Does Fermenting Beer Need to Be in the Dark?

Fermentation is one of the most important stages in creating beer. It is during this stage that the yeast multiplies and creates all the complexity in your beer.

This process lets your yeast consume the sugars that were added, turning them into alcohol and CO2 bubbles. The result is a crisp, refreshing beer with a smooth flavor profile and soft mouthfeel.

Even though the fermentation process is important, you need to know that it needs to have a dark place to perform it. No beer brewer can do the fermentation process in the daylight.

That’s why all traditional breweries and barrels are in the basement of old monasteries or churches. This is to ensure that the least possible daylight would be present.

Let’s see why dark is important to make your beer ferment faster. It would make you wiser about your beer’s necessities in light when it’s fermenting and after that.

How Can Sunlight Affect the Beer Fermentation Process?

The presence of sunlight causes an increase in the amount of CO2 in the air, which can affect how fast your beer is fermenting.

As you can understand, room air content where most beer is fermented must have around 100 ppm carbon Dioxide (CO2).

The amount of CO2 in your brew beer will change as soon as it’s exposed to sunlight. If not stopped completely, the added carbon dioxide could cause your fermentation to stop before it’s finished totally and ruin your brew.

It’s an unpleasant result of the presence of sunlight in your beer mix. That’s why you need to avoid any direct contact with your beer wort in the daylight.

Brewers usually use candles for lighting and even some other black lights to ensure that there is no direct approach of light to the beer mix. It’s the best thing they can do to ensure that the fermentation process happens easily and without any issues.

Why Brewers Keep the Beer Wort in the Dark?

Beer wort is an unfermented beer that still has the sugars and nutrients that are harvested during the brewing process.

In order to remove any unwanted flavors, and keep the beer in its best condition, brewers have traditionally kept it in a cool dark place – as this reduces contamination and helps maintain the right temperature for fermentation.

The reason is that the wort needs to be kept in the dark so as not to expose it to light while it is fermenting. Exposure will cause something known as photo-oxidation, which produces off flavors in beer.

While you may be wondering why brewers keep the beer wort in the dark, the reasons for doing so are actually quite simple.

Keeping the wort -which is the sweet liquid extracted from malted barley- in a bucket or covered container allows it to develop certain flavorful characteristics that its flavor will not enjoy if exposed.

Does Light Affect Temperature When Fermenting Your Beer?

Sunlight can increase the temperature of the beer mix in the barrel. If it is exposed to a range of light, the temperature will rise, and the wood will become more active.

When you leave a pot of water in the sunlight, especially during summer, you may expect it to have a temperature rise of at least one grade every hour.

If that happens to your beer barrel when your wort is in the fermentation process, you will ruin everything. So, it’s necessary to avoid any temperature fluctuations that happen due to the sunlight in your beer mix.

Do Bacteria in Yeast Work Better in the Dark?

The short answer is yes. Bacteria actually work better on yeast in the dark because their metabolism levels are higher.

This means that they can reproduce faster and produce more enzymes that help break down sugar. Moreover, when exposed to light, yeast produces alcohol instead of sugar, so it is not always a good thing to expose your starter to light.

Yeast has shown an ability to grow even in the absence of light at certain depths in oil. Indeed, this growth has been named anaerobic fermentative growth.

This was first described by Pfeiffer (1969) as having occurred in algal cells cultured without light 3 meters below the surface where they had a high oxygen content due to deep mixing of the water column.

There is a reason why bacteria work better in the dark, but this is an issue for a biology class.

Does Alcohol Gets Affected By Excessive Light Presence?

Alcohol actually gets a lighter color in clear glasses rather than a darker one. In reality, it’s the glass holding the beverage that influences how the alcohol looks.

The glass causes light to refract and scatter throughout the liquid, reflecting off it and appearing to make it less dark.

Also, alcohol does not get affected by a layer of light.

In fact, it reacts to the bending of light rays in bottles of alcohol. Since the chemicals in it act as a solvent that absorbs and scatters light, it is how it appears to be darker.

Are UV Rays in the Daylight Harmful to Your Beer Wort?

There are several different types of UV light, but not all of them are bad. Beer wort is actually much more resistant to UV rays than people may think.

The question really becomes whether or not the yeast can withstand exposure to these rays. This simple test will help you understand if your beer wort is at risk for a potential sunburn.

High levels of UV light can damage your beer and cause off flavors, so it’s important to secure your fermenter with a canopy or other device to avoid light exposure.

Final Words

Dark is the best possible condition for beer fermentation. If you are a home brewer, it’s better to perform the whole process in your basement.

Otherwise, brewing the beer in the open air with plenty of daylight will risk the final quality. Keeping it in the dark is the best way to have the right beer quality and enjoy it.



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