Process For Puffing Tobacco

Abstract

Tobacco having at least 6 percent moisture is impregnated with ammonia and carbon dioxide to introduce into the tobacco preferably from about 3 percent to about 6 percent by weight of ammonia and from about 2 percent to about 8 percent of carbon dioxide based on the weight of the tobacco. The tobacco is thereafter heated at a temperature of from 250.degree. F to about 700.degree.F for a time sufficient to puff the tobacco.

Description

BACKGROUND OF THE INVENTION

The art has recognized the desirability of increasing the bulk or volume of tobacco for various reasons. An early purpose was to make up the loss of weight caused by the curing process. A further reason for expanding tobacco was to improve the smoking characteristics of tobacco stems. Another purpose was to increase the filling power so that a smaller amount of tobacco would be needed to produce a firm cigarette rod or the like, which would produce lower tar and nicotine than a comparable product made of unexpanded tobacco.

A patent to Hawkins, U.S. Pat. No. 1,789,435 granted in 1931 describes a method and apparatus for expanding the volume of tobacco in order to make up the loss of weight caused in curing tobacco leaf. To accomplish this object the cured and conditioned tobacco is subjected to air, carbon dioxide or steam under pressure and then on release of pressure the tobacco tends to expand. The patent states the volume of the tobacco is increased to the extent of about 5-15 percent.

A series of patents to Burde, granted in 1968, specifically U.S. Pat. No. 3,409,022, 3,409,023, 3,409,027 and 3,409,028, describe procedures for enhancing the utility of tobacco stems for use in smoking products by subjecting the stems to a puffing operation utilizing various types of heat treatment or microwave energy.

A patent to Hind granted in 1969, U.S. Pat. No. 3,425,425 also relates to the use of carbohydrates to improve the puffing of tobacco stems. In the process, tobacco stems are soaked in an aqueous solution of carbohydrates and then heated to puff the stems. The carbohydrate solution may also contain organic acids and/or certain salts which are used to improve the flavor and smoking qualities of the stems.

A publication in the "Tobacco Reporter" of Nov. 1969 by P.S. Meyer describes and summarizes tobacco puffing or expansion procedures or investigations for expanding and manipulating tobacco for purposes of reducing costs and also as the means for reducing the "tar" content by reduction in the delivery of smoke. Mention is made in this publication of puffing tobacco by different procedures including the use of halogenated hydrocarbons, low pressure or vacuum operation, or high pressure steam treatment that causes leaf expansion from inside the cell when outside pressure is suddenly released. Mention is also made in this publication of freeze-drying tobacco which apparently causes an increase in volume.

Thus far, no completely satisfactory process has been found. The difficulty with the various earlier suggestions for expanding tobacco is that, in many cases, the volume is only slightly or at best only moderately increased, noting for example, the 15 percent expansion as the maximum achieved by Hawkins. On the other hand, while a substantial volume increase may be achieved by freeze-drying, this type of operation has the disadvantages of requiring elaborate and expensive equipment and very substantial operating costs. With respect to the teaching of using heat energy, infrared or radiant microwave energy to expand tobacco stems, the difficulty is that while stems respond to these heating procedures, tobacco leaf does not respond effectively to this type of process.

The use of special expanding agents, for example, halogenated hydrocarbons, such as are mentioned in the Meyer, publication for expanding tobacco, is also not completely satisfactory because these substances are generally relatively expensive and because a high temperature is generally required to volatilize or remove the substances after the tobacco has been expanded. The introduction, in considerable concentration, of materials which are foreign to tobacco presents the problem of removing the expansion agent after the treatment has been completed in order to avoid affecting aroma and other properties of the smoke due to extraneous substances used or developed from the combustion of the treated tobacco.

The present invention relates broadly to the puffing of tobacco with a relatively inexpensive, low combustibility, volatile and nontoxic agent and more particularly to the production of a puffed tobacco product of substantially reduced density produced by impregnating tobacco with ammonia and carbon dioxide and then subjecting the impregnated tobacco to expansion conditions such as heat, or reduced pressure or both, or to other known radiant energy conditions as previously mentioned.

To carry out the process of the invention, one may treat either whole cured tobacco leaf, tobacco in cut or chopped form, or selected parts of tobacco such as tobacco stems or reconstituted tobacco. In comminuted form, the tobacco to be impregnated may have a particle size of about 20 to >5 mesh, but preferably not less than about 30 mesh. The material treated may be in relatively dry form, or may contain the natural moisture content of tobacco. Preferably the tobacco should have at least about 6 percent moisture but less than 35 percent moisture. The reason for the upper limit will be provided in the further description of the invention.

