MXPA00004983A - A method for making a reconstituted tobacco sheet using steam exploded tobacco - Google Patents

Abstract

A process to improve the smoke quality and mechanical properties of reconstituted tobacco is accomplished by adding tobacco materials to an aqueous solution containing ammonium salts and urea. The resulting first tobacco slurry is then pressurized under steam pressure to at least 60 psi for a period of from 1 to 5 minutes then depressurized rapidly to ambient. The depressurized tobacco is then formed into a second tobacco slurry wherein the soluble components within the tobacco is removed. The resulting tobacco residue is then prepared into a reconstituted tobacco sheet and the extract is then concentrated to a solids level of at least 30 percent by weight of solids which is added back to the reconstituted tobacco sheet for further processing into smoking articles.

Description

A METHOD FOR MAKING A RECONSTITUTED TOBACCO LEAF USING STEAM EXPANDED TOBACCO TECHNICAL FIELD This invention relates to a tobacco treatment process with high pressure and temperature and more particularly to a process to improve the smoking quality and the mechanical properties of a tobacco sheet reconstituted by steam expanded tobacco. BACKGROUND OF THE INVENTION In the manufacture of smoking articles, such as cigarettes, pipe tobacco and the like, a substantial portion of the tobacco that has been processed for use in smoking articles was found to be unsuitable for use because of its proprietary properties. undesirable size or taste. For example, the stems and fines of the tobacco manufacturing processes are unsuitable for use in the manufacture of these smoking articles. Since stems and fines represent a substantial amount of investment in raw material, processes have been developed to further process these stems and fines in products such as reconstituted tobacco leaves, which can be used in relatively large quantities in a mixture with leaves. of processed tobacco acceptable. In the processing of reconstituted tobacco some of the components within the stems and fines are solubilized and separated from the tobacco solids. These solubilized components are either discarded or a portion thereof or re-introduced at a later stage of processing reconstituted tobacco leaves. For example, U.S. Pat. No. 4,744,375 issued to Denier et al. Teaches the process for using compounds imparting tobacco flavor, such as ammonia, to make a tobacco product which can be used in reconstituted tobacco leaves. SUMMARY OF THE INVENTION The present invention relates to a method for providing a reconstituted tobacco material, wherein the tobacco in the form of stems and fines is dispersed in water. The resulting tobacco slurry or paste is heated inside a closed vessel under pressure with saturated steam and maintained for sufficient time to allow swelling or explosion of the tobacco. The container is rapidly depressurized to the environment, resulting in fiber formation of the tobacco particles and chemical depolymerization of some of the constituents within the tobacco. This mechanical action also causes a release and solubilization of pectins, and a slight morphological and structural transformation of the tobacco compounds. The resulting tobacco product can then be extracted in water and the fibrous material formed into a sheet using known papermaking equipment. The aqueous extract is generally concentrated and applied to the formed sheet and further processing results in a reconstituted tobacco product having reduced irritation, better tobacco taste and improved smoking quality. Urea and an ammonium salt are added to the tobacco paste either before or after steam pressurization by preferably adding the urea and ammonium salt before steam pressurization. In the present invention, inverted sugars and active humectants as well as other selected chemical additives have also been found useful. It is therefore an object of the present invention to provide a tobacco product for use in reconstituted tobacco, resulting in less irritation, better tobacco flavor and better smoking quality. More particularly, the present invention is directed to a method for making sheets of reconstituted tobacco, comprising the steps of: adding from 50 to 100 parts by weight of tobacco materials to a container containing from 100 to 200 parts by weight of water , from about 1 to 10 parts by weight of an ammonium salt, and from about 1 to 10 parts by weight of urea; bring the first tobacco paste mixture from about 93 to 215.6 ° C ('200 to 420 ° F) and 4.2 to 28.12 kg / cm2 (60 to 400 psi) with saturated steam for a period of about 1 to 15 minutes; and reducing the pressure of the first mixture of tobacco paste to the environment in a time from 0.1 to 1.0 minute. Preferably the ammonium salt will be from 