CHEMICAL ANALYSIS.
Coffee has been analysed by several chemists, and though the results
obtained differ in some slight degree, yet it seems pretty clear that
the principal constituents to which its hygienic and medicinal
properties are due are caffeine, a peculiar volatile oil generated in
the roasting, and a kind of tannic acid.
The alkaloid caffeine, or theine, is found in one or two other plants
besides tea and coffee. It occurs in the seeds of _Paullinia sorbilis_,
a native of Brazil, and in the leaves of several species of holly,
natives of South America, which furnish the Paraguay tea, or Yerba mate,
so large an article of consumption in several of the South American
republics. The leaves and young shoots, dried, parched, and pulverised,
are used for a hot infusion. A kind of cake, called Guarana bread, is
made from the seeds of the _Paullinia_, which is highly esteemed in
Brazil and other countries when infused, like chocolate, for its
nutritive and febrifuge properties, and is sold generally as a necessary
for travellers, and as a cure for many diseases.
The nutritive and medicinal virtues of all these plants must certainly
be attributed in a great degree to the presence of this chemical
principle, and to the tannic acid which they also contain.
The use of coffee as a beverage has been examined in a chemical and
physiological point of view by Professor Lehmann. The general results of
his investigations are:
1. That a decoction of coffee exercises two principal actions upon the
organism, which are very diverse in character, viz. increasing the
activity of the vascular and nervous system, while at the same time it
retards the metamorphosis of plastic constituents.
2. That the influence of coffee upon the vascular and nervous system,
its reinvigorating action, and the production of a general sense of
cheerfulness and animation, is attributable solely to the mutual
modification of the specific action of the empyreumatic oil and the
caffeine contained in it.
3. That the retardation of the assimilative process brought about by the
use of coffee is owing chiefly to the empyreumatic oil, and is caused by
caffeine only when taken in large quantities.
4. That increased action of the heart, trembling, headache, &c., are
effects of the caffeine.
5. That the increased activity of the kidneys, relaxation of the bowels,
and an increased vigour of mental faculties, passing into congestion,
restlessness, and inability to sleep, are effects of the empyreumatic
oil.
Professor Lehmann considers it, therefore, necessary to regard the
action of coffee, and, in a less degree, that of tea, cocoa, alcohol,
&c., upon the organism, as constituting an exception to the general law,
that increased bodily and mental activity involves increased consumption
of plastic material.
Caffeine, on careful analysis, has been found to contain in 100 parts,
49·80 of carbon, 5·08 of hydrogen, 28·83 of nitrogen, and 16·29 of
oxygen. It is inodorous, but has a slightly bitter taste. The proportion
in which this principle is found to be present in coffee varies between
¾ lb. and 1¾ lbs. in 100 lbs. of berries.
The peculiar essential oil which is generated in coffee in the process
of roasting, by the action of heat upon some yet unascertained principle
contained in the berry, is also very similar to the volatile oil in
tea; but the quantity of it in coffee appears to be comparatively very
small; for whilst 100 lbs. of tea-leaves contain 1 lb. of volatile oil,
it takes 500 cwts. of roasted coffee to give a similar quantity; and yet
it is upon the presence of this oil that the flavour and value of the
several varieties of coffee mainly depend.
The tannic acid is, by some chemists, also said to be generated only in
the process of roasting; others maintain that it is present in the raw
bean.
The chemical properties of the coffee-berry are altered by roasting, and
it loses about twenty per cent. of weight, but increases in bulk
one-third or one-half. Its peculiar aroma, and some of its other
properties, are due to a small quantity of essential oil, only one
five-thousandth part of its weight, which would be worth about 100_l._
an ounce in a separate state. Coffee is less rich in theine than tea,
but contains more sugar and a good deal of cheese (casein).
Schrader has analysed raw and roasted coffee, with the following result:
raw. roasted.
Peculiar coffee principle 17·58 12·50
Gum and mucilage 3·64 10·42
Extractive 0·62 4·80
Resin 0·41 }
Fatty oil 0·52 } 2·08
Solid residue 66·66 68·75
Loss 10·57 1·45
-------------
|
100·00
“The examination of coffee,” observes Dr. F. Knapp, “has led to
interesting results, although they are still defective in pointing out
the quantitative composition of the berry.”
