All About Coffee by William H. Ukers (best new books to read .TXT) 📕

The exact effect which roasting with sugars has upon the flavor is not well understood; but it is known that it causes the beans to absorb more moisture, due to the hygroscopicity of the caramel formed. For instance, berries roasted with the addition of glucose syrup hold an additional 7 percent of water and give a darker infusion than normally roasted coffee. When the green coffee is glazed with cane sugar prior to roasting, the losses during the process are much higher than ordinarily, on account of the higher temperature required to attain the desired results. Losses for ordinary coffee taken to a 16-percent roast are 9.7 percent of the original fat and 21.1 percent of the original caffein; while for "sugar glazed" coffee the losses were 18.3 percent of the original fat and 44.3 percent of the original caffein, using 8 to 9 percent sugar with Java coffee.

Grinding and Packaging

It is a curious fact that green coffee improves upon aging, whereas after roasting it deteriorates with time. Even when packed in the best containers, age shows to a disadvantage on the roasted bean. This is due to a number of causes, among which are oxidation, volatilization of the aroma, absorption of moisture and consequent hydrolysis, and alteration in the character of the aromatic principles. Doolittle and Wright[174] in the course of some extensive experiments found that roasted coffee showed a continual gain in weight throughout 60 weeks, this gain being mostly due to moisture absorption. An investigation by Gould[175] also demonstrated that roasted coffee gives off carbon dioxid and carbon monoxid upon standing. The latter, apparently produced during roasting and retained by the cellular structure of the bean, diffuses therefrom; whereas the former comes from an ante-roasting decomposition of unstable compounds present.[176]

The surface of the whole bean forms a natural protection against atmospheric influences, and as soon as this is broken, deterioration sets in. On this account, coffee should be ground immediately before extraction if maximum efficiency is to be obtained. The cells of the beans tend to retain the fugacious aromatic principles to a certain extent; so that the more of these which are broken in grinding, the greater will be the initial loss and the more rapid the vitiation of the coffee. It might, therefore, seem desirable to grind coarsely in order to avoid this as much as possible. However, the coarser the grind, the slower and more incomplete will be the extraction. A patent[177] has been granted for a grind which contains about 90 percent fine coffee and 10 percent coarse, the patentee's claim being that in his "irregular grind" the coarse coffee retains enough of the volatile constituents to flavor the beverage, while the fine coffee gives a very high extraction, thus giving an efficient brew without sacrificing individuality.

In packaging roasted coffee the whole bean is naturally the best form to employ, but if the coffee is ground first, King[178] found that deterioration is most rapid with the coarse ground coffee, the speed decreasing with the size of the ground particles. He explains this on the ground of "ventilation"—the finer the grind, the closer the particles pack together, the less the circulation of air through the mass, and the smaller the amount of aroma which is carried away. He also found that glass makes the best container for coffee, with the tin can, and the foil-lined bag with an inner lining of glassine, not greatly inferior.

Considerable publicity has been given recently to the method of packing coffee in a sealed tin under reduced pressure. While thus packing in a partial vacuum undoubtedly retards oxidation and precludes escape of aroma from the original package, it would seem likely to hasten the initial volatilizing of the aroma. Also, it would appear from Gould's[179] work that roasted coffee evolves carbon dioxid until a certain positive pressure is attained, regardless of the initial pressure in the container. Accordingly, vacuum-packing apparently enhances decomposition of certain constituents of coffee. Whether this result is beneficial or otherwise is not quite clear.

Brewing

The old-time boiling method of making coffee has gone out of style, because the average consumer is becoming aware of the fact that it does not give a drink of maximum efficiency. Boiling the ground coffee with water results in a large loss of aromatic principles by steam distillation, a partial hydrolysis of insoluble portions of the grounds, and a subsequent extraction of the products thus formed, which give a bitter flavor to the beverage. Also, the maintenance of a high temperature by the direct application of heat has a deleterious effect upon the substances in solution. This is also true in the case of the pumping percolator, and any other device wherein the solution is caused to pass directly into steam at the point where heat is applied. Warm and cold water extract about the same amount of material from coffee; but with different rates of speed, an increase in temperature decreasing the time necessary to effect the desired result.

It is a well known fact that re-warming a coffee brew has an undesirable effect upon it. This is very probably due to the precipitation of some of the water-soluble proteins when the solution cools, and their subsequent decomposition when heat is applied directly to them in reheating the solution. The absorption of air by the solution upon cooling, with attendant oxidation, which is accentuated by the application of heat in re-warming, must also be considered. It is likewise probable that when an extract of coffee cools upon standing, some of the aromatic principles separate out and are lost by volatilization.

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° 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]