1883.] 



On a "Rennet" Ferment. 



57 



V. 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. 



VI. 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. 



Having thus determined the presence of a rennet ferment in the 

 seeds, I endeavoured to prepare an active extract, which should be 

 applicable for cheese-making purposes. All the extracts of the seeds 

 are of a deep brown colour, and it appeared, therefore, in the first 

 place, desirable to obtain less highly coloured , if not colourless, solu- 

 tions, which should still be active. In this I have so far failed. The 

 precipitate caused by alcohol carries down the chief part of the 

 colouring-matter also, so that on being subsequently redissolved the 

 solution is nearly as highly coloured as before the precipitation.. The 

 colour can be removed by using animal charcoal, but the ferment is at 

 the same time destroyed. If all excess of charcoal is avoided and the 

 solution is filtered at once, the filtrate is largely decolorised, but 

 contains only traces of the ferment. Animal rennet is similarly 

 removed by filtration through charcoal. The colour can be removed 

 by the addition of very finely-powdered kaolin in a dry state, but, as 

 before, the ferment activity is thereby destroyed. The same holds 

 good of animal rennet. The colouring-matter is scarcely soluble in 

 either ether or alcohol, so that no advantage is gained by a preliminary 

 treatment with these before extraction with the salt solution. I have 

 also endeavoured to get rid of the colour by treating the seeds as 

 rapidly as possible with successive quantities of water before making 

 the final extract. By using a centrifugal machine I was able to wash 

 the seeds six or seven times with large volumes of water without 

 their being exposed for any considerable time to the action of the 

 water. Each portion of water was highly coloured and the seeds 

 were thus freed from adherent colouring-matter. But, apart from the 

 fact that some, though not much, ferment is thus lost, no special 

 advantage is obtained, since the seeds are themselves coloured, and 

 even after prolonged treatment with water the final extract is always 

 of a dark brown colour. 



In order to obviate the disadvantages of this colouring-matter, if 

 disadvantage it is, I have found it best to prepare very concentrated 

 active extracts of the purified seeds, so that it should only be necessary 

 to add a very small quantity of the extract in order to coagulate the 

 milk and obtain a colourless curd. This I have done 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, sodic chloride solution that 

 the mass is still fluid after the absorption of water by the fragments 



