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.
Of late years the expressed juice of the closely allied fruits, limes and lemons, which we have already described in the previous chapter, have been extensively employed by manufacturers of carbonated beverages. Great stress has been laid on the improved quality of the goods of which they form a component part. Where intelligence and experience direct their use, the harmful effects, sometimes ascribed to them, are not likely to occur. The objection most frequently urged by many against lime or lemon juice is its tendency to create a cloudy or ropy appearance in the beverage. In using lemon or lime juice, it is well applied precaution to see that it is, first - the genuine article; and, second - that it is refiltered carefully before using. Deception is practiced in most cases, as shiploads of this article are manufactured in Europe from tartaric acid, citric acid and a good addition of sulphuric and acetic acids to make it more acid. It seems that its being imported, or represented as such, gains lime juice the full confidence of the bottler, whose honest intention is to use a fine article. The fruits are sliced and then squeezed in wooden presses, the juice being run into puncheons and quickly bunged up. This is a most important point in preparing the juice in a tropical climate, for if left exposed it would rapidly decompose. None but the choicest fruit should be used, and only about two-thirds the juice pressed out, thus insuring greater freedom from mucilaginous and pulpy matter. The further pressings, together with the juice of the unsound fruit, is evaporated to the consistence of molasses and shipped away for the manufacture of citric acid. It is stated that limes and lemons may be preserved by the very simple process of varnishing them with a solution of shellac in alcohol. Fresh juice is thus obtainable at all seasons.
Lime juice is very variable as to quality, which depends upon the method of extraction and the quality of the fruit. It contains citric acid, gum, sugar, albumen, extractive matter, inorganic salts and water. The most important and valuable constituent is the citric acid. There is only a mere trace of sugar, while the quantity of gum and albumen is much less than that contained in lemon juice, on which account some claim it is much less liable to fermentation and decomposition than the latter. The quantity of inorganic salts contained in lime juice is about the same, and is also of the same nature as is obtained from lemon juice.
According to good authority a good quality of lime juice should contain not less than 7.25 per cent, of free citric acid.
Lemon juice, owing to the fact that it contains much more sugar and mucilage than lime juice, is more liable to fermentation and decomposition, and the addition of at least one-tenth part alcohol will act as a preventive. Its clarification tends to remove the fermentative germs, and in this state it should be used in compounding carbonated drinks. Lemon juice is frequently adulterated with water, sugar or gum, and sulphuric or acetic acid. The modus operandi is to dilute the genuine juice with water, and then bring up the density with the sugar, or gum, and the percentage of acid with one or the other of the above acids. To guard against the catastrophies invariably following the use of adulterated or inferior grade goods, it is always advisable to purchase of none but reputable houses, whose standing as business men and manufacturers is above reproach. Both lime and lemon juice are so often spurious that this conservative course should be pursued, no matter what the price or inducement offered. Notwithstanding the prejudice that some carbohators bear against lime or lemon juice, the best quality of drinks now contain them. Citric and tartaric acids are good in their way; but, according to the testimony of experienced bottlers, there is a certain indefinable richness given beverages by the former articles which the latter cannot approach.