In lieu of the discussion in the bean cellar thread regarding light exposure, I figured it might make for an interesting topic of discussion. If there is a thread you know of that has this info, please do share. I couldn't find any using the search feature.

We've read it time and time again that whole beans should be kept away from light (more specifically, diret sunlight). Now, I have not been able to find any published studies (specifically, effects of light on roasted coffee), blind taste tests, or personal accounts where light has been actually blamed for ruining a batch of beans.

I am often inclined to conduct my own studies when thinking about things like this, but I figure let's see what I can find on Home-barista.com If there aren't any this should be a very simple test to set up and conduct.

I personally haven't gone out of my way to observe this rule beyond having bought airtight canisters which also happen to block sunlight. I concurrently use semi-transparent ziploc TwistNGo containers that sit out in the open and have never been able to detect any perceivable difference from the same coffee stored in the dark containers, for any period of time, from hours to several weeks (when I had surplus roasts). Perhaps it's because the only light I have in my kitchen is indoor lighting (my kitchen get no direct sunlight). So is it just direct sunlight we should be concerned about? That's what most of the written verbage on it indicates.

For those of us that don't let coffee sit around longer than their optimal period, is light even be perceivable factor (should it be present)? But I do understand that it's common knowledge that long-term light exposure has negative affects on most things, not just foods, and I think that is the basis for the concern, but for the short term storage and consumption of specialty coffee, is it really warranted?

Thoughts?

Beyond the top and perimeter layers how many beans are exposed to light anyway? I agree with your implication that staling is probably more of an issue.

I have a small "bed canopy" with Victorian curtains around my 2 oz mason jars. I pull back the curtains with a tiny yet elaborate drawstring (with golden thread weaved adornments ), pull my desired bean jar, and then close the veil as quickly as possible to avoid light exposure to the rest of the jars.

I tell bewildered visitors that it is the bed for my photosensitive cat.

omg that's a hilarious image I have in my head. I'm not sure if you're kidding or not but please do take a snapshot if the latter

SCAA has an article on coffee staling, but actually makes no mention specifically of the effect of light: What is the Shelf Life of Roasted Coffee? A Literature Review on Coffee Staling

I suspect that the claim that UV light negatively impacts coffee is just based on food science research establishing an effect of UV light on food degradation in general. Here's a summary of some causes of food spoilage (including light): Describe the different ways that food spoils

Compared to the impact of oxidation I would guess that the impact of light is secondary. Would be interesting to see if anyone can design a proper experiment to test its impact.

keno wrote:SCAA has an article on coffee staling, but actually makes no mention specifically of the effect of light: What is the Shelf Life of Roasted Coffee? A Literature Review on Coffee Staling

That's interesting. So if the so-called experts didn't bother to even mention light exposure, that lack of mention, to me, kind of illustrates the insignificance sun damage potential, at least from specialty coffee perspective, where staling is the overwhelming concern.

The SCAA is primarily a trade association. You'll need to spend more money or work for a larger, well funded coffee company to access the type of research that you're looking for. I was doing some searching and figured that one of the Illy books would have this, the Google Books preview didn't have the complete quote I was looking for in its page preview, but I was able to find a reference to this on Coffeed, but still no definitive answer on how long is too long. I suspect that most people have heard to avoid exposure to light when storing coffee and leave it at that.

From Illy, "Espresso Coffee", pg 244-245:

"Light plays a catalytic role in many chemical reactions; in the case of espresso (arabica) blends, particularly rich in unsaturated fatty acids, light catalyses the prime trigger of their auto-oxidation reaction, i.e. the formation of H*, R* (alkyl) and ROO* (peroxide) free radicals which then cause the reaction to propagate."

http://www.coffeed.com/viewtopic.php?f=21&t=1510

I started searching for the Lightstruck flavors that develop in beer when exposed to light first, and found this interesting reference in Coffee Flavor Chemistry by Ivon Flament, Yvonne Bessière-Thomas, John Wiley & Sons, 2002 that these flavors are present in roasted coffee but appear to be mostly due to roasting, not light expsoure:

The product was previously identified in beer by Andrews (1987) and in human sweat by Polak et al. (1988), and characterized as sunstruck or lightstruck off-flavor. The cause has been attributed to the degradation of bitter isohumulones from hops under the influence of ultraviolet light (Bondeel et al., 1987). By photofragmentation trans-isohumulone liberates a prenyl radical which can trap a thiol radical, producing an undesired flavor for beer. Holscher et al. (1982) have also shown that 3-methyl-2-buten-1-thiol and 3-mercapto-3-methylbutonal are primarily formed under pyrolytic conditions in roast model reactions of prenyl alcohol and sulfur-containing amino acids.

Food and Beverage Stability and Shelf Life by David Kilcast, P Subramaniam, Elsevier, Apr 8, 2011 pp. 33-34 has a general write-up on light-induced chemical changes.

Milk, chocolate, butter, and other foods, when exposed to light, such as sunlight or fluorescent light, may develop a characteristic off-flavor caused by photo-oxidation. Photooxidation may occur due to photolytic free radical autoxidation and/or photosensitized lipid oxidation. Both reaction pathways may lead to formation of free lipid radicals (Mortensen et al., 2004), thus initiating autocatalytic oxidative processes. In particular, dairy products, such as milk and cheese, are very sensitive to light oxidation because of the presence of riboflavin (vitamin B2), which functions as a strong photosensitizer. A photosensitizer is able to absorb visibile and UV light and transfer this energy into highly reactive forms of oxygen such as singlet oxygen, subsequently inducing a cascade of oxidation reactions, leading finally to lipid and protein oxidation, significant losses of vitamins and amino acids, discoloration, and formation of strong off-flavors, and even toxic products (e.g., cholesterol oxides) (Yang, 1998: Borle et al., 2001). Light-inducing oxidative processes are a major cause of deterioration in alcoholic beverages such as wines, degrading the flavor and color (Refsgaard et al., 1995). The potential of photooxidation is related to spectral distribution and intensity of a light source, its wavelength, presence of sensitizers, temperature, exposure time and the amount of available oxygen (IFST, 1993; Mortensen et al., 2004). Appropriate packaging material that properly protects foods from both light and oxygen is important to minimize the photooxidative deterioration of these products.

drgary wrote:Beyond the top and perimeter layers how many beans are exposed to light anyway? I agree with your implication that staling is probably more of an issue.

I would suspect that the life time of most varieties and roast level beans will survive just fine in the bean cellar for 8 to 10 days with no detectable ill effects as long as they are not placed outdoors where direct sunlight will impinge on the cellar from dawn to sunset. There will be exceptions though and each user will have to make the final determination.

What is being provided by the bean cellar is a time shifting device. They allow moving the time required to prepare each individual dose to a more convenient location on the clock and calendar.

OldNuc wrote: What is being provided by the bean cellar is a time shifting device. They allow moving the time required to prepare each individual dose to a more convenient location on the clock and calendar.

Exactomundo!

With the inherent capability to prep different types of coffee, so that choices are ready and waiting later.