Rate of coffee staling - Page 2

[welone]

Dear Alan

I have read a lot of valuable info about coffee from you and I have a great deal of respect for that work.
OTOH ".. your rule of thumb works as an approximation for dilute solutions. Complex organic solids??? No way." is just wrong!
if you don't believe me, go get a chemistry book like the one i referred to and read up again - i got a msc in chemistry too.. You can't apply the rule to the calculate the aging of the whole mixture of compounds but there's no problem in getting a good estimation for a particular compound of interest (even if it is a complex organic solid).
I'm aware that a statement of someone like me (with practically no history of whatsoever) is likely to be ignored - irrespective of it's validity; but this statement was just to arrogant to take without opposition..

[cafeIKE]

Thanks, you can send the $ to my P.O. box address. I've done the experiment, ground vs. whole beans, about an hour out of the roaster, vac packed in non-valved bags. You don't have to wait 2 weeks, the ground bag inflates within 20 minutes, and stays puffed. The whole beans bag did inflate after 24 hours, but never to the extent that the ground bag did.

Vac packing totally changes the equation, as Marco indicates, due to the ideal gas law.
How long was the test period?
How was the escaped gas measured?

[Alan Frew]

Dear Alan

I have read a lot of valuable info about coffee from you and I have a great deal of respect for that work.
OTOH ".. your rule of thumb works as an approximation for dilute solutions. Complex organic solids??? No way." is just wrong!
if you don't believe me, go get a chemistry book like the one i referred to and read up again - i got a msc in chemistry too.. You can't apply the rule to the calculate the aging of the whole mixture of compounds but there's no problem in getting a good estimation for a particular compound of interest (even if it is a complex organic solid).
I'm aware that a statement of someone like me (with practically no history of whatsoever) is likely to be ignored - irrespective of it's validity; but this statement was just to arrogant to take without opposition..

Hi Marco, nothing to do with being arrogant, just 15 years industrial experience with extremely complex polymer mixtures full of all sorts of interesting shite. The problem with your average coffee bean is that no-one has yet identified that particular organic compound that signifies "stale", let alone the reaction cascade that gets you there. The problem with other complex organic solids is similar.

Take a mix of simple polymers, chelates, plasticizers, catalysts and solvents and react them at (t) temperature for (h) time to get (y) yield of a particular product. Raise the temperature 10 degrees C; do you double the yield in (h) time? No way, because the increased temperature can have all sorts of wacky effects on reaction pathways, to the point where you might get zero yield and a great big kaboom! So the 10C increase in temperature may have actually decreased the speed of that particular desired reaction, or stopped it altogether. What is going on inside Mr. coffee bean is undoubtedly just as complex, otherwise some bright Illy chemist would already have figured it out.

Now, in his thought experiment (what Instaurator calls a "Data Free Observation") CafeIKE asserts that the majority of the CO2 and volatile aromatics outgassed from the bean are staling byproducts, that is the end points of unknown reactions which produce unidentified compounds which signify "stale". This is factually incorrect as considerable research has already established that the majority of the CO2 is produced during the roasting process and diffuses out of the cellular structure of the bean according to well known physical laws. Raising the storage temperature of the bean will speed this process up, lowering the temperature will slow it down. Immersing the bean in an inert gas for a month will allow most of the CO2 to escape but stop oxidation reactions thought to be the primary cause of staling.

Which, funnily enough, is precisely what Illy do to their roasts.

Alan

[barry]

it's likely that CO2 and aromatic compounds are by-products of the staling process.

If they were byproducts of staling, would not the rate of CO2 production increase, or at least remain constant, as the coffee ages/stales?

And yet, it has been clearly demonstrated that the rate of CO2 production decreases significantly in the first week post roast, with most CO2 propagation occuring in the first 24-48 hours.

[welone]

Hi Marco, nothing to do with being arrogant, just 15 years industrial experience with extremely complex polymer mixtures full of all sorts of interesting shite.

the arrogant wasnt meant as a general statement but as to generally restrict the 'van't hoff rule' to dilute conditions without mentioning an explanation.
In a fluid (or at least mobile) mixture that involves a buckload of different reaction types, I see why you would restrict the 'van't Hoff' equation to a dilute situation. In a coffee bean only the gaseous phase is mobile and this strongly limits the number of reaction types involved (foremost oxidations and hydrolysis). Then staling reactions seem to occur only one way - at least I've never heard of any kind of taste regeneration of natural products Furthermore; messing around in a sub ambient temperature range of 50°C is another strong argument for less dramatic changes in chemical behaviour: I guess you werent mixing the polymers and stuff at cold temperatures
So my assumption is, that for a specific coffee and roast there's a nearly constant empirical staling factor - within a temperature range of +25°C to -25°C. It's just that a coffee seems to go through the same aging stages everytime - depending on storage and ambient conditions. What could change the process in relation to its course at ambient temperature is strong differences in temperature dependences of the different staling reactions. This would change the balance between the staling products (and educts of course) - but that could as well be a good thing: Similar to the recent thoughts and experiments on 'aging' ground coffee for up to 12 hours.

What is going on inside Mr. coffee bean is undoubtedly just as complex, otherwise some bright Illy chemist would already have figured it out.

I enjoyed reading Illy (in 1 hour pieces) and trust most of their findings. Namely I also took with me that the CO2 gets produced during roasting and only neglible amounts are produced afterwards. But that doesn't mean researchers don't overlook or sometimes even plainly misinterpret aspects of reality.
Here's my favourite example:
'hydrophobic repulsion' - it is still widely used even in renowned scientific journals. here's a quick test to disprove this concept: take a flat teflon surface (e.g. pan) sprinkle some small water drops on it and turn it upside down. the water stays attached to the surface, even against gravitational force (it is actually the vanderWaals force). To say it simple: it's just that water likes itself much better than the teflon, but still prefers it to air. and more scientifically water has more attractive interactions with itself than teflon.

Immersing the bean in an inert gas for a month will allow most of the CO2 to escape but stop oxidation reactions thought to be the primary cause of staling.

According to their own statements in the book, the coffee would hold his CO2 for longer when the concentration around them is higher. So a container filled with CO2 instead of Nitrogen should preserve the CO2 on a much higher level - but then again CO2 is acutely toxic when breathed in concentrations above 5%.

grüess

marco