Acid curing of tobacco

A process for artificially curing mature green tobacco is provided wherein the tobacco is immersed in an acidic medium and incubated therein at at least room temperature until the desired color develops. Incubation at pH 1.5 to 3.5 at about 50.degree. C. for as little as 3 hours may be sufficient to eliminate the green color and green smoke taste and odor of the tobacco.

BACKGROUND OF THE INVENTION 
(a) Field of the Invention 
This invention relates to a method for artifically curing green tobacco by 
means of acid incubation. 
(b) State of the Art 
Green tobacco leaf curing and/or aging by suspending the leaves in darkness 
or otherwise disposing the leaves while controlling temperature and 
relative humidity of circulating air currents is disclosed in U.S. Pat. 
Nos. 1,113,902, 1,543,245, 1,545,811, 1,568,316, 2,343,345 and 3,086,553. 
Forced air flow through bundles of green leaves has also been suggested as 
a means to cure green tobacco in U.S. Pat. No. 3,225,456. Such 
conventional methods of curing tobacco, characteristically require several 
days and may entail substantial expenditures for fuel. Further such curing 
processes tend to be labor intensive. 
In U.S. Pat. No. 3,845,774 curing is effected by homogenizing yellowed 
tobacco leaf, incubating the homogenized material and then curing the mass 
as it is dried. The leaf characteristics may be manipulated during this 
homogenization curing method by chemical, physical or biological means; 
for example, ascorbic acid is added to the homogenate in Example 9. 
However, none of these prior art methods effect curing by means of acids. 
Further, in contrast to the majority of prior art curing methods, the 
present acid curing method provides means for eliminating the green color 
and green odor and taste of tobacco which is rapid and less labor and 
energy intensive. 
SUMMARY OF THE INVENTION 
In accordance with the invention mature green tobacco is cured rapidly and 
economically by immersing the tobacco in an aqueous acid solution and 
incubating the immersed tobacco until the green color of the tobacco is 
eliminated. 
DETAILED DESCRIPTION OF THE INVENTION 
The present invention provides a means for removing the green color and 
taste of tobacco. This artificial curing method comprises immersing 
tobacco in an aqueous solution having a pH in the acid range and 
incubating the immersed tobacco for a period of time sufficient to produce 
the desired color. 
The process of the invention has application to mature green tobacco 
including burley and bright tobaccos. When treated according to the 
invention, the tobacco may be in fresh untreated form or may have been 
pressed to express juices therefrom and thereby reduce the content of 
alkaloids, nitrogen, reducing sugars or the like in the tobacco material. 
The pressed tobacco may optionally be allowed to dry prior to treatment 
according to the invention. Further the tobacco to be treated may be whole 
leaf or in pieces. 
The medium employed to incubate the tobacco has a pH in the acid range in 
order to permit relatively rapid curing. Aqueous acid solutions have been 
found to work satisfactorily. Specifically aqueous solutions of acetic, 
ortho-phosphoric, hydrochloric, lactic, formic and 2-chloroethyl 
phosphonic acids are effective media for purposes of the present 
invention. 
The pH of the incubation medium will affect the rate of curing. Media 
having a pH between about 1.5 and 3.5 are particularly preferred since at 
these low pH's rapid curing is possible. The most effective pH will depend 
on the type of tobacco and its maturity. 
The temperature of the incubation likewise affects the rate of curing. Thus 
although curing can be effected at room temperature, slightly elevated 
temperatures of about 50.degree. C. are preferred in order to expedite the 
curing process. 
By employing reduced pH's and temperatures of about 50.degree. C., curing 
to acceptable colors is possible in as little as 3 hours. Generally curing 
effected in the preferred pH range and at temperatures between room 
temperature and about 50.degree. C. will require no more than a few days. 
Incubation is effected by simply completely immersing lossely packed 
tobacco in the aqueous acid medium under the above conditions for a period 
of time sufficient to produce the desired color. Incubation may be 
effected in sealed containers to avoid pH changes due to evaporation. 
However, the incubation can be effected in the presence or absence of 
oxygen. 
