Light is a bringer of life and without it, life could barely exist, yet not all organisms such as yeast need it to thrive and it sometimes comes with negative effects in homebrewing.
Light can cause problems in beer brewing at all stages after the brew day, so is the light exposure bad for a beer kept in a fermenter?
Fermenting homebrews like beer shouldn’t be in contact with sunlight or strong artificial light such as fluorescent light as such light can negatively affect hops. Light-exposed fermentation can give off a skunky taste and smell after the fermentation ends. Yeast also doesn’t like light, but won’t be as affected as hops.
As you can see, the primary reason why it’s important to keep the light away from the fermenter is that hops are extremely sensitive to the light.
Skunked beer is not a pleasant thing, so it’s important to avoid it at all costs.
1. Sunlight effects on homebrew
Sunlight is the most dangerous source of light for your brew as it emits a wavelength of around 500 nanometers. Comparatively, the brown bottles are among the best bottles with anti-light protection and they don’t protect over 450 nanometers.
It’s really difficult to block all sunlight with most types of containers used in homebrewing, so it’s recommended to keep the brew away from sunlight for as much as you can.
The beer can get skunked after only 20 seconds of direct sunshine exposure both prior to and after fermentation.
Hopefully, brown bottles offer good UV protection, so it would probably take at least 15 minutes of direct exposure for any damage to take place.
2. LED, fluorescent light effects on homebrew
Fluorescent lights are another danger to a fermenting brew just as they continue to be a danger after the fermentation.
LED light emits around 400 nanometers, which is considerably lower than sunlight wavelength, yet the beer can go skunky anywhere between 350 and 550 nanometers.
Don’t use LED light in the room with a fermenting brew unless you are sure you can completely prevent the light from entering the bucket.
LED can cause problems even during bottling, so if you need light use incandescent and halogen bulbs for the light sources.
3. Incandescent and halogen light effects on homebrew
Your typical incandescent and halogen bulbs emit a wavelength of around 350 nanometers which can still hurt the brew with hops but the effect is greatly reduced.
For any significant effect, you’d need to expose the beer really close to the bulb without any protection for a full hour or perhaps way longer than that.
This warmer range of wavelength isn’t a big issue so I wouldn’t fear using this type of light even during the bottling of a beer. However, glass fermenters offer almost no absorption protection, so you should still cover it with something so the direct light doesn’t affect it.
Any other type of fermenter such as plastic buckets absorbs enough light, so you won’t have to worry about incandescent and halogen light which can hardly do any damage even without any absorption effect.
Keep the fermenter in the dark
Plastic fermenters block out most indirect light and as such you only have to keep it somewhere outside of the direct light blast and it will be good. Steel fermenters completely block the light from entering and in theory, you could even keep the brew ferment in a steel fermenter in direct sunshine if it wouldn’t cause problems such as temperature change.
Yet, the light fully passes through glass carboys, so glass fermenters are a bad choice in a bright environment.
It’s recommended to keep your fermenter in a dark place such as a closet when minimal light exposure is present. The second thing you can do is to use a fermenting chamber as it’s not only a great tool for temperature control but also prevents light from entering the brew.
And finally, the most budget-friendly option you have is to wrap a black t-shirt, hoodie, towel, or any darker piece of cloth that will cover the entire volume of a fermenter.
Yet, it’s still important for plastic and glass fermenters to be kept out of direct light if possible as sometimes the light may find a way through.
I keep my plastic fermenter behind the couch where no direct light can strike it and the minimal amount of light from the bulb doesn’t affect it by any means.
How does light affect yeast fermentation?
There are studies that confirm that light has a positive effect on baker’s yeast as the photosynthesis cells found in yeast can benefit from the light similarly as the plants do. However, in brewing, we don’t typically use baker’s yeast, so I can’t say for a fact that light would benefit other yeast cultures, nor did I personally conduct a single experiment regarding this topic.
What I can say though, is that yeast isn’t sensitive to light like hops are and while light exposure will surely hurt hops, the yeast is way tougher.
Now, why I say it won’t be affected as much and not affected at all, is because UV lights are a different story as it has the ability to damage cells. If UV light can damage human cells, so it can damage yeast cells while halogenic light can’t.
So, don’t risk it and cap the yeast in a dark, cold place unless you pitch it. When fermentation kicks in, minimal light exposure from house bulbs (unless they are LED) shouldn’t be a big deal for yeast.