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 found in a crystalline state in the interior or on the surface of the vanilla bean, or dissolved in the ropy, oily liquid surrounding the seeds. It is obtained from the alcoholic extract of vanilla, and said to exist in the amount of about two per cent, in the vanilla bean. Vanillin crystallizes in hard, colorless prisms; has the odor of vanilla, and a pungent, warm taste, melts near 80° C. (176° F.), has a feeble acid reaction, and is freely soluble in boiling water, alcohol, ether, fats and volatile oils. Having very slight acid properties, it has been termed vanillic acid by some chemists.