During the incubation stage the tobacco loses its objectionable green 
color. The color after treatment varies from greenish-brown to yellow to 
brown. This color change or yellowing effected by the process removes the 
green smoke taste and odor from the tobacco. 
The incubation process of the invention provides flexibility in controlling 
the chemistry of tobacco. The soluble components of the tobacco including 
alkaloids, reducing sugars, potassium and the like are largely removed 
during acid incubation curing. If desired the incubation media may be 
processed to selectively remove particular constituents. The processed 
media can then be applied to cured tobacco to reintroduce desirable 
constituents therein followed by drying of the resultant product. 
When the tobacco solubles in the acid medium reach a concentration of about 
15% the tobacco no longer loses any solubles. Therefore, if the acid 
incubation is carried out in a solution that contains such an amount of 
tobacco solubles, loss of tobacco solubles during curing can be minimized. 
After the acid curing the tobacco may be placed on a perforated conveyor or 
screen to drain, and then if desired may be rinsed with water and dried. 
Optionally, the extracted tobacco solubles may be concentrated and 
reapplied to the tobacco prior to drying. 
A tobacco leaf treated in accordance with the curing process of the 
invention has a form and color similar to conventional flue-cured tobacco, 
but if the leaf has previously been pressed, stemming is not required. 
The following examples are illustrative of the invention:

EXAMPLE 1 
Coker 319 bright tobacco, mature upper stalk, harvested one week earlier 
and stored at -20.degree. C., was treated in three forms: unpressed, 
pressed, and pressed and dried. The pressed tobacco was obtained by twice 
passing the tobacco leaves between felt pads through a Noble and Wood 
Press at 650 pounds per linear inch. A sample of the pressed tobacco was 
dried at ambient conditions for 24 hours to yield tobacco having 13% OV. 
Aqueous acids were adjusted to pH 3.5 as follows: 20 ml of distilled water 
plus one drop of glacial acetic acid; 80 ml of water plus one drop of 
concentrated phosphoric acid; 30 ml of distilled water plus one drop of 
formic acid. Leaf sections measuring 3/8 by 3/8 inch were immersed in the 
solutions in stoppered vials and held at ambient temperature in a dark 
place to avoid and differentiate from photobleaching effects. Observations 
after 3 and 5 days are tabulated in Table 1. 
TABLE 1 
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Mature Green Bright Leaf--Room Temperature Incubation 
Appearance 
Liquid Sample 3 Days 5 Days 
__________________________________________________________________________ 
Distilled Water 
Unpressed 
yellowish green 
greenish yellow 
Pressed 
light green yellowish green 
Pressed, dried 
light green yellowish green 
Acetic Acid 
Unpressed 
very light greenish yellow 
brownish yellow 
Pressed 
slight greenish yellow 
brownish yellow 
Pressed, dried 
light greenish yellow 
slight greenish yellow 
Phosphoric Acid 
Unpressed 
yellow yellow 
Pressed 
slight greenish yellow 
slight greenish yellow 
Pressed, dried 
slight greenish yellow 
slight greenish yellow 
Formic Acid 
Unpressed 
brownish yellow 
brownish yellow 
Pressed 
slight greenish yellow 
slight greenish/brown yellow 
Pressed, dried 
light greenish yellow 
greenish yellow 
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EXAMPLE 2 
Samples of Coker 319 bright tobacco, harvested one week earlier and stored 
at -20.degree. C., were placed in two 2-gallon jars and immersed in 
aqueous acetic acid at pH 3.5. One jar was placed in an oven maintained at 
50.degree. C., the other in a closed cabinet at room temperature. After 
six hours, samples at 50.degree. C. were entirely bright yellow, those 
unheated were only very slightly yellow. 
EXAMPLE 3 
Burley leaf, Ky 14, mature but not yellow, harvested three days earlier and 
stored at -20.degree. C., was cut into 3/8.times.3/8-inch sections. 