The essential feature of the invention process is the expansion or puffing of the tobacco utilizing ammonia and CO as the primary expanding agents. It is believed that the ammonia under the conditions of operation and possibly in the presence of some moisture, causes the expansion of the tobacco to a greater and less reversible extent than can be obtained with various other expanding agents.

The pretreatment of tobacco may be with liquid or gaseous ammonia or with ammonium hydroxide to permit absorption of ammonia into the tobacco cellular structure. A preferred method is to introduce both ammonia and carbon dioxide into the tobacco or by contacting tobacco with either ammonium carbonate or ammonium bicarbonate applied directly, or formed in situ by the reaction of ammonia with carbon dioxide and moisture in the tobacco. In any of the procedures indicated, substantial expansion takes place on heating the impregnated tobacco either by means of the ammonia alone or the combined effects of both ammonia and carbon dioxide within the tobacco structure.

The treatment of tobacco with ammonia may be by direct contact with liquid ammonia, solutions of ammonia, ammonia vapor or by substances capable of evolving ammonia such as by incorporating ammonium carbonate or bicarbonate in the tobacco to be treated. Sufficient time is provided to result in impregnating at least 1 percent by weight of ammonia or its equivalent into the tobacco cell structure for acceptable expansion, with 2.5 percent to 8 percent by weight absorbed being preferred.

Various methods are contemplated for exposing the tobacco to the selected ammoniacal agent. One procedure is to use liquid ammonia applied in a form of a spray, followed by a period of stabilization or equilibration of a few minutes to 24 hours to effect the desired absorption and retention of the agent in the tobacco. Substantial addition of ammonia to the tobacco may thus be reached, amounting to as much as 100 percent by weight. However, a thorough spraying for five minutes is satisfactory requiring no further standing, with about 50 percent absorption being achieved.

Another method in the use of liquid ammonia is to dip the tobacco into liquid ammonia for a period of one to two minutes followed by draining and standing or retaining the treated tobacco in a closed vessel up to two to four hours. This will result in about eight to about 12 percent absorption. Satisfactory absorption may be achieved by dipping the tobacco into liquid ammonia for about five minutes and merely draining the tobacco on withdrawal. By this procedure about 50 percent of ammonia is absorbed. Concentrated ammonium hydroxide may alternatively be used as a substitute for liquid ammonia, the tobacco being held therein for about one to two minutes.

Ammonia vapor may also be used, for example, by exposing the tobacco to ammonia vapors from an aqueous solution of ammonia (ammonium hydroxide) for a period of one hour to one week but preferably from about four to 24 hours which results in an ammonia intake of from 1 percent to about 12 percent by weight with additional intake of some moisture. In general, where tobacco is exposed to ammonia long enough to absorb 2 percent or more, the impregnated tobacco should not be exposed to the air for more than a few minutes before puffing, so that undesirable darkening is avoided.

By following the above described ammonia vapor procedure for ammonia absorption, the tobacco can be impregnated with from 1 percent to as high as 50 percent by weight ammonia depending on the partial pressure of the ammonia vapor over the aqueous ammonia. As indicated previously, about 2.5 to 8 percent ammonia impregnation is preferred.

While ammonia by itself is a satisfactory puffing agent, it has been found that excellent results are achieved by combining the effects of ammonia and carbon dioxide puffing by introducing both of these expansion agents into the tobacco. To obtain the combined effects, a preferred procedure is to expose tobacco to ammonia vapors or gas, then CO.sub.2 gas or the reverse, and, if desired, adding powdered carbon dioxide, allowing the ammonia and carbon dioxide sufficient time to be absorbed. About 10 minutes to an hour of exposure to the ammonia vapor followed by the same length of time for CO.sub.2 with cooling by the use of a water jacket or the like will yield a satisfactory amount of impregnation. The absorption may be improved if the impregnation vessel is first evacuated to a low initial pressure up to 26 in. of mercury absolute. Th amounts and rates of absorption are determined by the rates at which heat can be dissipated from the mass of tobacco undergoing treatment and the final temperature attained since there is an exothermic heat of solution and reaction of the ammonia, carbon dioxide and the moisture in the tobacco. It is therefore best to keep the temperature of the tobacco undergoing absorption at a reasonably low point, below about 100.degree.F. and preferably in the neighborhood of about 75.degree.F. by cooling, to achieve satisfactory absorption and formation of ammonium carbonates in the tobacco.

