Yeast

Yeast has been used in the preparation of food and drink for as long as there have been leavened bread and beer, but it was only in the 19th century, thanks to the work of pasteur, that its nature was understood.

Even now, yeast can understandably be treated as a sort of miracle. Elizabeth David (1977), in a fine account of the history of yeast in English baking, remarks that:

In Chaucer’s England one of the names for yeast or barm was god-disgoode ‘bicause it cometh of the grete grace of God’. These words imply a blessing. To me that is just what it is. It is also mysterious, magical. No matter how familiar its action may become nor how successful the attempts to explain it in terms of chemistry and to manufacture it by the ton, yeast still to a certain extent retains its mystery.