GB2115677A - A method for expanding tobacco - Google Patents

Abstract

A process for expanding tobacco which comprises: (a) contacting tobacco at a temperature above the freezing point of its moisture content with a gas (for example, carbon dioxide) under pressure, (b) cooling the tobacco until its moisture content freezes to entrap a portion of the gas in solid solution with the frozen moisture, (c) reducing the pressure, and (d) rapidly heating the frozen tobacco to melt the moisture and release the dissolved gas, thereby expanding the tobacco, and fix it in its expanded condition. <IMAGE>

Description

SPECIFICATION Method for expanding tobacco Background of the Invention The present invention relates to a method for increasing the filling power of tobacco, using a gas such as carbon dioxide as an expanding agent.

There are numerous processes for expanding tobacco, or increasing its filling power, which vary widely in performance and cost. Most such processes utilize an expanding agent with which the tobacco is impregnated and which changes into the gas phase, or otherwise expands, within the tobacco structure to effect the expansion of that structure.

Carbon dioxide has been found to be a useful expanding agent in obtaining a high degree of expansion, but processes which employ it are costly in terms of both equipment and operating costs. This is because said processes employ either very high pressures or cryogenic process temperatures, or both.

U.S. Pat. No. 4,165,618 describes a complex system of autoclaves and holding chambers to submerge tobacco in liquid CO2 at a very high pressure. In the commercially available DIET process for expanding tobacco, such equipment is used to impregnate said tobacco with dry ice, or solid CO2, at --1 0 F.

U.S. Pat. No. 4,250,898 describes a process which is operable at lower pressure, but requires refrigeration down to about -900F.

U.S. Pat. No. 4,253,474 describes still another expansion process using carbon dioxide, which requires both high pressure and low temperature.

It is an object of the present invention to provide a method of utilizing the high performance expansion characteristics of 9 gas such as carbon dioxide which requires only moderate temperature and pressure in processing.

It is a further object of the invention to provide a method which is compatible with continuous, rather than batch, operation.

And it is still a further object to provide a method which is relatively simple and inexpensive, in operation and in the equipment required.

Summary of the Invention This disclosure relates to a process for expanding tobacco in which (1) said tobacco is exposed to a gas such as carbon dioxide under pressure while said tobacco and gas are at a temperature above the freezing point of the moisture content of said tobacco, (2) said tobacco is cooled to a temperature sufficient to freeze its moisture content, while still under pressure, to retain a portion of said gas as an impurity in solid solution in said frozen moisture, (3) the pressure under which said tobacco is held is reduced, and (4) said frozen tobacco is rapidly heated to melt said frozen moisture and release said retained gas inside the tobacco structure, to expand said tobacco.

Detailed Description of the Invention This invention relates to a means of expanding tobacco with a gas such as carbon dioxide, utilizing relatively moderate temperature and pressure in processing. In accordance with the invention, tobacco at a temperature above the freezing point of its moisture content is preferably brought into contact with carbon dioxide under pressure. In practice, the moisture content of said tobacco may conveniently be about 12% by weight or more. Its temperature at this stage may be ambient, or about 700 F. However said tobacco may also be pre-chilled to a temperature above about 320F in order to minimize the consumption of carbon dioxide in processing if said carbon dioxide is used as a refrigerant as well as an expanding agent.

Carbon dioxide is ideally suited for use in accordance with the invention, because it is highly soluble in water and also innocuous in terms of possible side effects on said tobacco's product characteristics. Nitrogen may be used, for example, but its solubility in water is substantially less than that of carbon dioxide at an equivalent pressure, so a much higher process pressure would be required with nitrogen. Other gases, such as hydrogen sulfide or sulfur dioxide, may be far more soluble than carbon dioxide but may yield undesirable product characteristics chemically, or may be impractically expensive as compared with carbon dioxide.

The solubility of any gas in water is roughly proportional to pressure. It is desirable to impregnate said tobacco with a substantial quantity of said expanding agent, and this may be accomplished by freezing said tobacco under a high pressure, or by utilizing a gas that is particularly soluble in water, or by moistening said tobacco with a substantial quantity of water prior to its impregnation, or hy some combination of such measures. However the use of extreme high pressure is unattractive because of the expense thereof, and it is desirable to limit the moisture content of said tobacco to a level approximating that prevalent in normal tobacco processing. It has been found that said tobacco is impregnated with an adequate quantity of carbon dioxide at pressure as low as about 60 psig, with said tobacco having a moisture content of about 20% by weight.

Following the impregnation of said moistened tobacco with carbon dioxide, said tobacco is chilled to a temperature sufficient to freeze its moisture content. Water as a component in organic materials such as tobacco typically does not freeze at the normal 320Ffreezing point of free water, and its freezing point may be further depressed if it contains a gas such as carbon dioxide in solution. It has been found that chilling said tobacco to a temperature of about --30"F is adequate, although it may also be possible to obtain the desired freezing at a temperature as high as about +100F if said chilling is uniform and well controlled.

