Grading tobacco leaf for sale uses more labour than any comparable operation and also requires many hours of supervision if the job is to be done properly. Good grading can increase the value of the crop while bad grading can cost the farmer a great deal of money. The purpose of grading is to sort the leaves into different categories according to type, colour, quality and size so that the crop is sold in uniform parcels. The foundation of good grading is laid when the crop is being grown. Good land selection and preparation, fumigation and fertiliser applications, seedling selection, reaping and curing should aim at producing a uniform crop so that the final sorting out is made easier.
2. THE GRADING SHED
Tobacco should be graded in a well‐built waterproof shed situated near the tobacco barns and storage shed. The main requirements are good lighting, floor space, layout of the grading tables and a system for conditioning the leaves while they are being handled and packed.
This should be either natural or artificial lighting but never a mixture of both. If natural lighting is being used the shed should be sited so that the windows face south and no direct sunlight shines in. Shadows should be avoided and remember that on an overcast day the intensity of light can be 25% less than on a sunny day. A problem with natural light is that grading can only begin after the sun has risen in the morning.
The alternative to natural lighting is to have no windows in the shed and rely entirely on electric lights. The recommendations for this are to have one 40 watt fluorescent tube, 1,25 metres long hanging about 1,25 metres directly above the head of each grader. Every light fitting should have a reflector and the tubes and reflectors should be cleaned at regular intervals to maintain the maximum light output. All the tubes should be replaced every third season.
The old tube can be used to light other parts of the shed.
The size and shape of existing grading sheds vary a great deal but provided the design and layout is good, it is possible to have a system whereby the tobacco moves in one direction through the shed. It is undesirable to have tobacco crossing over the shed from one side to the other as this causes extra handling which wastes both time and labour. A good design for a grading shed is shown in figure 1 on the next page.
Figure 1: Grading Shed layout
The tobacco is unloaded from the barns and taken into the shed. The sticks which have been used to hang the tobacco in the barns are removed and stored and the leaves are bulk stored in the bulk rooms. When grading begins the leaves are taken out of the bulk room conditioned by passing through steam and weighed into small lots called scales, for each grader. After grading, the loose leaves are tied and pass on through the shed where they are then baled, the bales sewn up and stored until they can be loaded for transporting to the auction floors for selling.
The recommended type of grading table is shown in figure 2 on the following page. The surface of the table should slope towards the grader like a school desk and the surface should be made of smooth material like wood or hardboard to prevent damage to the leaves. Grade divisions should be arranged in an arc around the grader with the dividers made of wire loops. It should be possible to move the loops depending upon the number of grades required and to make wider compartments for the common grades. The edge of the table should be 25 ‐ 75 mm below the level of the grader’s elbow, as output will be reduced if the table is too high or low.
Figure 2: Typical Grading Table
3. THE TOBACCO CLASSIFICATION SYSTEM
Under this system tobacco is graded and given symbols up to 5 in number. These symbols are understood in most tobacco growing and manufacturing countries in the world. There are more than 3 240 possible grade combinations in all, but the system itself is fairly simple to understand and operate.
When grading a crop, five major factors determine the grade of a leaf.
- Leaf Position on the plant. Figure 3 below shows the different plant positions together withthe shape of the leaf and symbol.
Figure 3: Points of Identification when Grading Tobacco
There is no symbol for Cutters because the crop has tended to become heavier over the years. Cutters are thin and stretchy leaves with good cutting properties and they are classified as L or X, depending on whether they are more like Lugs or Leaf. The plant position of the leaf is important because as you can see from the diagramme, the body of the leaf, the thickness and weight, and the nicotine content increase as you go up the plant. Tips (T) have a lower manufacturing value than Lugs (X) because they have a thicker stem and less lamina.
It is most important to keep leaves from different plant positions separate, partly because of their different chemical compositions and because of their different lengths. Short and long leaves of similar appearance should not be packed together because of difficulties in manufacturing. Once the leaves have been cured and removed from the barns they should be identified and stored according to their positions on the plant.
- Qualities: Each type of leaf is given a number according to its quality and this will depend on theamount of disease, blemish, waste and other factors on the leaf.
The numbers are:
- Poor and;
NG (No Grade) ‐ too poor to make the 5 quality.
These are the numbers for Primings (P), Lugs (X) and Leaf (L). Tips (T), Strip (A) and Scrap (B) have three numbers, 1, 2, 3 and NGA.
Figure 4: Numbers for Primings
The symbol NGA is used to distinguish between leaf that is sold tied in bundles or ‘hands’ and Strip and Scrap which is baled loose without being tied.
The quality numbers are given according to the amount of dead or unusable tissue which cannot be used by the manufacturer.
- Colours: These are the third symbol and are letters given according to the colour of each leaf.Colours are important because a mixture of colours can spoil the appearance of a bale and because they represent nicotine and sugar amounts in the leaf.
The Colour Symbols are:
Colour Symbols apply to all qualities of tobacco except NGA and NG (No Grade), B (Scrap) and PTL and TTL (Loose Leaf).
E (white) and L (lemon) leaves have a high sugar and low nicotine content while O (orange), R (light mahogany) and S (dark mahogany) are lower in sugar and higher in nicotine, with S having the
highest nicotine content. R and S only apply to Leaf and Tips and the scrap from those two types.
At this stage it is possible to describe many of the total grades of leaf, and examples are shown below and are called True Standard Grades:
Medium bodied, fairly open grained Priming, and 2nd Quality, White in colour
Medium bodied, fairly open grained Lug, 3rd Quality, Lemon in colour
L10Medium bodied, fairly open grained Leaf, 1st Quality, Orange in colour
T3S Medium bodied, fairly open grained Tip, 3rd Quality, Dark Mahogany in colour
Standard Grades may require further description.
The following make up the Fouth and Fifth factors.
4. OTHER FACTORS
|Higher maturity, thin leaf with good filling qualities
|Slightly sub‐standard due to sponge or water staining
|is not a factor but may have other symbols added to it
|Medium bodied, close grained and carrying a fair amount of slate
|Heavy bodied, close grained, slick and carrying slate
5. DETRIMENTAL FACTORS
|Spotted tobacco due to disease
|Leaf tinged with green colour
|Leaf with a lot of green colouring in it
J factor might have A or V added if the leaf is carrying Spot or Green and would beshown as JA or JV.
Q This is scorched leaf with a reddish colour showing that the sugar in the leaf has beenchanged by too high a temperature; smoking quality is affected;
D Harsh, sun baked, flaky tobacco caused by either drought or too much rain; and
Y Leaf carrying Guinea Fowl Spot and only affects primings and lugs giving the leaf a poorsmoking quality.
It is important to keep leaves with Q, D or Y grades out of the bales of better tobacco as it will affect the price of the whole bale.
Length of leaf
If grading is properly organised and the leaves from the different positions on the plant have been stored separately length should be no problem. However, if the leaves do vary in length, short and long leaves should be separated. In a bale of tobacco the difference in length for leaves should not be more than 75mm for leaves under 400mm, and 125mm for leaves over 400mm long.
Strips and scraps
Strips are pieces of leaf that have had most of the mid rib removed and all signs of Barn rot or Mould. All the strips in a bale should be from the same plant position e.g. all Lugs or all Leaf etc. Strips and Scrap are generally graded into Light, Dark and Green.
Scrap should be of a similar size in each bale and this is done by screening. Scrap from Lugs and Primings may be baled together but Scrap from thin leaf grades and heavier bodied Leaf and Tips should be baled separately.