Withania. Withania coagulans. Vegetable rennet.
Withania. Withania coagulans Dun. (Stocks.) Vegetable Rennet. (Fam. Solanaceae.)—This shrub, common in Afghanistan and East India, has the property of coagulating milk, and has been used for preparing a vegetable rennet ferment for making cheese. Sheridan Lea found upon examination that the substance which possesses the coagulating power is a ferment closely resembling animal rennet. The active principle is soluble in glycerin, and can be extracted from the seeds by this solvent; the extract possesses strong coagulating powers even in small amounts. Alcohol precipitates the ferment body from its solutions, and the precipitate, after washing with alcohol, may be dissolved again without having lost its coagulating powers. The active principle of the seeds will cause the coagulation of milk when present in very small quantities, the addition of more of the ferment simply increasing the rapidity of the change. The coagulation is not due to the formation of acid by the ferment. If some of the active extract be made neutral or alkaline, and added to neutral milk, a normal clot is formed, and the reaction of the clot remains neutral or faintly alkaline. The clot formed by the action of the ferment is a true clot, resembling in appearance and properties that formed by animal rennet, and is not a mere precipitate. Lea prepared an active extract, applicable for cheese making purposes, by grinding the dry seeds very finely in a mill, and extracting them for twenty-four hours with such a volume of 5 per cent. sodium chloride solution that the mass is still fluid after the absorption of water by the fragments of the seeds as they swell up. From this mass the fluid part may be readily separated by using a centrifugal machine (such as is used in sugar refining), and it can then be easily filtered through filter paper; without the centrifugal machine the separation of the fluid from the residue of the seeds is tedious and imperfect; forty grammes of the seeds treated as above, with 150 mils of 5 per cent. sodium chloride solution, gave an extract of which 0.25 mil clotted 20 mils of milk in twenty-five minutes, and 0.1 mil clotted a similar portion of milk in one hour. When added in these proportions the curd formed is quite white. The presence of the coloring matter is, however, perhaps on the whole unimportant, since even if a larger quantity of the ferment extract is added in order to obtain a very rapid coagulation, the coloring matter is obtained chiefly in the whey, the curd being white; by adding sufficient common salt to make the percentage up to 15 per cent., and alcohol up to 4 per cent., the preparation would retain its activity very well. (P. J., 1884, 606.)