[Sca-cooks] Leven: yeast or sourdough?

[David Friedman]

Recipes frequently don't say--and if they do refer to yeast, 
especially in a translation, the word might actually mean sourdough. 
I gather that sourdough, technically, is not yeast but a different 
organism with similar effects, but even assuming that's right, there 
is no reason to expect people in period to know.

Our working assumption is that "berme" means yeast from beer residue 
and that otherwise the leven is beer yeast in beer drinking areas, 
sourdough in areas that don't drink beer, including the Islamic 
world. But I don't think we have any really solid evidence on the 
subject--does anyone else?
-- 
David/Cariadoc
www.daviddfriedman.com