5 to 10 parts by weight, the urea will be from 3 to 8 parts by weight and the total chemical additives for the tobacco / water mixture will be from 10 to 25 parts by weight. In the processing of the first pulp to a tobacco leaf, the process generally includes the additional steps of: adding water to form a second tobacco paste having 15 to 40 weight percent tobacco; heating the second tobacco paste mixture resulting from 48.9 to 82.2 ° C (120 to 180 ° F), for about 2 to 5 minutes, removing water and solubles from the second tobacco paste to form a third tobacco paste containing about 50 to 60 weight percent water and an extract; reduce the size of tobacco particles; adding water to form a fourth tobacco paste having about 1 to 4 weight percent tobacco; and forming a tobacco leaf having from about 10 to 30 weight percent moisture, preferably from about 13 to 16 weight percent moisture. In the processing of the extract, the extract is generally concentrated from about 30 to 35 weight percent of soluble and the resulting extract is then used to coat the formed sheet of tobacco. Preferably, in the present invention the ammonium salt is selected from the group consisting of diammonium phosphate, ammonium acetate, ammonium chloride, ammonium phosphate and mixtures thereof. Humectants, such as glycerin and propylene glycol, as well as inverted sugars, such as glucose and fructose, may also be employed. The preferred temperature at which the first tobacco paste must be heated will be about 168 ° C (335 ° F) with about 7.03 kg / cm2 (100 psi) of saturated steam where the tobacco will be subjected to vapor pressure and temperature for a time of about 3 minutes. In an alternate embodiment, the chemical additives are added to the first tobacco paste after the first tobacco paste has been subjected to saturated steam from approximately 93 to 215.6 ° C (200 to 420 ° F) and 4.2 to 28.12 kg / cm2 (60 to 400 psi) for a period of about 1 to 15 minutes and then reduce the pressure to the environment, prior to the next processing in a molded sheet of tobacco. A better understanding in the present invention will be achieved from the following processes and the examples following said description.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic of a preferred process of the present invention; and Figure 2 is an elevation view of a preferred system for explosion with tobacco vapor of the present invention. DETAILED DESCRIPTION OF THE PREFERRED MODALITY In a preferred method for carrying out the portion of the vapor explosion of the present invention, as illustrated in Figure 2, tobacco materials in the form of fragments cured with combustion gases, fragments of thin-leaved and light-colored tobacco (burley), manufacturing and threshing powder, fragmented tobacco flour, stems cured with exhaust gases, thin-leaved and light-colored tobacco stems (burley), and the like, are introduced at the entrance 12 of a pressure vessel 16 containing water, an ammonium salt, and urea. A humectant and an inverted sugar can also. { in being added. The total amount of tobacco is in the range of about 50 to 100 parts by weight to about 100 to 200 parts by weight of water, from about 1 to 10 parts by weight of ammonium salt, from about 1 to 10 parts by weight of urea, less than one part by weight of humectant and less than one part by weight of invert sugar. A valve 14 is provided by the inlet 12 to close the container 16 after loading and before steam pressurization. Ammonium salts which have been found useful in the present invention include diammonium phosphate, ammonium acetate, ammonium chloride, ammonium phosphate and the like and mixtures thereof. Preferably, the ammonium salts are from 1 to 5 parts by weight. Other additives that have been found useful in the present invention include potassium sorbate, citrus pectin, also as a citric or lactic acid. Usually these additives are from 1 to 10 parts by weight and preferably less than 5 parts by weight. The resulting tobacco / water mixture or the first tobacco paste is then vaporized through the steam inlet 20 where steam with from 4.2 to 28.12 kg / cm2 (60 to 400 psi) has been introduced until the temperature of tobacco paste is increased from about 15.6 to 204.4 ° C (60 to 400 ° F). The resulting temperature is then maintained for about 1 to 15 minutes. Preferably, the vapor will be at approximately 7.03 kg / cm2 (100 psi) and approximately 168 ° C (335 ° F) with a retention time of 3 minutes. The steam pressure treated tobacco is rapidly depressurized to the environment of approximately 0.1 to 1.0 minute. The discharge valve 22 is then opened and the first tobacco paste is transferred through the conduit 26 into a cyclone separator 28 where the steam has been discharged through the outlet 24 and the resulting product is discharged from the discharge bottom. 