All About Coffee Part 31

_Artificial Aging_

In consideration of the higher prices which aged products demand, attempts have naturally been made to shorten by artificial means the time necessary for their natural production. Some of these methods depend upon obtaining the most favorable conditions for acceleration of the enzyme action; others, upon the effects of micro-organisms; and still others, upon direct chemical reaction or physical alteration of the green bean.

One of the first efforts toward artificial maturing was that of Ashcroft[109], who argued from the improved nature of coffee which had experienced a delayed voyage. His method consisted of inclosing the coffee in sweat-boxes having perforated bottoms and subjecting it to the sweating action of steam, the boxes being enclosed in an oven or room maintained at the temperature of steam.

[Ill.u.s.tration: STRUCTURE OF THE GREEN BEAN

Showing thick-walled cells enclosing drops of oil]

Timby[110] claimed to remove dusts, foreign odors, and impurities, while attaining in a few hours or days a ripening effect normally secured only in several seasons. In this process, the bagged coffee is placed in autoclaves and subjected to the action of air at a pressure of 2 to 3 atmospheres and a temperature of 40 to 100 F. The temperature should seldom be allowed to rise above 150 F. The pressure is then allowed to escape and a partial vacuum created in the apparatus. This alteration of pressure and vacuum is continued until the desired maturation is obtained. Desvignes[111] employs a similar procedure, although he accomplishes seasoning by treating the coffee also with oxygen or ozone.[112] First the coffee is rendered porous by storage in a hot chamber, which is then exhausted prior to admission of the oxygen. The oxygen can be ozonized in the closed vessel while in contact with the coffee. Complete aging in a few days is claimed.

Weitzmann[113] adopts a novel operation, by exposing bags of raw coffee to the action of a powerful magnetic field, obtained with two adjustable electro-magnets. The claim that a maturation naturally produced in several years is thus obtained in 1/2 to 2 hours is open to considerable doubt. A process that is probably attended with more commercial success is that of Gram[114] in which the coffee is treated with gaseous nitrogen dioxid.

By far the most notable progress in this field, both scientifically and commercially, has been made by Robison[115] with his "culturing" method.

Here the green coffee is washed with water, and then inoculated with selected strains of micro-organisms, such as _Ochraeceus_ or _Aspergillus Wintii_. Incubation is then conducted for 6 to 7 days at 90 F. and 85 percent relative humidity. Subsequent to this incubation, the coffee is stored in bins for about ten days; after which it is tumbled and scoured. With this process it is possible to improve the cupping qualities of a coffee to a surprising degree.

_Renovating Damaged Coffees_

Sophistication has often been resorted to in order ostensibly to improve damaged or cheap coffee. Glazing, coloring, and polis.h.i.+ng of the green beans was openly and covertly practised until restricted by law. The steps employed did not actually improve the coffee by any means, but merely put it into condition for more ready sale. An apparently sincere endeavor to renovate damaged coffee was made by Evans[116] when he treated it with an aqueous solution of sulphuric acid having a density of 10.5 Baume. After agitation in this solution, the beans were washed free from acid and dried. In this manner discolorations and impurities were removed and the beans given a fuller appearance.

The addition of glucose, sucrose, lactose, or dextrin to green coffees is practised by von Niessen[117] and by Winter[118], with the object of giving a mild taste and strong aroma to "hard" coffees. The addition is accomplished by impregnating, with or without the aid of vacuum, the beans with a moderately concentrated solution of the sugar, the liquid being of insufficient quant.i.ty to effect extraction. When the solution has completely disseminated through the kernels, they are removed and dried. Upon subsequent roasting, a decided amelioration of flavor is secured.

Another method developed by von Niessen[119] comprises the softening of the outer layers of the beans by steam, cold or warm water, or brine, and then surrounding them with an absorbent paste or powder, such as china clay, to which a neutralizing agent such as magnesium oxid may be added. After drying, the clay can be removed by brus.h.i.+ng or by causing the beans to travel between oppositely reciprocated wet cloths. In the development of this process, von Niessen evidently argued that the so-called "caffetannic acid" is the "harmful" substance in coffee, and that it is concentrated in the outer layers of the coffee beans. If these be his precepts, the question of their correctness and of the efficiency of his process becomes a moot one.

