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.
Several means of preserving and clarifying fruit juices are known. A usual way in which they are kept from fermenting is by the use of salcyli or benzoic acid, or some other antiseptic substance, which kills the fermentative germ, or arrests its action for a long time. About two ounces of salicylic acid, previously dissolved in some alcohol, to twenty-five gallons of juice or ten grains to a quart, will be the proper quantity. Another method quite practicable is to fill the freshly prepared cold juice in bottles until it reaches into the neck of the bottle, and on the top of this fruit juice, carefully using the neck of the bottle as a guide, a little glycerine is placed. Juices thus preserved will keep in an unchanged condition in any season.
Probably the best method of preserving fruit juices is to add fifteen per cent, of alcohol of 95°. On this addition mucilaginous matter and albumen will be deposited. The juices can then be kept in demijohns or barrels, tightly closed, and when at rest, they become perfectly clear, so that clarification is unnecessary provided the vessel has not been moved. The liquid is then syphoned off with a hose.
Fig. 424. - Fruit Press.
Fruit juice may be clarified by heating it either alone or mixed with a small quantity of egg albumen, in an enameled vessel, that has a tight-fitting lid to close, without stirring, to near the boiling point of water, until the impurities have coagulated, which will occur at 70° C. (158° F.), and either risen to the top or sunk to the bottom. Then filter through felt or flannel bag. This heating process will entirely destroy the germs of fermentation, and the subsequent filtration will clarify the juices, which should be kept in a cool place, and will remain unchanged, and keep indefinitely if properly and carefully prepared. If the corks are coated or the neck of the bottles dipped in melted paraffine to prevent access of air through the pores, it is a wise precaution. The utmost care must be observed in heating the juices; heat no more than absolutely required, as the delicate aroma would considerably suffer.
Fig. 425. - Juice Filter.
Fig. 426. - Sectional View of Fig. 425.
For filtering and clarifying the fruit juices and fruit essences, the fil-tering apparatus illustrated by the above two engravings is of practical service, since it is closed and the air can thereby be excluded, which is rather advantageous. By this process the juice is poured into the reservoir of the filter, and passing through seven double bags of peculiar construction, is run off perfectly bright. All inside parts of the filter coming in contact with the juice or fruit essence must be carefully lined with pure tin or best with silver, to protect against contaminations. All fruit juices and fruit essences contain fruit acid in solution; therefore whenever a clarifying powder is desired to be employed, the carbonate or calcined magnesia, chalk (carbonate of lime), must never be used, as the fruit acid would become neutralized. Pure silica or glass sand or powdered pumice stone are the only means permitted for this purpose.