Sunday, June 13, 2010

Yeast - one of the best fungi around

Image borrowed from

There are a few things that all beers utilize: water, hops, yeast, and malt. Over the past few weeks I have been thinking about the great effects that yeast has on the flavor of beer. I have set out to investigate the qualities of beer that I enjoy that I can thank yeast for. lists the following as flavor qualities beer yeast can impart:
  • acetaldehyde (green apple aroma)
  • diacetyl (taste or aroma of buttery, butterscotch)
  • dimethyl sulfide (DMS) (taste or aroma of sweet corn, cooked veggies)
  • clove (spicy character reminiscent of cloves)
  • fruity / estery (flavour and aroma of bananas, strawberries, apples, or other fruit)
  • medicinal (chemical or phenolic character)
  • phenolic (flavour and aroma of medicine, plastic, Band-Aids, smoke, or cloves)
  • solvent (reminiscent of acetone or lacquer thinner)
  • sulfur (reminiscent of rotten eggs or burnt matches)
To receive such qualities from such a small organism made me want to learn more about where yeast came/comes from. I began by researching the scientist who first discovered the role of yeast in fermentation of alcoholic beverages: Louis Pasteur.

Image of Louis Pasteur borrowed from

In 1857 Louis Pasteur proved alcoholic fermentation was performed by living yeasts and not a chemical catalyst (he reported these findings in his paper entitled "Mémoire sur la fermentation alcoolique"). An aside for you homebrewers: in the aforementioned paper Pasteur also showed that you can increase yeast cell growth by bubbling oxygen into the yeast broth. Keep in mind that adding O2 inhibits fermentation (this detail is called the Pasteur effect). In other words, introducing air to your fermenting wort increases the amount of yeast cell growth but it weakens the amount of fermentation those yeast cells can perform.

Image of Emil Christian Hansen borrowed from

In the late 1800s and early 1900s a fellow from Denmark named Emil Christian Hansen studied the difference between top and bottom fermented yeast while working at the Carlsberg brewery. Yes, his great contribution can be summed up in one sentence, but because of Mr. Hansen we are able to better pair yeast with the wort we make at home, and the goals we have for our brewing endeavors.

The life span of yeast

Based on what I have read, yeast need a few things to live (seemingly for perpetuity):
  • Sugar to eat
  • Air to create energy to continue their work
  • A constant temperature (typically for lagers and for ales) to work in
  • Something to grow in (such as a 'solid growth media' or a liquid broth

    These days there are numerous strains of beer yeast available for brewers as a result of the work of Pasteur, Hansen, and many other scientists. More than enough to keep brewers busy for a long time figuring out which strains they like, and which ones work best for their brewing system.

    Yeast is (still) such a mystical being, that people continue to explore, test, learn from/about, and play with. I hope you will do your part and continue to brew and try new beer with as many different yeast types as possible.

    If you want to learn more about yeast, I suggest checking out this article.
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