It is on this foundation that the whole art of fractional distillation or rectification rests. While we have for illustration been considering a mixture of pure alcohol and water, the wash or liquid formed by the fermentation of grain, etc., contains a variety of ingredients of different boiling points, some more volatile than alcohol, some less. The fermented wash consists first of non-volatile or only slightly volatile matters, such as salts, proteins, glycerin, lactic acid, yeast, etc., and second, volatile bodies such as alcohol, water, various ethers, etc., fusel oils and acetic acid.
When wash is distilled in the ordinary simple or pot still, the first part to come over consists of the very volatile matters,—more volatile than alcohol even,—that is, the ethers mixed with some alcohol. This is known as the fore-shot or first runnings, and is collected separately. When the spirit coming over possesses no objectionable odor, the second stage has begun. This running would be of the alcohol proper, getting weaker and weaker, however, as the running continues and this would be caught separately as long as it is of sufficient strength. At last would come the weak spirit containing much fusel oil. It is to be understood, however, that there is no defined line between these divisions. They graduate one into the other. The first and last runnings in the old practice were mixed together and distilled with the next charge. When a strong spirit was required, rectification would be repeated several times. It is customary, however, with the improved modern apparatus, to produce at the outset spirit containing but little fusel oil and at least 80 per cent of alcohol. This is then purified and concentrated in the above manner and afterwards reduced with water to the required strength.
Another cause of the offensive flavor of the products of distillation is the presence of various acids, which exist in all fermented liquors; they are chiefly tartaric, malic, acetic, and lactic acids. The excessive action of heat upon liquors which have been distilled by an open fire has also a particularly objectionable influence upon the flavor of the products.
Fig. 35.—Rectifying Still.
The first operation in the process of rectification is to neutralize the above-mentioned acids; this is effected by means of milk of lime, which is added to the liquor in quantity depending upon its acidity; the point at which the neutralization is complete is determined by the use of litmus paper. In the subsequent process of distillation, the determination of the exact moments at which to begin and to cease collecting the pure spirit is very difficult to indicate. It must be regulated by the nature of the spirits; some may be pure 20 or 30 minutes after they have attained the desired strength; and some only run pure an hour, or even more, after this point. The product should be tasted frequently, after being diluted with water, or a few drops may be poured into the palm of the hand, and after striking the hands together, it will be known by the odor whether the spirit be of good quality or not; these two means may be applied simultaneously.
The process of rectification may be carried on in the apparatus shown in Figs. [35] and [36]. A is a still which contains the spirit to be rectified; it should be four-fifths full. The condenser E and the cooler G are filled with water. After closing the cocks L and I, the contents of the still are heated by steam, which is introduced at first slowly. The vapors of spirit given off pass, by tubes b, above each plate a, of the series in column B, and escape through C and D into the condenser E, where they are condensed on reaching the lentils d d′, and return in a liquid state through pipe f and connections g g′ to the upper plates of the column B. In these return pipes the liquid is volatilized, and constantly recharged with alcohol to be again condensed, until the water in the condenser is hot enough to permit the lighter alcoholic vapors to pass into the coil c c c, without being reduced to the liquid state. When this is the case, the vapors pass through F into the cooler G, where they undergo complete condensation. Great care must be taken that the heat is not so great as to permit any of the vapors to pass over uncondensed or to flow away in a hot state; and also to keep up a constant supply of water in the cooler without producing too low a temperature; the alcoholic products should run out just cold. The highly volatile constituents of the spirit come over first, that which follows becoming gradually purer until it consists of well-flavored alcohol; after this comes a product containing the essential oils. The more impure products are kept apart from the rest and re-distilled with the next charge. Some hours generally elapse before alcohol begins to flow from the cooler. The purest alcohol is obtained while its strength is kept between 92° and 96° Baume, and the operation is complete when the liquid flowing through the vessel marks not more than 3° or 4° Baume; it is better, however, to stop the still when the backing or “faints” indicate 10°, because the product after this point contains much fusel-oil, and is not worth collecting.
