Knowledge Base

Efficient Curing


Some common faults in Flue-curing

Yellowing too long
If the leaf is not dried soon enough it tends to darken in colour and become harsh, trashy and difficult to condition.  Reapings from the top half of the plant may sponge, while leaf from lower reapings is more inclined to become spotted and lifeless.  A trace of green leaf in a cure probably shows that colour was fixed at the correct time.


Too much green tobacco
(i)   Green along the midribs and veins on  a large proportion of the cure suggests that it has not been yellowed long enough and was reaped green.  This can be prevented in the future cures by reaping riper leaf or opening the vents slightly later or raising the temperature more slowly in the range from 100 - 120 ºF.

(ii)  A solid green on the tip end of the leaf is sometimes found on the lower tiers of the barn.  This is usually due to the temperature being raised too high for a short period in the first 24 hours of curing.  A similar green colour can be caused by Sun Scald if the leaf is left in the sun after reaping.

(iii) Small green lines, mostly near the butt end of the leaf, are caused by bruising, mainly during the reaping and tying.  These bruises can lower the value of the leaf.


In some cures the leaf turns to a dull grey or brown colour although still maintaining normal texture and elasticity.  This is known as sponging and is usually considered to be caused by drying the leaf too slowly.

Adequate ventilation and even raising the temperature between 110 - 140 ºF will help to prevent sponging.  Certain types of leaf appear to sponge more easily than others and it should be remembered that large, heavy leaf reaped when wet contains water and requires a longer time to get rid of moisture- or even ventilation - than small, thin leaf.


  This produces a slate grey or even greenish colour and the cured leaf often becomes rather stiff and lacking in texture. The cause and prevention of this problem are similar to those of sponging, except that it usually occurs at temperatures over 135 ºF.  Advancing the temperature too fast, or insufficient ventilation, can contribute to scalding.


If the temperature drop or humidity in the barn is too high for the midrib to dry rapidly, moisture may move out from the midrib into the already dried leaf.  This may produce a dark brown discolouration along the midrib or, in some cases, a distinct brown line on the lamina parallel to the midrib.


Fat midribs
If the leaf is taken from the barn with some of the midribs not completely cured they will be soft and pliable and larger than the dry midribs.

Under no circumstances should leaf be bulked in this condition as it will go mouldy.  If there are many fat midribs in the barn, drying should continue at 160


Black tobacco
  This problem is most prevalent in lower reapings from well grown plants, and types of leaf which do not readily lose moisture.  It occurs on all tier positions.  Tobacco should be reaped slightly greener than normal and a Wilt Cure used.  Ventilation is allowed at the beginning of colouring in order to encourage an early loss of moisture and ensure wilting after 24 hours.

It may be necessary to introduce moisture in the form of wet bags to prevent the bottom tier fixing green.  The air should be to lose much more moisture throughout the colouring period than normal, so that the lamina begins to dry when 155 ºF is reached.  subsequent drying may then be very rapid to fix the colour.


Wilting during the colouring period
  Wilting is carried out when growers have difficulty in curing their tobacco due to the mixed reapings and excess moisture in the leaf.  Initially, tobacco is hung in the barn for 36 hours with all the vents and doors wide open. This is not a fixed time as a lot depends on the condition of the tobacco when it is reaped.  During the first eight hours or so of this period it is essential to try and get all surface moisture of the leaf to enable a natural wilt to start.

After this initial hanging the  doors of the barn are shut and the temperature is taken up to 85 ºF with all the vents open.  This second phase, which takes 12 - 18 hours, should produce a fully wilted leaf which has started to colour and which hangs flaccid, allowing air to circulate from top to bottom.

Once this wilted tobacco begins to turn yellow, all the vents are shut and the temperature is then taken up to 95 ºF to get full colouring.  This period lasts from 2 - 4 hours and the grower must watch this tobacco carefully during this phase as the full colouring comes quickly.

Finally the drying process begins.  The vents are re-opened and temperatures freshened up fairly rapidly at the rate of 5 ºF every 4 hours until 160 ºF have been reached.  With this method the rate of drying is much quicker as this type of wilt and colouring allows the leaf to open up.  It becomes more porous, giving a more open-grained leaf, from which the moisture is easily removed.  By curing this way, Barn Rot and leaf discolouration are eliminated.




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