Now, here's a difficult spot. In lock-down England everyone has decided to make their own bread and so I haven't even heard of their being any yeast in the shops for months.
So, given that ready-packaged yeast isn't available to spot, where else might we find it?
Well, more or less everywhere, really, and the existence of sourdough bread proves it.
Sourdough bread relies on the fact that there is wild yeast already present in flour and in the air, and so that, given a bit of encouragement (that is, warmth and moisture) the yeast will soon start, um, giving off gas to make bubbles in the dough to make the bread rise.
This is all a bit odd, when you come to think about it.
A yeast is a single-celled fungus, and this means it's too small for us to see a single yeast organism. Strangely, yeasts seem to have have evolved from multi-celled organisms, but are now quite happy living a simpler life. The habit of one kind of yeast, Saccharomyces cerevisiae, of turning carbohydrates into carbon dioxide and alcohol may explain this contentment. (This yeast can also produce ethanol to make biofuel.)
There is yeast in alcoholic drinks, bread, yeast extract (obviously) and also drinks like root beer and kvass and kefir.
And there are other yeasts about. The velvety bloom on the skins of grapes and other fruit shows the presence of a yeast colony. Other sorts of yeasts exist in the moist places of animals, including man, and can occasionally cause disease.
A substantial amount of medicines are produced with the help of ordinary baking yeast. These include insulin and even some vaccines.
So, you never know: in this time of plague yeast might even be our saviour, yet.
Spot the Frippet: yeast. This word was giest in Old English. The Sanskrit form of the word is yasati.