I thought the ideal way to start a blog about yeast, fermentation, cocktails, and fermentation products would be to first pay homage to the cells that make our delicious beverages. I recently got back from a distillery conference in Oregon as well as tasting wine throughout Oregon. I also spent a fair bit of time talking with various yeast producers, especially my own yeast company, Lallemand, about fermentation; specifically talking about ways to optimize fermentation. In this first post let’s explore what yeast are, what fermentation is, and some basics of fermentation.
At its most basic point, yeast are single celled eukaryotic organisms that are ubiquitous in nature. The principal difference between prokaryotic and eukaryotic cells are that eukaryotic cells have the full complement of intracellular organelles while prokaryotic cells are much simpler and don't have organelles such as nuclei. In other words yeast are more complex organisms than bacteria. Yeast are in the Kingdom fungi and there are more than 1000 species. The most important yeast for alcoholic fermentation is a yeast called Saccharomyces cerevisiae, though there are other yeast, and indeed bacteria, that participate in alcoholic fermentation. Yeast are able to undergo aerobic or anaerobic metabolism so they were able to grow in the absence or the presence of oxygen.
Fermentation is extremely interesting. If you look in history, many cultures have fermented food types. Everything from kefir to yogurt to kimchi to sauerkraut are produced through fermentation. Of course, our favorite fermentation by products are the vast array of alcoholic beverages. Each of these uses a different consortium of prokaryotic or eukaryotic flora to make the unique flavors found in each of the substances. This blog will be focusing primarily on alcoholic fermentation, but who knows, there probably will be some intermittent digressions into the other fermentation products as we go along.
One of the other aims of this blog is to share with individuals, in an easy-to-understand way, the amazing aspects of Biochemistry, organic chemistry, and microbiology. Biochemistry and organic chemistry were some of my favorite classes in college and medical school as it helped to explain the underpinnings of so many aspects of the world around us. So, what is fermentation? Fermentation is what happens when organisms breakdown sugar in the absence of oxygen. Let's take a quick look into what's happening on a basic biochemical level. When yeast are presented with sugar, they quickly digest that sugar in a process called glycolysis. Glycolysis is the process that all organisms, with a few exceptions, use to breakdown sugar. At the end of glycolysis you're left with pyruvate. What happens next depends on a bunch of variables including the absence or presence of oxygen and what intracellular enzymes the organism has available in its repertoire. The most efficient pathway that produces the most energy is to take the pyruvic acid into the citric acid cycle. However, this pathway requires intricate intracellular enzymatic activity as well as mitochondria to produce this energy. It also requires oxygen.
In the absence of oxygen organisms still must metabolize the pyruvate. In humans, in the absence of oxygen that pyruvate becomes lactic acid. The buildup of lactic acid in your muscle cells is one of the things that makes your muscles hurt after you've exercised very hard. Lactobacillus, or yogurt bacteria, use the same enzymatic pathway to produce lactic acid which gives yogurt its tart flavor. Yeast, if they have oxygen, can also go through the citric acid pathway but in the absence of oxygen yeast predominantly metabolize pyruvate into ethanol.
These pathways are relatively simple but each step in the pathway is a potential stumbling block. We will be exploring some of these stumbling blocks in upcoming blog posts. I thought happy yeast was a good title for these thoughts because that’s ultimately the aim of everything we do as beer makers, wine makers, distillers, or other purveyors of fermented food types. Happy yeast makes happy flavors. Yeast that are not having their nutritional or environmental needs met during fermentation become unhappy and make unhappy flavors. So when you are drinking a beverage that you don’t like, rather than just saying you don’t like it, explore it a little bit. Does it have a subtle taste like a bandaid or a rotten egg? Those are commonly problems with fermentation and unhappy yeast. But, the next time you are enjoying an alcoholic beverage, think about the yeast and how happy the makers were making them!