When it comes to brewing, the question comes up often. How does a yeast cell multiply in a brewery, fermentation or no fermentation? After all, if you don’t fully understand yeast cells, their life cycle, and their reproduction process, you might think that fermentation would kill them off. Nothing could be further from the truth. So, what does happen?
What Is a Yeast Cell?
Let’s start with the basics. It is hard to understand the behavior of an organism we don’t fully grasp at its core.
Yeast is one of the oldest forms of life on earth. A type of fungi, which is indeed the oldest living organism on the planet, scientists now believe that, far from being the opposite of bacteria, yeast likely evolved from bacteria.
So, yes, bacteria came first.
Bacteria are single celled, prokaryotic life forms. This means they have no enclosed nucleus.
Many of those early bacteria cells lived in water, as most of the earth’s surface is water, and most of life originated there.
Those early bacteria, as such, got most of their food from tiny microbes on the surface of the water that got their food from the sun. Think of the way plankton converts the sun’s rays to energy.
Well, in those early days, it is thought that, in order to make finding food easier, some of the bacteria evolved into a single celled eukaryotic life form.
Eukaryotic cells have an enclosed nucleus, which gives them a competitive edge over prokaryotic cells. They are also able to grow in size as a result.
For this reason, while there are fewer yeast cells on earth than there are bacteria cells, yeast takes up more space than bacteria because yeast cells are bigger.
Yeast cells occupy pretty much any space that is warm and moist with plenty of sugar.
So, most spaces on earth. Even in excessively cold environments, they will simply lie dormant and await warmer temperatures and a food source. The same goes with an absence of food. They will not starve to death. They will simply lie dormant. The only thing that will kill yeast is extreme heat – like a volcano, or excessive amounts of alcohol.
It’s tricky, right, because yeast is the only living organism that can make alcohol. The product of its own creation can be the product of its destruction.
In the end, yeast cells spend their existence in pursuit of food, its energy source, which is sugar. It can consume sugar from fruits, vegetables, grains, starches, and other plants. As long as the plant has some form of fermentable sugar, yeast cells can consume it for energy.
As a waste product, yeast cells will expel water, alcohol, and carbon dioxide.
As long as yeast has an ample supply of its energy source, it will reproduce. Which brings us to our next question.
How Does Yeast Multiply?
When the food source of yeast is plentiful, yeast cells will produce a daughter cell from their own body. The daughter cell will remain attached to the mother cell until the daughter cell reaches 50% volume of the mother cell. At that point, it will detach and begin to seek its own food source and begin to reproduce asexually as well.
Yeast cells can reproduce, or “bud” up to 80 times in their lifetime, and each cell lives about a week. They will bud about once every 90 minutes as long as they remain alive.
How Does a Yeast Cell Multiply in a Brewery?
Thus, the answer to the question, “how does a yeast cell multiply in a brewery?” is a simple one. As long as it is being fed a steady diet of sugar, it will continue to bud until it dies. Those daughter cells will do the same, and so on and so on.
While many people think that fermentation kills yeast cells, it actually does the opposite. It provides fertile ground for yeast cells to continue to multiply. The dead yeast cells you find in your brew after fermentation have simply lived their full lifespan.
In most cases, the alcohol a yeast cell produces will not kill it. The yeast cells have a tolerance for the alcohol they are able to produce.
When alcohol kills yeast, it is typically when brewers add alcohol to beer to “fortify” it.
In the end, yeast cells multiply, or reproduce, any time they have an energy source – sugar. So, if you want to keep your yeast cells happy, just keep them well fed. Many brewers indeed have learned to cultivate their own yeast supply, ready to be pitched into the next waiting brew, by simply keeping the yeast warm, moist, and fed. It is a simple process that dates back millennia. Ask any domestic housewife or house husband who has a sourdough starter sitting on the kitchen counter. As long as there is food, yeast will reproduce.
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