Intricacies of Yeast #1 - Introduction
This is the first article in a series called “Intricacies of Yeast”. Click here to view the rest of the series.
Yeast is a single cell organism that is responsible for converting sugar to alcohol and carbon dioxide. In short, it provides the chemical reaction that allows wort (”unfermented beer”) to become beer. Without yeast, we would have a flat sticky mess that no one would want to drink much less create themselves. Since yeast is so central to the brewing process, quite literally, it’s worth learning about the chemical reactions that occur when you pitch the yeast into a fresh batch of wort.
What is Yeast?
According to the Wikipedia entry, yeast is a growth form of eukaryotic microorganisms. At this page we also learn that yeast are single cell organisms that reproduce asexually through a method referred to as budding. Since I am not a chemist and this is not a biology blog I am not going to go into details about what budding or asexual reproduction is - mainly because my high school education is not giving me a real clear understanding of these topics. Wikipedia also has this little nugget of information:
Yeast is the microorganism that is responsible for fermentation in beer. Yeast metabolizes the sugars extracted from grains, which produces alcohol and carbon dioxide, and thereby turns wort into beer. In addition to fermenting the beer, yeast influences the character and flavour. The dominant types of yeast used to make beer are ale yeast (Saccharomyces cerevisiae) and lager yeast (Saccharomyces uvarum); their use distinguishes ale and lager. Brettanomyces ferments lambics, and Torulaspora delbrueckii ferments Bavarian weissbier. Before the role of yeast in fermentation was understood, fermentation involved wild or airborne yeasts. A few styles such as lambics rely on this method today, but most modern fermentation adds pure yeast cultures directly to wort.
What is important to note however is that the species of yeast that we are most concerned with is Saccharomyces cerevisiae for ale brewing and Saccharomyces uvarum for lager brewing. Given that the majority of home brewers brew ales and not lagers the rest of this article is going to be primarily concerned with ale yeast or S. cerevisiae. Doing a bit more reading at Wikipedia yields this interesting bit of trivia:
“Saccharomyces” derives from Greek, and means “sugar mold”. “Cerevisiae” comes from Latin, and means “of beer”. Other names for the organism are: Brewer’s Yeast, Ale yeast, Top-fermenting yeast, Baker’s yeast or budding yeast.
So this tells me that brewing yeast (as I shall refer to it throughout this text) is really a mold that eats the sugar in beer.
History of Yeast
There are many varied accounts on when exactly yeast was discovered and used in the brewing process. Of course, yeast was used in the process since the Sumerians first made beer almost 15,000 years ago but knowledge and controlled use of brewing yeast came much later. In fact, the Reinheitsgebot (some sort of beer brewing code) does not mention yeast as an allowed ingredient in the beer brewing process.
So if we, as a race, did not know about yeast until sometime around 1800 then how could we have brewed beer? Most of the brewing that was done before Louis Pasteur’s discovery of yeast’s effects during fermentation relied on wild yeast which found the way into the wort by floating on the airwaves. To me, that sounds very unpredictable and unreliable but in fact a popular style of beer relies on this method: Lambic beer.
Fast forward to the modern day. Today we have available to us over a hundred carefully cultivated strains of S. cerevisiae. Each strain has a different effect on the finished product and it’s taste, aroma and appearance. Knowing the differences between each of these strains is the mark of a dedicated brewer - someone who is serious about understanding all the intricacies of their craft.
Differences Between Brewer’s Yeast and Bread Yeast
As you read this article, you may notice that the same species of yeast is used both in brewing and baking. The next logical question that comes to mind is why use yeast that you buy for $6.50 a pack if you can get the same species for $.97 for three packs.
However, know that bread yeast or baker’s yeast is specifically designed to make dough rise. To use this kind of yeast for making beer would be the same as using a screwdriver to pound a nail. It may work, but it certainly isn’t the best way to accomplish the desired end result.
Also, with liquid brewing yeast you will find a much wider selection of yeasts. Later in this series I will show you how to harvest, store and re-use yeast so if the price is a concern don’t let it worry you. With good technique you can re-use one strain of yeast for up to seven generations. If yeast viability were not a concern you could get over 5,000 uses out of one $6.50 strain of yeast (for the financially inclined that is a total savings of over $32,500). However I will cover this in more detail later on in this series.
Leave a Reply