The invention relates to a method for processing tobacco. In particular, the invention relates to a method of processing partially cured tobacco.

Generally, tobacco needs to be cured and dried after it has been harvested to develop its desired aroma and flavour. Initially, tobacco leaves have a green color. During curing, the color of the tobacco leaves change slowly to yellow, a process which is referred to as yellowing. During the yellowing process, the metabolism of at least some of the cells is still active, and when the tobacco leaf reaches a yellow color, most cells have died. For flue-curing processes, it has been found that the cells mainly die from dehydration, while for air-curing processes, it has been found that the cells mainly die from starvation. However, this is not mutually exclusive, as, depending on the conditions of the curing processes, cells may die either of dehydration or starvation in different types of curing processes.

As is known in the art, the curing process continues after the yellowing process until the tobacco is dried and has a brown color. In this state, the tobacco leaf is relatively dry and, therefore, may be brittle.

It is also known in the prior art to cure and dry full tobacco leaves. However, this may have the drawback that the drying process takes longer, as the stems need a significantly longer time to dry than the lamina.

Further, the stem typically is removed before or during threshing of the tobacco leaf, as the stems are often excluded from the tobacco blends. This stem removal process is typically performed either before curing and drying, or after curing and drying. Where the stems are removed after curing and drying, the removal process is typically a standard threshing process.

Where the stems are removed before curing and drying, the removal process is often performed by the tobacco farmer In a labor intensive process. In addition, this has to be carried out relatively carefully to avoid damaging the tobacco leaf and, regardless, the leaf will at least be damaged where the leaf is cut to separate the lamina from the stem. Because of this, proper yellowing may not occur in at least some of the leaf, as the cells of the leaf are damaged and do not have the necessary metabolic function to allow the yellowing process to progress normally.

According to some curing methods, tobacco leaves are in a wrapped up configuration during the yellowing process. In other methods, the tobacco goes through the yellowing process as individual leaves or whole plants. In yet other methods, lamina separated from the stem goes through the yellowing process separately.

Further, in some curing processes, it is known to wrap up the yellowed leaves, cut them into small pieces, and dry them in the sun. However, wrapping up of the leaf may be difficult for leaves with stems, as additional holding means, such as a pin, have to be provided to keep the leaves in the wrapped up form against the elastic force of the stem. It is the object of the invention to provide a method that allows more efficient processing of tobacco into a cured state with a high yield.

This object is attained by a method for processing tobacco, comprising the following steps:

In a first curing step, a tobacco leaf is cured until the lamina of the tobacco leaf reaches a yellow color. In a second step, at least the stem of the yellow tobacco leaf is flattened. In an optional third step (which may be referred to as the second curing step), the flattened tobacco leaf is subsequently dried.

Thus, while the tobacco leaf is still in the yellow state of curing, and before it has turned brown, the stem of the tobacco leaf is flattened.

As the whole tobacco leaf is cured until it reaches a yellow color, the ceils in the tobacco leaf are not damaged prior to yellowing, which allows the yellowing process to proceed while the cells of the leaves are still alive. However, when the leaf is already in the yellow state, live cells are not necessary, as the remaining drying process does not rely on cell metabolism. Thus, after the yellowing process is complete, the majority of cells are either already dead or have provided the necessary metabolic activities required during the yellowing process.

Furthermore, in the yellow state, the tobacco leaf is not yet fully dried, such that the leaf is not brittle. Thus, during the flattening of the stem of the tobacco leaf, the leaf, particularly the lamina, is less likely to break and is therefore less likely to produce tobacco dust. In addition, if the leaves were flattened shortly after harvest, the moisture content would be relatively high such that water would be squeezed from the leaves. Further processing and storing of the leaves with this moisture may degrade the quality of the leaves. Flattening the leaves after they are yellow, and therefore after they have had the chance to at least partially dry, allows the leaves to be somewhat pliable, but at the same time prevents excessive water from being released from the leaves due to the flattening.

In the first curing step, the tobacco leaf is preferably initially a green tobacco leaf. Thus, the cells of the leaf are still alive during the curing in the first curing step, and most of the cells of the lamina will die by the time the yellowing process is complete for the tobacco leaf. However, the cells in the yellow tobacco leaf typically still comprise a significant amount of water, therefore the tobacco leaf is not brittle.

Without being bound by the theory, it is thought that the yellow color of a tobacco leaf is an indication that the chlorophyll has degraded, the polyphenols in the leaf remain unoxidized, and most of the starch has been hydrolyzed to sugar.

The flattening of the stems in the flattening step relates to processing at least the stem of the integral tobacco leaf, such that the structure of the stem is broken down and its thickness is significantly reduced. Depending on the type and size of the tobacco leaf, the unprocessed stem may have a wood-like structure. In the flattening step, the stem is compressed, such that the woody stem material is broken down and the stem is substantially flat. The lamina of the tobacco leaf may also be flattened together with the stem. Damage to the lamina is not as critical as prior to the yellowing process because active cell metabolism is no longer needed.

