Sunday, April 15, 2018

The Fungus Among Us: Fantastical Yeasts

Bread. It's one of the most basic of foods - 15% of the world's calorie intake comes from wheat - and also one of the oldest processed foods. Even before the advent of agriculture, people realised they could turn ground grain into a leavened loaf (as well as alcoholic beverages...). However, they likely didn't know about the little microbes causing their bread to rise. For these fermentation processes to happen, we need our little fungal friends, namely Saccharomyces cerevisiae (and its various strains). And that, my friends, is what we will talk about today - yeast.

This past week, I skipped yoga to listen to a researcher from the University of Queensland regale us with tales about catching and cultivating local yeast species and strains and brewing beer. These funghi are important in the brewing process, feeding on sugars in the grain, converting them to carbon dioxide (fizzy!) and ethanol (alcohol). Different species and strains metabolize sugars in different ways, affecting the flavour (like acidity) and texture (like carbonation). But all this talk of yeasts, got me thinking about bread, and the microbiota involved in my weekly bake.

Now when you buy those little packets of dried yeast, or any bread from the grocery store, you're getting a bountiful monoculture of S. cervisiae. Sourdough starters are more likely a slightly untamed backyard garden - a mix of yeast species (typically Candida milleri, S. exiguous, S. cerevisiae, and C. humilis) and lactobacillus bacteria. These little guys, naturally found in our surrounding environment, will colonize a flour and water mixture left out for a few days (after they've fought off the less deliciously fragrant microbes). When mixed with flour and water and used to make bread dough, a bit of biochemistry takes place. The lactobacilli convert sugars (maltose in this case) to lactic and acetic acids, giving the bread a slightly sour taste. And the yeast do the same thing they do in beer-brewing ...  metabolise sugars (sucrose, and others) to make ethanol and carbon dioxide, giving the bread additional depth of flavour and some lift.

This may seem a bit high-brow, and sourdough bread has definitely developed a reputation as the new hip thing. But it is also commonplace and central to daily life. As a critical component of many diets around the world, the cost of bread, and the essential grain ingredients, is a useful indication of the state of a country and the welfare of its people. We've seen in the past how the rising price of bread can play a role in social unrest and protest. While some of us may get pre-occupied dwelling on the fascinating microcosm within this tasty baked good, it is important not to forget that bread is at its core sustenance - wheat is the primary food of 35% of world's population. I'll be trying to subsist for five days, with mostly this fabulous fermented grain serving as the basis of my diet. Please join me for another year of Live Below the Line and contribute to the Oaktree Foundation.

Read more:
The Biology of ... Sourdough - Discover Magazine 2003
Let Them Eat Bread - My Munchable Musings 2015
Secrets of Sourdough - The Atlantic 2017


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