Our Little Friend of the Week: Yeast

~Well hey there~ This weeks ‘Little friend of the Week’, as I had mentioned last week, will not be a bacteria…but a fungus. I’m talking about Yeast…and don’t make that face. Yes, Yeast is a fungus. It is a eukaryotic microorganism classified under the fungi kingdom. But don’t worry so much about the fungus part (for all the non-biology loving people), you will enjoy the many ways this fungus has positively influenced our lives. That, however, will come a bit later.

*Pro-Tip: A lesson on pronunciation. It is not pronounced fun-GUY <— H A T E…it is pronounced fun-jy (the ‘g’ sounds like a ‘j’ and you sound out the ‘y’ like you would in guy, like you’re saying “I”). It’s a pet peeve of mine 😛 (Don’t piss of biologists).

First, a bit of info about this lovely specimen. I’ll start with a side note: Yeasts do not form a single taxonomic (or phylogenetic)grouping. The term yeast is often referred to as a synonym for the species Saccharomyces cerevisiae, but the phylogenetic diversity of yeasts is shown by their placement in two separate phyla: the Ascomycota and the Basidiomycota.  The budding yeasts (“true yeasts”) are classified in the order Saccharomycetales.  Just to clarify, lol

The term “Yeast” comes from Old english word “gist” or “gyst” and from Indo-European root ‘yes’, meaning boil, foam or bubble. Yeast microbes are probably one of the earliest domesticated of all organisms. Yeast has been used for fermentation and baking throughout history. Archaeologists have found early grinding stones and baking chambers for yeasted bread, as well as drawings of ancient bakeries or breweries. So, using Yeast in many products has been going on for a lot longer than you’d think…the techniques have just been improved and perfected over time. But this is not a new concept.

Ecologically speaking…Yeasts are very common in the environment. Examples include naturally occurring yeasts on the skins of fruits and berries (such as grapes, apples or peaches) and parts from plants (such as plant saps or cacti). Some yeasts are found in association with soil and insects. Some yeasts like Candida albicans or Trischosporon cutaneum have been found living in between people’s toes as part of their skin flora. Yum :P. Yeasts are also present in the guts of  mammals and some insects.

Enough about all the technical stuff and onto something more relevant. How is yeast really used?


I like to drink beer…so I thank Yeast every friday and saturday night for bringing me beer. You should too. Yeast is the most important ingredient in beer brewing. When added, the yeast reacts and feed off the sugar, in what is called the fermentation. The yeast continues to grow and metabolize in the sugar solution, creating an alcohol by-product. The yeast will continue this process until the alcohol content reaches a high enough level that kills the yeast cells.  Basically, without the yeast there would be no beer. Yeast is also the final component that determines the flavor of the beer.

The two main varieties of yeast used for beer brewing are top-fermenting yeast (Saccharomyces cerevisiae) and bottom-fermenting yeast (Saccharomyces uvarum). The names of both are descriptive of where fermentation takes place in the wort when the yeast is used. The top-fermenting yeast is similar to the yeast for baking bread. It is applied for making ales and stouts. The bottom-fermenting yeast is utilized for production of lagers and steam beer.

Saccharomyces cerevisiae (zoomed in on a petri plate)

Clearly not a picture of the microbe in question…but, I figured a picture of beer SOMEWHERE had to happen lol Don’t judge. ❤

Wine (for you Wine-O’s out there…)

In wine making, Yeast is used where it converts the sugars present in grape juice into ethanol. Yeast is normally already present on grape skins. Fermentation can be done with this wild yeast but this procedure gives unpredictable results, which depend upon the exact types of yeast species present. For this reason, a pure yeast culture is usually added ; this yeast quickly dominates the fermentation. The wild yeasts are repressed, which ensures a reliable and predictable fermentation

Most added wine yeasts are strains of S. cerevisiae. However, not all strains of the species are suitable. Different S. cerevisiae yeast strains have differing physiological and fermentative properties, therefore the actual strain of yeast selected can have a direct impact on the finished wine…which may or may not be a positive thing.

More Saccharomyces

Wine fermentation.


Many breads are leavened by yeast. The yeast used for leavening bread is (once again) Saccharomyces cerevisiae. This yeast ferments carbohydrates in the flour, including any sugar producing carbon dioxide. Many bakers leaven their dough with commercially produced bakers yeast.  Baker’s yeast has the advantage of producing uniform, quick, and reliable results, because it is obtained from a pure culture. Many artisan bakers produce their own yeast by preparing a growth culture that they then use in the making of bread.I don’t believe I need to post another photo of Saccharomyces since I have twice already.

As you can see, these few fungi serve multiple purposes industrially…which I think is pretty awesome. I hope that this was at least a bit informative. I didn’t know about the particulars of yeast, bread/beer/wine production and all that until I took a formal Mycology class (a class about fungi…). So, I’m hoping this isn’t all common knowledge. If you walked away learning SOMETHING, I’m happy with that.  I hope you all enjoyed this weeks ‘Little friend of the week’. I actually partook in said friend today when I had a  few beers myself. I hope you go forth and do the same. Or drink wine…or eat a piece of toast, or something.

Next week! I am not totally sure about what next weeks edition will bring…BUT, I have been itching to do something ‘gross’. To an extent, have no fear people with weak stomachs! I think I will present my first ‘disease’ that I find interesting and the microbe behind it. I kind of wanted to stray away from the microbiology aspect and post a blog about ‘Stone man’ syndrome…which is a fascinating (albeit sad) connective tissue disease. I also wanted to start my first disease post with one of the more deadly: the bubonic plague (believed to be one of the causes of the famous Black Death). So I will start with that and then the following week (or maybe do two posts that day) progress to Stone Man Syndrome. Can’t wait to see you all there.

~Biology: Cause it works~


About therocknwriter

Yours truly. A somewhat cranky, highly sarcastic, but usually mild mannered poet with a love for Coheed and Cambria, body modification, smoothies, video games, a good book, and vegetarian delights. I love being an Oreo, and I hope you'll love me for it too

Posted on June 12, 2012, in Our Little Friend of the Week and tagged , , , , , , . Bookmark the permalink. 7 Comments.

  1. Very informative, I’d ask for a pint or two. Stone Man Syndrome would be interesting to read about, especially after I sent you the picture of that woman with it.

    Question: would it be used in making vodka, or how do the potatoes become booze? Would that be also yeast at work?

    • Yeast is used to ferment the grains (or potatoes), and create the alcohol but there is no yeast in any spirits. The distillation process used to create vodka and other distilled spirits removes the alcohol and leaves the yeast and other unwanted products behind.

      Alcoholic drinks that are not distilled, such as beer and ale, may still have yeast in them.

  2. Nice article. I’ve been a fan of the wild strains of yeast from the Brettanomyces group that are being used to create wild and funky beers. Normally an enemy of brewing, but a tradition of many Belgian beers and now experimental American breweries.

  3. Nice article. As a lover of bread and beer, I’ve always been a fan of S. cerevisiae. My first job was studying some (somewhat) related fungi, but I also got to grow plenty of the good stuff in the lab – there’s nothing like the smell of a robust, healthy culture (of yeast – other stuff typically reeks).

    • Really? That’s pretty cool. I’d love to have a job working with fungi…that would be awesome. Well, without being a teacher that is lol And yeah, agreed on the interesting smells. Oh science lol

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