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.
This is a matter of great importance, which has been settled according to the individual preferences of the manufacturer. Salicylic acid, sodium salicylate and bisulphite of lime, are sometimes used as preservatives for lime and lemon juice, also alcohol is employed to fortify the juice. The finest quality of juice may keep for some time without any preservative, it being filled into clean dry bottles after having been allowed to deposit, and securely corked. If evaporated to dryness, the residue is apt to become musty. Sugar is undesirable, on account of increase of bulk. It is obviously often very desirable to have lime-juice in a highly concentrated yet instantly available state. If to 100 ounces of lime or lemon juice, fifteen ounces of glycerine be added, and the whole evaporated in vacuo to twenty-five ounces, we get a juice concentrated to one-fourth, with perfect keeping power. If alcohol be added to the concentrated juice, much of the vegetable matter is thrown out of solution, which may probably deteriorate its power; with glycerine this is not the case, the resulting product being a most stable and elegant one. The best way to preserve non-concentrated lime or lemon juice is to add ten per cent, of alcohol of 95° to the fresh juice, and to bottle and seal.