A procedure which aims at cleaning and refining raw coffee, and which has been the subject of much polemical discussion, is that of Thum[120].

It entails the placing of the green beans in a perforated drum; just covering them with water, or a solution of sodium chloride or sodium carbonate, at 65 to 70 C.; and subjecting them to a vigorous brus.h.i.+ng for from 1 to 5 minutes, according to the grade of coffee being treated.

The value of this method is somewhat doubtful, as it would not seem to accomplish any more than simple was.h.i.+ng. In fact, if anything, the process is undesirable; as some of the extractive matters present in the coffee, and particularly caffein, will be lost. Both Freund[121] and Harnack[122] hold briefs for the product produced by this method, and the latter endeavors a.n.a.lytically to prove its merits; but as his experimental data are questionable, his conclusions do not carry much weight.

_The Acids of Coffee_

The study of the acids of coffee has been productive of much controversy and many contradictory results, few of which possess any value. The acid of coffee is generally spoken of as "caffetannic acid." Quite a few attempts have been made to determine the composition and structure of this compound and to a.s.sign it a formula. Among them may be noted those of Allen,[123] who gives it the empirical formula C_14_H_16_O_7; Hlasiwetz,[124] who represents it as C_15_H_18_O_8; Richter, as C_30_H_18_O_16; Griebel,[125] as C_18_H_24_O_10, and Cazeneuve and Haddon,[126] as C_21_H_28_O_14. It is variously supposed to exist in coffee as the pota.s.sium, calcium, or magnesium salt. In regard to the physical appearance of the isolated substance there is also some doubt, Thorpe[127] describing it as an amorphous powder, and Howard[128]

as a brownish, syrup-like ma.s.s, having a slight acid and astringent taste.

The chemical reactions of "caffetannic acid" are generally agreed upon.

A dark green coloration is given with ferric chloride; and upon boiling it with alkalies or dilute acids, caffeic acid and glucose are formed.

Fusion with alkali produces protocatechuic acid.

K. Gorter[129] has made an extensive and accurate investigation into the matter, and in reporting upon the same has made some very pertinent observations. His claim is that the name "caffetannic acid" is a misnomer and should be abandoned. The so-called "caffetannic acid" is really a mixture which has among its const.i.tuents chlorogenic acid (C_32_H_38_O_19), which is not a tannic acid, and coffalic acid.

Tatlock and Thompson[130] have expressed the opinion that roasted coffee contains no tannin, and that the lead precipitate contains mostly coloring matter. They found only 4.5 percent of tannin (precipitable by gelatin or alkaloids) in raw coffee.

Hanausek[131] demonstrated the presence of oxalic acid in unripe beans, and citric acid has been isolated from Liberian coffee. It also has been claimed that viridic acid, C_14_H_20_O_11, is present in coffee. In addition to these, the fat of coffee contains a certain percentage of free fatty acids.

It is thus apparent that even in green coffee there is no definite compound "caffetannic acid," and there is even less likelihood of its being present in roasted coffee. The conditions, high heat and oxidation, to which coffee is subjected in roasting would suffice to decompose this hypothetical acid if it were present.

In the method of a.n.a.lysis for caffetannic acid (No. 24) given at the end of this chapter, there are many chances of error, although this procedure is the best yet devised. Lead acetate forms three different compounds with "caffetannic acid," so that this reagent must be added with extreme care in order to precipitate the compound desired. The precipitate, upon forming, mechanically carries down with it any fats which may be present, and which are removed from it only with difficulty. The majority of the mineral salts in the solution will come down simultaneously. All of the above-mentioned organic acids form insoluble salts with lead acetate, and there will also be a tendency toward precipitation of certain of the components of caramel, the acidic polymerization products of acrolein, glycerol, etc., and of the proteins and their decomposition products.

