Coffee: To Freeze or Not to Freeze?

[Ken Fox]

Here's your chance to critique the article, supplement it with your own experiences, or suggest further research on this topic (not that I'd be up for it, but maybe someone else would be )

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ken

[RapidCoffee]

He's baaaack.... and with a bang! Great article, Ken, and nice to see you back on H-B.

[Rainman]

Wow! nicely done, Ken- if I didn't know any better, I'd swear you've had experience doing drug studies in the past. Good transparent methodology, BUT- it's just one study, and it would be great if someone else could repeat it and find the same results. One silly question- can you post your roast curve? I'm wondering what sort of temp ramp you did (especially up to and through 1st crack- looks like it was pretty quick, but you still got a nice FC+ roast?

Nice "myth-busting" btw!

Ray

[Ken Fox]

Wow! nicely done, Ken- if I didn't know any better, I'd swear you've had experience doing drug studies in the past. Good transparent methodology, BUT- it's just one study, and it would be great if someone else could repeat it and find the same results. One silly question- can you post your roast curve? I'm wondering what sort of temp ramp you did (especially up to and through 1st crack- looks like it was pretty quick, but you still got a nice FC+ roast?

Nice "myth-busting" btw!

Ray

I actually have a research background in my distant past, having published articles in (the now supplanted) American Journal of Physiology, as a college student, and in the Journal of Clinical Oncology and International Journal of Radiation Oncology, Biology, and Physics when I was in post graduate training and in practice as a physician. Jim Schulman, who came up with the experimental design and who did the data analysis, has recently obtained a ph.D in Sociology at the University of Chicago. So both of us have experience in experimental design and statistics.

I have cobbled together an idealized roast curve which is reproduced here:

I am calling it idealized because although I roast with the aid of a rigid thermocouple mounted in the drum of my roaster, along with a fluke datalogger, I haven't datalogged any roasts in 6 or more months. The only change I've made in my roast technique since the previous datalogged roasts is that I let the drum cool down slightly more before introducing the beans, although it was always under a real temperature of 380F.

I have taken my last set of logged roasts, which were logged every 20 seconds, and instead taken the first number and every 3rd measurement thereafter, which corresponds to one measurement every minute after "charging" the roaster. I think this makes the graph more easily understood since otherwise I'd have to explain that each data point was taken at 20 second intervals.

[EDIT: I made a data transcription error in constructing the first graph I put in this post, which I have just corrected. If you saw this post in the last hour, I apologize for any confusion I may have caused you]

I have years of experience with this roaster at this point and have gotten a lot of feedback from both professionals and serious amateurs on roast samples I've sent out. The type of roaster I am using is well known in the professional roasting community, and I have had several comments over the years that this type of roaster produces its best roasts when the roast is completed fairly quickly, with considerably poorer results if the roasts are extended out beyond 14 minutes (the coffee tends towards "flatness" with that sort of roast profile in this roaster). Earlier on I used to extend my roasts out much longer and the results were in fact, inferior to what I get now.

Finally, it is really hard if not impossible to extrapolate roast profiles from one roaster to another, and what works well on my drum might work very poorly in another roaster; you just have to experiment to find what works best in any particular roasting setup.

ken

[Java Man]

Well done, Ken! Thanks for your continued contribution to the art and science of home espresso!

Cheers,

Rick

[Rainman]

I actually have a research background in my distant past, having published articles in (the now supplanted) American Journal of Physiology, as a college student, and in the Journal of Clinical Oncology and International Journal of Radiation Oncology, Biology, and Physics when I was in post graduate training and in practice as a physician. Jim Schulman, who came up with the experimental design and who did the data analysis, has recently obtained a ph.D in Sociology at the University of Chicago. So both of us have experience in experimental design and statistics.

I had a feeling... I'm familiar with a CT surgeon (same name as yours) who we trained (I'm the clinical pharmacist for surgery/critical care at the Tucson VA) a few short years ago, but- ahem, he may be a bit younger than you? I can't imagine he's retired yet, but maybe I'm the one who's getting old... I digress.

I have cobbled together an idealized roast curve ...
I am calling it idealized because although I roast with the aid of a rigid thermocouple mounted in the drum of my roaster, along with a fluke datalogger, I haven't datalogged any roasts in 6 or more months. The only change I've made in my roast technique since the previous datalogged roasts is that I let the drum cool down slightly more before introducing the beans, although it was always under a real temperature of 380F.

EDIT: I made a data transcription error in constructing the first graph I put in this post, which I have just corrected. If you saw this post in the last hour, I apologize for any confusion I may have caused you

Nope- just got in from a quickie bike ride. Thank you for putting this up; I was just curious about your roasting setup, and didn't see too many details mentioned in the article (other than the photo). Which sample roaster is that?