30 for further processing. As illustrated in Figure 1, the pulp of the steam explosion portion in the process including the cyclone separator 28 is transferred to a pulp tank where the water is added to produce a second tobacco paste that has up to from about 1 to 4% by weight solids. In an alternate embodiment, urea, ammonium salt, and other chemicals can be added to a second tobacco paste. The resulting second tobacco paste is then heated to approximately 48.9 to 82.2 ° C (120 to 180 ° F) and maintained at this temperature for approximately 2 5 minutes to extract the water-soluble components of the tobacco that has expanded by vapor compression . This mixture is then centrifuged with the extracted residue which is generally about 40 to 50 weight percent of tobacco which is further refined by reduction of the particle size of the tobacco fibers. This is generally achieved in a mixer or other type of equipment adapted to agitate or spray the tobacco. The refined pasta is then transported to a blooming operation where the tobacco paste is mixed with water wherein the solids are reduced from 1 to 4 weight percent of the mixture. The mixture is then formed into reconstituted tobacco leaves using commercially available papermaking equipment and techniques such as for example a Fourdiner type machine. The extract of the centrifuge is transferred to an evaporator, such as a vacuum evaporator wherein the solids contents of the extract are increased from about 30 to 35 weight percent solids and then applied through known coating techniques to the resulting tobacco leaf. The resulting sheet is then prepared for further processing in quality tobacco for smoking. EXAMPLES 1 TO 9 For a better understanding of the present invention, the following examples are incorporated herein to illustrate the present invention without intending to be unduly limited in that manner. EXAMPLE 1 A mixture of tobacco materials of 4.54 kg (10 pounds) including waste or fragments of tobacco, manufacturing and threshing powder, fragmented tobacco flour, stems cured with exhaust gases, tobacco stems of thin leaves and light colored ( burley), is dispersed in 9.08 kg (20 pounds) of water containing .114 kg (.25 pounds) of urea, .136 kg (0.30 pounds) of diammonium phosphate, and .272 kg (0.6 pounds) of inverted sugar . The chemical-tobacco-water mixture is then loaded into a steam vessel where saturated steam is introduced at 7.03 kg kg / cm2 (100 psi) to bring the temperature inside the vessel to 168 ° C (335 ° F). The temperature of 168 ° C (335 ° F) was maintained for three minutes. After three minutes, the pressure vessel is depressurized to the environment in less than 1 minute and simultaneously transferred to a cyclone separator where the steam has been discharged and the tobacco product has been recovered. A sample of .499 kg (1.1 pounds) of tobacco subjected to steam pressure was added to a vessel containing 4.5 kg (9.91 pounds) of water. This mixture was then heated to 76.7 ° C (170 ° F) and maintained at this temperature for 30 minutes to allow the water to extract soluble components from the tobacco subjected to steam pressure. This mixture is then centrifuged in a Bock centrifugal extractor for 2 minutes at 12,000 rpm. A sample of 300 grams of extracted residue is mixed with 700 ml of water, refined and paper-like sheets in a Fourdiner wire paper machine. The extract is subjected to a Buchi Rotavapor 150 vacuum evaporator, where the extract is evaporated to approximately 35 percent solids. This extract containing 35 percent solids is then applied again to the reconstituted tobacco leaf previously prepared by coating the leaves leaving the paper production machine. The laminar material was incorporated in cigarettes. EXAMPLE 2 A reconstituted tobacco sheet was made in the same manner in Example 2 as in Example 1, except that the vapor pressure vessel is subjected to saturated steam of 4.71 kg / cm2 (67 pounds) by raising the temperature to 148.9. ° C (300 ° F). The pressure vessel is steamed at 4.71 kg / cm2 (67 psi) and 148.9 ° C (300 ° F) for 6 minutes. The resulting reconstituted sheet material was then incorporated into cigarettes. EXAMPLE 3 This example was carried out in the same way and with the same amounts of materials that were used in Example 1, the only change is that the tobacco was subjected to a tobacco pressure of 29.5 kg / cm2 (420 psi) and 204.4 ° C (400 ° F) and maintained at this pressure and temperature for 5 minutes. The resulting molded reconstituted tobacco sheet was incorporated into cigarettes. EXAMPLE 4 This example was carried out in the same manner and with the same amounts of materials as used in Example 1, except that the tobacco was steam treated at 4.71 kg / cm2 (67 psi) and 148.9 ° C (300 ° F) for 10 minutes.

