COFFEE

Coffee is the seed of the _Caffea Arabica_, indigenous to Abyssinia
and southern Arabia, and since naturalised in the West Indies, Ceylon,
Brazil, and other tropical countries. Its importance as an almost
universal beverage is only equalled by that of tea. The ancient history
of coffee is shrouded in great obscurity. It was unknown to the Romans
and Greeks, but its use is said to have been prevalent in Abyssinia
from the remotest time, and in Arabia it formed an article of general
consumption during the fifteenth century. From its introduction, in
1575, into Constantinople by the Turks, it gradually made its way into
all civilised countries. In 1690 it was carried by the Dutch from Mocha
to Java, whence specimens of the tree were taken to Holland and France.
Coffee houses were opened in London about the middle of the seventeenth
century, and in 1809 the first cargo of coffee was shipped to the
United States. As with many other articles of diet, the adulteration of
coffee has kept well apace with its increased consumption. The bean is
deprived of its external fleshy coatings before exportation, and is met
with in commerce in a raw, roasted, or ground condition. Bell[9] gives
the following analyses of two samples of coffee, both in the raw and
roasted state:–

—————————+———————+——————–
| Mocha. | East Indian.
+———-+———-+———-+———
| Raw. | Roasted. | Raw. | Roasted.
—————————+———-+———-+———-+———
|per cent. |per cent. |per cent. |per cent.
Caffeine | 1·08 | 0·82 | 1·11 | 1·05
Saccharine matter | 9·55 | 0·43 | 8·90 | 0·41
Caffeic acids | 8·46 | 4·74 | 9·58 | 4·52
Alcohol extract (containing| 6·90 | 14·14 | 4·31 | 12·67
nitrogen and colouring | | | |
matter). | | | |
Fat and oil | 12·60 | 13·59 | 11·81 | 13·41
Legumin or Albumin | 9·87 | 11·23 | 11·23 | 13·13
Dextrine | 0·87 | 1·24 | 0·84 | 1·38
Cellulose (and insoluble | 37·95 | 48·62 | 38·60 | 47·42
colouring matter). | | | |
Ash | 3·74 | 4·56 | 3·98 | 4·88
Moisture | 8·98 | 0·63 | 9·64 | 1·13
+———-+———-+———-+———
|100·00 |100·00 | 100·00 |100·00
—————————+———-+———-+———-+———

Other authorities have obtained the following results:–

—————————+——————-+———+————-
| König. | | Smethan.
+———+———+ Payen. |(Average of
| Raw. | Roasted.| Raw. |7 Varieties.)
| | | | Roasted.
—————————+———+———+———+————-
|per cent.|per cent.|per cent.| per cent.
Substances soluble in water| 27·44 | 27·45 | .. | ..
Nitrogen | 1·87 | 2·31 | .. | 2·26
Nitrogenous substances | 11·43 | 12·05 |11 to 13 | ..
Caffeine | 1·18 | 1·38 | 0·8 | ..
Caffetannic acid | .. | .. |3·5 to 5 | ..
Fat | 13·23 | 15·03 |10 to 13 | 10·99
Ethereal oil | .. | .. | 0·013 | ..
Sugar | 3·25 | 1·32 | .. | ..
Sugar and Dextrine | .. | .. | 15·5 | ..
Other non-nitrogenous | 31·52 | 38·41 | .. | ..
substances. | | | |
Cellulose | 27·72 | 24·27 | 34·0 | 29·28
Ash | 3·48 | 3·75 | 6·7 | 4·19
Soluble ash | .. | .. | .. | 3·37
Moisture | 11·19 | 3·19 | 12·0 | 2·87
—————————+———+———+———+————-

It will be noticed from these analyses that the amount of sugar is
greatly diminished by the process of roasting. According to some
analysts, the proportion of fat experiences an increase, but it is more
probable that this constituent is simply rendered more susceptible to
the action of solvents by a mechanical alteration of the structure of
the berry. Recent determinations of the ash in coffee place its average
proportion at 4 per cent.; 3·24 being soluble in water, and 0·74 per
cent. insoluble. The soluble extract in roasted coffee usually amounts
to about 30 per cent.

