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according to this research:

Red LED light (630 nm) stimulated cell growth but slightly inhibited ethanol formation. In contrast, Blue LED light (470 nm) significantly inhibited cell growth but stimulated ethanol formation.

is it good idea to put our batch under red light exposure for first 3 days and then keep it under blue light for the rest of fermentation?

if that bit of LED light can increase the production of ethanol i guess we can have our batch ready sooner, right?

what if we use red and blue light at the same time?

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    You may be overthinking your homebrewing...
    – Robert
    Commented Jul 6, 2018 at 7:34
  • @Robert: for me, people using kegs, and keezers, and CO2, are also overthinking their homebrewing. Building a brewing fridge and adding panels of red and blue LEDs inside it are not that far from each other. Building your own entire gear in stainless is much more expensive. :-)
    – chthon
    Commented Jul 6, 2018 at 10:03
  • @robert ; we don't do traditional homebrew anymore. adding yeast nutrient and all other chemicals maybe is "overthinking" but it helped us to have a healthy fermentation. using science to improve what we do does make sense, at least to me...
    – ElectronSurf
    Commented Jul 6, 2018 at 11:19
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    I don't think any one has any experience with this sort of practice. I highly encourage you to try it and report the results back here. You do need to consider though. The shape, the material and color of your fermentation vessel affect the light wave length and there for its color
    – WildLAppers
    Commented Jul 6, 2018 at 12:43
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    very interesting article, thanks for sharing
    – Mr_road
    Commented Jul 11, 2018 at 8:36

3 Answers 3

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While that paper is interesting. I think it applies more for ethanol production as a fuel rather than beer.

While light can effect yeast In good and bad ways, In general light is bad for beer.

This article explains what spectrums of light are worse than others. https://byo.com/mr-wizard/effect-of-light-on-beer/

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While light might have a slight effect on cell growth, the question is whether or not it's worth the hassle. Keeping in mind that if this were a good idea, commercial breweries would have adopted the practice. Which they haven't, and as a general principle keep in mind that if nobody's doing it, there are usually good reasons for that. :-)

Light (esp. blue) could, on the other hand, interfere with hops and other delicate complex molecules, causing light struck off-flavors and aromas.

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  • do you have a link to the blue light - hop interaction source?
    – mattrices
    Commented Jul 8, 2018 at 17:06
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    The sensitivity of hops to light is well known. The interaction is responsible for "lightstruck" and "skunk-like" aromas. E.g. see beerandbrewing.com/dictionary/eIXf22Zwnt/lightstruck As with all photochemical reactions, the energy level of the light is key to the degree in which the reaction manifests itself. Blue light has a higher energy level then red light (remember the red light in dark rooms for developing the old black-and-white film?) which is why red light is more permissible and blue should be avoided.
    – Frank van Wensveen
    Commented Jul 10, 2018 at 9:06
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It may be a good idea to use red light in your yeast starters when you have the most cell growth. Using it in primary may over populate your batch by diverting glucose that would have gone to EtOH production to biomass production unless you use a smaller starter.

The blue light may be useful for maximizing attenuation. If blue light supplies additional energy to the yeast as the paper suggests, they may be able to metabolize more sugar than would be otherwise possible.

Use both and tell us what happens! In plants using the red and blue spectrum has synergistic effects so it could be beneficial depending on how the yeast are utilizing this light as energy.

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