Finally, it is really hard if not impossible to extrapolate roast profiles from one roaster to another, and what works well on my drum might work very poorly in another roaster; you just have to experiment to find what works best in any particular roasting setup.

ken

You mean my iRoast won't produce the same cup using your profiles?

Thanks again, Ken.

Ray

[Ken Fox]

[ Thank you for putting this up; I was just curious about your roasting setup, and didn't see too many details mentioned in the article (other than the photo). Which sample roaster is that?


Ray

It is a copy of an old Probat/Jebez/Burns sample roaster whose patents must have run out decades ago. They were being sold by roasters exchange (http://www.roastersexchange.com) --- no I did not make up that URL --- a few years ago but I think they are either no longer being sold by them, or they may be a special order item. I had to wait about 4 months to get mine when it was ordered. The drum was cast in S. America but a lot of the rest of it was apparently made in the shop of Roaster's Exchange.

Judging by what I have seen offered for sale in the recent past, I think that most sample roasters being sold these days roast considerably smaller batches than what mine does. Mine is big enough to allow fairly time-efficient roast sessions as long as you do, say, 5 or more batches each session. I can get up to more than 3 roasted pounds (after roast weight) per hour when I get rolling. Not efficient from the standpoint of a shop, but for something in your garage it isn't bad.

My roaster has been substantially modified from its condition when delivered. It was necessary to replace the burner because the one supplied could not produce enough heat at my altitude (almost 6000 feet) to properly roast coffee. Barry Jarrett was very helpful in locating a new burner for the roaster. In addition I ordered a custom made ensheathed thermocouple from Omega, which has been epoxied in to a constant position and which allows me to monitor the roast temperatures with a high degree of consistency. Finally, as originally supplied it ran on propane but it now is plumbed in and uses natural gas, plus has been mounted permanently under a custom made smoke hood that was fabricated for a friend of mine who has prior experience in HVAC work.

ken

[Matthew Brinski]

Phenominal.

I am actually surprised at your finding that coffee which has been frozen does not deteriorate faster (after defrost) than if it were not frozen initially. I have always had a perceived impression that it does in my use. I don't frequently roast at home though, so the coffee that I experiment with freezing is usually frozen anywhere 2 to 4 days out from roast when it arrives via shipping, as opposed to you freezing within an hour of roast completion. I wonder if that's a considerable variable? Probably not.

Thanks for posting the project. Awesome effort, seriously.

[Ken Fox]

Phenominal.

I am actually surprised at your finding that coffee which has been frozen does not deteriorate faster (after defrost) than if it were not frozen initially. I have always had a perceived impression that it does in my use. I don't frequently roast at home though, so the coffee that I experiment with freezing is usually frozen anywhere 2 to 4 days out from roast when it arrives via shipping, as opposed to you freezing within an hour of roast completion. I wonder if that's a considerable variable? Probably not.

Thanks for posting the project. Awesome effort, seriously.

I think it is true, based upon this experiment, that within a certain period of time, previously frozen coffee doesn't deteriorate faster than fresh/never frozen coffee. But none of the coffee in this experiment was tasted at a period older than 8 days. It might be, that had we done a cupping experiment and gone out further, say to 14 days, that we would have found faster degradation.

Aside from a lot of negative stuff that has been said previously about freezing, most of which is unfounded, it is hard for me to come up with a specific mechanism that would cause previously frozen coffee to degrade faster than never frozen coffee. It isn't like you are freezing a head of lettuce, after all. The coffee has already been roasted and whatever cell structure and moisture were there beforehand are mostly lost.

When coffee ages and degasses there are chemical and physical changes going on in the roasted beans. Some of these changes are "good" and some are "bad;" it can't be any other way or we would all strive to drink coffee within a day of its roasting. Most espresso lovers believe that the coffee "improves," over all, during the first several days to a week out of the roaster, and then continues to "hold" for a while after that until the overall quality declines.

My opinion is that freezing greatly slows down these chemical and physical processes, and that the extent to which they are arrested is largely a function of how cold a freezer one uses, and possibly how soon after roasting one does the freezing.

ken

[jrtatl]

Thanks for the great article Ken.

As a side note to anyone interested in anecdotal evidence, I almost always freeze my coffee -- with great results.

I buy in bulk to save $$. As soon as the beans arrive in the mail, I use a Foodsaver to vacuum seal 8 - 10 oz of beans in several bags. I then put the vacuum bags in my freezer. I typically use the coffee within 2 months, and it works pretty much as good as the fresh stuff.

[Ken Fox]

Thanks for the great article Ken.

As a side note to anyone interested in anecdotal evidence, I almost always freeze my coffee -- with great results.