In a typical prior art process for tobacco that has been dried as whole leaves without flattening the stem, the stem is usually separated from the leaf. Some of the stem material is sometimes used in a tobacco blend after separately treating the stem material. A potential benefit of the flattening process of the present invention is that the structure of the flattened stems is broken up in a manner such that all or most of the tobacco leaf (including the stem) may then be used in the tobacco blend. In some cases, all of the flattened leaf is then used in the tobacco blend, whereas in other cases a portion of the stem is still removed from the leaf before the leaf material is used in the tobacco blend. In this way, the amount of stem material in the tobacco blend may be adjusted depending on the desired taste and flavour of the tobacco blend.

A further benefit of flattening the stem is that the moisture of the stem of the tobacco leaf can easily evaporate, such that the tobacco leaf can dry quicker. Furthermore, during flattening, some of the moisture of the stem may be pressed out of the stem.

Additionally, a tobacco leaf with a flattened stem is more flexible, such that it can easily be wrapped up. It is known in the prior art to wrap up tobacco leaves before drying. Typically, these processes require holding means to hold the leaves in a folded or rolled up configuration. These holding means may be problematic, as they are often made of non-tobacco material and, therefore, have to be removed at a later stage. However, when the tobacco leaf of the inventive method with the flattened stem is optionally wrapped up, no (or fewer) holding means are necessary, which can make the folding or rolling up process more efficient.

In some embodiments, the yellowing stage takes between about 40 and about 80 hours, preferably between about 48 and about 72 hours. These durations are preferred for the usual types of tobacco leaves. However, depending on the type of tobacco leaf and the curing method, the yellowing may require more or less time. During the yellowing process, the chlorophyll in the leaf is slowly degraded.

The green tobacco leaves typically comprise mostly water, for example more than about 95% water by weight, or more than 98% by weight water. During the yellowing process, the leaves are at least partially dried, reducing the water content to between about 50% and about 90% by weight, more preferably between about 70% and about 90% by weight, and most preferably to between about 70% and 80% by weight water. The yellowed leaves are then subjected to the flattening step.

In some embodiments, after the flattening step has been carried out, the leaves are subjected to a second curing step that comprises a drying process. Preferably, the drying process takes between about 24 and about 48 hours. In some cases, because some of the moisture has been released by the flattening process, this is an improvement with respect to the drying of tobacco leaves with unflattened stems, which typically require between 48 and 72 hours. After the drying process, the tobacco leaf is preferably between about 10% and about 15% water by weight, more preferably about 12% water by weight, and is in a condition to be packed and transported.

Preferably, the leaf is flattened to a height of less than 1.5 mm. In particular, the stem of the leaf is flattened to a height of less than 1.5 mm. The flattening height is set by adjusting the height of a roller gap through which the tobacco leaf is conveyed. Alternatively, it can be set by adjusting the minimal gap between two press plates between which the tobacco leaf is pressed.

In some embodiments of the method, the leaf is flattened to a height of less than 1 mm. In particular, the stem is flattened to a height of less than 1 mm. A lower height of the stem may enable a quicker drying process.

In addition or in the alternative, the leaf, and in particular the stem of the leaf, is flattened to a height greater than about 0.5mm. Maintaining at least this minimal flattening height may prevent excessive damage to the lamina of the leaf. In other embodiments, the flattening height is greater than the thickness of the lamina portion of the leaf, or at least about 0.2 mm greater than the thickness of the lamina portion of the leaf. Alternatively, the whole leaf, including some or all of the lamina, may be flattened.

In one embodiment, the leaf is laid down on a surface, preferably with the tip of the leaf pointed up, for the yellowing process. After yellowing, the leaf may then be flattened as described further below. After flattening, the leaves may are then folded, cut, or both folded and cut, and may be subjected to further curing in order to dry the leaves, as further described below.

In another embodiment of the method, the leaf is folded before the curing process. The leaf is folded in a green state before it is cured and reaches a yellow color. Thus, the yellowing of the leaf occurs in a folded configuration and the leaf is unfolded before the flattening step. However, in other embodiments, the leaf may be unfolded during the yellowing step.

In some embodiments, the leaf is folded by wrapping up the leaf, and more particularly spirally wrapping up the leaf.

In one embodiment, the curing of the tobacco leaf during yellowing of the leaf is carried out as sun-curing. In particular, the leaf is arranged on trays, for example bamboo trays, and subjected to the sun. In other embodiments, the leaf may be air-cured during yellowing. This is particularly applied for Burley tobacco. In yet another embodiment, the leaf is flue-cured during yellowing. This applies particularly for Virginia tobacco.

The inventive method may be applied to a variety of tobacco types, in particular Kasturi, Virginia, Burley or Oriental tobacco.

