The Most Important Microbe in Half Way House


Recently, a young visitor followed his parents into the historic brewery. He stopped suddenly, sniffed, and exclaimed, “It smells like bread!”

Our young visitor was quite right! After all, bread and beer share many ingredients: water, grains, and yeast. Of course, the process of baking and brewing is quite different (just ask our interpreters upstairs in the Half Way House kitchen), but the action of yeast lies at the heart of both.

Casks
There is yeast in these casks! Yeast and fermenting wort!

 

The same species of yeast is used for both brewing and baking: Saccharomyces cerevisiae. The name itself is Latinized Greek – saccharo derives from the word for “sugar,” and myces, “fungus.” Cerevisiae means “beer.” So…Saccharomyces cerevisiae literally means “Beer Sugar-Fungus.” Unappealing name? Absolutely.

Accurate? Surprisingly so!

You see, at the most basic level, yeast metabolizes sugar (glucose, maltose, or trehalose) and converts it to alcohol and carbon dioxide. It is a living organism – we sometimes refer to S. cerevisiae as being a “top-fermenting yeast” because its surface is hydrophobic: it avoids liquids if possible. Thus, the yeast organism clings to the carbon dioxide bubbles it produces and floats to the top of the cask.

S. cerevisiae likes dark fruits very much. In fact, it’s part of that white, dusty film you see on plums and grapes! This becomes particularly interesting when we consider very, very early beers: qi from the Yellow River Valley was a mixture of honey, barley, rice, and grapes, while beers from Egypt and Mesopotamia often contained dates, figs, grapes, or plums. The yeast clinging to these fruits’ skins was most likely instrumental in fermenting the beers!

In the 1600s, a Dutch tradesman and lens-crafter named Anton von Leeuwenhoek (LAY-when-hook) observed yeast for the first time, as globules floating in liquid. He didn’t realize that the yeast was alive, though: he thought the globules were grain particles floating in the wort. Through the 1600 and 1700s, then, people were well aware of yeast’s existence and role in fermentation; they just thought that it was a chemical agent, rather than a biological one.

Louis Pasteur (WikiMedia Commons)
Louis Pasteur (WikiMedia Commons)

However, a major paradigm shift occurred in the 1835, when French inventor Charles Cagniard de la Tour observed yeast budding and multiplying during fermentation. The yeast was a living microorganism! Twenty years later, chemist Louis Pasteur demonstrated that fermentation and yeast multiplication occur hand-in-hand. Moreover, he demonstrated that certain microorganisms, yeast among them, are capable of living without oxygen, and that only certain microorganisms can convert sugars into alcohol – fermentation is a biological process, not a chemical one.

By our time period here at Black Creek, Pasteur was deep into his publications on fermentation, beginning with  “Mémoire sur la fermentation alcoolique” in 1857.

Interestingly, the other strain of yeast commonly used in brewing – bottom-fermenting or lager yeast – is named after Pasteur. Saccharomyces pastorianus received its name in 1870. This yeast is commonly called Saccharomyces carlsbergensis (yes, as in that Carlsberg), but this is technically invalid as S. pastorianus was first.

For a tiny microorganism, yeast packs a powerful punch! Between the brewery and the kitchen, it is the most important microbe in Half Way House. 🙂

-Katie

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