An analysis made by Beckurts and Kauder[10] gives the general
composition of roasted chicory, dried at 107°, as follows:–

Per cent.
Substances soluble in water 57·40
„ insoluble „ 41·90
Ash 7·66
Fat 0·73
Nitrogenous substances 7·12
Grape sugar 4·35
Cane sugar and dextrine 5·33
Starch 2·45
Other non-nitrogenous substances 49·13
Woody fibre 26·23

The most common adulterations to which coffee is liable consist
in the addition of chicory, caramel, and numerous roasted grains,
such as corn, wheat, and rye, as well as such roots and seeds as
dandelion, mangold wurzel, turnips, beans, peas, etc. The roasted and
ground article is naturally most exposed to falsification, although
letters patent have been issued for the fictitious manufacture of a
pressed “coffee bean,” containing absolutely no coffee. The addition
of chicory is by far the most prevalent adulteration of coffee. Of
thirty-four samples examined by Hassall, thirty-one (91 per cent.)
contained this root. In regard to the moral aspects of its use, it
can safely be asserted that, while the addition of chicory to coffee
is largely sanctioned, and indeed demanded by the existing tastes of
many coffee-drinkers, its use constitutes a true adulteration, and
should be condemned, unless its presence is prominently stated on the
label of the package. In chicory the active principles of coffee, which
exert valuable physiological effects on the system (viz. caffeine, the
essential oil, etc.), are totally absent; moreover, its comparative
cheapness is a constant temptation to employ a proportion largely in
excess of the amount requisite to produce any alleged improvement in
the flavour of the resulting admixture.

The sophistications of coffee may be detected, in a general way, by
physical tests, by chemical analysis, and by microscopic examination,
in which processes great aid is derived from the characteristic
properties exhibited by the pure roasted and ground berry which
distinguish it from its more usual adulterants.

(_a_) _Physical Examination._–The following tests, while not always
decisive in their results, are often of service.

A small portion of the suspected sample is gently placed upon the
surface of a beaker filled with cold water, and allowed to remain at
rest for about fifteen minutes. If pure, the sample does not imbibe the
water, but floats upon the surface without communicating much colour to
it; if chicory or caramel be present, these substances rapidly absorb
moisture and sink, producing brownish-red streaks in their descent,
which, by diffusion, impart a very decided tint to the entire liquid. A
similar coloration is caused by many other roasted roots and berries,
but not so quickly or to so great an extent. The test may be somewhat
modified by shaking the sample with cold water, and then allowing
the vessel to stand aside for a short time. Pure coffee rises to the
surface, little or no colour being imparted to the water; chicory,
etc., fall to the bottom as a sediment, and give a brownish colour to
the liquid.

If a small quantity of the sample is placed upon a clean plate of
glass, and moistened with a few drops of water, the pure coffee berries
remain hard, and offer resistance when tested with a needle; most
grains employed for their adulteration become softened in their texture.

A considerable portion of the mixture is treated with boiling water and
allowed to settle. Genuine coffee affords a clear and limpid infusion;
many foreign grains yield a thick gummy liquor, resulting from the
starchy and saccharine matters contained. An infusion of pure coffee,
if treated with solution of cupric acetate and filtered, will show
a greenish-yellow colour; if chicory be present, the filtrate will
be reddish-brown. As a rule, samples of ground coffee which are much
adulterated, pack together when subjected to a moderate pressure.

Owing to the low density of a coffee infusion (due to its almost entire
freedom from sugar), as compared with that of the infusions of most
roots and grains, it has been suggested by Messrs. Graham, Stenhouse
and Campbell, to apply the specific gravity determination of the
infusion obtained from the suspected sample as a means for detecting
adulteration. The results afforded are fairly approximate. The solution
is prepared by boiling one part of the sample with ten parts of water
and filtering. The following table gives the densities, at 15°·5, of
various infusions made in this manner:–

