discovered from the oxidation of nicotine to form nicotinic acid. When the properties of nicotinic acid were discovered, it was thought prudent to choose a name to dissociate it from nicotine, in order to avoid the perception that vitamins or niacin-rich food contains nicotine. The resulting name ‘niacin’ was derived from nicotinic acid + vitamin.”

    “Niacin is also referred to as Vitamin B3 because it was the third of the B vitamins to be discovered. It has historically been referred to as “vitamin PP”, a name derived from the term “pellagra-preventing factor”.

    Degradation of Trigonelline, another pyridine alkaloid like nicotine,by roasting.

    Basic Chemical Reactions Occurring in the Roasting Process

    “The best cup characteristic are produced when the ratio of the degradation of trigonelline to the derivation of Nicotinic Acid remains linear. The control model of this reaction ratio is a time/temperature/energy relationship. The environment temperature (ET) establishes the pyrolysis region for the desired chemical reactions while the energy value (BTU) and system transfer efficiency (STE) determines the rate of reaction propagation and linearity of Nicotinic Acid derivation to degradation of trigonelline”

    • junican Says:

      Gosh, Rose, you are overloading my mind!

      It seems to me that the ‘curing’ of tobacco leaves is a simple process. It is simply a matter of allowing natural processes to occur. Green tobacco leaves will, naturally, attract Oxygen to their surfaces and thus change chemically, and change their appearance (colour). This change affects the ‘taste’ of the tobacco when it is smoked.
      Or, one can expedite the process by interfering – by, for example. subjecting tobacco leaves to extra heat, and thus speeding up the Oxygen intake. But if you are to subject the leaves to extra heat (in order to expedite the process), you must also ensure that the heating process does not ‘incinerate’ the leaves! And so, we see the recommendation that we should introduce, artificially, extra moisture! The whole system begs the question: “Why bother introducing ‘extra heat’, and therefore, ‘extra moisture’? Why not let nature do its thing?” The obvious answer to that is that it is in the interests of tobacco manufacturers to expedite the process!
      We are not ‘tobacco manufacturers’, therefore we have no need to expedite the process. We can let the process occur naturally. We are in no rush.

      So Customs and Excise want to charge us excise duty on our homemade tobacco? First, let us not forget that, as individuals, we have no DUTY to tell these people anything at all! We are not a totalitarian state! As an Englishman, I am a free individual. I can do what I want to, provided that I harm no other persons. If I wish to grow tobacco plants, I can do. (As an aside, this idea militates against the idea that The State can stop people growing cannabis plants if they wish to – but that idea is curious – yet to be tested in the Courts).

      And so on.

      Damn it, Rose! I am sick and fed up with describing the idiocy of our politicians!


  3. mummy Says:

    Getting more interesting by the day. I think that Deborah Arnott has been censoring all the information on the web that tells of easy methods of making tobacco into a decent smoke !!

    I am up for the hanging up the leaves in my unheated shed. I will get a large darning needle with twine and pierce it through the thick central vein of the leaf and hang the leaves from hooks in the shed.

    I am not sure if I should wait until the leaves start to turn yellow before I pick them (the video above showed the leaves quite green when they were harvested ?)

    IF the leaves start to turn brown, but are getting too dry I will finely mist them with a water spray.

    After that ?????

    • junican Says:


      It seems that, on the contrary, as a result of the idiot ASH (Tobacco Control) actions, tobacco companies were forced to reveal all their ‘secret’ studies. As a result, it has become apparent that there is nothing ‘weird’ about ‘preparing’ tobacco. Tobacco companies use ‘quick’ ways, but we do not have to use those ways,

      Do what you wish to do!

      If you string your leaves in your garden shed, there may be an increased possibility of fungi affecting your leaves. I do not know. If I was you, I would check the leaves very carefully. In particular, I would open up the door of your shed as often as possible to allow air to circulate – the better the circulation of air, the less likely that fungi spores will affect your leaves. On the other hand, YOU ARE EXPERIMENTING! Might it be a good idea to see what happens if you DO NOT allow an airflow!

      OK. Because of the fact that I can also hang leaves in my garage and my loft, I COULD make it my business to put a few leaves in my little outdoor shed AND NOT allow an airflow. That is, just see what happens to those leaves. We could use the two different ideas – you allow airflow, but I will not. We can compare notes over the winter – if you wish to stay in touch.

      Let me know what you think.

      • junican Says:

        Oh…….I forgot.

        I was a bit surprised that you saw the leaves collected in the video as ‘green’. To me, the leaves that were collected were ‘yellower’ than the leaves that were not collected! That is, that the person collecting the leaves collected the ‘yellowest’ leaves! Or at least, the ‘least green’ leaves!