An alternative method employs ammonium carbonate or ammonium bicarbonate for supplying both ammonia and carbon dioxide as expansion agents for tobacco. One procedure for obtaining impregnation of these compounds is to subject the tobacco in an enclosed zone from 24 to 96 hours to the ammonia and carbon dioxide gas that is given off or released from the ammonium carbonates, permitting these gases to be absorbed and to react with the moisture present to form ammonium carbonates. Penetration of the gases and formation of ammonium carbonates in the tobacco is expedited if the tobacco impregnation chamber is first evacuated. Pressures ranging up to 26 in. of Hg absolute may be used. Absorption is enhanced by cooling the contents to hold the temperature of the tobacco below about 100.degree.F. Following the impregnation, completed when the temperature is in the neighborhood of about 75.degree.F., the tobacco is held for about 15 minutes to one hour before the final puffing step.

Still another procedure is to utilize ammonium carbonate or ammonium bicarbonate in the form of a dust applied to tobacco leaf in an amount of about 1-25 percent by weight of the tobacco. The treated tobacco is then held for about 18 to 96 hours but preferably about 24 hours is sufficient for equilibration and retention of about four to eight percent of the carbonates within the tobacco structure.

A still further method for impregnating tobacco with ammonium carbonate or bicarbonate is to contact the tobacco with these salts suspended or partially dissolved in a suitable liquid medium for about 1 to 48 hours, permitting the carbonates to be absorbed along with some absorption of the liquid medium itself. Examples of liquid carriers or solvents that may be used are methylene chloride or highly concentrated methanol or ethanol aqueous solutions comprising about 75 to 95 percent alcohol. The liquid solvent or carrier may be removed in good measure by exposing the tobacco to a flow of inert gas or air before puffing.

In the impregnation of tobacco with carbonates, whether by contacting the tobacco with ammonia and carbon dioxide, or when these gases are produced from impregnation with ammonium carbonate or bicarbonate, good subsequent expansion to densities of about 0.25 has been found when the individual levels of ammonia and CO.sub.2 in the penetrated tobacco is in the range of about 3 to 6 percent by weight of ammonia and 2 to 8 percent by weight of carbon dioxide.

An important advantage in the use of ammonium carbonate or bicarbonate is the fact that these compounds easily decompose at temperatures quite substantially below the charring temperature of tobacco. A still further advantage is that the treated tobacco need not be expanded immediately but may be stored or handled for short periods in air without loss of puffing capacity.

Following the impregnation of the tobacco by the various means described above, the impregnated tobacco is then exposed to expansion conditions by subjecting the treated product to heat or the equivalent, or to reduced pressure or a combination of these effects. This may comprise the use of hot surfaces, or a stream of hot air, a mixture of gas and steam, or exposure to radiant energy such as radiant microwave energy or infrared radiation. Another method for causing expansion after the ammonia treating step is to subject the treated leaf to a sudden decrease in pressure as for example in "guns" such as are commonly used for puffing cereals. A convenient means of expanding treated tobacco is to entrain it in a stream of heated gas, such as superheated steam, which serves to carry away the expelled ammonia which may subsequently be recovered for reuse.

As is well known in processing of any organic matter, overheating can cause damage, first to color, such as undue darkening, and finally, to the extent of charring. The necessary and sufficient temperature and exposure time for puffing without such damage is a function of these two variables as well as the state of subdivision of the tobacco. Thus, to avoid undesirable damage in the heating step, the impregnated tobacco, at heating temperatures in the neighborhood of 700.degree.F., should not be exposed to such temperatures for longer than the time it takes for the tobacco particles to attain a temperature of about 285.degree.F., which is normally about 0.1 seconds.

One method for causing the expansion of the tobacco cells is to use the radiation methods described in either U.S. Pat. No. 3,409,022 or No. 3,409,027. Another method involves the use of a heat gun such as the Dayton heat gun or the equivalent, operating at an exit air temperature of 375.degree.-650.degree.F. for a period of about 0.2 seconds to four minutes, the shorter times of course being given for the higher temperatures. In this operation, the tobacco never attains a temperature above about 285.degree.F., being cooled by the rapid evolution of gases.