I buy in bulk to save $$. As soon as the beans arrive in the mail, I use a Foodsaver to vacuum seal 8 - 10 oz of beans in several bags. I then put the vacuum bags in my freezer. I typically use the coffee within 2 months, and it works pretty much as good as the fresh stuff.

The one thing I'd reconsider about your method is the vacuum freezing. I doubt it hurts anything but unless there were some obvious benefit it may be a waste of time and money to do so. We did not do any vacuum sealing with our frozen coffee and it obviously did not matter in this study.

Thanks for your comments.

ken

[jesawdy]

As a side note to anyone interested in anecdotal evidence, I almost always freeze my coffee -- with great results.

In the more anecdotal evidence column, I too regularly freeze fresh roasted coffee, but have never held anything longer than two months yet. Seems as good as fresh to me.

I typically order 10 lbs of coffee per month (not all for my lone consumption - home, work, friends) from a local roaster. I order 5 lbs around the 1st and another 5 lbs around the 15th. I have been letting the coffee rest a few days before I freeze it, so I am typically freezing it after 3 days rest. The coffee is in individual 1lb bags with one-way valves. I simply tape over the valve, and toss it in the freezer. When I need coffee, I pull the bag out, let it come to room temp, pull the tape off the valve, and start using it right away. Obviously, as often as I am ordering, most coffees are only frozen for 2-3 weeks at most. (I should add that my freezing procedure was inspired by Ken's comments on freezing here some time ago.)

I did stock up on some other roaster's coffees during the HB Holiday promotions. I kept a few pounds of that around as long as two months, and they seemed fine to me. I did make a conscious effort to NOT discuss my experience with these "older" coffees, as I didn't want to consider it exactly identical to fresh, giving the benefit of the doubt to fresh and never frozen coffees.

[Ken Fox]

In the more anecdotal evidence column, I too regularly freeze fresh roasted coffee, but have never held anything longer than two months yet. Seems as good as fresh to me.

I typically order 10 lbs of coffee per month (not all for my lone consumption - home, work, friends) from a local roaster. I order 5 lbs around the 1st and another 5 lbs around the 15th. I have been letting the coffee rest a few days before I freeze it, so I am typically freezing it after 3 days rest. The coffee is in individual 1lb bags with one-way valves. I simply tape over the valve, and toss it in the freezer. When I need coffee, I pull the bag out, let it come to room temp, pull the tape off the valve, and start using it right away. Obviously, as often as I am ordering, most coffees are only frozen for 2-3 weeks at most. (I should add that my freezing procedure was inspired by Ken's comments on freezing here some time ago.)

I did stock up on some other roaster's coffees during the HB Holiday promotions. I kept a few pounds of that around as long as two months, and they seemed fine to me. I did make a conscious effort to NOT discuss my experience with these "older" coffees, as I didn't want to consider it exactly identical to fresh, giving the benefit of the doubt to fresh and never frozen coffees.

Just to add that the part about taping over the valve is something that was suggested to me by Barry Jarrett a few years ago in an alt.coffee thread.

I have quite a few valve bags in inventory, but when I run out of them I'll seek out coffee bags with no valve. The valves add considerable cost to the bag cost and I think they are unnecessary the way I use them. It would be easier to just freeze a non-valve bag, then put a pinprick into the valve when the coffee defrosts. Since I roast for some friends as well as myself, I do go through coffee bags. For my own consumption I use glass jars, but they are not very convenient if you are going to give the coffee to friends and then have to harrang them about getting the glass jars back.

ken

[luca]

So how are people doing this ...

Ken, it looks to me like you freeze immediately after roasting, defrost, then allow a few days to degas. Others seem to allow a few days to degas, freeze, then defrost and use. Is that right?

Cheers,

Luca

[Rainman]

So how are people doing this ...

Ken, it looks to me like you freeze immediately after roasting, defrost, then allow a few days to degas. Others seem to allow a few days to degas, freeze, then defrost and use. Is that right?

Cheers,

Luca

I'm pretty sure he froze them w/o degassing, but I don't remember him commenting on how long they thawed the beans before grinding.. Ken?

Thanks for the great article Ken.

As a side note to anyone interested in anecdotal evidence, I almost always freeze my coffee -- with great results.

While not exactly controlled, the more anecdote we accumulate the bigger the "n", and the better the power of this "study". Just gotta find somebody to keep track!

Ray

[Dogshot]

Great stuff Ken. I can't believe the quality of the work that you and Jim, among others, are able to do on a consistent basis.

So how are people doing this ...

Ken, it looks to me like you freeze immediately after roasting, defrost, then allow a few days to degas. Others seem to allow a few days to degas, freeze, then defrost and use. Is that right?