Preferably said steps of impregnation and freezing under pressure take place within a single pressurized chamber, having a warm region and a cold region. Said tobacco preferably enters said chamber at its warm region and is conveyed to its cold region to be frozen after an adequate period for impregnation, such as about one minute or less, and then said frozen tobacco preferably exits said chamber through a rotary valve or lock device, the entire procedure taking place with a continuous flow of said tobacco.

Witnin said cold region of said chamber, said tobacco may be frozen by convection by means, for example, of gas circulated through cooling coils. Alternatively carbon dioxide itself may be utilized as the refrigerant, for example, by spraying it in liquid form into the cold region, as carbon dioxide in normal commercial storage as a liquid at about 300 psig and OOF is an excellent refrigerant.

Once said tobacco has been thoroughly and uniformly frozen, the pressure in which it is held must be reduced as the last essential step prior to expansion. The pressure to which it is reduced may be any pressure substantially lower than that at which it was impregnated, but most conveniently and preferably said pressure is reduced to atmospheric pressure as said tobacco exits said charnber. The pressure reduction is necessary so that gas liberated by the melting of said tobacco's moisture content will have a greater actual volume than during impregnation, and wi!l thereby expand said tobacco.

The final step in the expansion of said tobacco in accordance with the invention is the heating of said tobacco to melt said frozen moisture content and liberate the gas dissolved therein, and to fix said tobacco in its expanded condition. The structure of tobacco is porous, and gas generated therein will tend to escape from within said structure without building up sufficient pressure for expanding said tobacco unless said gas yeneration is rapid. Preferably said tobacco is neated for expansion in a downdraft belt dryer as described in copending application Serial No.

304,713, although a gas transport dryer or any other intense heating means may be used.

Practice of the invention will become more apparent from the following examples.

EXAMPLE 1 About 5 g of tobacco containing about 20% moisture by weight was placed in a vessel comprising a length of 1" pipe with a full-diameter ball valve at one end and a small metering valve at the other end, and including a temperature probe.

The vessel was connected via said small valve to a regulated source of CO2 gas at about 70 psig, and said small valve opened to purge said vessel gently with a flow of CO2. Then said large valve was closed, and the pressure in said vessel brought to 70 psig.

A styrofoam container was placed around said vessel and said vessel was sprayed with liquid nitrogen, regulated in flow to bring the temperature to about -300F and maintain said temperature for about 10 minutes to allow said tobacco inside said vessel to be cooled to its wall temperature of --300F. Then said small valve was ciosed and said vessel disconnected from said CO2 source, following which said small valve was then opened again very slightly to discharge the pressure in said vessel. When pressure was reduced to about one atmosphere, as evidenced by the cessation of apparent escaping gas flow, said ball valve was opened and said tobacco poured onto a table.

Said tobacco expanded visibly when breathed at, the temperature of exhaled air being about body temperature or 98.60 F. Said expansion coincided in time with the visible disappearance of all frost from said tobacco, indicating that the temperature of said tobacco was about the freezing or melting temperature of water at the moment of its expansion.

EXAMPLE 2 A second sample of tobacco was impregnated in the manner of example 1. However said impregnated tobacco was poured from said vessel onto a surface of 50 mesh stainless steel screen, and then rapidly heated for about 4 seconds with a flow of gas downward through said screen, said gas having a velocity about 30 ft/sec and temperature about 4000 F.

Said tobacco was left in an open dish to reach moisture equilibrium with the ambient atmosphere for three days. Then a 2.5 g portion of said tobacco was placed in a 100 cc graduate and compressed under a piston with about 2.7 psi pressure for 5 minutes. The volume of said compressed 2.5 g portion was about 27 cc.

A 2.5 g portion of unprocessed tobacco from the same source from which the processed sample had been drawn, and also in moisture equilibrium with the ambient atmosphere, had a volume of 1 5 cc when measured as described above. The processed sample was therefore expanded by about 80%.

Claims (8)

1. A method for expanding tobacco, the improvement comprising the steps of: a. Contacting tobacco at a temperature above the freezing point of its moisture content with a gas under pressure, b. cooling said tobacco to below the temperature at which its moisture content freezes, to entrap a portion of said gas in solid solution with said frozen moisture content, c. reducing said pressure, and d. rapidly heating said frozen tobacco to melt said moisture content and release said dissolved gas, thereby expanding said tobacco, and to fix said tobacco in its expanded condition.

2. The method of claim 1 wherein said pressurized gas is carbon dioxide.

3. The method of claims 1 or 2 wherein the pressure in steps (a) and (b) is about 50 psig to 200 psig, and is reduced in step (c) to about 1 atmosphere.

4. The method of claims 1 or 2 wherein said tobacco is cooled in step (b) to about + 100 to 300 F.

5. The method of claims 1 or 2 wherein said tobacco is heated with a hot gas by convection in step (d), said hot gas having a temperature of about 2000 to 6000F.

6. The method of claim 5 wherein said convection heating takes place by means of a downdraft of said hot gas through a porous belt on which said tobacco is conveyed.

7. The method of claim 2 wherein said moisture content of said tobacco is about 12% to 30% by weight.

8. A method for expanding tobacco substantially as described herein with reference to Example 1 or Example 2.