Acorns 1·0073
Peas 1·0073
Mocha coffee 1·0080
Beans 1·0084
Java coffee 1·0087
Jamaica coffee 1·0087
Costa Rica coffee 1·0090
Ceylon coffee 1·0090
Brown malt 1·0109
Parsnips 1·0143
Carrots 1·0171
Yorkshire chicory 1·0191
Black malt 1·0212
Turnips 1·0214
Rye meal 1·0216
English chicory 1·0217
Dandelion root 1·0219
Red beet 1·0221
Foreign chicory 1·0226
Mangold wurzel 1·0235
Maize 1·0253
Bread raspings 1·0263

Assuming the gravity of the pure coffee infusion to be 1·0086, and that
of chicory to be 1·0206, the approximate percentage of coffee, C, in a
mixture, can be obtained by means of the following equation, in which D
represents the density of the infusion:–

C = (1·00(1·020 – D)) / 12.

This was tested by mixing equal parts of coffee and chicory, and taking
the specific gravity of the infusion; it was 1·01408, indicating the
presence of 49 per cent. of coffee. Some idea of the amount of foreign
admixture (especially chicory) in ground roasted coffee may be formed
from the tinctorial power of the sample. It has already been mentioned
that coffee imparts much less colour to water than do most roasted
grains and roots. The table below shows the weights of various roasted
substances which must be dissolved in 2·000 parts of water in order to
produce an equal degree of colour:[11]–

Caramel 1·00
Mangold wurzel 1·66
Black malt 1·82
White turnips 2·00
Carrots 2·00
Chicory (darkest Yorkshire) 2·22
Parsnips 2·50
Maize 2·86
Rye 2·86
Dandelion root 3·33
Red beet 3·33
Bread raspings 3·36
Acorns 5·00
Over-roasted coffee 5·46
Highly-roasted coffee 5·77
Medium-roasted coffee 6·95
Peas 13·33
Beans 13·33
Spent tan 33·00
Brown malt 40·00

The comparative colour test may also be applied as follows:[12]–One
gramme each of the sample under examination, and of a sample prepared
by mixing equal parts of pure coffee and chicory, are completely
exhausted with water, and the infusions made up to 100 c.c. or more;
50 c.c. of the filtered extract from the suspected sample are then
placed in a Nessler cylinder, and it is determined by trial how many
c.c. of the extract from the standard mixture, together with enough
distilled water to make up the 50 c.c., will produce the same colour.
In calculating the chicory present, it is assumed that this substance
possesses three times the tinctorial power of coffee.

(_b_) _Chemical Examination._–Some of the chemical properties of
roasted coffee afford fairly reliable means for the detection of an
admixture of chicory. Coffee ash dissolves in water to the extent of
about 80 per cent.; of the ash of roasted chicory only about 35 per
cent. is soluble. Coffee ash is almost free from silica and sand, which
substances form a notable proportion of the constituents of the ash of
chicory.

The following (see p. 36) are the results obtained by the writer from
the analysis of the ash of coffee and chicory.

It will be observed from these analyses, that the most distinctive
features presented by coffee ash are the absence of soda, and the
small amounts of chlorine, ferric oxide and silica present. In these
respects, it is very different from the ash of chicory. The proportion
of phosphoric acid found in the latter is in excess of that given by
some authorities. Several analyses of chicory ash have been made by
the author, and, in every instance, the amount of phosphoric acid was
over 8 per cent.; in one sample of the ash of commercial chicory it
approximated 13 per cent.

——————————-+————–+————–
| Java Coffee. | Chicory Root
——————————-+————–+————–
| per cent. | per cent.
Percentage of ash | 3·93 | 4·41
——————————-+————–+————–
Potassa | 53·37 | 23·00
Soda | .. | 13·13
Lime | 5·84 | 9·40
Magnesia | 9·09 | 5·88
Alumina | 0·43 | ..
Ferric oxide | 0·53 | 5·00
Sulphuric acid | 3·19 | 9·75
Chlorine | 0·78 | 4·93
Carbonic acid | 15·26 | 4·01
Phosphoric acid | 11·26 | 8·44
Silica and sand | 0·25 | 16·46
——————————-+————–+————–
| 100·00 | 100·00
——————————-+————–+————–

Blyth gives the annexed table, showing the characteristic differences
between coffee and chicory ash:[13]–

