YEAST!

Many of us have 'kneaded' something to do over the past couple of years, and some of us found refuge in sourdough. But how old is that essential ingredient, yeast?

Rob - The crucial ingredient in sourdough is actually a mixture. So, it's yeast and then different species of bacteria. And so the yeast are producing carbon dioxide, which makes the dough rise and the bacteria are making it sour and producing all sorts of lightweight chemicals that add aromas and flavours. But the first use of yeast goes back certainly 14,000 years. It probably was first used to ferment in China. And then spread to the fertile crescent and then spread around the world from there. And so we've been using it for a long, long time.

Chris - How do you know, 14,000 years? That's a very long time.

Rob - Well, so that's the oldest piece of bread anybody's found. The oldest beer is about the same time period. And if we look at the yeast, the evolutionary tree, we also see, sort of a branching in the tree that more or less maps to that same period of time. Probably as we make more discoveries that time will push back farther and farther. And we're starting to think that some of our other ancestors may have fermented things. And some of the evidence comes from capuchin monkeys. And some capuchin monkeys appeared to have learned how to knock down fruits that they can't eat. And then to come back to them three or four weeks later after they've rotted and become kind of like a Simian kombucha.

Chris - Right? So they knew that this was a way of converting the in digestible into the digestible.

Rob - Yeah. They figured out a series of steps that allowed them to produce a new product

Chris - When we consider yeast. I mean, I presume we as humans have exerted some degree of sort of evolutionary pressure on the microbial world, including things like yeasts to make them do those sorts of jobs better for us, become better yeast for brewing, become better yeast for baking.

Rob - We know that we've tended to favour brewing yeast that are able to survive the presence of lots of alcohol. But we also know that yeast when it was moved around the world, that it was under different selective pressures in different places because people used it to make different things. And so what we're starting to see is depending on where you look, you see different varieties of yeast in the same way that you might see different kinds of tomatoes. And then on top of that, what we've seen recently is that the industrialization of bread and beer production is favoured by varieties of yeast that aren't so good at producing wonderful flavours, but they're just really good at being consistent and working in an industrial context. And so that's a really strong selection pressure that's recently been documented, but it's a big evolutionary story. It's like Darwin's finches, except at the end you get beer.

Chris - It's my favourite example of synthetic biology that is the brewing industry.