This section is from the book "The Manufacture Of Liquors, Wines, And Cordials, Without The Aid Of Distillation", by Pierre Lacour. Also available from Amazon: Manufacture of Liquors, Wines, and Cordials, Without the Aid of Distillation.
Arranging the Stands or Rectifiers. - The material used for stands or filters may be adapted to all circumstances, thus: water casks, pipes, barrels, dec, will answer as well as the regular filter. The only objection to the barrels is the loss of the liquid and labor consequent upon the frequent filtrations necessary for the effectual removal of the grain oil, whereas a cistern of sufficient dimensions would obviate this difficulty.
The greater the surface presented to the action of the fluid, the greater the benefit. Usually, in all large establishments in America and Europe, the stands vary in size, say from twelve to thirty feet in height, and six to twelve feet in diameter. Again, others give the preference to filters six feet high; a series of these are arranged from the fourth or fifth story to the basement. These are packed alternately with charcoal and bone black; the two last stands being packed with charcoal alone, which removes the animoniacal taste and fetor peculiar to spirit filtered through bone black.
In small establishments, stands twelve feel high, and six to ten feet in diameter, will answer. The most simple and economical stands are made of barrels, so arranged at their bottoms with pipes, that the liquid flows from one barrel to the other, of course acting on the charcoal in its course, regardless of their out-ward structures. All stands are arranged, internally, alike, viz. in having a false bottom perforated with half inch holes. This false bottom rests from about four to eight inches above the main bottom, according to the size of the stand; for example, if a common cask or barrel is used for a stand, the space between the two heads need not be more than four inches, whereas a stand thirty feet in height would require a space of eight to ten inches. The number of holes in the false bottom are generally about twelve to twenty to the square foot; and beneath this false bottom should be fitted one or more faucets, as the operator may deem fit for the convenience of drawing off the spirit. This false bottom should be securely braced from the main bottom, as the entire weight of the contents comes upon it. The first process towards packing, consists in laying a blanket over the perforated bottom, which prevents the passage of any substance whatever. On this blanket, place clean, washed, sharp, white sand, to the depth of ten to twenty-five inches, according to the size of the stand. The object of the sand is to remove any particles of coloring matter that the liquid may have acquired in its passage through the charcoal, and the liquid passes off perfectly transparent - and all that does not, should be returned until it does. A second blanket is now placed upon top of the sand; this prevents particles of charcoal being forced, by hydraulic pressure, through the sand. The stand is now to be filled from this blanket up two thirds full, or to within fifteen or twenty inches of the top, with either bone black or charcoal, for reasons known to the reader. Bone black is objectionable, and many, from motives of economy, prefer charcoal, which can be found in all large commercial cities, prepared for the manufacturers of liquors. Almost all kinds of charcoal will answer, except that prepared from pine, which not being sufficiently carbonized, imparts to the liquid a turpentinish taste and odor. Any wood that imparts taste or color to spirit, is unsuitable to any of the purposes of the manufacturer of liquors. The common charcoal of the country, prepared from chestnut, walnut, ash, oak, beech, etc, needs no other preparation than pulverizing to small particles, one third smaller in size than a garden pea, and to separate by sifting the fine powder consequent upon pul verization, which, if allowed to remain, would render the liquor "inky." The stand or filter being filled as above, a blanket or gunny bags are spread over the whole, and a well fitting and strongly secured perforated head is placed on the charcoal. The object of the perforations in the head, is to cause the liquid to filter uniformly through the charcoal. The filtering is greatly facilitated by the use of "Digesting Barrels," and the grain oil is more effectually removed and presents all the advantages of filtration.
Digesting barrels consist of either wine, brandy, or water casks; and are filled through the bung one third full of bone black, and it is then filled with alcohol or whiskey; the bung is then tightly replaced, the barrel is rolled over several times, daily, from three to six days. It is then filtered through the charcoal, which removes the objectionable taste that was acquired in the digesting barrels. Manufacturing on the small scale, barrels will answer, but otherwise, digesting boxes are used. They are made of any convenient size, close jointed, without the use of any metallic lining, and air-tight coverings to prevent evaporation of the spirit; the inside is provided with loose jointed shelving, about ten inches apart from the bottom of the box to the covering. Bone black is deposited on these shelves to the depth of two to three inches; these boxes are filled from the top through a funnel, and so arranged that the spirit in its fall, will not displace any of the bone black from any of the shelves. These digesting apparatuses must of course be placed above the stands or filters, and so arranged that the liquid can be conducted to the stands for filtration.
The advantages of barrels over boxes are innumerable. The pecuniary advantage is an important one, as old barrels can be made available at an insignificant cost compared to the boxes. The rotary motion of the barrel brings the particles composing both bodies in contact, a matter not attainable in the boxes. It will be seen that this rotary motion is highly beneficial, as the grain oil is diffused throughout the entire mass of the spirit. The multiplicity of barrels required is the only objection to them.
To make a spirit that will show no traces of grain oil with the nitrate of silver (see preparation of the test), requires the spirit to be digested with and filtered through bone black; the digestion should continue from four days to a week, and the peculiar taste the spirit acquires from the bone black not having been sufficiently burned to have disengaged the animal matter that it contains, can be removed by a subsequent filtration through charcoal; after a few barrels of alcohol have been passed through, the disagreeable taste and odor disappear, that is, in the majority of cases. Instances may occur, when, the bone black not being burned sufficiently, to attempt the use of an article of this kind, would be to realize results not agreeable, and the best preventive in this instance, would be in testing a portion of bone black in spirit by digestion, and note the result. If it should prove unfit for use, it can be saturated in a strong solution of potash, and burned to a low red heat; and this course is to be pursued with bone black that has exhausted its absorbing powers by long use.
When filtration is to proceed rapidly in the rectifiers, the sand should have a quantity of small shells or gravel mixed throughout it, which prevents the mass from becoming too solid. Straw is sometimes used in alternate layers with the sand. Straw is liable to decomposition, and imparts a slight taste to the fluid, which renders its use objectionable. Alternate layers of gunny bags and sand are used by some operators.
When spirit is rectified for neutral spirit, it should not be taken from the rectifiers until the nitrate of silver test has shown the entire absence of fusel oil. Some manufacturers add one gallon of Jamaica rum to every hundred gallons of neutral spirit; the effect of the rum is to conceal any traces of the grain oil that might be perceptible to the nasal organ.
When spirit is rectified for the manufacture of common liquors, viz. domestic brandies, gin, and fancy brands of whiskey, etc, the object sought is to remove the oil, as far as practicable, by a single filtration, and to conceal the remaining portion by the addition of aromatics, and the nitrate of silver test would be useless with these liquids, as the sense of taste will answer every purpose.
The stands or rectifiers should never be used for decolorizing or discharging color from fluids, as the rectifier will soon become charged to such an extent, that any liquid filtering through it will become contaminated in color. Separate cisterns should be arranged for the purpose. See Clarifying and Filtering.
When spirit is rectified or freed of grain oil, for the manufacture of domestic brands of rum or whiskey, it should pass through a bed of oatmeal; this should be placed on the bottom of the last stand or filter that the spirit has to pass through. The usual depth of this bed is twelve to sixteen inches.
But when clear and transparent liquors are required, the spirit should be filtered through the same depth of equal parts of rice and rice flour. The use of the whole grains of rice is to prevent the flour from lying in a too compact and solid body, which would impede the free filtration of the fluid.