Profitable Wonders
Improbable as it might seem, Saccharomyces cerevisiae – the minuscule, oval-shaped sugar fungus, or yeast – was the prime mover in the rise of human civilisation.
Through its facilitation of baking and brewing, it enabled that pivotal transition from hunting and gathering to settled agrarianism.
The advent of baking 8,000 or so years ago produced the surplus food, in the form of bread, that nourished the builders of the first cities in the fertile crescent of Mesopotamia.
Bread built the monumental pyramids of the Old Kingdom of Egypt and the fortifications and temples of ancient Rome and, as ‘the staff of life’, has fed the citizens of Europe through two millennia of peace and war.
In parallel fashion, down through the centuries, the brewing of fermented alcohol has been enormously beneficial in promoting good cheer and social cohesion (obviously). Wine and beer, being sterile and free of pathogens, have been a ‘hygienic’ alternative to drinking effluent contaminated water, thus protecting against the ravages of cholera and other illnesses.
To breakfast in Homer’s Greece – akratidomai – was to ‘drink undiluted wine’. In the Middle Ages beer, an integral, nutritious component of the diet, was drunk throughout the day.
Baking and brewing, though the earliest of technological innovations, require far more than a simple series of essential and often onerous stages – threshing, winnowing and grinding the grain, sifting and refining, malting and mashing, kneading and proving.
After all this hard work, the yeast, when added, appears to possess almost magical properties, effortlessly causing the dough to rise or the fermenting liquid to bubble; to produce, respectively, a deliciously warm, freshly baked loaf, with its comforting aroma, and a draught of tangy, thirst-quenching beer.
The nature of that seemingly magical
transformation remained obscure until scientists in the early 19th century, peering down their microscopes, identified the presence in fermented beer of ‘globules’ of the sugar fungus.
Soon after, a couple of French chemists crushed germinated barley in cold water, together with a solvent, and extracted a white precipitant that proved to be quite staggeringly potent – capable of breaking down almost instantaneously 2,000 times its own weight of starchy carbohydrate into its component simple sugars.
They had found the first enzyme – a vast array of differently-shaped proteins, each specifically designed to facilitate one or other of the numerous chemical reactions that drive the great energising circle of life.
In 1859, Louis Pasteur drew these two observations together, demonstrating that the alcohol and gas (carbon dioxide) produced by those minuscule globules of yeast – which cause the dough to rise and the beer to bubble – are the waste products of its enzyme-driven, energygenerating metabolism, fuelling its phenomenal rate of reproduction. A new ‘baby’ yeast is budded off every 90 minutes – that’s 1,000 offspring in just 24 hours.
This has turned out to be a most elegant, if complex, process, involving no fewer than 20 different enzymes. The first enzyme transforms the glucose molecules, absorbed from dough and fermenting beer, into glucose-6phosphate. Then, through a cascade of further chemical intermediaries – releasing a bolus of energy at every stage – the process culminates in alcohol.
To grasp what is entailed, imagine stepping through the yeast cell’s silky outer wall into its interior. You find yourself in the midst of a terrific agitation where, at any one moment, tens of thousands of copies of each of those 20 different enzymes are grabbing and modifying the glucose molecules and chemical intermediaries of the cascade.
Meanwhile, controlling the process, a further set of chemical instructions, encoded by the yeast’s 6,000 genes (composed of 12 million letters or nucleotides), are streaming out of the nucleus, to be processed by the mitochondria, ribosomes and other structures within the cell.
And, to cap it all, simultaneously the entire micro-machinery of the cell, along with the 6,000 genes, is being replicated 15 or more times a day in anticipation of the next ‘budding’.
The mighty yeast thus epitomises the central paradox of modern biology. While we know more of the detailed workings of Saccharomyces cerevisiae than of any other organism, the totality of its functioning, internal dynamics and powers of replication remains profoundly unknowable.
That certainly merits a moment’s pause when you’re next appreciating the fruits of its endeavours – or reflecting on the rise of human civilisation.