Another system, usually preferred, is to use a dispersion dryer, for example, one that is supplied either with steam alone or in combination with air. An example of such a dryer is a Proctor & Schwartz PB dispersion dryer. The temperature in the dryer may range from about 250.degree.-700.degree.F. with contact time in the dryer of about four minutes at the lowest temperature to about 0.1 to 0.2 seconds at the highest temperature. In general, a 0.1 to 0.2 second contact time is utilized when the hot gas temperature is 500.degree.-600.degree.F. or somewhat higher. As stated before, other known types of heating means may be used as long as they are capable of causing the impregnated tobacco to puff without excessive darkening. It should be noted, that where a high percentage of oxygen is present in the hot gases, it will contribute to darkening, so that if a hot-steam mixture is employed, a high proportion (e.g., over 80 percent by volume) of steam is preferred.

When tobacco with very high moisture content is treated with ammonia and puffed by heat, or ammonia-treated tobacco is heavily moisturized before heat puffing, the product may become unnecessarily darkened. It has not been shown that smoke flavor or other properties are particularly affected, but where light color is desired excess moisture should be avoided. The moisture level that has been observed to cause darkening is in the neighborhood of about 35 percent or higher. The moisture content in the tobacco prior to the above described treatment should be in the range of about 3 percent to 25 percent and preferably from about 5 percent to about 20 percent to avoid undesirable darkening effects.

A measurement of the expansion effect produced in the tobacco by the above procedures may be carried out by determining the percentage of the product that floats on a specific low density liquid such as acetone, alcohol, petroleum ether or hexane, or by measuring the density of the product by a simple application of the weight in air vs weight in liquid method, with acetone as the immersion liquid. A perforated metal case (conveniently a tea ball) holds the sample (3-5g.). The weight in liquid is recorded when the balance has come to rest (60 to 90 seconds). The only precaution is to see that all bubbles have been released by tapping the case, if necessary, during both the tare and sample weighings.

As described herein, a density of the final puffed tobacco product in the range of 0.25 to 0.60g./cc. is preferred.

The following examples will serve to illustrate the techniques in greater detail. It should be noted that percentages as given in the examples are on a weight basis, unless otherwise indicated.

EXAMPLE 1

Bright tobacco in the form of cut filler and having a moisture content close to 12 percent is sprayed with a mist of liquid ammonia for a period of five minutes. The flow rate of gas through a Proctor & Schwarz "P.B." dispersion dryer (attached at outlet to a cyclone separator) is set at 2200 ft/min., at a superheated steam/air mixture in a ratio (volume) of about 90/10. Inlet temperature is 550.degree.F. The treated filler is fed into the system and the estimated exposure time is two seconds. The product is well puffed and has color equivalent to that before treatment or slightly lighter.

EXAMPLE 2

Tobacco as cut filler was exposed for 16 hrs. at room temperature in a closed vessel containing vapors from an open container of aqueous ammonium hydroxide.

The filler when placed on a hot plate, surface temperature 480.degree.F, expanded noticeably. Filler similarly prepared was passed through a Proctor & Schwarz dispersion dryer set at 2000 ft/min. steam/air (5:1) flow, inlet and outlet temperatures 500.degree.F and 400.degree.F (minimum) respectively. Microscopic examination showed puffing had occurred; about 50 percent of the product floated on petroleum ether.

EXAMPLE 3

Cut filler weighing 15 g. was sprayed in a polyethylene bag with 10 ml. of aqueous ammonium hydroxide (30 percent NH.sub.3) and left in the closed bag several days. With the dispersion dryer set at 2200 ft/min. superheated steam/air (5:1 approx. volume ratio) flow, 525.degree.F and 420.degree.F at inlet and outlet, respectively, the filler was given two passes through the system for an estimated four-second exposure (after one pass it was still damp). The product was puffed and about 95 percent floated on absolute ethanol.

EXAMPLE 4

Cut filler was exposed over aqueous ammonium hydroxide over-night to impregnate it with ammonia. The filler was then exposed to CO.sub.2 gas and finally it was mixed with powdered solid carbon dioxide to allow the ammonia, carbon dioxide, and moisture to react. The filler was passed through the dispersion dryer (2000 ft/min. steam/air, approx. 5:1, 550.degree.F and 450.degree.F at inlet and outlet). The filler was puffed and 95 percent floated on absolute ethanol.

