Here's a spread sheet of Staling Ratios based on 1/2 life to illustrate Ken's point that all components might not decay at the same rate.



The Qty column is the amount of a compound in the coffee.
The Ratio column is the ratio of the Qty to 1000.
The first group of numbers is for a sample left at room temperature for 12 days.

The second group of numbers is for a 16x increase in half life as one would expect going from 20°C to -20°C, typical of a mode home refigerator freezer. No allowance made for weird, atypical compounds that speed up their rates when cooled. Note that the ratios are still 'close' to day 1 after 12 days.

The third group of numbers is for 1, 4, 16 and 32 months. While the 30 day column ratios are not too bad, by 120 days, things are beginning to get ugly and pretty much blow Ken's assertion that coffee frozen for two years would be drinkable, if one assumes he's correct that the compounds in coffee decay at varying rates.

Of course, in reality it's much more complicated as some compounds decay into undesirables and don't just dissipate.

shadowfax wrote:As for the rest, I'm a little skeptical of how you could reasonably taste-test the hypothesis that "various flavor-contributing compounds and gases in coffee decay at differing rates that vary non-proportionally with temperature" (this is your implicit contention, right?). I'll chuckle at that, but I can't say I'll do more than blow air about it--that kind of testing is more suited to a laboratory running chemical tests than the kind of triangle-cupping that's been done to establish the relative safety of freezing roasted coffee in sealed containers for a couple of months.

I'm not sure I understand exactly what you are implying is my contention, above.

I'm basing what I wrote on my non-scientific observation that it appears that one can freeze coffee long enough that it no longer will obviously outgas after removal from the freezer, yet it still tastes fresh. I'm suggesting that the outgassing of C02 is retarded by cold temperatures however not quite as much as the deterioration in flavors that gives the appearance of staled coffee, e.g. the observable gas goes before the flavor does. The absence of further outgassing after freezing is a necessary but not sufficient condition for making an observation that the previously frozen coffee tastes "stale." I think it is rational to assume that some of the aromatics we value are dissolved in the coffee oils and hence do not depart the coffee as fast as does the gas, when the coffee is in a freezer.

I'm no physicist (that being obvious) however one possible explanation that makes sense to me would be that the oils in coffee change physical state when frozen -- they go from being a liquid to a solid. The gas in beans does not change state, it remains as a gas however it just becomes colder. Perhaps this explains what I'm observing however it does sound kind of simplistic.

ken

Ian, thanks for that table. Given that the table presumes a presence of a variety of 'flavor-contriubuting compounds in a coffee in widely disparate ratios (between 1:1 and 1:10 for any given pair of compounds), and if I understand the data, it would suggest that freezing the coffee can 'prop up' the remaining amounts of the compounds that were initially relatively low, such that they remain in considerably stronger 'concentration' after freezing for a month or two than they would in a room-temperature-aged sample. But wouldn't that suggest that coffee aged in a freezer ought to taste quite a bit different than room-temperature-aged coffee? Certainly a plausible thought, except that it would seem to contradict the basic experimental data that Jim and Ken have collected... or that the chemicals aren't typically present in such disparate ratios (or something else that's not occurring to me).

Ken, I must have misunderstood you on the degassing thing. I can't make any meaningful claims about perceived freshness vs. CO2 degassing, and I am sure Illy and Henry (and you) are right that the two processes are independent (and can probably be manipulated independently to some degree, to what end I can't imagine). I was just observing that I see very strong outgassing even when storing roasted coffee >24 hours after it's roasted, vacuum sealing it, and storing it for a month in a relatively warm freezer. The claims made about this don't have anything to do with flavor, that I'm aware--I'm just guessing based on that that gases are surprisingly well-preserved by the freezing process.

Here's a sheet with lower ratios and closer half lives. Things get far less out of hand.




This sheet shows unwanted components that are produced, rather than dissipate, in the yellow rows. The production rate is reduced by a factor of 16 by freezing. The components in the white rows still decline, but the proportion of unwanted components remains minuscule compared to room temperature.



This is probably closer to what is happening.

Granted, this discussion is perhaps getting off in the weeds, a bit.

Still, it is my observation that frozen coffee seems to disperse its gases, while frozen, faster than it seems to show obvious signs of deterioration (in taste) when used to make espresso. I don't know what the *real* scientific explanation for this is, and I don't know if other people have made the same observation.

Forgetting about the explanation, for the moment, and assuming that I have made a valid observation, it would seem that degassing of previously frozen coffee is a necessary but not sufficient event in the process of the eventual staling of previously frozen coffee. This is not terribly surprising since, as I noted a while ago, it is at least my observation that most coffee seems to disgorge most of its obvious gas by about day 4 after roasting, and the peak espresso-making period for most coffees, after roasting, at least to my observation, is roughly from day 3-4 to day 7 or 8, largely after obvious degassing is complete.

I'm simply proposing that the end of obvious degassing may precede the end of the period of usability by a larger relative time period in the case of frozen coffee, than it does in the case of fresh, never-frozen, coffee. The only potentially useful tidbit in this hypothesis is the idea that if your previously frozen coffee doesn't puff up in the bag after you take it out of the freezer, it might still be perfectly good to use.

ken

The graph on page 238 of Illy showed the Arrhenius equation of volatile released, as relating to freshness. It was a study by Nicoli, which was presented at a scientific convention in 1993, and not published until 2006, in a paper titled "Modeling the Secondary Shelf Life of Ground Roasted Coffee" in J Agric Food Chem, 2006, 54, 5571-5576. It answers part of Jim's question about opening and closing the storage container. The abstract can be found here:

http://pubs.acs.org/doi/abs/10.1021/jf0 ... istoryKey=

At the closing of the Illy chapter, it was stated: "The concentration of specific volatile compounds in the headspace of the package or of the cup, measured by gas chromatography, had been used to determine the degree of spoilage. For instance, the ratio of 2-methylfuran to butanone, the "aroma index" M/B, drops from 3.2 in fresh coffee to 2.33 in spoilt coffee".

Coffee freshness has nothing to do with carbon dioxide.

Jim, I am merely agreeing with you. I am so very thankful of you and Ken's landmark posts on freezing coffee, which I now regularly do, and your paper on water quality.

I started freezing my roasts in the deep freezer after finding this patent.
http://www.freepatentsonline.com/6514552.html