The effect of fermentation temperature on beer

How Does Air Temperature Affect Fermentation?

Air Temperature does not have a direct impact on wort temperature for fermentation. Still, it has an indirect relationship through convective heat exchange by acting as a heat sink or source.

In terms of the actual effect, yeast is very sensitive to temperature. In the simplest of terms:

• To Hot, they get overworked and possibly die.

• Too Cold, they become lazy and lethargic.

• At Just Right, they work efficiently to turn sugar into alcohol, aka beer.

For a homebrewer who brews in an environment with air temperature swings, it can be devastating for fermentation.

A closed vessel with temperature control is advised in places with unstable air temperatures. Or perhaps a cellar would work since these places usually maintain a constant temperature. And if you can afford it, a fully air-conditioned room with mechanical ventilation would be sweet.

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How Does Cold Weather Affect Fermentation?

Cold Weather tends to slow down any process, be it fermentation or human motivation. This is why Lagers were developed to address brewing downtime in winter. If you did not already know, lager yeasts evolved in colder climates.

In terms of actual effect, yeast in fermentation stick together and get out of suspension. How this happens exactly is not fully understood, and is a matter of scholarly pursuit. This phenomenon reduces yeast contact with sugars, which slows down the conversion process. Of course, the yeast strain plays a vital role in this situation, therefore, the actual temperature that fosters this effect will vary.

What Temperature Is Best for Beer Fermentation?

Here are two sets of ranges for the biggest classes of beers:

• Ales: 55 to 70°F (13 to 21°C)

• Lager: 40 to 54°F (4 to 12°C)

Note, however, that these temperatures are not doctrine. Peruse your specific beer recipe to know the exact value to maintain.

Cold Fermentation vs. Warm Fermentation

On a fundamental level, Cold and Warm Fermentation yields Lagers and Ales, respectively.

But to be more accurate, you use Cold Fermentation to minimize flavors resulting from yeast action, e.g. fruitiness. If you want a simple alcoholic beverage that has no surprises from yeast, cold is the way to go. That is not to say that simplicity cannot be exciting. How you process your grains will be the biggest contributor to your beer’s palatability.

For Warm Fermentation, complexity is gained from the by-products of the yeast’s work, on top of any other ingredient contributions. Theoretically, you would get a beer bursting with signature flavors from all the components, including yeast.

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Why Does Fermentation Increase With Temperature?

You cannot know the “why” without getting familiar with biological processes and terms.

The yeast produces enzymes that work under a specific temperature range. The enzymes that convert sugar into alcohol only work up to a certain temperature. This is the reason why yeast can get “overworked,” as some people say, but their tools are what is disabled.

Moreover, yeast reproduction increases with temperature. However, even this has a range with limits depending on yeast strain. Yeast is a life-form that reproduces best in moderate temperatures.

The funny thing with these explanations is that they open the topic up to more questions. Unfortunately, this is as deep into it as is relevant to brewing beer.

How Much Heat Does Fermentation Give Off?

The temperature rise you would get from active fermentation is approximately 10 to 15°F (5.5 to 8.3°C). Relative to the ideal target temperatures, these values are quite high.

You can conjecture that this is the reason why you should start your fermentation at a lesser temperature. This is in anticipation of this particular occurrence. You would not want to overheat your yeast before they get anything worthwhile done.