Preferably, for the flattening step the tobacco leaf is subjected to a roller that flattens at least the stem. The tobacco leaves are in particular individually subjected to the roller. In particular, two rollers are used, which engage opposite sides of the stem. The rollers have parallel rotation axes. Furthermore, the rollers may be of the same diameter. Generally, the rollers are cylindrical bodies, wherein the outer surface of the roller is engaging the unfolded tobacco leaf, in particular the stem of the tobacco leaf. In other embodiments, only one roller may be used, which flattens the stem together with an opposed stationary plate. Alternatively, the tobacco leaf may be subjected to a press that flattens the stem. In particular, a layer of tobacco leaves with little or no overlap between the leaves may be provided to the press. The press comprises a press plate that can be moved towards a stationary plate. The leaf may be arranged on a stationary plate of the press, and a moveable press plate may be lowered, such that at least the tobacco stem is flattened.

Preferably, the roller gap, in particular the distance between the rollers, or the minimum distance between the plates of the press is smaller than the thickness of the stem, and greater than the thickness of the lamina of the leaf. The gaps between rollers or plates may be any of the flattening heights discussed above.

Preferably, a single leaf is flattened at a time. In other embodiments, several leaves may be flattened simultaneously. In any case, the leaves may be arranged such that there is little or no overlap between the leaves when the leaves are flattened. In other embodiments, leaves are arranged to overlap one another and are flattened together.

After flattening, the tobacco leaves are optionally subjected to a further drying process. In one embodiment, the flattened yellowed leaf is folded before it is dried. The leaf may be wrapped up, particularly spirally wrapped up.

After flattening, the leaf may be optionally cut. In particular, the leaf may be cut while the leaf is in a folded configuration. This provides the benefit that the cutting process may be facilitated, as in the wrapped-up leaves, several layers of the leaf are closely adjacent to each other, such that with only one cut through the folded leaf, a long cut can be provided in the tobacco leaf. The cutting step may be performed before or after the optional drying step.

In one embodiment, the tobacco leaf is flattened when it comprises a reduced amount of water, as described above. As this moisture content is lower than the usual moisture content of the green leaves, it prevents that excessive water is squeezed from the leaves. Thus, a degradation of the quality of the leaves due to free moisture in between the leaves during processing and storing can be avoided.

Preferably, the flattened tobacco leaf is sun-dried. In particular, the leaf or the cut leaf pieces are arranged on a tray, preferably a bamboo tray. The flattened whole or cut leaf pieces may also be dried using hot air.

When the dried tobacco leaf pieces are further processed, the flattened stem material may at least partially remain in the blend, as it is softer in its structure than non-flattened stem material. Thus, it is suitable for the production of machine made cigarettes, whereas unprocessed stem material is typically used in tobacco blends at low levels, or not used at all.

Increasing the amount of stem material in the blend can be beneficial because a larger percentage of the leaf can be used, and the stem material comprises less nicotine. In some cases, the total yield of the material that can be used for the blend is 90% or higher of the tobacco leaf when the stem is flattened according to the invention. On the contrary, when the stem is removed from the leaf, lower yields are typically obtained.

The invention also relates to cured tobacco processed with the method as described above. The cured tobacco may for example be in the form of processed full tobacco leaves, processed tobacco leave parts or a tobacco blend which is ready for smoking and which may comprise further ingredients.

The method for processing tobacco according to the invention will now be explained by means of an exemplary embodiment with respect to

Fig. 1 , which shows a flattening apparatus.

Initially, the tobacco is harvested from tobacco fields. Soon or immediately after the green tobacco leaves are reaped, the leaves are subjected to a yellowing process for two to three days until they have a yellow color, but are still flexible and moist.

The leaves are then subjected to a flattening apparatus, as shown in figure 1. The tobacco leaves 1 are arranged on a conveying means 2, in particular a conveyor belt, and are fed into a rolling device 3 that comprises an upper roller 4 and a lower roller 5. Preferably, the tobacco leaves 1 are fed individually into the rolling device 3. The distance between the outer surface of the upper roller 4 and the outer surface of the lower roller 5 forms the roller gap 6, through which the leaves are conveyed and, at the same time, flattened. The roller gap 6 is preferably less than 1.5 mm, more preferably less than 1 mm. Thus, the stems of the tobacco leaves 1 are compressed to the height of the roller gap 6.

The speed of the conveying means 2 and the rolling device 3 is preferably synchronized. Thus, the tobacco leaves 1 are conveyed at the same speed on the conveying means 2 and in the rolling device 3. The conveying speed is preferably about 40 meters per minute. After the flattening, the tobacco leaves are wrapped and cut. The tobacco leaf pieces are then dried, preferably by spreading them on trays in the sun. The drying process usually takes one to two days, which is an improvement to drying tobacco leaves or leaf pieces that comprise unflattened stems or stem pieces where the drying process would usually take two to three days.