EXAMPLE 5 This example was carried out in the same manner and with the same amounts of materials as used in Example 1, except that the tobacco was steam treated at 7.03 kg / cm2 (100 psi) and 168 ° C (335 ° F) for 3 minutes. The tobacco was also kept in contact with the additives for 5-6 hours before the steam treatment. EXAMPLE 6 A total of .454 kg (10 pounds) of tobacco materials in the form of .272 kg (.6 pounds) of waste or snuff cured tobacco fragments, .409 kg (.9 pounds) of waste or fragments of thin-leaved and light-colored tobacco (burley), .545 kg (1.2 pounds) of manufacturing and threshing powder, .136 kg (.3 pounds) of fragmented tobacco flour, and 1,407 kg (3.1 pounds) of small stems cured with exhaust gases, and .136 kg (.3 pounds) of small and .409 kg (.9 pounds) large tobacco stems of thin leaves and light colored (burley), dispersed in 9.08 kg (20 pounds) ) of water. The tobacco-water mixture then loaded into a steam pressure vessel and treated with 7.03 kg / cm2 (100 psi) of saturated steam increasing a temperature of 168.3 ° C (335 ° F) and kept under these conditions for 3 minutes . Subsequently, .499 kg (1.10 pounds) of tobacco subjected to steam pressure are added to 4.5 kg (9.91 pounds) of water containing 008 kg (.018 pounds) of urea and .014 kg (.03 pounds) of phosphate. diamonium The mixture is heated to 76.7 ° C (170 ° F) and maintained at this temperature for 30 minutes to extract the water-soluble components of the steam-treated tobacco. The mixture is then centrifuged in a Bock centrifugal extractor for 12 minutes at 12,000 rpm. A total of 300 grams of the extracted residue are mixed with 700 ml of water, refined and formed into paper-like sheets in a Fourdiner-type paper machine. The extract is concentrated by vacuum evaporation in a Buchi 150 rotavapor at 60 ° C (140 ° F) to about 35 percent solids and invert sugar is added to form 3.3% by weight of the finished product. The concentrated extract is applied to the sheet with a sizing press. The resulting reconstituted sheet tobacco is incorporated into cigarettes. EXAMPLE 7 A total of .454 kg (10 pounds) of tobacco materials in the form of .272 kg (.6 pounds) of waste or snuff cured tobacco fragments, .409 kg (.9 pounds) of waste or fragments of thin-leaved and light-colored tobacco (burley), .545 kg (1.2 pounds) of manufacturing and threshing powder, .136 kg (.3 pounds) of fragmented tobacco flour, and 1,407 kg (3.1 pounds) of small stems cured with exhaust gases, and .136 kg (.3 pounds) of small and .409 kg (.9 pounds) of large tobacco stems of thin leaves and light colored (burley), dispersed in 9.08 kg (20 pounds) of water. The tobacco-water mixture then charged into a steam pressure vessel and treated with 29.6 kg / cm2 (422 psi) of saturated steam increasing a temperature of 204.4 ° C (400 ° F) and maintained under these conditions by minutes Subsequently, .499 kg (1.10 pounds) of tobacco subjected to steam pressure are added to 4.5 kg (9.91 pounds) of water containing 008 kg (.018 pounds) of urea and .014 kg (.03 pounds) of phosphate. diamonium The mixture is heated to 76.7 ° C (170 ° F) and maintained at this temperature for 30 minutes to extract the water-soluble components of the steam-treated tobacco. The mixture is then centrifuged in a Bock centrifugal extractor for 12 minutes at 12,000 rpm. A total of 300 grams of the extracted residue are mixed with 700 ml of water, refined and formed into paper-like sheets in a Fourdiner-type paper machine. The extract is concentrated by vacuum evaporation in a Buchi 150 rotavapor at 60 ° C (140 ° F) to about 35 percent solids and invert sugar is added to form 3.3% by weight of the finished product. The concentrated extract is applied to the sheet with a sizing press. The resulting reconstituted sheet tobacco is incorporated into cigarettes.