EXAMPLE 5

Burley filler (moisture 12-15 percent) was sprayed with liquid ammonia for varying lengths of time, then exposed in a rotating wire cage to air from a Dayton heat gun at approximately 400.degree.F for one minute, followed by one minute of air with the heat off. The degree of puffing was noted by the fraction of filler which floated on various solvents: ethanol, d. 0.794; petroleum ether, d. 0.733; hexane, d. 0.687. Results are shown in Table I.

Table I

Puffing of Burley Filler

(Con- NH.sub.3 spray, min. 1 3 5 0 trol)* % Floating on absolute ethanol 100 100 100 10 % Floating on petroleum ether 50 100 100 <5 % Floating on liquid hexane 25 90 100 <5 *Heating just 15 sec. to avoid charring.

Bright filler with five minute spray also showed 100 percent floating. Microscopic examination of sectioned particles led to estimate of at least 100 percent expansion in cross-section thickness.

EXAMPLE 6

Cut Burley filler at varying moisture levels was sprayed with anhydrous liquid ammonia for five minutes and treated with air at 400.degree.F for 70 seconds from the Dayton heat gun. Results are shown in Table II. Acetone has d. 0.782.

TABLE II

Puffing of Burley Filler

% Moisture 2.8 12.0 17.8 20.8 % Floating on acetone 0 100 100 100 % Floating on petroleum ether 0 70 100 100 % Floating on liquid hexane 0 70 100 100

In another test, appreciable puffing occurred at 5.5 percent initial moisture, and puffing at 19.4 and 25.3 percent initial moisture was approximately equal.

EXAMPLE 7

A 4.8 liter glass resin-flask was fitted with a chromel-alumel temperature probe connected to a recorder, and with connections to sources of vacuum, gaseous CO.sub.2, gaseous ammonia and a vacuum gage. 40 grams of bright tobacco was placed in the container. A vacuum of 20 inches (of mercury) was drawn or about 1/3 of an atmosphere absolute pressure and CO.sub.2 was introduced to a vacuum of 10 inches. Then ammonia was introduced to a vacuum of two inches. During the next 20 minutes, ammonium bicarbonate deposited in the tobacco causing a temperature rise of 11.7.degree.C. After two hours, the temperature had returned to ambient (26.degree.C) and the pressure had returned to 10 inches. The container was then filled with more CO.sub.2 (to ambient pressure) and almost no further temperature change was observed.

Calculations, based on the amounts of CO.sub.2 and ammonia added, indicated that nearly 25 percent excess CO.sub.2 appeared to have been present initially. Converting the temperature rise to calories of heat evolved, it was calculated that about 60 percent of the ammonia present had reacted on the tobacco to the equivalent of ammonium bicarbonate. The sample was subsequently puffed as in Example 4 at 500.degree.F and showed 70 percent floaters on petroleum ether.

EXAMPLE 8

One hundred and ninety grams of flue cured tobacco at 7.7 percent moisture was stored for 72 hours with 68 grams of commercial ammonium carbonate at a partial pressure of 44 mm. The pressure rose to an equilibrium of 180 mm after a few hours. About nine grams of the carbonate sublimed, and a total of nearly six grams of ammonia and CO.sub.2 was found on the tobacco by analysis.

The treated tobacco from the above experiments was expanded in the dispersion dryer at 400.degree. and 550.degree.F with 1.8 percent NH.sub.3 and 1.2% CO.sub.2 produced in the tobacco, expansion densities found were 0.60 at 400.degree.F and 0.41 at 550.degree.F.

EXAMPLE 9

Cut bright leaf filler was dipped in methylene chloride saturated with ammonium carbonate. It was exposed for two days to the air. When this filler was placed on a hot plate, it puffed with some audible popping but without the more violent and irregular popping observed with methylene chloride. Most of the solvent had apparently been lost before the puffing.

EXAMPLE 10

In equipment like that used in Example 7, 40 grams of E-7 bright tobacco filler was evacuated and exposed to ammonia vapor at atmospheric pressure. After about 30 minutes the tobacco was removed and subjected to steam/air (90/10) in the dispersion dryer at an inlet temperature of 500.degree.F. approx. Density was found to be 0.27g./cc. as compared with 1.14g./cc. for the filler before treatment.

