Coffee, like tea, contains three active principles. These are the alkaloid caffeine, which is identical with, and has the same properties as theine; secondly, an astringent substance resembling tannin is present in much smaller quantities than in tea; and thirdly, a volatile oil developed in roasting, which gives the coffee its aromatic odour. Coffee, like tea, also contains a considerable amount of gluten, which is only slightly soluble in water.

The following approximate analysis will show the differences between tea and coffee:-

From this table it will be seen how closely tea and coffee resemble one another. Tea is, however, the more astringent drink, and coffee the more stimulating and aromatic. In Europe, the ground coffee berry is generally simply infused, when its theine, tannic acid, and volatile oil are dissolved into the water. Among some of the Eastern nations the custom prevails of pounding the coffee in a mortar till a fine powder is produced. The coffee grounds are left in the cup, and are swallowed with the coffee. In this way the gluten and nutritive properties of the coffee berry are consumed, and thus a cup of coffee becomes a nutritious food.