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.
It will not deteriorate by exposure to light or heat, nor by keeping any length of time, if the bottle is kept corked. But the carbonated beverage flavored with this essence will have a slightly milky appearance, even if the compound syrup has been filtered. However, where the bright appearance of a beverage is not so much an object we prefer this essence, which imparts a rich flavor to syrup and beverage, is easily prepared and preserved. For lemon syrups prepared for the dispensing counter, we prefer its use. The slight milky appearance of the drink does not so strikingly appear, being at once consumed, as is the case with bottled beverages. One ounce to a gallon of plain syrup, will impart a rich flavor; however, a little more may be used to suit the taste.
To improve the aroma of lemon essence the addition of a small quantity of oil of rose or of oil of neroli, either one or both, or, instead of the oils, the addition of a corresponding proportion of their respective concentrated essences, is highly recommended. Making this combination in advance, and keeping it -in a well-closed bottle, will improve its aroma. When this concentrated lemdn essence is wanted for bottling purposes, prepare the soluble essence as directed.
This is the proper preparation for bottling purposes, where a bright appearance of the beverage is of importance. Prepare as follows: Lemon oil, one ounce; alcohol of 95 per cent, eight ounces; water, eight ounces. Cut the oil with powdered pumice, etc., and some sugar, in a mortar; triturate until absorbed; first add by degrees the eight ounces of alcohol, agitate until all is dissolved; then add gradually the eight ounces of water, and continue to agitate, filter and re-filter until bright.
N. B. - As commercial oil of lemon usually needs more than eight ounces of alcohol to be dissolved, we propose rather to use twelve to sixteen ounces of alcohol to dissolve it, and an equal amount of water to dilute, thus economizing oil, which otherwise would separate, and probably be wasted; of this diluted essence use proportionally more to flavor. Pure oil will dissolve in eight ounces of alcohol, and where we refer in the appended receipts for flavored syrups to "soluble essence of lemon," the former strength is denoted.