EXAMPLE 11

Fifty pounds of filler-cut flue-cured tobacco at 11 percent (dry basis) moisture was charged to a large tumbler cooled by water at 42.degree.F. The tumbler was set in motion at 6 RPM and evacuated to about one inch Hg (absolute pressure). Then, four pounds of liquid ammonia was injected in a period of 10 mins., followed by six pounds of CO.sub.2 (gas) during a period of 30 mins. The use of liquid rather than gaseous ammonia greatly reduced the amount of heat evolved when tobacco is ammoniated. The residual vacuum was then discharged by admitting air. The impregnated tobacco was analyzed and contained 4.4% NH.sub.3, 5.3% CO.sub.2 and 18.6 percent (dry basis) total oven volatiles. It was injected into a high velocity turbulent stream of combustion gases and steam at 500.degree.F. and yielded a low density (0.28), (The density was measured by an acetone displacement method.) light yellow-colored, expanded product.

When equilibrated after treating in a fine water spray to 13 percent moisture, this material showed a filling index about twice as great as untreated tobacco at a similar moisture content.

It should be noted that ammonia is naturally present in tobacco but obviously at levels substantially below that needed for significant expansion. The fact that ammonia is a natural constituent of tobacco is a material advantage in carrying out the puffing process of the invention as described here. Thus, it is not necessary to remove every trace of the expansion agent before the product is incorporated into smoking articles as is clearly necessary when using such foreign and extraneous materials as hydrocarbons or halogenated compounds for expansion purposes. Ammonia also has the advantage of being relatively much less hazardous in forming explosive mixtures with air than would be encountered if one used some of the organic liquids that have been previously suggested.

Ammonia is especially efficacious in causing puffing of tobacco parts because first it readily penetrates the cell walls and second at least in the presence of moisture is believed to have a softening effect on the cell structure which facilitates the puffing. Moreover, its low boiling temperature (vapor pressure) makes possible the use of relatively low puffing temperatures. A further advantage is the relatively low cost of ammonia which means that losses due to incomplete recovery are of no great concern.

An important advantage in the use of ammonium carbonate or bicarbonate is that these compounds not only have negligable explosion hazard as compared to other substances but also have the advantage of producing ammonia and carbon dioxide at relatively low temperatures whereas excessive darkening and charring temperatures could be incurred with other substances capable of furnishing a gaseous puffing agent but only at a relatively high decomposition temperature. Thus, tobacco puffed with ammonia that is either absorbed or produced in situ shows little or no darkening in the absence of an excess amount of moisture. The latter, of course, can be prevented by avoiding the deliberate addition of water as is sometimes believed necessary in prior processes.

Claims

The invention claimed is:

1. The process of puffing tobacco comprising the steps of contacting tobacco containing at least about 6 percent moisture by weight in an impregnation zone with ammonia and with carbon dioxide at or above atmospheric pressure to introduce into the tobacco from about 3 percent to about 6 percent by weight of ammonia based on the weight pressure below atmosphere of about 26 inches mercury absolute or less to absorb carbon dioxide into the tobacco and then puffing the impregnated tobacco by heating to 250.degree. to about 700.degree.F for a time sufficient to puff the tobacco.

2. The process of claim 1, wherein the ammonia is separately added to the tobacco and the carbon dioxide is thereafter separately added to the tobacco, both additions being prior to the heating step.

3. The process of claim 1, wherein carbon dioxide is separately added to the tobacco and the ammonia is thereafter separately added to the tobacco, both additions being prior to the heating step.

4. The process of claim 1, wherein the ammonia and carbon dioxide are added simultaneously to the tobacco prior to the heating step.

5. The process of claim 1, wherein said heating is effected by means of a member selected from the group consisting of steam, hot air and mixtures thereof.

6. The process of claim 5, wherein said heating is conducted at a temperature of from about 375.degree. to about 650.degree.F. for a period of time of from about 0.1 second to about four minutes.

7. The process of puffing tobacco comprising the steps of contacting tobacco containing at least about 6 percent moisture in an impregnation zone with from about 1 to 12 percent by weight of ammonia at a low pressure below atmospheric to absorb ammonia into the tobacco, then contacting the tobacco with carbon dioxide at a pressure below atmospheric to absorb carbon dioxide into the tobacco, the temperature of contact being significantly below 100, and then puffing the impregnated tobacco by heating to a temperature in the range of 250.degree. -700.degree.F.

8. The process of claim 7, wherein the ammonia impregnation is carried out with liquid ammonia.

9. The process of claim 7, wherein the moisture content of the tobacco prior to ammoniacal treating is in the range of about 5 to about 20 percent by weight.