Yeast is an indispensable ally for the preparation of a large number of edible specialties that are part of the cuisines of much of the world: different types are used, starting from mother yeast, through beer yeast and then chemical yeast. . Today we are focusing on the latter, chemical yeast: why is it defined like this? The same is given by the union of bicarbonate (usually sodium) with a starch (it is usual to use corn starch) to which cream of tartar is also added: generally it is used to prepare all those recipes where leavening must take place directly during cooking in the oven.