————————+—————-+—————-
| Coffee Ash. | Chicory Ash.
————————+—————-+—————-
| per cent. | per cent.
Silica and sand | none | 10·69 to 35·88
Carbonic acid | 14·92 | 1·78 „ 3·19
Ferric oxide | 0·44 to 0·98 | 3·13 „ 5·32
Chlorine | 0·26 „ 1·11 | 3·28 „ 4·93
Phosphoric acid | 10·00 „ 11·00 | 5·00 „ 6·00
Total soluble ash | 75·00 „ 85·00 | 21·00 „ 35·00
————————+—————-+—————-

The following formula has been suggested for determining the percentage
of pure coffee, in mixtures:–

C = 2 ((100S – 174) / 3)

where S represents the percentage of soluble ash.

Another noteworthy difference between roasted coffee and chicory, is
the amount of sugar contained. As a rule, in roasted coffee, it ranges
from 0·0 to 1·2 per cent.; in roasted chicory, it varies from 12· to
18· per cent. The quantity of sugar in a sample can be determined by
Fehling’s method as follows:–

A standard solution of pure cupric sulphate is first prepared by
dissolving 34·64 grammes of the crystals (previously ground and dried
by pressing between bibulous paper) in about 200 c.c. of distilled
water; 173 grammes of pure Rochelle salt are separately dissolved
in 480 c.c. of a solution of sodium hydroxide of sp. gr. 1·14. The
solutions are then mixed and diluted with distilled water to one litre.
Each c.c. of the above solution represents 0·05 gramme of grape sugar.
The test is applied by taking 10 c.c. of the copper solution, adding
about four times its volume of water, and bringing it to the boiling
point. The coffee infusion is then gradually added from a burette,
until the copper salt is completely reduced to the red sub-oxide,
which point is recognised by the disappearance of its blue colour, and
can be more accurately determined by acidulating the filtered fluid
with acetic acid and testing it (while still hot) for any remaining
trace of copper with potassium ferrocyanide. In preparing the coffee
solution for the foregoing test, it is advisable to exhaust a weighed
quantity of the sample with hot water. The infusion is treated with
basic plumbic acetate so long as a precipitate forms; it is then
filtered, the precipitate being well washed, and the lead contained
is removed by conducting sulphuretted hydrogen gas through the fluid
which is subsequently again filtered and boiled until the dissolved gas
is expelled. The sugar determination is now made. Wanklyn employs the
following equation to estimate the amount of chicory in an adulterated
sample:–

E = ((S – 1)100) / 14,

where E is the percentage of chicory, and S the percentage of sugar.

According to the analysis of König, the proportions of sugar and other
constituents in some of the adulterants of coffee, are as follows:–

—————————-+———+———+———+———
|Chicory. | Figs. | Acorns. | Rye.
—————————-+———+———+———+———
|per cent.|per cent.|per cent.|per cent.
Water | 12·16 | 18·98 | 12·85 | 15·22
Nitrogenous substances | 6·09 | 4·25 | 6·13 | 11·84
Fat | 2·05 | 2·83 | 4·61 | 3·46
Sugar | 15·87 | 34·19 | 8·05 | 3·92
Other non-nitrogenous | 46·71 | 29·15 | 62· | 55·37
substances. | | | |
Cellulose | 11·0 | 7·16 | 4·98 | 5·35
Ash | 6·12 | 3·44 | 2·12 | 4·81
Substances soluble in water | 63·05 | 73·8 | .. | 45·11
—————————-+———+———+———+———

Estimations of the amount of sugar obtained upon boiling the suspected
coffee with water containing a little sulphuric acid (see p. 37), and
the proportion of the sample which is soluble in hot water should be
made. The presence of chicory is shown by a decided increase in the
amount of soluble substances; that of rye, by the notable quantity of
sugar produced by the inversion with acid, due to the starch contained
in the grain.

