| Table IV—Analysis of Santos Coffee Extract (Dry Basis) | |
| Ether extract, fixed | 1.06% |
| Total nitrogen | 1.06% |
| Caffein | 1.06% |
| Crude fiber | 1.06% |
| Total ash | 1.06% |
| Reducing sugar | 1.06% |
| Caffetannic acid | 1.06% |
| Protein | 1.06% |
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.
The body, or what might be called the licorice-like character, of coffee, is due conceivably to the presence of bodies of a glucosidic nature and to caramel. Astringency, or bitterness, is dependent upon the decomposition products of crude fiber and chlorogenic acid, and upon the soluble mineral content of the bean. The degree to which a coffee is sweet-tasting or not is, of course, dependent upon its other characteristics, but probably varies with the reducing sugar content. Aside from the effects of these constituents upon cup quality, the influence of volatile aromatic and flavoring constituents is always evident in the cup valuation, and introduces a controlling factor in the production of an individualistic drink.
Coffee Extracts
The uncertainty of the quality of coffee brews as made from day to day, the inconvenience to the housewife of conducting the extraction, and the inevitable trend of the human race toward labor-saving devices, have combined their influences to produce a demand for a substance which will give a good cup of coffee when added to water. This gave rise to a number of concentrated liquid and solid "extracts of coffee," which, because of their general poor quality, soon brought this type of product into disrepute. This is not surprising; for these preparations were mainly mixtures of caramel and carelessly prepared extracts of chicory, roasted cereals, and cheap coffee.
Liquid extracts of coffee galore have appeared on the market only soon to disappear. Difficulty is experienced in having them maintain their quality over a protracted period of time, primarily due to the hydrolyzing action of water on the dissolved substances. They also ferment readily, although a small percentage of preservative, such as benzoate of soda, will halt spoilage.[182]
So much trouble is not encountered with coffee-extract powders—the so-called "soluble" or "instant" coffees. The majority of these powdered dry extracts do, however, show great affinity for atmospheric moisture. Their hygroscopicity necessitates packing and keeping them in air-tight containers to prevent them running into a solid, slowly soluble mass.
The general method of procedure employed in the preparation of these powders is to extract ground roasted coffee with water, and to evaporate the aqueous solution to dryness with great care. The major difficulty which seems to arise is that the heat needed to effect evaporation changes the character of the soluble material, at the same time driving off some volatile constituents which are essential to a natural flavor. Many complex and clever processes have been developed for avoiding these difficulties, and quite a number of patents on processes, and several on the resultant product, have been allowed; but the commercial production of a soluble coffee of freshly-brewed-coffee-duplicating-power is yet to be accomplished. However, there are now on the market several coffee-extract powders which dissolve readily in water, giving quite a fair approximation of freshly brewed coffee. The improvement shown since they first appeared augurs well for the eventual attainment of their ultimate goal.