YEAST IS A JERK: A BRIEF DESCRIPTION OF FERMENTATION
Fermentation: the act of living. Fermentation is a bond we share with the tiniest of creatures. It has kept our food safe for millennia, it has created distinct, cultural specific dishes in the process. Fermentation is wildly complex, yet relies on very simple principles. Millions of different organisms can work together to produce thousands of different fermentation by-products and like snowflakes, no two ferments are the same. The beauty of fermentation is that virtually anything that is slightly sweet and mildly damp will undergo an artistic and collaborative transformation. And like art, not every project is universally appreciated (I'm looking at you, Kimchi!). With the sheer amount of coordination carried out by groups of microorganisms, one would think each organism works as a team to accomplish this massive feat. This is unfortunately not true. Yeast, which is responsible for bread, beer, mead, wine, kombucha and much more, is a selfish jerk, and I'll tell you why.
Before I discuss how yeast doesn’t play nice, I wanted to briefly describe fermentation. Fermentation at it’s most basic is the transformation of one chemical to another in the absence of oxygen in order to provide energy. The fuel for this reaction is usually a simple sugar (sucrose, dextrose, maltose, glucose, etc) and the product ranges from alcohol to organic acids. To get fermentation started, organisms also need water to move around in and nutrients to form enzymes (just like us). Lastly, some organisms will burst when in the presence of oxygen and others don’t need it and don’t mind it being around, so fermentation yields very different results in the presence and absence of oxygen. So basically, if you leave something out that is sweet and moist, it will remind you in a few days, and it won’t be pleasant.
Home-Brew Tip: If you experience a stuck fermentation (when there is no visible sign that fermentation is occurring) there are 4 common causes:
- There are not enough microorganisms to produce visible signs of fermentation. To fix this, add more starter or gently stir periodically if it is a wild ferment.
- The organisms do not have sufficient nutrients to continue fermentation. Adding a nutrient blend like fermaid K will quickly fix this problem.
- The simple sugars have been depleted or there are not enough to sustain fermentation. This problem can be alleviated by adding an enzyme to break starch into sugar or simply adding more sugar.
- The environment is inhospitable and no longer supports fermentation. This is a much less common problem that is much harder to solve, but may be caused by an excessively low or high pH or the presence of preservatives.
The 3 Reasons Yeast is a Jerk:
1. Yeast has masochistic behavior. There are instances where yeast sacrifices a healthy, productive lifestyle to screw over its competition. Let me explain. While most single celled organisms can only undergo fermentation, yeast, like us, can take part in respiration when oxygen is around. Respiration digests the sugar fully into harmless gas and yields significantly more energy than fermentation. Why yeast is such a jerk stems from the fact that even in the presence of oxygen, some sugars cause yeast to conduct fermentation (Crabtree Effect), which produces much less energy. On top of that, yeast fermentation produces alcohol, which is not great for yeast but very toxic to most other microorganisms. Some scientist believe the crabtree effect occurs when yeast finds itself in a nutrient rich area such as the skin of a grape, where bountiful presence of sugar initiates the release of alcohol as a way to reduce competition. In this case, yeast is a jerk because instead of using oxygen to generate a ton of energy for itself, it switches to fermentation just to screw over its neighbors by producing toxins. Imagine if you and your twin brother were given a single Swagway to share for your birthday and he peed all over it. He might not enjoy it as much as he could have, but he is still enjoying it more than you. Jerk!
Home-Brew Tip: Aeration as opposed to fermentation produces many more cells during propagation, the process of growing a yeast colony before pitching into a fermentation vessel. It is not uncommon for professional breweries to add air once an hour for 5 minutes to their propagation tank. While 5 minutes an hour would definitely kill a small starter, an initial short burst of oxygen or replacing the air-lock with a sponge will do wonders for cell growth.
2. While on the subject of the anti-microbial properties of alcohol, the next selfish aspect of yeast is a bit more dastardly. Yeast is grossly outperformed by bacteria when it comes to reproduction. In fact, in the time it takes yeast to double it’s population, bacteria has already doubled several times. In order to level the playing field, yeast has become very good at surviving high levels of alcohol. Some strains (ninja yeast) can live in up to 30% alcohol by volume. When yeast finds itself outnumbered, instead of competing in the numbers game, it gradually toxifies its environment until it is the last man standing and beyond. This would be like competing in a cake eating competition in a closed room and resorting to particularly foul flatulence instead of cake eating prowess to clear the room and slowly enjoy your delicious bounty in peace. This is definitely something a jerk would do, a very gross jerk.
3. Yeast is an elitist. Sure, yeast may produce a biofilm called a pellicle or SCOBY on top of a fermenting batch of Kombucha to help his friends access oxygen without being exposed to its harmful effects. It may even seem like a pretty gregarious species when you see the long chains of buddies hanging out together. But upon further inspection, yeasts biases become apparent. Most cultured yeasts rarely take part in sexual reproduction. Instead, yeast makes identical copies of itself. I can’t think of a better example of an organism with a superiority complex than yeast, who is so self-absorbed, it prefers itself over everyone it meets nearly every time . Come on Yeast, test the waters, you might meet someone you like, jerk…
This wraps up the first section of fermentation. In future blogs I will discuss specific microbes and how they contribute to the making of delicious food. If you feel that I have besmirched the name of the noble yeast and would like me to apologize for my blasphemous ways, please comment below.
2. White, Chris and Zainasheff, Jamil. (2010) Yeast: The Practical Guide to Beer Fermentation. Brewers Publishing.
3. Kunze, Wolfgang. (2014) Technology: Brewing and Malting. VLB Berlin.