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Facts relative to the Preparation of a dry Leaven or 

 Yeast, for making good Bread. Communicated to 

 James Mease, M, D. by Samuel L. Mitchill, M, D, 

 of NexV'York, Honorary Member of the Philadelphia 

 Society for promoting Agriculture ; in a Letter dated 

 June \st, 1814. 



Read June 14, 1814. 



One of the important improvements in the econo- 

 mical arts, is the preparation of bread from seeds or 

 grain. A further convenience in the manufacture of 

 this article, is the extrication of air through the dough 

 or paste of which it is made, to puff it up. This con- 

 stitutes the chief difference between leavened and un- 

 leavened bread. 



Leaven is a material or mixture, which on being- 

 kneaded with meal or flour, and exposed for some time 

 to a convenient warmth, undergoes fermentation and 

 produces carbonic acid gas. This aerial product fills 

 the soft and plastic mass with bubbles, dilates it into 

 cells, and imparts to it the quality of sponginess so 

 much approved. The leaven itself is a raised portion 

 of a former batch, reserved for the next occasion. It 

 is rendered fit for elevating a new mass of dough, by 

 incorporation with water, wort, or some other fer- 

 mentable liquid, capable of increasing its intestine ac- 

 tion. And the product of leaven thus mingled with 

 water or wort, is a foaming compound called emptyings. 

 Experience has shewn that leaven and emptyings, are 

 liable to sourness, moulding, and spoiling : and when 