In view of this condition of uncertainty in composition, necessity for great care in manipulation, and ever-present danger of contamination, the significance of "caffetannic acid a.n.a.lysis" fades. It is highly desirable that the nomenclature relevant to this a.n.a.lytical procedure be changed to one, such as "lead number," which will be more truly indicative of its significance.

_The Alkaloids of Coffee_

In addition to caffein, the main alkaloid of coffee, trigonellin--the methylbetaine of nicotinic acid--sometimes known as caffearine, has been isolated from coffee.[132] This alkaloid, having the formula C_14_H_16_O_4_N_2, is also found in fenugreek, _Trigonella foenum-graec.u.m_, in various leguminous plants, and in the seeds of strophanthus. When pure it forms colorless needles melting at 140 C., and, as with all alkaloids, gives a weak basic reaction. It is very soluble in water, slightly soluble in alcohol, and only very slightly soluble in ether, chloroform or benzol, so that it does not contaminate the caffein in the determination of the latter. Its effects on the body have not been studied, but they are probably not very great, as Polstorff obtained only 0.23 percent from the coffee which he examined.

Caffein, thein, trimethylxanthin, or C_5_H(CH_3)_3_N_4_O_2, in addition to being in the coffee bean is also found in guarana leaves, the kola nut, mate, or Paraguay tea, and, in small quant.i.ties, in cocoa.

It is also found in other parts of these plants besides those commonly used for food purposes.

A neat test for detecting the presence of caffein is that of A.

Viehoever,[133] in which the caffein is sublimed directly from the plant tissue in a special apparatus. The presence of caffein in the sublimate is verified by observing its melting point, determined on a special heating stage used in connection with a microscope.

The chief commercial source of this alkaloid is waste and damaged tea, from which it is prepared by extraction with boiling water, the tannin precipitated from the solution with litharge, and the solution then concentrated to crystallize out the caffein. It is further purified by sublimation or recrystallization from water. Coffee chaff and roaster-flue dust have been proposed as sources for medicinal caffein, but the extraction of the alkaloid from the former has not proven to be a commercial success. Several manufacturers of pharmaceuticals are now extracting caffein from roaster-flue dust, probably by an adaptation of the Faunce[134] process. The recovery of caffein from roaster-flue gases may be facilitated and increased by the use of a condenser such as proposed Ewe.[135]

Pure caffein forms long, white, silky, flexible needles, which readily felt together to form light, fleecy ma.s.ses. It melts at 235-7 C. and sublimes completely at 178 C., though the sublimation starts at 120.

Salts of an unstable nature are formed with caffein by most acids. The solubility of caffein as determined by Seidell[136] is given in Table I.

TABLE I--THE SOLUBILITY OF CAFFEIN

Solubility: Grm. Caffein per 100 Grm. of Sp. Gr. of Sp. Gr. of Temperature Saturated Saturated Solvent Solvent of Solution Solution Solution

Water 0.997 25 2.14 Ether 0.716 25 0.27 Chloroform 1.476 25 11.0 Acetone 0.809 30-1 2.18 0.832 Benzene 0.872 30-1 1.22 0.875 Benzaldehyde 1.055 30-1 11.62 1.087 Amylacetate 0.860 30-1 0.72 0.862 Aniline 1.02 30-1 22.89 1.080 Amyl alcohol 0.814 25 0.49 0.810 Acetic acid 1.055 21.5 2.44 Xylene 0.847 32.5 1.11 0.847 Toluene 0.862 25 0.57 0.861

The similarity between caffein and theobromin (the chief alkaloid of cocoa), xanthin (one of the const.i.tuents of meat), and uric acid, is shown by the accompanying structural formulae.

