Staling: the effect of light

[Alistair Durie]

Oxygen, heat, moisture, light, and time. Variables that cause staling. perhaps there are others.

How critical is the light factor? are some types of light worse than others? is it only UV? daylight? or any light? would a clear UV container protect coffee against light?

What is happening really, when we shine a light on coffee?

[MarkG]

Ohh, I like the question in this thread

We were air roasting in a Gene Cafe and found the beans took a couple of days more than gas roasts to de-gas to a sweet spot for our taste. We have always used resealable one-way valve silver bags to store roasts, but I have been experimenting by keeping the beans in Bodum glass jars with a degree of air extraction (you can hear it sucking out) when the lid is put in place and leaving them in a room with no windows, but some light filtering through from another room. The beans are now maturing at around the same rate as those roasted using gas and kept in the silver bags.

I don't understand the science beyond air roasting removing more moisture from the beans, but I do find it very interesting.

[Alistair Durie]

Does anyone know anything about this?

[Alistair Durie]

BUMP!

I'm starting to think that my bar spotlights shining on my hoppers all day is not so bad after all.

[LiftOff]

I have been under the impression that at least the Mazzer hoppers had a UV protective coating applied to them. I'm not sure why I believed this to be true though as I've been driving myself crazy trying to remember where or from whom I heard this. If grinder hoppers don't have any UV protection(assuming that UV is harmful to coffee), it's time they did!

[Matthew Kolehmainen]

Applying my limited knowledge of organic chem and physics:

I am sure that certain staling reactions can by helped along by light, in that the light provides the energy necessary for that reaction to occur. Oxidation comes to mind, but with the myriad of organic reactions possible in coffee, I am certain that there are other reactions occurring that would lead to what we call staling. UV light is focused on because it is the most energetic light we usually have to deal with. Visible light has less energy, and is thus less able to help reactions proceed.

Matthew

[James Hoffmann]

I was talking about this the other day and came to the conclusion that whilst strong light would certainly accelerate certain reactions it is more likely the associated heat doing the damage. It would be interesting to try and expose some coffee to quite a lot of light whilst maintaining the same temperature in its environment as a dark control sample.

[Vince Piccolo]

It would be interesting to try and expose some coffee to quite a lot of light whilst maintaining the same temperature in its environment as a dark control sample.

Then both samples would be oxidized. I believe once you take the coffee out of a one way valve, you can not stop the oxidative process. Now does light or no light speed it up? It's hard to prove what causes more oxidative destruction since it's already exposed to 20% oxygen anyways.

[barry]

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."

[Jim Saborio]

Totally unscientific, but at my last job we'd store our French press coffees in a hot room just off the kitchen (probably in the 80s). The room was lit by fluorescent lights and had no windows or direct natural light.

They were kept there because it was where the water tower, grinder and presses were stored. Coffee not in "active use" was stored in our wine cellar (mid 60s).

I'd notice something like this:

We'd get a Rwandan in... It would be really great, but after four days of sitting in that hot room it would lose almost all of its complexity.

When we'd worked through the pound, we'd run to the cellar and grab another bag of the same stuff (presumably the same batch, but definitely the same roast date). The cellar-stored coffee seemed to retain its complexity much more.

Coffee in the hot room was subject to infrequent opening and closing of its glass storage jar. Our press coffees were shipped and "cellared" in non-valve craft bags.

I always wondered if the heat was making the big difference.