The following is the composition of the ash according to Levi:
Potash 50·94
Soda 14·76
Lime 4·33
Magnesia 10·90
Oxide of iron 0·66
Phosphoric acid 13·59
Sulphuric acid trace
Chlorine 1·22
Silicic acid 3·58
------
99·98
According to the analysis of Payen, the unroasted coffee-berry has the
following composition:
Moisture 12·0
Glucose and dextrine 15·5
Nitrogenous matters 13·0
Chlorogenate of caffeine, &c. 3·5 to 5·8
Fatty substances 10 to 13·0
Cellulose and woody fibre 34·0
Mineral substances in ash 6·7
Essential oil ·003
-----
100·0
Or to define the per-centage more closely, we may put it thus:
Water 12·000
Caffeine, or theine 1·750
Casein 13·000
Aromatic oil 0·002
Sugar 6·500
Gum 9·000
Fat 12·000
Potash, with a peculiar acid 4·000
Woody fibre 35·048
Mineral matter 6·700
-------
100·000
In another form this shows us:
Water 12·00
Flesh-formers 14·75
Heat-givers 66·25
Mineral matter 7·00
------
100·00
As gluten is only very sparingly soluble in boiling water, in the usual
way of making coffee the flesh-formers are thrown away with the dregs;
the addition of a little soda to the water partly prevents this waste.
The various components in one pound of coffee will be--
oz. grs.
Water 1 407
Caffeine, or theine 122
Casein, or cheese 2 35
Aromatic oil 1½
Gum 1 192
Sugar 1 17
Fat 1 402
Potash 280
Woody fibre 5 262
Mineral matter 1 31
The part roasted is the albumen, which is of a hard, horny consistence;
and Lindley remarks that it is probable that the seeds of other plants
of this or the stellate order, whose albumen is of the same texture,
would serve as a substitute. This would not be the case with those with
fleshy albumen.
Coffee loses in weight by roasting, but gains in bulk in proportion to
the heat applied.
Payen found the following amount of nitrogen in 100 parts dried:
nitrogen. ash.
Martinique 2·46 5·00
Bourbon 2·54 4·66
Mocha 2·49 7·84
The coffee from Martinique lost 11·58 per cent. of its weight by drying.
This description of coffee also afforded the following results:
-----------------+-------------+-------------+-------------+--------------
|Unroasted. | Slightly | Chesnut | Brown.
| | reddened. | brown. |
-----------------+-------------+-------------+-------------+--------------
Loss in roasting | -- | 15 per cent.| 20 per cent.| 25 per cent.
Increase in bulk | -- | 1·3 times | 1·53 times | --
Extract |40 per cent. | 37 per cent.| 37·1 per ct.| 39·25 per ct.
Insoluble residue|48·5 “ | -- | -- | --
-----------------+-------------+-------------+-------------+--------------
Coffee, as ordinarily prepared for beverage, contains only two-sevenths
of the nitrogenous or nutritive matter of the fresh bean, but two-thirds
of the roasted, and the mineral ingredients are all present.
M. Lebreton (“Agriculteur praticien”) has estimated the loss of weight
of coffee in roasting at 18 to 20 per cent. in Porto Rico, Rio, and
Martinique coffee; and at 16 to 18 per cent. in Malabar, Bourbon,
Ceylon, and Guadaloupe coffees; while in Mocha coffee it amounts to only
14 or 16. The loss of weight depends upon the time of roasting and the
degree of heat. Damp or damaged coffee loses more than dry sound coffee.
He considers that these substances have the capability of rendering the
individual insensible of a certain deficiency of food, in virtue of
their retardation of the assimilative process. He thinks it probable,
likewise, that these substances have a direct nutritive value,
especially coffee as drank by the Turks and Arabs with the grounds.
Professor Lehmann considers that the singular preference for one or
other of these beverages by particular nations, as well as the Eastern
custom of drinking coffee with the grounds, are not accidental, but have
some deeper reason. This reason, he thinks, is to be found in the
different effects of the coffee, tea, &c., and the various requirements
of the nations by whom they are used, and instances the use of tea by
the English, and of coffee by the Germans and French, as in accordance
with this view. The diet of the former affords a larger supply of
plastic material than that of the latter people; and while,
consequently, the retardation of the assimilative process is an
important influence for the German, the proportionately greater nervous
stimulus caused by tea is more desirable for the former. The use of
coffee with its grounds has its analogue in the use of tea mixed with
meal, milk, and butter among the Mongols, and other inhabitants of the
Central Asiatic steppes.
M. Payen, from elaborate experiments, shows that coffee slightly roasted
is that which contains the maximum of aroma, weight, and nutrition. He
declares coffee to be very nourishing, as it contains a large quantity
of nitrogen, three times as much nutriment as tea, and more than twice
the nourishment of soup. Chicory contains only half the nutriment of
coffee.