What Inhibits Yeast Fermentation?

It’s not uncommon to ask, “what inhibits yeast fermentation?” If you’re in any area of the fermentation industry, you might be seeking to inhibit fermentation for a number of reasons, or you might be trying to avoid this inhibition and keep your fermentation flowing. In any event, it helps to understand the living organism you’re working with.


Yeast is a single celled life form that has been on the planet since almost the dawn of time, certainly since earliest signs of life.

Since those days, billions of years ago, yeast has existed to perform one basic function — find sugar. Like most living being on this planet, the energy source of yeast is sugar, and it doesn’t need micronutrients like humans and animals to live a long, healthy life. It simply needs enough energy to keep looking for sugar, consume it, and expel the waste products.

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Lucky for humans, those waste products are alcohol, carbon dioxide, and hundreds of other secondary metabolites — many of them beneficial to humans who do need micronutrients.

Yeast Fermentation

This finding of sugar, consuming it, and excreting alcohol and CO2 has come to be known as fermentation, or alcoholic fermentation, and yeast is the only creature on earth that can do it.

In ancient times, humans likely encountered fermentation accidentally. A woman out picking grapes could have stored them for later and found the fermented juices at the bottom of a barrel a week later. Of course, she would not have wasted those juices; she would have drunk them, only to find a delightfully euphoric effect was the result.

A man boiling grain for a nutritious oatmeal or barleymeal may have left his batch out for too long, only to return and find a fizzy, foamy beer-like meal to enjoy.

Tea has been fermented in China for two thousand years.

Fruit punch has also been fermented in Latin America for likely thousands of years.

And of course, honey mead has been fermented likely since humans first discovered fermenting.

The bottom line is that yeast fermentation is about as natural a process as you can find in the history of food and beverages, and it was likely occurring long before humans ever came along. After all, yeast ferments fruits and vegetables in nature in gardens and on jungle floors the world over.

This point is an important one to understand because often the thing that gets in the way of fermentation isn’t nature but humans.

Thing about it — for millennia, people have been crushing grapes and leaving the juice to sit out in an open air vessel. Within a week, they have wine. Within another few weeks, they have really good wine!

The same goes for beer. Boil some grain, add some hops, and allow the wort to sit out in a giant barrel. After about five days, you’ve got beer!

Sure, you can take in interest in various soils, strains of grapes, mix grains, introduce various substrains of yeast, and more to mix things up and get different flavors and aromas, but in the end, fermentation is a straightforward process.

Yeast gets into the food or beverage, consumes the sugars, excretes alcohol and CO2 as waste products, and you have beer, wine, cider, bread, and other fermented foods and beverages to enjoy.

So what gets in the way of that process?

Fermentation Inhibitors

Well, one of the foods included above is a perfect indicator of what inhibits fermentation — bread.

After all, bread does not have alcohol in it, which is strange if you think about it. The same ingredients lie in bread that exist in beer — grains.

And yeast does indeed ferment inside of bread dough, consuming all the germinated grain sugars and converting them to alcohol and carbon dioxide; that is where we get the light, fluffy texture of leavened bread. The CO2 pushes outward against the dough, but with no escape, it simple causes the dough to expand and “rise.”

It’s the Heat

So, why don’t we get drunk when we eat bread? The heat. Heat inhibits the fermentation process and everything involved therein. It kills yeast and alcohol alike, leaving behind only the light, fluffy results of the fermentation.

Thus, if you’re brewing beer or making wine and you raise the temperature of your beverage to above 140, you will kill off the yeast and halt fermentation. Of course, you will also likely lose a lot of alcohol as well.


Alcohol is another way to inhibit fermentation. All yeast cells have a particular alcohol tolerance, some higher than others. But at some point, the alcohol in the beverage will stop the yeast fermenting either because the sugars are all gone or because the alcohol is killing the yeast cells off.

Now, typically, alcohol produced by yeast won’t kill off that yeast. Instead, the yeast will simply lie dormant, awaiting collection and another batch of yeast.

But, if you add alcohol to a fermenting beverage, a strategy called “fortification,” you will likely kill off any remaining yeast and instantly halt fermentation.


Temperatures that drop too low can also halt fermentation. Of course, Saccharomyces pastorianus, or lager yeast, can ferment at rather low temperatures, but even this cold lover will slow down and lie dormant if the temps drop too low. So, if your wort or must is stagnating, make sure your room and your vessel are warm enough to keep your yeast active.

In much less frequent cases, you might find yeast refusing to ferment for lack of nutrients or because they are simply overwhelmed by the sugars and alcohol in your beverage. This case is relatively rare however because vital, viable, active yeast in a batch of healthy grain or fruit liquid, rich in sugar are highly unlikely to resist the pull of the sugar.

If you do find this happening in your batches, be sure to check your yeast manufacturer, and, of course, you can always consider using wild, local yeast, which are often happy to ferment under most conditions.


Are you still pitching fresh yeast every time? By reusing your yeast, you can save up to hundreds of thousands of dollars per year on just yeast alone!

Join the hundreds of brewers and vintners from all around the world using the Smartest Automated Yeast Cell Counter! Request a Free Demo Account today and experience firsthand how Oculyze can take your brewery or winery to the next level! 

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