All About Coffee by William H. Ukers (best new books to read .TXT) π
CHAPTER II
HISTORY OF COFFEE PROPAGATION
A brief account of the cultivation of the coffee plant in the Old World, and of its introduction into the New--A romantic coffee adventure Page 5
CHAPTER III
EARLY HISTORY OF COFFEE DRINKING
Coffee in the Near East in the early centuries--Stories of its origin--Discovery by physicians and adoption by the Church--Its spread through Arabia, Persia, and Turkey--Persecutions and Intolerances--Early coffee manners and customs Page 11
CHAPTER IV
INTRODUCTION OF COFFEE INTO WESTERN EUROPE
When the three great temperance beverages, cocoa, tea, and coffee, came to Europe--Coffee first mentioned by Rauwolf in 1582--Early days of coffee in Italy--How Pope Clement VIII baptized it and made it a truly Christian beverage--The first Europe
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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 65Β° to 70Β° C.; and subjecting them to a vigorous brushing 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 washing. 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 analytically 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 assign it a formula. Among them may be noted those of Allen,[123] who gives it the empirical formula C14H16O7; Hlasiwetz,[124] who represents it as C15H18O8; Richter, as C30H18O16; Griebel,[125] as C18H24O10, and Cazeneuve and Haddon,[126] as C21H28O14. It is variously supposed to exist in coffee as the potassium, 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 mass, 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 constituents chlorogenic acid (C32H38O19), 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, C14H20O11, 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 analysis 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 analysis" fades. It is highly desirable that the nomenclature relevant to this analytical 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, trigonellinβthe methylbetaine of nicotinic acidβsometimes known as caffearine, has been isolated from coffee.[132] This alkaloid, having the formula C14H16O4N2, is also found in fenugreek, Trigonella fΕnum-grΓ¦cum, in various leguminous plants, and in the seeds of strophanthus. When pure it forms colorless needles melting at 140Β° 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 C5H(CH3)3N4O2, in addition to being in the coffee bean is also found in guarana leaves, the kola nut, matΓ©, or Paraguay tea, and, in small quantities, 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 EwΓ©.[135]
Pure caffein forms long, white, silky, flexible needles, which readily felt together to form light, fleecy masses. It melts at 235β7Β° C. and sublimes completely at 178Β° C., though the sublimation starts at 120Β°. 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.
Solvent Temperature
of Solution Solubility:
Grm. Caffein
per 100
Grm. of
Saturated
Solution Sp. Gr. of
Saturated
Solution Water 0.997 25 2.14 ββ Ether 0.716 25 0.27 ββ Chloroform 1.476 25 11.0 ββ Acetone 0.809 30β1 2.18 0.832 Benzene 0.872 30β1 1.22 0.875 Benzaldehyde 1.055 30β1 11.62 1.087 Amylacetate 0.860 30β1 0.72 0.862 Aniline 1.02 30β1 22.89 1.080 Amyl alcohol 0.814 25 0.49 0.810 Acetic acid 1.055 21.5 2.44 ββ 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 constituents of meat), and uric acid, is shown by the accompanying structural formulæ.
These formulæ 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 (CH3) 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 classic researches by Emil Fischer.[137]
Gorter states that caffein exists in coffee in combination with chlorogenic acid as a potassium chlorogenate, C32H36O19, K2(C8H10O2N4)2Β·2H2O, 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.
COFFEE SCENES IN BRITISH INDIA
Table IIβCoffee Analyses Santos
Green Santos
Roasted Padang
Green Padang
Roasted Guatemala
Green Guatemala
Roasted Mocha
Green Mocha
Roasted Moisture April 20th 8.75 3.75 8.78 2.72 9.59 3.40 9.06 3.36 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 ββ 1.69 ββ 1.39 ββ 1.44 ββ 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 ββ 13.68 ββ 11.53 ββ 9.41 ββ 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 1.0404 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 103.60 120.20 167.30 151.35 189.20 165.80 119.52 100.00 1,000 kernel weight, dry basis 119.1 115.7 154.1 147.2 171.0 160.1 108.6 96.6 Dextrose ββ 0.72 ββ 0.81 ββ 0.54 ββ 0.46 Caffetannic acid .58 17.44 15.37 16.93 16.27 17.13 15.61 16.89 Acidity by titration 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 class 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,
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