Yeast in Medieval Recipes

Perhaps the earliest evidence in the recipe corpus for a direct recognition of yeast occurs in a late 13th century Anglo-Norman collection (B.L. MS Additional 32085), recipe number 4 in which ("Mincebek") includes the ingredients "un poi de gest ou un poi de past egre", that is, "a little yeast or a little sourdough". In the 14th century, two recipes from _Forme_of_Cury_ (number 154, "Frytour of pasternakes, of skirwittes, & of apples", and number 156, "Frytour of erbes") call for "ale & 3est"* and "a lytel 3est" respectively.

A 15th century recipe from MS Harleian 279 (recipe LV 54, "Fretoure") indicates specialization of yeasts by calling specifically for "Ale 3est", as do MS Harleian 4016 recipe 133 ("Lente ffrutours": "Ale yeest"), MS Beineke 163 recipe 107 ("Bastons": "A lytyll yest of new ale"), and the _Noble_Boke_off_Cookry_ recipe 46 ("To mak rostand": "alitill yest of new ale").

In addition to recipes that specifically call for yeast by name, there are six more to my certain knowledge that call for barme (two in MS Harleian 279, three in MS Harleian 4016, and one in _Noble_Boke_off_Cookry_. Significantly, of these, two are for rastons, and one is for fritters -- both dishes other recipes for which call for yeast, suggesting that the cooks who developed these recipes recognized yeast as the active ingredient in barme.

A 14th century French manuscript provides further evidence of specialized yeast strains. In the _Menagier_de_Paris_, the recipe for "Bouchet" (a weak mead) under the heading "Beverages for Invalids", includes the following passage: "and add one chopine ... of beer-yeast, for it is this which makes it the most piquant, (and if you use bread yeast, however much you like the taste, the colour will be insipid),...."

In short: by the late 1200s -- six hundred years before Pasteur -- recipes called for yeast by name, and by the 1400s, recipes routinely specify a particular variety of yeast (ale yeast). The existence of dishes for which one recipe calls for yeast and another, in its place, for barme strongly suggest that the authors of the collections recognized barme as containing yeast; and the presence, in the 13th century recipe, of sourdough as an alternative to yeast indicates the awareness that yeast is what makes dough work.