While we finally know that yeast is involved in the fermentation process, many misunderstandings and confusions still abound around yeast, how it works, and where we use it. For example, the role oxygen plays in yeast – does yeast need oxygen or not? There is still much to learn about yeast for the average person, and it is a fascinating topic to explore.
Yeast is arguably one of the oldest forms of life on the planet. After all, yeast is a fungi, and fungi are believed to be the very first life forms on Earth.
Yeast versus Bacteria
Yeast is a single celled organism that is eukaryotic. This reality means that the yeast cells are enclosed within a distinct nucleus, making yeast quite different from bacteria, which is prokaryotic. While bacteria are more widespread than yeast because they grow much more rapidly, yeast are larger than bacteria.
The two are often confused because they serve the same purpose in some ways.
Yeast and bacteria can both function within the fermentation process, but bacteria cannot create alcohol alone.
Yeast, Bacteria, and Alcohol
Yeast serves one primary function as it thrives and reproduces on Earth: it converts carbohydrates to alcohol and carbon dioxide.
Fermentation in yeast can occur without… a food source (?)
In beer, grain is malted and cracked then boiled and steeped. Once the liquid (wort) cools, yeast is added.
Yeast gets right to work consuming all of the starches in the liquid and converting them to alcohol and carbon dioxide, along with hundreds of other micronutrients.
In wine, grapes are crushed and boiled and steeped, then left to cool. Once that liquid (must) is cooled, yeast is added. The yeast performs the same function here as it does in wine, converting the sugars in the grapes to alcohol and carbon dioxide.
Kombucha, Sauerkraut, Yogurt, and other Fermented Foods
The same process applies to other fermented foods. The food is prepared in a way so that the starches are most readily available for the yeast, the yeast is added, and then it gets to fermenting.
In the case of bread, yeast is added and the alcohol and carbon dioxide created are what make the bread rise. During the baking process, almost all of the alcohol is evaporated out by the heat.
When it comes to all of these foods and beverages, bacteria can play an additional role. Lactobacillus is the most common bacteria added to these foods, and it is what contributes the good bacteria we need for healthy guts.
A healthy gut manages all aspects of human health, from inflammation to moods. Thus, there is a big misconception around both yeast and bacteria. Both can be either good for you or bad for you, depending on the strain.
Fermentation in yeast can occur without… oxygen (?)
In most cases, yeast does need oxygen to do its work. When we brew beer, make wine, or prepare bread, we leave the tanks or bread bowls available to oxygen so that yeast can ferment.
Yeast needs energy, and the energy it needs access to is trapped inside of the carbohydrates.
Here’s how it works:
When we think of energy, we think of carbohydrates, and that is accurate, to a point. All stored energy is indeed stored inside of carbohydrates, be it in our food or in our bodies.
When we need to access that energy for whatever purpose, typing this article, reading this article, running a marathon, getting out of bed, converting sugar to alcohol, we need to break that energy out of the carbohydrates because carbs don’t provide that resource.
So, when an organism demands energy, it draws on oxygen to convert the carbohydrate to another form of energy called ATP, or adenosine triphosphate. ATP carries energy to where we need it, in our muscles, or in our wine, beer, or bread.
Thus, when yeast is fermenting, it is demanding the carbs in the food provide energy for that fermentation process. Oxygen steps in and converts the carbs to ATP, which then allows the yeast to complete its own conversion process.
This is called aerobic respiration.
Now, yeast, just like humans or any other living organism, can actually ferment without oxygen for a short time.
This is called anaerobic respiration and it can happen in the absence of oxygen.
Here’s how that works:
The human body is out exercising, running for miles. You breathe short and fast, not supplying your body with enough oxygen to convert your carbs to ATP fast enough to meet your energy needs. The process then takes place anaerobically, which is actually called fermentation in human biology.
You can only do this anaerobic fermentation for so long before your stores are depleted and you need more oxygen to continue on.
Yeast operates in the same way. For a certain period of time, it can actually ferment without oxygen. But eventually, in the absence of oxygen, it will grow too stressed and either stagnate or die off. It will eventually require oxygen to keep fermenting.
Pretty cool, right?
Different Strains of Yeast
Another thing to remember when it comes to yeast is that there are so many different strains and all behave in different ways, some small and some big. Some serve humanity, and some harm us.
In most cases, you can use brewer’s yeast in bread and baker’s yeast in beer, interchanging them, because they both ferment. But you will get different processes as well as flavors and aromas.
It is worth experimenting with various strains of yeast, as well as bacteria, to see what different results you get, and along the way, you can examine what happens with and without oxygen during the fermentation process.
Maybe you can even head out for a run and let your own body undergo some fermentation!
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