        I will leave my leaves as long as possible on the plant. This is because I am not obliged by a manufacturing process to harvest leaves according to a fixed schedule.I do not have, or wish to have, a multi-million dollar machine which demands a continuous flow of tobacco leaves.

        Enough for tonight!

  4. Rose Says:

    “Gosh, Rose, you are overloading my mind!”


    I have no sympathy whatsoever, what do you think I’ve been doing every day for the last 5 years?
    All this stuff is now stuck in my brain.

    Required reading.

    Curing, theory and practice

    Including very simple methods by farmers


    Stages Of Curing

    These stages are

    Yellowing of leaf,
    Fixing of colour,
    Drying of leaf.

    Yellowing of leaves

    In the yellowing process of leaves, which usually requires 24-36 hours or slightly longer, only gentle heating is done with a temperature ranging between 90 to 100°F and relative humidity between 85 to 90 per cent.
    It is a slow starvation process and the object of slow heating is to give optimum humidity and retain, as much moisture in the leaves as is possible to keep them alive for 30-36 hours.
    At the end of this stage the leaves attain a bright lemon yellow colour and the starchy matter in them gets converted into sugars.”

    • junican Says:

      That was a very interesting read, Rose.

      My plants are Virginia. In general terms, all the methods for treating Virginia are much the same – flue-curing. But there are variations.

      I am still not getting a clear picture in my mind. Am I stupid?

      As regards the last para in your comment – yellowing. If one takes a developed leaf off the plant and puts it in a dry place – ANY place, whether in the shade or not – it should go yellow of its own accord, shouldn’t it? What is the problem? – Unless one wants to speed up the yellowing. Once the leaf has naturally yellowed,…….BUT…see below:


      “”The curing consists of DRYING GREEN LEAVES [my caps] under artificial atmospheric conditions by adopting a process which does not allow the GREEN [my caps] leaf to come in direct contact with smoke or flames of the fuel and which permits the regulation of temperature and humidity.
      The main feature of flue curing is the drying of leaf under controlled conditions, where the starch gets converted into sugars and the GREEN [my caps] tobacco becomes bright, aromatic and fine textured.
      This method is adopted in almost entire Virginia cigarette tobacco areas like Guntur, Godavari, Mysore and other areas at Hyderabad, Madras, U.P, M.P. and Orissa. “”

      Am I dreaming, or is there a contradiction there? Are the leaves yellow or are they green?

      There seem to be many variations in treatment:

      1. Type of tobacco plant.
      2. Use of tobacco (cigs, cigars, pipe, chewing, etc).
      3. Quality required.
      4. Speed and cost of production.
      5. Quantity of tobacco involved.
      6. And all the rest (climate, storage, etc)

      What I am NOT seeing is information about what will happen if one does NOT follow the recommended procedures.

      So here is what I have just done. I have been outside and ‘primed’ (plucked) a leaf from the bottom of a plant. It is GREEN! I have rinsed it under the cold water tap to wash of bits of soil and such. I have placed it on my little table next to where I sit. I will leave it there and see what happens to it (as to yellowing and that).

      As it happens, I am away on holiday for a couple of weeks from Monday, but daughter and grandson are here. So, I will give them instructions NOT TO TOUCH.

      As I see it, there is no reason for not experimenting with a single leaf.

      We shall see.

  5. Rose Says:

    I would hazard a guess that depending on conditions you will end up with a dry green leaf.

    If you wrap it in a towel and slow down the drying, it may change colour depending on the temperature in the room.

    Look out of the window and you can see this process in action.


    “The shortening days and cool nights of autumn trigger changes in the tree. One of these changes is the growth of a corky membrane between the branch and the leaf stem. This membrane interferes with the flow of nutrients into the leaf.

    Because the nutrient flow is interrupted, the production of chlorophyll in the leaf declines, and the green color of the leaf fades.”

    “the nutrient flow is interrupted”

    That’s what you just did rather abruptly when you picked the leaf.

    Have a very good and restful holiday.

    : )

    • junican Says:

      Another interesting piece of info from you, Rose – what would we do without you!

      As you will know, tobacco leaves, while being ‘bendy’, have quite a strong structure. Within an hour of plucking the leaf, it became ‘floppy’ – its structural strength deteriorated rapidly.

      I feel sure that you will turn out to be right about the leaf staying green as it dries. I noticed that the leaf became slightly sticky as it became floppy. Now, the leaf feels reasonably dry; it has lost the stickiness; it is still floppy; it is still green.

      I have accepted your suggestion. I have plucked another, similar leaf and put it inside a tea towel. I have placed it on top of the hot water cistern. It is not hot because of the insulation, but it is warm. We will see what has happened when I get back.

      Thanks for your good wishes.

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