laboratory scale and suitable industrial scale methods of selectively reducing the amount of certain constituents in tobacco are described along with test data detailing the effectiveness of such methods . notably , these methods are performed on tobacco itself . in addition , the tobacco can be from any source , including dried , cured , or processed , and can further be in the form of finished products , e . g ., cigarettes , snuff ( moist or dry ), and cigars . these methods can reduce the amount of one or more constituents without substantially removing tobacco attributes . as shown in fig1 , an industrial type system utilizing , e . g ., liquid carbon dioxide under subcritical conditions , can be used to reduce the amount of one or more constituents in tobacco . although only one vessel 6 is shown in fig1 , it is understood that a plurality of such vessels can be utilized , in series , in a large - scale system . as further shown in fig1 , tobacco 5 is charged to vessel 6 , which is then sealed so as to be able to operate under elevated pressure conditions , e . g ., necessary to maintain a subcritical fluid as a liquid therein . subcritical fluid 2 , e . g ., carbon dioxide , initially stored as shown in supply vessel 1 , is directed through and is pumped to a desired pressure by inlet pump 3 . after pressurized subcritical fluid 2 passes through inlet pump 3 , the liquid proceeds , via circulation pump 4 into vessel 6 and through the charge of tobacco 5 . as the liquid subcritical fluid 2 flows through tobacco 5 , the amount of constituents in tobacco 5 is reduced . after exiting vessel 6 , a subcritical fluid stream , which at this point may be gaseous , flows into and through separator vessel 7 . the separator vessel may contain a substance 8 , which traps basic constituents and , thereby , depletes the subcritical fluid of any dissolved or suspended constituents . the substance 8 can be drained from separator vessel 7 via drain valve 9 , particularly after the solution accumulates a significant amount of constituents . a suitable substance 8 is an aqueous citric acid solution . other possible substances effective for separating out constituents include , for example , solid magnesium silicate or any other such solution or solid capable of binding the desired constituents . the subcritical fluid , once depleted of any dissolved or suspended constituents may be recirculated to the vessel 6 , as shown , via line r . circulation pump 4 may be designed such that subcritical fluid entering its inlet from line r may , once again , be pressurized so as to liquify before entering vessel 6 . those having ordinary skill in the art will recognize that pump 4 may thus act to re - pressurize the subcritical fluid entering pump 4 from either supply vessel 1 or line r . following completion of the reduction process , the system may be depressurized and constituent - reduced tobacco 5 removed . the process time may vary depending on a variety of processing parameters . one of ordinary skill in the art will readily be able to determine suitable process times . ranges of appropriate process times are discussed below in connection with trial runs performed on a laboratory - scale system . the virtually continuous circulation of subcritical fluid and the inherent capability of reducing constituents from multiple charges of tobacco residing in a plurality of vessels are two clear advantages to be exploited . elimination of costly down time brought about by emptying and recharging of a single vessel 6 is achievable with use of several ( typically three or four ) valved vessels 6 operating in series . vessels may also be operated in parallel . as noted above , subcritical fluid is pumped in series through the several vessels 6 . when the charge of tobacco in one of the vessels has become constituent - reduced and is ready to be removed , the subcritical fluid can be diverted from that vessel to another vessel containing tobacco or a separation vessel . this subcritical fluid may still be effective for reducing constituents from other charges of tobacco in other vessels . the vessel from which tobacco is ready to be removed may be isolated from the system without interfering with on - going reductions in other vessels . new tobacco may then be placed into the vessel , and the process can continue without overall system interruption . preferably , treated tobacco substantially retains the taste and aroma of untreated tobacco . alternatively , any flavor or aroma compounds removed during treatment may be re - deposited in the tobacco , e . g ., after removal of any constituents from the subcritical fluid . the flavor and aroma content of tobacco can be determined by taste and smell tests . the following examples illustrate various embodiments of the present invention and are not intended to be