In this connection, the following determinations of Krausch are of
interest:–

———————————+———-+————+———-
|Substances|Ready-formed| Sugar
|Soluble in| Sugar. | after
| Water. | |Inversion.
———————————+———-+————+———-
| per cent.| per cent. | per cent.
Roasted coffee | 23·81 | 0·20 | 24·59
„ chicory | 65·42 | 23·40 | 22·14
„ rye | 31·92 | .. | 75·37
„ coffee | | |
+ 10 per cent. chicory | 30·63 | 2·30 | 23·15
„ coffee | | |
+ 10 per cent. rye | 25·98 | 0·19 | 29·60
———————————+———-+————+———-

The presence of roasted rye, corn, and other grains in coffee, may be
qualitatively recognised by testing the cold infusion of the sample
with iodine solution for starch, which is not contained in a ready
formed state in coffee. Caffeine is absent in chicory and the other
usual adulterants of coffee, and the estimation of this alkaloid is of
decided service (see p. 21). Roasted coffee contains about 1 per cent.
of caffeine.

A popular brand of ground coffee received by the author for
examination, and labelled “Prepared Java Coffee,” had the following
approximate composition:–Coffee, 38; peas, 52; rye, 2; and chicory, 7
per cent.

A sample of “acorn” coffee, analysed by König, gave the following
results:–

Per cent.
Water 12·85
Nitrogenous substances 6·13
Fat 4·01
Sugar 8·01
Other non-nitrogenous substances 62·00
Cellulose 4·98
Ash 2·02

The non-nitrogenous constituents contained from 20 to 30 per cent. of
starch, and from 6 to 8 per cent. of tannic acid.

The composition of the well-known German coffee-substitutes, prepared
by Behr Bros., is stated to be as follows:–

“_Rye Coffee-substitutes._”

Per cent.
Substances soluble in water 61·33
Substances insoluble in water 36·45
Cellulose 9·78
Starch 8·34
Dextrine 49·51
Nitrogenous substances 11·87
Other non-nitrogenous substances 9·83
Fat 3·91
Ash 4·54
Moisture 2·22

“_Malt Coffee-substitute._”

Per cent.
{ Albuminoid substances 4·22
Soluble { Dextrine 50·19
in { Alcoholic extract 7·57
hot water { Inorganic matter, }
{ containing } 2·27
{ phosphoric acid, 0·54 }
Insoluble in hot water 35·00
Moisture 0·35

The raw coffee bean is sometimes subjected to a process termed
“sweating,” which consists in treating it with moist steam, the object
being to artificially reproduce the conditions present in the holds
of vessels, by means of which the bean is increased in size, and also
somewhat improved in colour and flavour. Another form of manipulation,
analogous to the facing of tea, is to moisten the raw bean with water
containing a little gum, and agitate it with various pigments, such as
indigo, Prussian blue, Persian berries, turmeric, alkanet, Venetian
red, soap-stone, chrome-yellow, and iron ochre. Mexican coffees are
sometimes made to resemble the more expensive Java in appearance.
The chemist of the New York City Board of Health has found in the
quantity of such treated coffee commonly taken to make a cup of the
beverage 0·0014 gramme of cupric arsenite. Indigo may be detected in
the artificially coloured product by treating a considerable portion
of the sample with dilute nitric acid, filtering and saturating the
filtrate with sulphuretted hydrogen. If indigo be present, it can now
be extracted upon agitating the solution with chloroform. Alkanet root
and Prussian blue are separated by warming the coffee with solution of
potassium carbonate, from which these pigments are precipitated upon
addition of hydrochloric acid.

(_c_) _Microscopic Examination._–Great aid to the chemical
investigation is afforded by the microscopic examination of ground
coffee. It is necessary to first become familiar with the appearance of
the genuine article–low magnifying powers being employed–and then
make comparative examinations of the adulterant suspected to be present.

The coffee bean mainly consists of irregular cells inclosed in very
thick walls which are distinguished by uneven projections. The cells
contain globules of oil. Most of the roots added to coffee exhibit
a conglomeration of cells (provided with thin walls) and groups of
jointed tubes, often quite similar to one another in structure. The
microscopic appearance of some of the starch granules, occasionally met
with in coffee mixtures, is represented on p. 100.

Of 151 samples of ground coffee recently purchased at random and tested
by various American chemists, 69 (45·7 per cent.) were found to be
adulterated.