Pressed samples were produced as described in Example 1. Samples were 
immersed in 20 ml of the treating solutions as indicated in Table 2 in 
vials. The vials were then heated to 50.degree. C. and sealed, wrapped in 
aluminum foil, and maintained at that temperature. Observations at the 
specified intervals are recorded in Table 2. 
TABLE II 
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Mature Burley Green Leaf--Incubation at 50.degree. C. 
Treating Appearance 
Solution Sample 1 Day 21/2 Days 4 Days 
__________________________________________________________________________ 
2 drops Pressed 
slight brownish yellow 
light brownish yellow 
very light yellow brown 
2-chloroethyl- 
Unpressed 
brownish yellow 
brownish yellow 
yellowish brown 
phosphonic acid 
Acetic acid, 
Pressed 
slight brownish yellow 
light brownish yellow 
very light yellow brown 
pH 3.5 Unpressed 
brownish yellow 
brownish yellow 
yellowish brown 
Pressed, dried 
slight brownish yellow 
light yellowish brown 
-- 
Distilled 
Pressed 
light green 
light brownish yellow-green 
pale greenish yellow 
Water Unpressed 
brownish yellow 
brownish yellow-green 
light greenish brown 
Pressed, dried 
light greenish yellow 
light greenish brown 
-- 
4 Drops Pressed 
slight brownish yellow 
light brownish yellow 
very light yellow brown 
lactic acid 
Unpressed 
brownish yellow 
brownish yellow 
yellowish brown 
Sodium chloride, 
Pressed 
green light greenish yellow 
light greenish yellow 
5% (brine) 
Unpressed 
brownish green 
greenish brown 
greenish brown 
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The results indicate that acid incubation is much more effective than 
neutral (water or brine) treatment. 
EXAMPLE 4 
Small samples of mature green bright tobacco, Coker 319, stored in a cool 
room for two weeks after harvesting, were placed in vials as in Example 1 
and covered with water adjusted to a range of pH levels as follows: for pH 
less than 7, addition of phosphoric acid; for pH greater than 7, addition 
of concentrated aqueous KOH; and for pH 7.0, addition of potassium 
phosphate (monobasic)/sodium hydroxide as buffer. The vials were stoppered 
and wrapped in foil, placed in constant temperature bath at 50.degree. C., 
and opened at intervals for observation. Table 3 gives the color changes 
noted in the leaf sections. 
TABLE 3 
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Mature Green Bright Leaf - Incubation at 50.degree. C. 
Color Code: 
1. green; 2. light green; 
3. yellowish green; 4. greenish yellow; 
5. yellow; 5.5 light brownish yellow; 
6. brownish yellow; 7. yellowish brown; 
8. light brown; 8.5 brownish green; 
9. light greenish brown; 10. greenish brown; 
11. brown. 
Color Rating 
Treat- 41/2 
ment hours 1 Day 2 Days 
3 Days 
4 Days 
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Unpressed 
pH 1.5 5 5 5 5 5 
2.5 2 6 6 8 8 
3.5 1 4 4 6 7 
4.5 1 4 4 6 7 
5.5 1 4 4 6 6 
7.0 1 3 3 6 7 
8.5 1 3 4 6 6 
9.5 1 3 4 6 6 
10.5 1 3 4 6 6 
11.5 1 1 2* 2 2 
12.5 1 1 1* 1 1 
Tap H.sub.2 O 
1 3 9 9 9 
Pressed pH 1.5 6 7 7 11 11 
2.5 3 7 11 9 8 
3.5 1 4 8.5 9 8 
4.5 1 3 8.5 9 8 
5.5 1 3 8.5 9 8 
7.0 1 2 2 2 9 
8.5 1 2 3 3 9 
9.5 1 2 8.5 3.5 8 
10.5 1 2 3 3 9 
11.5 1 1 1* 2 2 
12.5 1 1 1* 1 1 
Tap H.sub.2 O 
1 1 1 8.5 8.5 
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*Solution had light green color. 
As the greenish tinges are least desirable, the results indicate that 
acceptable coloration (codes 5 through 8 or 11) is rapidly achieved at 
very low pH, 1.5 to 2.5. Longer exposures may produce similar results at 
higher pHs.