This section is from the book "The Manufacture Of Liquors, Wines, And Cordials, Without The Aid Of Distillation", by Pierre Lacour. Also available from Amazon: Manufacture of Liquors, Wines, and Cordials, Without the Aid of Distillation.
As tannin is extensively used in one form or another, viz. as tanning oak bark, catechu, and terra japonica, for the bitter and astringent principle and coloring matter that it yields, which is well adapted to brandies, whiskey, and some wines - it requires that it should have more than a passing notice. The term tannin was originally applied to a principle existing in many vegetables having a very astringent taste, and the property of producing a white, floc-culent precipitate, with a solution of gelatine and black precipitate, with the salts of the sesquioxide of iron. As obtained, however, from different plants, it was found to exhibit some difference of properties, and chemists have recognised two kinds; one exist ing in oak bark, galls, etc., and the other in Peruvian bark, catechu, etc. One striking peculiarity of the tannin of galls is its facility of conversion into gallic acid, which is wanting in the other varieties.
Pure tannic acid is solid, uncrystallizable, white or slightly yellowish, inodorous, strongly astringent to the taste, without bitterness; soluble in water, much less in alcohol and ether, and insoluble in the fixed and volatile oils. It can be kept unchanged in the solid form, but its aqueous solution, when exposed to the air, gradually becomes turbid, and deposits a crystalline matter, consisting chiefly of gallic acid. Tannic acid precipitates solutions of starch, albumen, and gluten, and forms with gelatin an insoluble compound which is the basis of leather.
Tannin, in the form of oak bark and catechu, or terra japonica, is the form best suited to the purposes of the manufacturer of liquors. A spirit formed by nitration, that is, a liquor that has had a body given to it by starch, etc., will receive but little assistance from tannin, and an excess of tannin would precipi tate the starch. Tannin generally enters into extern poraneous formulas for liquors - and some manufac turers use oak bark for coloring domestic brandies, which adds considerably to the taste.
Where tannin or catechu would be incompatible with a liquid, alum should be substituted. Catechu is suited to brandies, whiskeys, Port wine, etc. Alum to the astringent wines, as the water the wine contains will hold the alum in solution. The quantities and proportions of tannin necessary in the manufacture of liquors, will be mentioned in the various receipts throughout this work.
The operator will recollect that, where a transparent liquor requires an astringent property, alum will be the best suited for the purpose, as the color of the tannin would render it objectionable. The alum should be first dissolved in water before adding it to the spirit.