This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
A method we have followed for years, in preparing ginger in soluble essence, with good practical results, we found lately advocated and published by L. F. Stevens; we append it here, also, having already recommended this method for preparing water-soluble extracts, etc., in general on page 662. Into a half-gallon bottle put the following: Fluid extract of ginger, one pint; powdered pumice stone, four ounces avoirdupois; water, two pints. If the weak or strong tincture of ginger is employed, use the same proportion of water, but a greater proportion of the soluble essence must be applied in flavoring a certain quantity of syrup; the proportions are one ounce to two or four respectively. Pour the fluid extract into the bottle, and add to it the pumice. Then add if desired a few drops of essential oil of ginger or from half an ounce to an ounce of the concentrated essence of ginger oil; shake well occasionally during several hours, and then slowly add the water in portions of about four fluid ounces, with plentiful agitation, and alternate periods of rest and subsidence. Continue this at intervals during twenty-four hours, then filter, and upon the mass in the filter pour water until three pints are obtained, or until the three pints of partly alcohol liquid originally mingled are pushed through without allowing much water to pass. If the filtrate thus obtained is not quite clear, it may be shaken with a little more pumice, or a very little clean talc; the latter, however, must be used with care. Allowance of time for the exchange of solvents from strong to weak spirits, is necessary in this process. The finished product is a delightful representative of the ginger, minus the hot taste, is miscible with water, and produces a clear beverage.
Mr. Stevens adds the following remarks: "Endeavors to increase the strength of the finished preparation - that is, to make it represent more than 33 per cent, of the soluble portions of the fluid extract - are not economical, as there is loss of gingerol upon the filter, and increase of alcoholic strength causes more resin to pass through, which afterward is slowly deposited. That the soluble essence as thus produced contains volatile oil is proved by distillation, or easily by throwing a teaspoonful upon the surface of hot water in a cup, when it becomes evident to the nose. That it contains essence of dinger or gingerol is proved by physiological test, by swallowing some, when shortly a genial glow is felt extending throughout the circulation.
"The mass remaining upon the filter, if dried and washed with alcohol, yields a solution of hot resin of value for cooking, or for the delectation of 'old drunks.' If the alcohol is recovered by distillation it is found to be sweet, clean and pure, fit for any purpose, which shows that no volatile oil clings to the filter, and the resin will be left behind, thick, black and hot, and about three fluid drachms of it from sixteen troy ounces of Jamaica ginger. This sample shown weighed 177 grains - a little over two per cent. (Thresh averages about two per cent.) Without doubt there will be plenty of use found for it. The pumice may be regained after the washing, white and handsome, ready to be used again".