Magnier de la Source[92] has recently made some investigations concerning the difference in chemical composition of natural and plastered wine; he gives the following constituents of 1 litre of wine:-- --------------------------------------+--------+------------ |Natural.| Plastered. +--------+------------ | gr. | gr. Tartar | 1·94 | 0 Sulphuric acid | 2·58 | 3·10 Potassium | 1·12 | 2·46 Calcium (in soluble portion of ash) | 0 | 0·037 Calcium (in insoluble portion of ash) | 0·179 | 0·151 --------------------------------------+--------+------------ _Adulteration of Wine._--Although there may be some question in regard to the moral status of the foregoing methods of improvement of natural wine, numerous other practices are resorted to concerning which no doubt can exist. The more common forms of wine adulteration include plastering, sulphuring, fortification, blending, flavouring, colouring, and the manufacture of fictitious imitations. The “plastering” of wines consists in the addition of plaster of Paris (often mixed with lime), either to the unpressed grapes or to the must. The process, which is rather hypothetically claimed to aid in the preservation of the wine and correct any excessive acidity, is very objectionable, in that it determines the formation of free sulphuric acid and acid sulphates, as well as of calcium tartrate and potassium sulphate. The lime salt, being insoluble, is deposited with the lees; the potassium sulphate, however, remains in solution, and as it exerts a decided purgative effect, its presence in wine cannot fail to be detrimental. In France, the sale of wine containing over 0·2 per cent. of potassium sulphate is prohibited. The plastering of wine is chiefly carried on in Spain, Portugal, and southern France. The ash of pure wine does not exceed 0·3 per cent., but in the samples of sherry usually met with it reaches a proportion of 0·5 per cent., and is almost entirely composed of sulphates. The “sulphuring” of wines is also extensively practised. It is effected either by burning sulphur in the casks or by conducting sulphurous acid through the wine itself, the object sought being to preserve the product and impart to it the ripeness naturally acquired by age. Sulphured wines, while not necessarily showing an increase in the amount of ash, can often be recognised by the abnormally large proportion of sulphates present.