Cheers,

Luca

These are my thoughts as well. It is a very interesting and enjoyable read, and the question it seems to address is "is using coffee that is frozen 1-2 hours after roasting as good as using fresh coffee that is never frozen?". My suspicion is that very, very few people are in a position to benefit from roasting their coffee (or buying 1-hour old coffee) and freezing it immediately. While this study might convince home roasters to look into 1kg+ roasting units, or at least spring for the 5lb BBQ drum, it does not seem to directly address the question "is using coffee that is frozen 4-5days after roasting as good as using fresh 4-5 day coffee that is never frozen?". My guess is that the vast majority of us are probably more in this situation. Any interest in doing the study again with 4-5 day old coffee?


Mark

[Ken Fox]

So how are people doing this ...

Ken, it looks to me like you freeze immediately after roasting, defrost, then allow a few days to degas. Others seem to allow a few days to degas, freeze, then defrost and use. Is that right?

Cheers,

Luca

For my own consumption I freeze immediately in semi-airtight jars, then when I need coffee I try to remove it maybe 3 days before I need it so it can degas a bit before I use it. Occasionally there is no possibility to wait, such as when I return home from a trip and the only coffee I have is in the freezer. In the latter case I will take the coffee out of the freezer as soon as I get back home, and it will have least overnight to degas a little before I use it. In this situation I am generally returning home from a trip during which I have had no espresso or very little of it, for example one of my trips to France for studying the language or to San Diego to visit family. Just having espresso, even if the beans are "too fresh" is novel after such a trip so I don't even notice it, especially if the espresso is used in a milk drink.

Some others are freezing after a few days' degassing, which is as quick as it is possible for them to do, or by personal choice. There are others, however, like Greg Scace and I believe Jim Schulman and maybe some of the other "larger batch" home roasters (bbq drum, maybe heat gun/dog dish) who do as I do, e.g., freeze immediately.

My guess is that the results are equivalent but this is a hypothesis that could be tested, just I'm not keen on being the person to test it

ken

[Ken Fox]

Great stuff Ken. I can't believe the quality of the work that you and Jim, among others, are able to do on a consistent basis.



These are my thoughts as well. It is a very interesting and enjoyable read, and the question it seems to address is "is using coffee that is frozen 1-2 hours after roasting as good as using fresh coffee that is never frozen?". My suspicion is that very, very few people are in a position to benefit from roasting their coffee (or buying 1-hour old coffee) and freezing it immediately. While this study might convince home roasters to look into 1kg+ roasting units, or at least spring for the 5lb BBQ drum, it does not seem to directly address the question "is using coffee that is frozen 4-5days after roasting as good as using fresh 4-5 day coffee that is never frozen?". My guess is that the vast majority of us are probably more in this situation. Any interest in doing the study again with 4-5 day old coffee?


Mark

probably not. I'm almost certain Jim Schulman, the person I usually do this sort of thing with, would have no interest. For myself, these sorts of studies are very tedious and burn you out quickly. In order to do this right, what you'd want to do would be to compare (1) fresh/never frozen/ degassed to (2) degassed/ frozen/ used immediately to (3) frozen/ degassed coffees, which would mean comparing all three to each other. In the study just published we used fresh/never frozen as a control, and compared it to both 8wk frozen and 4wk frozen; we did not compare the 8wk to the 4wk. Very likely you would need to compare even more than 64 pairs of shots in order to have any likelihood of finding a statistical difference, barring some huge difference among them, which I sincerely doubt would be present. You would need to either have 2 identical machine/grinder setups or you would need to balance that as well.

To me, this is too much of a PITA to warrant the effort for a study whose results I think I could predict in advance, e.g. no significant differences.

ken

[Wescott]

Ken, thank you very much for the exacting work on this topic.

The conclusion is cheering too. We can expect freezing to be a major help in preserving coffee flavor. In your scenario of freezing right after roasting, we can consider it proven unless someone can produce equally rigorous contrary results (not likely). And as you indicate, there is not much a priori reason to expect that freezing will not assist to some degree in many other situations.

It's a major contribution to peace of mind for those who freeze.

[ronpistolero]

Hi. Very interesting and helpful article indeed. This somehow gives me hope regarding "preserving" coffee. After having tried the Black Cat (best aroma and taste to my mind). I asked my brother to send another pound back here in the Philippines. He included a pound of Artigiano from Vancouver. I decided to "glad wrap" it, twice, in its original package without taping the valve, and keep it in the freezer. It was, I believe, 11 days old then. After having enjoyed the Artigiano, I thawed the Black Cat on the 21st day. I pulled a shot and, to my dismay, the aroma was nearly gone. It tasted like ordinary espresso (though not a "sink shot) to me. Could it be that I hadn't sealed it well enough? I haven't measured the temperature of my freezer, but could it be not cold enough? Was it too "old" prior to freezing? Having great tasting coffee is a rarity here in the Philippines so stretching the life of the ones I am able to acquire from abroad is very important to me. Help!

Ron