These formulae show merely the relative position occupied by caffein in the purin group, and do not in any wise indicate, because of its similarity of structure to the other compounds, that it has the same physiological action. The presence and position of the methyl groups (CH_3) in caffein is probably the controlling factor which makes its action differ from the behavior of other members of the series. The structure of these compounds was established, and their syntheses accomplished, in the course of various cla.s.sic researches by Emil Fischer.[137]

[Ill.u.s.tration: FORMULA FOR CAFFEIN, SHOWING ITS RELATION TO THE PURIN GROUP]

Gorter states that caffein exists in coffee in combination with chlorogenic acid as a pota.s.sium chlorogenate, C_32_H_36_O_19, K_2(C_8_H_10_O_2_N_4)_22H_2_O, which he isolated in colorless prisms. This compound is water-soluble, but caffein can not be extracted from the crystals with anhydrous solvents. To this behavior can probably be attributed the difficulty experienced in extracting caffein from coffee with dry organic solvents. However, the fact that a small percentage can be extracted from the green bean in this manner indicates that some of the caffein content exists therein in a free state. This acid compound of caffein will be largely decomposed during the process of torrefaction, so that in roasted coffee a larger percentage will be present in the free state. Microscopical examination of the roasted bean lends verisimilitude to this contention.

[Ill.u.s.tration: PLANTER'S BUNGALOW WITH COFFEE TREES IN FLOWER, MYSORE]

[Ill.u.s.tration: COOLIES BAGGING COFFEE ON THE DRYING GROUNDS]

[Ill.u.s.tration: COFFEE SCENES IN BRITISH INDIA]

TABLE II--COFFEE a.n.a.lYSES

Santos Green Santos Roasted Padang Green Padang Roasted Guatemala Green Guatemala Roasted Mocha Green Mocha Roasted Moisture 8.75 3.75 8.78 2.72 9.59 3.40 9.06 3.36 April 20th Moisture September 20th 8.12 6.45 8.05 6.03 8.68 6.92 8.15 7.10 Ash 4.41 4.49 4.23 4.70 3.93 4.48 4.20 4.43 Oil 12.96 13.76 12.28 13.33 12.42 13.07 14.04 14.18 Caffein 1.87 1.81 1.56 1.47 1.26 1.22 1.31 1.28 Caffein, dry basis 2.03 .... 1.69 .... 1.39 .... 1.44 ....

Crude fiber 20.70 14.75 21.92 14.95 22.23 15.23 22.46 15.41 Protein 9.50 12.93 12.62 14.75 10.43 11.69 8.56 9.57 Protein, dry basis 10.41 .... 13.68 .... 11.53 .... 9.41 ....

Water extract 31.11 30.30 30.83 30.21 31.04 30.47 31.27 30.44 Specific gravity, 10 percent extract 1.0109 1.0101 1.0107 1.0104 1.0105 1.0104 1.0108 1.0108 Bushelweight 47.0 28.2 45.2 27.8 52.2 27.2 48.8 30.2 1,000 kernel weight 130.60 120.20 167.30 151.35 189.20 165.80 119.52 100.00 1,000 kernel weight, dry basis 119.1 115.7 154.1 147.2 171.0 160.1 108.6 96.6 Dextrose .... 0.72 .... 0.81 .... 0.54 .... 0.46 Caffetannic acid 15.58 17.44 15.37 16.93 16.27 17.13 15.61 16.89 Acidity by t.i.tration apparent 1.50 2.08 1.47 2.00 1.39 2.13 1.11 1.87

As may be seen in Table II,[138] the caffein content of coffee varies with the different kinds, a fair average of the caffein content being about 1.5 percent for _C. arabica_, to which cla.s.s most of our coffees belong. However, aside from these may be mentioned _C. canephora_, which yields 1.97 percent caffein; _C. mauritiana_, which contains 0.07 percent of the alkaloid (less than the average "caffein-free coffee"); and _C. humboltiana_, which contains no caffein, but a bitter principle, cafemarin. Neither do the berries of _C. Gallienii_, _C. Bonnieri_, or _C. Mogeneti_ contain any caffein; and there has also been reported[139]

a "Congo coffee" which contained no crystallizable alkaloid whatever.

Apparently the variation in caffein content is largely due to the genus of the tree from which the berry comes, but it is also quite probable that the nature of the soil and climatic conditions play an important part. In the light of what has been accomplished in the field of agricultural research, it does not seem improbable that a man of Burbank's ability and foresight could successfully develop a series of coffees possessed of all the cup qualities inherent in those now used, but totally devoid of caffein. Whether this is desirable or not is a question to be considered in an entirely different light from the possibility of its accomplishment.