What is Brewers Yeast and How Does it Ferment?

Facts About Brewers Yeast

Yeast is an important part of the beer brewing process. Without yeast, there would be no fermentation. When the yeast is “pitched”, or added to the cooled wort, fermentation begins.

The brewers yeast eats the glucose in the wort and converts it into ethyl alcohol and also a gas called carbon dioxide.

This process with supply both the alcohol content and also carbonation to the beer, but remember that conditions have to be just right for this process to occur.

As a side effect, yeast also performs other function. It contributes a great deal to the flavor of beer, and also adds to the aroma. When people speak of a fruity flavor they detect in beers, this is most likely coming from the type of yeast strain you use.

The supplier who put together your ingredient kit will have taken the guesswork out of the equation for you by choosing the best yeast for your beer.

Using brewing yeast for fermentation can be accomplished in many ways, and this is a subject that causes much debate among homemade beer makers.

If you’re making your beer from a kit, most likely the recommended method will be to sprinkle the yeast on top of the cooled wort.

While this works perfectly fine, some brewers will argue that they get better results if they rehydrate their yeast before pitching. Rehydrating involves mixing the yeast with water to make a slurry, and then adding this mixture to your wort and stirring it in.

Beer yeasts really likes a warm environment, typically around 90 degrees Fahrenheit, but if conditions become too warm, over 100 degrees, yeast cells will quickly die off.

We would never, however, ferment our beer at 90 degrees. Every type of beer has an optimum fermentation temperature that we need to pay strict attention to.

Isn’t science wonderful, especially when it comes to making homemade beer?!


Different Yeasts For Different Beers

For making beer at home, there are generally two types of yeast we take into consideration.

And don’t worry about where to buy brewing yeast. If you don’t have a supply house near where you live, you can always rely on the Internet.

Take a look at the sections below to find out all about the yeast you’ll be using for home brewing.

• Top Fermenting Yeast – This type of yeast prefers warmer temperatures – in the range of 65-75 degrees as a rough guide. They are commonly referred to as ale yeasts.

They generally produce a foamy, very thick head when they fermenting, and that’s how they probably got their name “top-fermenting”. Most home brewers refer to these types of yeasts as ale yeasts, although they are also used when making stouts, porters, and wheat beers.

• Bottom-Fermenting Yeast – These types of yeasts are called Lager yeasts. Lagers tend to be brewed under cooler conditions that ales.

Lager yeast will still continue to ferment in temperatures down to as low as 45 degrees Fahrenheit even though they do so slowly, whereas ale yeast would cease to ferment.

The reason they’re called bottom-fermenting yeasts is that at certain temperatures the yeast will actually settle to the bottom to finish their fermentation process.

The flavors contained in lager beers are largely due to the temperature they’re fermented at, as well as the strain of yeast used for fermentation. By the way, lagering is just a term used for cold storage.

One thing worth mentioning briefly is spontaneous fermentation.

This type of fermentation can happen automatically, because wild yeast is everywhere in our environment, even in the air we breathe.

Some people still do brew beers by relying solely on spontaneous fermentation, but generally speaking, we home brewers like to be more in charge of our beer, and inoculating beer with a certain type of home brew yeast lets us be more in control of the fermentation process.


Temperature For Fermentation

Thermometer For Beer Brewing

So I mentioned temperature briefly above, but we should discuss it more because it’s so important to the fermentation process.

The reason you’ll need to monitor the temperature is to give your beer the best chance at a good fermentation.

Let’s say you’re making an ale – we know from the discussion above that these beers like to ferment around 68-72 degrees Fahrenheit.

If the temperature in the environment where you’re brewing you beer falls below the acceptable range for top fermenting yeast, the fermentation could slow down considerably or even stop altogether.

Restarting a stuck fermentation is not an easy task; it can be done but you’re better off not going there.

If the temperature rises too much during fermentation, yeast reproduction will become extremely vigorous.

While this might not seem like a bad thing, yeast that’s been exposed to high temperatures can sometimes impart off flavors to your home brew.

Besides that, if the environment becomes too warm the yeast will die off and fermentation will cease.

The fermentation itself will also produce heat, and keep in mind that that the liquid inside the fermentation vessel could be up to as much as 8 degrees warmer than the air surrounding it.

Sometimes it’s necessary to cool your fermentation to keep it under control.

Remember not to place your fermenter where the sun can heat it. This type of temperature fluctuation can lead to disaster.

While all this may seem complicated, rest assured that we all felt the same way when first beginning our beer brewing journey.

Soon all these terms will become second nature to you, and you’ll be discussing yeast strains and fermentation temperatures with other homemade beer makers before you know it!

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