EXAMPLE 8 A total of .454 kg (10 pounds) of tobacco materials in the form of .272 kg (.6 pounds) of waste or snuff cured snuff, 409 kg (.9 pounds) of waste or fragments of thin-leaved and light-colored tobacco (burley), .545 kg (1.2 pounds) of manufacturing and threshing powder, .136 kg (.3 pounds) of fragmented tobacco flour, and 1,407 kg (3.1 pounds) of small stems cured with exhaust gases, and .136 kg (.3 pounds) of small and .409 kg (.9 pounds) of large tobacco stems of thin leaves and light colored (burley), dispersed in 9.08 kg (20 pounds) of water. The tobacco-water mixture then loaded into a steam pressure vessel and treated with 29.6 kg / cm2 (422 psi) of saturated steam increasing a temperature of 204.4 ° C (400 ° F) and maintained under these conditions for 5 minutes . Subsequently, .499 kg (1.10 pounds) of tobacco subjected to steam pressure are added to 4.5 kg (9.91 pounds) of water containing 008 kg (.018 pounds) of urea and .014 kg (.03 pounds) of phosphate. diamonium The mixture is heated to 76.7 ° C (170 ° F) and maintained at this temperature for 30 minutes to extract the water-soluble components of the steam-treated tobacco. The mixture is then centrifuged in a Bock centrifugal extractor for 12 minutes at 12,000 rpm. A total of 300 grams of the extracted residue are mixed with 700 ml of water, refined and formed into paper-like sheets in a Fourdiner-type paper machine. The extract is concentrated by vacuum evaporation in a Buchi 150 rotavapor at 60 ° C (140 ° F) to about 35 percent solids and invert sugar is added to form 3.3% by weight of the finished product. The concentrated extract is applied to the sheet with a size press and the resulting reconstituted sheet is incorporated into cigarettes. EXAMPLE 9 A total of .454 kg (10 pounds) of tobacco materials in the form of .272 kg (.6 pounds) of waste or snuff cured tobacco fragments, .409 kg (.9 pounds) of waste or fragments of thin-leaved and light-colored tobacco (burley), .545 kg (1.2 pounds) of manufacturing and threshing powder, .136 kg (.3 pounds) of fragmented tobacco flour, and 1,407 kg (3.1 pounds) of small stems cured with exhaust gases, and .136 kg (.3 pounds) of small and .409 kg (.9 pounds) of large tobacco stems of thin leaves and light colored (burley), dispersed in 9.08 kg (20 pounds) of water. The tobacco-water mixture then loaded into a steam pressure vessel and treated with 29.6 kg / cm2 (422 psi) of saturated steam increasing a temperature of 148.9 ° C (300 ° F) and maintained under these conditions for 10 minutes .

Subsequently, .499 kg (1.10 pounds) of tobacco subjected to steam pressure are added to 4.5 kg (9.91 pounds) of water containing 008 kg (.018 pounds) of urea and .014 kg (.03 pounds) of phosphate. diamonium The mixture is heated to 76.7 ° C (170 ° F) and maintained at this temperature for 30 minutes to extract the water-soluble components of the steam-treated tobacco. The mixture is then centrifuged in a Bock centrifugal extractor for 12 minutes at 12,000 rpm. A total of 300 grams of the extracted residue are mixed with 700 ml of water, refined and formed into paper-like sheets in a Fourdiner-type paper machine. The extract is concentrated by vacuum evaporation in a Buchi 150 rotavapor at 60 ° C (140 ° F) to about 35 percent solids and invert sugar is added to form 3.3% by weight of the finished product. The concentrated extract is applied to the sheet with a sizing press. Cigarettes prepared with molded reconstituted tobacco of Examples 6-9 were found to have mild and pleasant taste but those made with reconstituted tobacco of Examples 1-5, which were prepared by adding urea and ammonium salt, prior to steam pressurization they were found to have a milder and more pleasant flavor than those cigarettes using reconstituted tobacco of Examples 6-9.

The above detailed description and the Examples are given first for further understanding and unnecessary limitations will not be understood from there since they will be obvious modifications for those skilled in the art when reading the description and can be made without departing from the spirit of the invention and scope of the appended claims.

Claims (27)

1. CLAIMS 1. A method for producing a tobacco paste for use in the manufacture of molded reconstituted tobacco sheets, characterized in that it comprises the steps of: a) adding from 50 to 100 parts by weight of tobacco materials to a container containing from 100 to 200 parts by weight of water, from about 2 to 40 parts by weight of chemical additives including from about 10 parts by weight of ammonium salt, from about 1 to 10 parts by weight of urea, the resulting mixture is a first tobacco paste, b) bring the first tobacco paste to a temperature from about 93 to 215.6 ° C (200 to 420 ° F) with 4.2 to 29.53 kg / cm2 (60 to 420 psi) of saturated steam and maintain that temperature and pressure for a period of about 1 to 5 minutes; c) reduce the pressure of the first tobacco paste to the environment from 0.1 to 1.0 minute.
