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Buckley
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Posted Mon Feb 24, 2014, 4:44am
Subject: Re: Another coffee freezing question
 

jpender Said:

It's not hard to fool yourself.

Posted February 23, 2014 link

I do it all the time.

Thank you for the clarification.  I did not want to start down the Lenny-Bruce-slippery-slope...

If you observe condensation on the polyethylene, it just tempts me to rationalize that the specific heat of poly is lower than whole beans.  In truth, I do not know and, I suspect, research documenting the specific heats of food-grade polyethylene and roasted coffee beans is nonexistent or difficult to find.

The beans might (again, I do not know, but your weighing experience may be correct) absorb liquid water that contacts them from the bag surface more readily than adsorb water vapor onto their surface.

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jpender
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jpender
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Posted Mon Feb 24, 2014, 4:28pm
Subject: Re: Another coffee freezing question
 

Buckley Said:

If you observe condensation on the polyethylene, it just tempts me to rationalize that the specific heat of poly is lower than whole beans.  In truth, I do not know and, I suspect, research documenting the specific heats of food-grade polyethylene and roasted coffee beans is nonexistent or difficult to find.

The beans might (again, I do not know, but your weighing experience may be correct) absorb liquid water that contacts them from the bag surface more readily than adsorb water vapor onto their surface.

Posted February 24, 2014 link

The ziplocks are made from LLDPE which has a specific heat of 3.2 J/g-K whereas glass is about 0.8 and coffee (according to Scott Rao) is about 1.7. But I think it's got to be more complicated than just comparing specific heats. I suspect the heat capacity, shape of the object and probably the thermal conductivity influence how quickly the surface of an object rises above the dew point.

Anyway, yesterday I chilled two samples of beans and repeated what I'd tried last year. But this time the weight of each sample did not increase as they warmed up. That surprised me.
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Buckley
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Posted Mon Feb 24, 2014, 6:01pm
Subject: Re: Another coffee freezing question
 

Wow!  Out-geeked.  You belong on H-B, man.  But the shape of the object is also a factor.  Perhaps the thinness of the poly accounts for a relatively fast heat up.  Where did you find the coffee data, because it would depend on what form the specific heat was measured?  Not that important and I am not looking for debate material; just interested.

jpender Said:

Anyway, yesterday I chilled two samples of beans and repeated what I'd tried last year. But this time the weight of each sample did not increase as they warmed up. That surprised me.

Posted February 24, 2014 link

Was there a difference in whether or not the beans were in contact with the ziplok surface between your two trials?

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jpender
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jpender
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Posted Mon Feb 24, 2014, 7:18pm
Subject: Re: Another coffee freezing question
 

Buckley Said:

Where did you find the coffee data, because it would depend on what form the specific heat was measured?

Posted February 24, 2014 link

A member posted this here on CG (he has since deleted his post): "the specific heat capacity of ground coffee is 0.4 that of water (as in Scott Rao's book)".

Buckley Said:

Was there a difference in whether or not the beans were in contact with the ziplok surface between your two trials?

Posted February 24, 2014 link

No. The beans were sealed in plastic in the freezer. Then I transferred them onto a small alumium foil tray. The temperature and humidity were in the same ballpark. The coffee beans were different.

I should elaborate: There was a small gain in weight. The initial weighings fresh out of the freezer were slightly greater than the weights before I put the beans in the freezer. What was different was that when I tried this last year the weight continued to rise for a couple of minutes. That didn't happen this time.
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jpender
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Posted Fri Mar 14, 2014, 4:52pm
Subject: Re: Another coffee freezing question
 

I measured the weight gain due to condensation on freezer-cold beans by cycling between freezer and open air.

I weighed two samples (10g each), sealed them in ziplock bags and put them in the freezer for a minimum of 4 hours. Then I removed them, placed them in an open foil tray for about 2 minutes, reweighed them and then returned them to the freezer for another 4 hours or more. I repeated this cycle 5 times. On average, each exposure increased the weight by a little over 0.1% and the total weight gain after the 5 exposures was 0.6%. As a check I oven dried these two samples along with two others that had not gone through the freeze/warm cycles and the difference in their dried weights was 0.5% of their initial weights (2.9% vs 2.4%).

This suggests that repeatedly removing a container of beans from the freezer, opening it and then returning it to the freezer could lead to a large accumulation of moisture.
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jpender
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Posted Fri Mar 14, 2014, 4:55pm
Subject: Re: Another coffee freezing question
 

To test whether the moisture really accumulates I split a 12oz bag of coffee (5 days post roast) in half. The first half I measured out 20g doses and sealed them in individual ziplock bags. The other half I sealed as one single 6oz group of beans. Each brew session I removed one of the individually sealed bags and also opened the larger bag and measured out a dose, thus exposing the contents of that bag to the warm, moist air before returning it to the freezer. There were 7 brew sessions over a period of two weeks. I compared the coffees blind and could not perceive a consistent taste preference. At the end I ground and oven dried two samples of each (individual bagged and group bag). The grouped beans had a dried weight loss of only 0.1% more than the individually packaged beans (2.8% vs 2.7%).

So the moisture weight gain did not accumulate. A possible explanation is that the beans on top that were most exposed to the warm, moist air were also the next to be removed from the bag. And the beans that were in the bag longer were protected to some degree by being under other beans. More important to me was that I couldn't tell the two groups of beans apart by taste, although admittedly two weeks isn't very long.

I know this is far from conclusive but thought it was worth sharing.
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Buckley
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Posted Fri Mar 14, 2014, 5:04pm
Subject: Re: Another coffee freezing question
 

Your investigation really deserves its own post because it answers a fundamental question that gets asked on tihs forum every two months. I, for one, wouldn't mind if you cross-posted your last post (or last two posts combined) under some easy to search-for title like "Returning beans to the Freezer Does Not Kill Them" :) or something more straightfaced. :|.  Thanks for your time and attention to detail.
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jpender
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Posted Mon Mar 17, 2014, 12:55pm
Subject: Re: Another coffee freezing question
 

Buckley Said:

Your investigation really deserves its own post because it answers a fundamental question that gets asked on tihs forum every two months.

Posted March 14, 2014 link

One coffee, one set of environmental conditions, one person tasting, one run. It's not enough to make a broad statement. Besides I could have screwed up somehow. Or maybe there's another explanation, e.g. CO2 loss balanced the moisture gain so it looked like zero. It's just a starting point, assuming anybody is interested.
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jpender
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jpender
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Posted Tue Apr 1, 2014, 8:56am
Subject: Re: Another coffee freezing question
 

I brewed a cup from the last of the "group bag" beans this morning. I had been taking that bag of beans out of the freezer, opening it, weighing out some beans, and then returning it to the freezer. I had done this eight times over a period of two weeks. Now, one month after putting it in the freezer (36 days post-roast) I measured out the final dose from that bag. Upon brewing it seemed that the bloom was a little less than I remembered. But the coffee was as delicious as ever.

Since that little experiment I had since bought another bag of the same coffee (Four Barrel Ethiopia Hunda Oli) and had been struggling with it, changing grind and temperature, never really getting a great cup. And then this 5 week old coffee, a month in the freezer, repeatedly exposed while freezer-cold to warm, moist air, and it comes out tasting fabulous.
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Buckley
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Posted Wed Apr 2, 2014, 5:37am
Subject: Re: Another coffee freezing question
 

It becomes increasingly obvious that, collectively, we CGs obsess about differences that do not make a difference.  For my part, Greenway's Daterra Sweet roast just arrived, so I jettisoned my unused Ceremony Daterra back into the freezer in a half-filled glass jar.  No problem.
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