limiting in any way . fig2 shows a schematic representation of a laboratory - scale system that can be used to produce reduced constituent content in tobacco . the representative data of table 1 were developed using such a system , which was operated in the following manner . a sample of tobacco 16 was placed in vessel 15 , and the vessel was sealed . gaseous subcritical fluid 12 was supplied from cylinder 11 and admitted to the system . when pressure ( as measured by gauges a and b ) reached cylinder pressure , compressor pump 13 was energized to liquify the fluid 12 . temperature was adjusted and controlled using preheater 14 and was measured with thermocouples c and d . flow of subcritical fluid 12 was then started using adjustable flow control valve 17 that was set so as to operate at a selected flow rate measured by flow meter 19 . the range of flow rate may be between about 5 grams / min to 150 grams / min ; for convenience 20 - 30 grams / min rate was chosen for the experimental runs . pressure was reduced across valve 17 , resulting in the gaseous subcritical fluid passing into filter flask 18 into which constituent - rich extract could be collected . alternatively , the subcritical fluid was vented to a waste vessel . the total flow of subcritical fluid 12 passed through the charge of tobacco 16 during the duration of a run was measured by dry test meter 20 . in this laboratory system , no separation vessel was used to facilitate recirculation of subcritical fluid 12 . vessel 15 was a stainless steel tube having a length of 10 inches , an outside diameter of 1 inch , and a volume of about 60 ml . after treatment , the tobacco 16 was analyzed for its constituent content and the percent reduction of constituent content . the run time necessary to produce such tobacco may be anywhere between about 2 and 14 hours , preferably in the range of about 4 - 8 hours . the carbon dioxide utilized according to the present invention should be a subcritical fluid ( critical point 31 ° c . and 1070 psi ), e . g ., a liquid . in practicing the process of the present invention , carbon dioxide temperature , pressure , or both can be adjusted to ensure that it is a subcritical fluid , for example , by an inlet heat exchanger ( not shown ). the run pressure was held essentially constant ( in the range of between about 1000 and 2200 psi ) for a given run . runs were performed at essentially constant temperatures ranging between about 0 ° c . and 24 ° c . although a range of mass of subcritical fluid : mass of tobacco ratios can be used , typically between 21 to 50 grams of carbon dioxide per gram of tobacco were used to reduce the maximum amount of constituent . table 1 shows data on the reduction of constituents in tobacco employing the laboratory - scale system described above . as shown in table 1 , the process is selective for the reduction of secondary alkaloids relative to primary alkaloids . additional experiments according to the method of example 1 were carried out using freon 22 ( chlorodifluoromethane ) ( critical point 96 ° c ., 716 psi ) instead of carbon dioxide . the data are shown in table 2 . exemplary conditions for use of freon 22 include 0 to 50 ° c ., 100 to 2000 psi , and a mass of freon 22 to mass of tobacco ratio of 20 to 100 . additional experiments according to the method of example 1 were carried out using propane ( critical point 96 . 7 ° c ., 617 psi ) instead of carbon dioxide . the data are shown in table 3 . in general , the conditions for use of propane are 0 to 50 ° c ., 100 to 2000 psi , and a mass of propane to a mass of tobacco ratio of 20 to 100 . the amount of constituents in tobacco may also be reduced using the methods of the invention by employing ethane ( critical point 32 . 2 ° c ., 708 psi ) or nitrous oxide ( critical point 36 . 5 ° c ., 1046 psi ). exemplary conditions for use of ethane include 0 to 30 ° c ., 500 to 2000 psi , and a mass of ethane to a mass of tobacco ratio of 20 to 100 . exemplary conditions for use of nitrous oxide include 0 to 35 ° c ., 500 to 2000 psi , and a nitrous oxide to tobacco ratio of 20 to 100 . the description of the specific embodiments of the methods and tobacco obtained therefrom is presented for the purposes of illustration . it is not intended to be exhaustive nor to limit the scope of the invention to the specific forms described herein . although the invention has been described with reference to several embodiments , it will be understood by one of ordinary skill in the art that various modifications can be made without departing from the spirit and the scope of the invention , as set forth in the claims .
methods of selectively reducing constituents in tobacco as well as the tobacco obtained by such methods are disclosed . subcritical fluids , e . g ., liquid carbon dioxide , serve as the reduction media .