2. 2. - A method according to claim 1, characterized in that the ammonium salt is selected from the group consisting of ammonium acetate, ammonium chloride, ammonium phosphate and mixtures thereof.
3. 3. - A method according to claim 1, characterized in that it includes the addition of up to 1 part by weight of a humectant.
4. 4. - A method according to claim 3, characterized in that the humectant is selected from the group consisting of glycerin and propylene glycol.
5. 5. - A method according to claim 1, characterized in that it includes the addition of other chemical additives that are chosen from the group consisting of citric acid, lactic acid, and inverted sugars and mixtures thereof.
6. 6. A method according to claim 5, characterized in that the inverted sugars include fructose and glucose.
7. 7. - A method according to claim 5, characterized in that the inverted sugars are up to 1 part by weight.
8. 8. A method according to claim 6, characterized in that the inverted sugars are added with the urea and ammonium salt.
9. 9. A method according to claim 6, characterized in that the invert sugar is added after step c) of claim 1.
10. 10. A method according to claim 1, characterized in that the ammonium salt having from 1 to 5 parts by weight.
11. 11. - A method according to claim 1, characterized in that the urea is present from 1 to 5 parts by weight.
12. 12. A method for producing a reconstituted tobacco sheet comprising the steps of: a) adding from 50 to 100 parts by weight of tobacco materials to a container containing from 100 to 200 parts by weight of water, from about 2 to 40 parts by weight of chemical additives including from about 1 to 10 parts by weight of ammonium salt, from about 1 to 10 parts by weight of urea, the resulting mixture is a first tobacco paste, b) carrying the first paste of tobacco at a temperature of approximately 93 to 215.6 ° C (200 to 420 ° F) with 4.2 to 28.12 kg / cm2 (60 to 400 psi) of saturated steam and maintaining said temperature and pressure for a period of approximately 1 to 5 minutes; c) reduce the pressure of the first tobacco paste to the environment from 0.1 to 1.0 minute; d) adding water to the first tobacco paste to form a second tobacco paste having 15 to 40 weight percent tobacco; e) heating the second tobacco paste from 48.9 to 82.2 ° C (120 to 180 ° F) for about 2 to 5 minutes; f) removing water and solubles from the second tobacco paste containing from about 50 to 60 weight percent water and a first extract; g) reducing the particle size of the tobacco materials in the third tobacco paste; h) adding water to the third tobacco paste to form a fourth tobacco paste having from 1 to 4 weight percent of tobacco; and i) forming a tobacco sheet using the fourth paste having about 10 to 30 weight percent moisture.
13. 13. - A method according to claim 11, characterized in that the ammonium salt is selected from the group consisting of diammonium phosphate, ammonium acetate, ammonium chloride, ammonium phosphate and mixtures thereof.
14. 14. - A method according to claim 12, characterized in that it includes the addition of up to 1 part by weight of a humectant.
15. 15. A method according to claim 14, characterized in that the humectant is selected from the group consisting of glycerin and propylene glycol.
16. 16. A method according to claim 12, characterized in that it includes the addition of other chemical additives that are chosen from the group consisting of citric acid, lactic acid, inverted sugars and mixtures thereof.
17. 17. - A method according to claim 16, characterized in that inverted sugars include fructose and glucose.
18. 18. - A method according to claim 16, characterized in that the inverted sugars are up to 1 part by weight.
19. 19. A method according to claim 12, characterized in that step f) includes a centrifuge to remove the water including the solubles to form the first extract and the third tobacco paste.
20. 20. A method according to claim 12, characterized in that it includes reducing the particle size in step g) in a vessel having stirring means.
21. 21. A method according to claim 12, characterized in that step i) includes a paper producing machine.
22. 22. - A method according to claim 21, characterized in that the paper producing machine includes a Fourdiner wire to discharge the water through.
23. 23. A method according to claim 12, characterized in that it includes the following additional steps: j) concentrating the first extract to a solution containing 30 to 35 weight percent of soluble; and k) coating the tobacco leaf formed in step i).
24. 24. A method according to claim 12, characterized in that the chemical additives are from 10 to 25 parts by weight.
25. 25. A method according to claim 12, characterized in that the ammonium salt is from 5 to 10 parts by weight.
26. 26. A method according to claim 12, characterized in that the urea is from 3 to 8 parts by weight.
27. 27. A method according to claim 12, characterized in that the tobacco leaf has approximately 13 to 16 weight percent moisture.