Best Conditions for Yeast Fermentation

While we talk a lot about the wonders of yeast, many people still understand very little about it. It is a living organism that has thrived in the wild on its own with no interference from humans for millions of years. Maybe even billions. It will ferment our foods and beverages without any help from us. So, what are the best conditions for yeast fermentation, aside from simply leaving it alone? We’ve got a few tips.

How Yeast Grows in the Wild

First, recognize that yeast is a wild organism. It was not created by humans nor is it easy to manipulate by humans. Yeast was here on earth long before humans, or even our apelike ancestors, were even a blip on the biological radar.

It is a cousin to fungi, which are the oldest life forms on earth.

And it is thought to have evolved from bacteria, which does not have its own contained nucleus. Yeast evolved to have its own enclosed nucleus, making it a eukaryotic cell, which feeds in competition with bacteria on sugars.

Thus, for millions of years, yeast has thrived, hovering, ever present, in the atmosphere, in virtually every environment, in search of its only energy source — sugar.

Yeast gets the sugar it needs from plant life, of which there is plenty.

For this reason, you can go outside with a jar of water and a few dried fruits, leave that jar, with the lid on, under a tree, and in a couple of days, you will have bubbling, fizzing yeast fermenting that dried fruit and making you a nice concoction of an alcoholic beverage.

It’s really that easy.

Today, many brewers and winemakers, as well as those who make kombucha and even ethanol, wander out into the wild, collect plants, and cultivate the yeast they find on those plants in their warehouses.

It is safe to say then that yeast can thrive in any environment that is relatively warm, as in not freezing and not burning, moist, and rich with sugar.

What Is Yeast Fermentation?

Before we move on, let’s address the issue of fermentation.

Fermentation is defined as a sort of alchemical change. When one organism converts one ingredient into another ingredient, fermentation takes place.

Our cells undergo anaerobic fermentation when we do strenuous exercise.

We run out of breath, our cells lack oxygen, and the stress forces our cells to convert to ATP, which is the energy we need. That’s fermentation. When those cells get too stressed and we continue to not provide our cells with oxygen, we pass out.

With yeast, the living cells consume sugar and then produce water, alcohol, and carbon dioxide as waste products. In the presence of oxygen, yeast produces water. In the absence of oxygen, yeast produces alcohol.

Here’s the trick though: when yeast consumes sugar there will almost certainly be an absence of oxygen as the yeast creates a sort of bubble around the feeding frenzy. This bubble locks oxygen out, which forces them to produce alcohol.

How Yeast Grows in Captivity

Now, the trouble begins when we try to contain the yeast cells.

We humans are not great at mimicking, or controlling, nature, which results in a loss of viability, vitality, and in a lot of dead yeast cells.

Fortunately, the earth has an abundance of yeast cells, so we can continue to experiment to get it right.

Ask anyone who has ever tried to grow their own sourdough starter and they will tell you “Don’t forget to feed it!”

Truly, as long as you keep your yeast fed, you should have no trouble keeping it alive in captivity.

For sourdough starters, you can continue to feed it flour as it grows, and be sure to bake with it regularly, or you’ll end up with a giant blob of growing yeast!

In breweries and wineries, most will keep the yeast as a slurry, or a combination of sugars and grains to feed the yeast, in a collection vessel. You can also store it under a layer of beer or pressed into a yeast cake, kind of like that sourdough starter.

The key is to ensure it has access to a vent so the carbon dioxide it produces does not cause whatever container it is in to explode.

The only thing you really have to do?

Feed it!

Make sure your yeast always has access to sugar.

Best Conditions for Yeast Fermentation

Now, once you start fermenting your yeast, you want to be mindful of a few things when pitching:

Temperature

Remember that we have two basic kinds of yeast when fermenting – Saccharomyces cerevisiae and Saccharomyces pastorianus.

S. cerevisiae calls for warmer fermentation temperatures, between 68- and 72-degrees Fahrenheit, and S. pastorianus ferments at the cooler ranges between 45 and 55 degrees.

This range means that if you go higher or lower than your yeast calls for, the yeast may either lie dormant or die off. Pay close attention to which strain you have and follow the temperature requirements closely.

Sugar

You need sugar!

While yeast will accept a range of temperatures, they cannot work without sugar. You must provide enough fermentable sugar to feed the yeast but not so much that it gets overwhelmed and stressed. Not enough sugar will put your yeast to sleep. You can always go a little high, but too low can result in off-flavors and stagnant fermentation.

In general, you want to provide .2 grams of sugar for every gram of yeast at a minimum.

Nutrients

While most yeast cells get plenty of nutrients from the fruit or grain they are feeding on, if you are working with pure ethanol, or a fruit or grain depleted of nutrients, or a yeast that has been mass produced, you may want to provide yeast nutrients. These will help build up your yeast and keep them fermenting.

Air Lock

Finally, if you are not fermenting in an open-air vessel, be sure to provide an air lock. You want both the absence of oxygen and the release of carbon dioxide. Otherwise, your vessel may explode.

In the end, yeast fermentation is a simple process that requires little intervention from humans, but as we hope to master our craft, we can learn to work with yeast as it does its fermentation work for us, and we can provide the best conditions possible.

Cheers!

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