Coffee is prepared from the seeds of Caffea arabica, the seeds being stripped of their covering and dried, and specially prepared by a roasting process, in which the berries lose about 20 per rent, of their weight by water, and about half the caffeine present in their composition. The roasting process sets free a volatile oil which imparts the characteristic aroma of coffee, Alter grinding, this volatile oil tends to disappear; hence the importance of using freshly ground coffee. The essential constituents of coffee are: -

Caffeine.

Tannin and cafieo-tannic acid.

Fat.

Gummy matters.

Cellulose.

Ash.

The relative proportion of these is shown in the following tabular analysis (Blyth): -

Caffeine.

Tannin and Caffeine.

Gummy matters.

Cellulose.

Ash.

Tannic Acid.

Fat.

Finest Jamaica ...

1.43

22.7

14.76

25.3

23.8

3.8

Finest Green Mocha..

0.64

23.1

21.79

22.6

29.9

4.1

Ceylon ....

1.53

20.9

14.87

23.8

36.0

4.0

Washed Rio..

1.14

20.9

15.95

27.4

32.5

4.5

Costa Rica . ..

1.18

2I.I

21.12

20.6

33.0

4.9

Malabar ....

0.88

207

16.80

25.8

31.9

4.3

East Indian . ...

1.01

19.5

17.00

24.4

36.4

40

When coffee is made by infusion, in the ordinary ways of this country, there is extracted about 20 per cent. To obtain the full strength of the coffee, the example of the East should be followed, and the beverage prepared by infusion and decoction combined. When so prepared, coffee should yield fully one-third of its weight of extract. Like tea, coffee is not a food, except for the milk and sugar added to it. As ordinarily prepared, the amount of caffeine and tannin in a cup of coffee is very similar to that in a cup of tea. The most common adulterant is chicory, and many people prefer coffee with a chicory flavour. It differs from coffee in having very little caffeine, tannin, or volatile oil, and it is much richer in sugar, having over 10 per cent, of sugar, whereas ground coffee has less than 1 per cent.