The method of extracting coffee which gives the most satisfaction is practised by using a grind just coarse enough to retain the individualistic flavoring components, retaining the ground coffee in a fine cloth bag, as in the urn system, or on a filter paper, as in the Tricolator, and pouring water at boiling temperature over the coffee. During the extraction, a top should be kept on the device to minimize volatilization, and the temperature of the extract should be maintained constant at about 200 deg. F. after being made. Whether a repouring is necessary or not is dependent upon the speed with which the water passes through the coffee, which in turn is controlled by the fineness of the grind and of the filtering medium. _The Water Extract_ Although many analyses of the whole coffee bean are available, but little work has been reported upon the aqueous extracts. The total water extract of roasted coffee varies from 20 to 31 percent in different kinds of coffee. The following analysis of the extract from a Santos coffee may be taken as a fair average example of the water-soluble material.[180] TABLE IV--ANALYSIS OF SANTOS COFFEE EXTRACT (DRY BASIS) Ether extract, fixed 1.06% Total nitrogen 3.40% Caffein 5.42% Crude fiber 0.25% Total ash 17.43% Reducing sugar 2.70% Caffetannic acid 15.33% Protein 7.71% It is difficult to make the trade terms, such as acidity, astringency, etc., used in describing a cup of coffee, conform with the chemical meanings of the same terms. However, a fair explanation of the cause of some of these qualities can be made. Careful work by Warnier[181] showed the actual acidities of some East India coffees to be: TABLE V--ACIDITY OF SOME EAST INDIA COFFEES Coffee from Acid Content Sindjai 0.033% Timor 0.028% Bauthain 0.019% Boengei 0.016% Loewae 0.021% Waloe Pengenten 0.018% Kawi Redjo 0.015% Palman Tjiasem 0.022% Malang 0.013% These figures may be taken as reliable examples of the true acid content of coffee; and though they seem very low, it is not at all incomprehensible that the acids which they indicate produce the acidity in a cup of coffee. They probably are mainly volatile organic acids, together with other acidic-natured products of roasting. We know that very small quantities of acids are readily detected in fruit juices and beer, and that variation in their percentage is quickly noticed, while the neutralization of this small amount of acidity leaves an insipid drink. Hence, it seems quite likely that this small acid content gives to the coffee brew its essential acidity. A few minor experiments on neutralization have proven that a very insipid beverage is produced by thus treating a coffee infusion.