Does LED light make milk go bad?

Bright lights in the big cooler
CC BY 2.0 Lloyd Alter/ Milk cooler in Robinson's General Store

Reading the news these days, you would think that LEDs are the new Gorebulbs, foisted on the public to save energy but in fact fraught with problems. So recently there were stories of how LED streetlights are making people sick, sleepy and fat, and now all the blogs are writing that they ruin milk, with headlines like Got Milk? Keep it away from LED lights, Milk Deteriorates Faster Under LED Lights and Consumers sour on milk exposed to LEDs. That's because of a new study from Cornell, summarized in their press release:

Cornell researchers in the Department of Food Science found exposure to light-emitting diode (LED) sources for even a few hours degrades the perceived quality of milk more so than the microbial content that naturally accumulates over time. Their study determined milk remained at high-quality for two weeks when shielded from LED exposure, and consumers overwhelmingly preferred the older, shielded milk over fresh milk stored in a typical container that had been exposed to LED light for as little as four hours.

Now TreeHugger has been covering LEDs since they first hit the market, and the fact of the matter is, light is light, and the standard Phosphoric LED works in much the same way as a fluorescent bulb does, where blue or UV photons are generated by the LED and excite the phosphor coating. So if pretty much the same light is coming out of the LED as used to come out of fluorescent lights, what’s happening here? What’s new and different?

In fact, not much at all. When you actually dig into the study published in the Journal of Dairy Science, Exposure of fluid milk to LED light negatively affects consumer perception and alters underlying sensory properties, it becomes clear that it has been known for decades that light affects the flavour of milk. From the study:

Light-induced flavors in dairy products are in no way an unexpected or novel observation (Browne, 1899). This study differed from earlier work in the use of more modern LED light illumination and the incorporation of a large consumer study with descriptive sensory measures. Light-activated flavors have been shown to produce robust negative consumer response (White and Bulthaus, 1982)…. Producing milk in packaging protected from sunlight has been discussed for almost 100 yr.

Intense bulbsLloyd Alter/ Intense white LED lights in milk cooler/CC BY 2.0

In particular, the colour of light matters.

The pattern of wavelength produced by LED lighting of course varies significantly from that of fluorescent lighting. Whereas LED lights typically are of a lower total power, they emit strongly in the blue spectrum around 460 nm (Heffernan et al., 2007; Narukawa et al., 2010) in a broader emission peak than fluorescents. This lies adjacent to the 450 nm absorption maximum of riboflavin found to be most destructive by Choe et al. (2005)), and thus may be more effective in degrading riboflavin and releasing energy to the milk.

Because the light is bluer and brighter, the reaction is happening faster.

Although we did not compare the effects, on fluid milk, of fluorescent and LED lights, the data clearly show that LED light exposure for a relatively short period of time (4 h) will readily induce light-oxidized flavor, reducing consumer liking to a similar level noted in previous studies of fluorescent lighting, for example, Hoskin and Dimick (1979)) noting a similar 0.5-point drop in liking on a 9-point scale, after 6 h of exposure in clear containers.

light levels© Spectra of different light sources

So what is really happening here?

  1. It’s not LED light that is causing the deterioration, it’s blue light. Since LEDs work by mixing blue light with the yellow light made by exciting the phosphors, bluish LEDs appear brighter and are a bit more efficient. But LEDs can be mixed to any colour temperature; as shown above, cool LEDs spike in the blue, while warm ones do not.
  2. Studies have shown that brighter light levels increase retail sales, and that cool white light (bluer light) appears “cleaner”. The LEDs are way more efficient and cooler than the fluorescent lights previously used, so the manufacturers of the display cases are pumping up the light levels (hello, Stanley Jevons) and using the most efficient cool bulbs.

There is nothing intrinsic in LEDs that are making milk go bad; it is simply the decision to put in lights that are too bright and too blue. Don’t blame the LEDs; blame the people that pick’em. The headline says "Milk Deteriorates Faster Under LED Lights" but really, it should read "Milk deteriorates under too much bright blue light." But that won't get nearly as many pageviews. Or as TreeHugger emeritus Ruben Anderson noted on another website after complaining about clickbait titles,

This research points the way to home milk delivery, in brown or blue glass bottles, as is used for other beverages whose flavour we care about. Singling out LED is irresponsible.

Tags: LEDs | Lighting

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