In Praise of Yeast
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Sometime between 10,000 and 15,000 years ago, a Mesopotamian farmer discovered that the water some grain had been soaking in had developed a funny taste. He woke the next day having made two important discoveries, beer and hangovers!
The first written records of brewing come from Sumeria about 6,000 years ago. But all that drinking was making people hungry, so in Egypt around 5,000 years ago, they starting making bread (or at least, they wrote down the recipe). Before that, bread was tough, dry stuff that tended to break your teeth and made your jaw ache. Bread made with yeast was wonderful, light, tasty stuff. The secret? Saccharomyces cerevisiae.
Yeasts such as Saccharomyces cerevisiae are single-celled fungi which multiply by budding, or in some cases by division (fission), although some yeasts such as Candida albicans may also grow as simple irregular filaments (mycelium). They can also reproduce sexually, forming asci which contain up to eight haploid ascospores. If you look closely at the video, you can see examples of budding cells.
Saccharomyces cerevisiae has thick-walled, oval cells, around 10 µm long by 5 µm wide and is commonly known as “bakers yeast” or “brewers yeast”. The yeast ferments sugars present in the flour or added to the dough, giving off carbon dioxide (CO2) and alcohol (ethanol). The CO2 is trapped as tiny bubbles in the dough, which rises.
So why does yeast do this? To gain energy from the breakdown (fermentation) of carbohydrates. The fermentation of beer and wine was originally caused by naturally occurring yeasts present in the environment. Some wineries still use natural yeast strains, however most modern brewers use highly cultured isolates, e.g. Saccharomyces carlsbergensis, named after the Carlsberg Brewery in Copenhagen. The bubbles in beer and sparkling wines such as Champagne are trapped CO2, the result of yeast fermenting sugars in the grape juice. One yeast cell can ferment approximately its own weight of glucose per hour, giving rise to large volumes of CO2!
Not all yeasts are good. Some, such as Candida albicans, can cause infections. Candida is a commensal organism found in 40-80% of healthy people, and is present in the mouth, gut, and vagina. Problems start when a person experiences some alteration in their cellular immunity, normal body flora, or normal physiology. Although Candida most frequently infects the skin and mucosal surfaces, it can cause systemic infections manifesting as pneumonia or septicaemia or in severely immunocompromised patients. Overall though, yeast is surely a good thing!
Beer is proof that God loves us and wants us to be happy.
Benjamin Frankin
[...] Yeasts are unicellular fungi, normally oval or spherical in shape. Typically, yeasts replicate by budding rather than by binary fission like bacteria. During budding, the cytoplasm and dividing nucleus from the parent is initially continuous with the bud, or daughter yeast, before a new cell wall forms to separate the two. In some cells, these buds fail to detach and may form a short chain of cells called a pseudohypha. Although yeasts are single cells and produce smooth bacterial-like colonies on laboratory agar media, unlike bacteria they have a distinct nucleus and are thus clearly eukaryotes. An example of a yeast is Saccharamyces cerevisiae that produces alcohol during anaerobic fermentatio…. [...]
[...] from the ashes: The 5 million year old virus. The month also included our first video podcast, In Praise of Yeast (more of those to come next year). Coming up to date, recently we looked at Ocean Viromes, [...]
Yeast is a fascinating substance; how it grows and manifests. But as you say, not all yeasts are good. I’ve suffered yeast infections myself, and can tell you just how unpleasant they are. But my Husband likes his Beer…so in that kind of yeast is good (for him anyway). It’s all in the perspective, and th type of yeast I guess.
[...] spotting cDNAs onto filter paper with pins. The first analysis of a complete genome (that of yeast, Saccharomyces cerevisiae) using a microarray was published in 1997 (Yeast microarrays for genome wide parallel genetic and [...]
[...] center” that directs cell division. The researchers used regular baker’s yeast (Saccharomyces cerevisiae) – commonly used in bread, wine and beer making – because many of the yeast cell’s processes [...]