Freeze/Thaw, Freeze/Thaw, Freeze/Thaw Greens?

Discuss roast levels and profiles for espresso, equipment for roasting coffee.
GDM528
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#1: Post by GDM528 »

Has anyone tried multiple freeze/thaw cycles of the same batch of greens, and noticed any negative effects?

In particular I'm thinking about the expansion/contraction of the water trapped in the bean structure, but perhaps the percentage is low enough and uniformly distributed enough such that the beans don't start fracturing from the thermal cycling. In retrospect I should have subdivided the original bag - but that would require a time machine. Is vacuum sealing and refrigerating a decent alternative?

Marcelnl
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#2: Post by Marcelnl »

cant you just take out enough for a roast and leave the rest frozen, like with frozen peas? (I never froze greens, freezer is always far too full with other stuff)
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GDM528 (original poster)
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#3: Post by GDM528 (original poster) replying to Marcelnl »

In my particular case, I already pulled a vacuum-sealed bag of greens out of the freezer, carefully thawed them (to minimize condensation issues), and now a couple weeks later, wish I had pulled a different bag. Ooops. I'd like to put them back, but I'm concerned they might disintegrate from the thermal cycling.

Re: freezer space, I hear ya. I had to reduce my food storage to make room for my greens. Priorities.

Jonk
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#4: Post by Jonk »

I don't freeze greens for the same reason, not enough space. But I've often wish that I did, because sometimes wonderful greens can taste mediocre after 6 months in room temperature. Sometimes there's barely any difference even after a year or more, but that's a best case scenario.

My hunch would be that if thermal cycling was an issue perhaps freezing wouldn't be a good idea to begin with, but plenty of roasters do and report good results. Also, if there is any change it doesn't have to be a bad one: I have tried a bunch of experiment rehydrating greens 1:1 with water or other liquids and drying again. There's a drastic change even with pure water, but usually flavor has been improved even though cell structure / chaff and distribution of moisture all take a hit.

Trjelenc
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#5: Post by Trjelenc »

At work we have a thermal shock chamber that can run cycles in excess of -50C to over 140C. It would be a fun experiment to temp cycle green coffee from something like -20C to 25C for a few dozen cycles and see if there's a detectable taste difference

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Brewzologist
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#6: Post by Brewzologist »

I store my greens vacuumed sealed in aluminized bags in deep freezer where there is no defrost cycling, and they last years with no degradation. But, in a frost-free freezer I don't think they'd last as long due to defrost cycling. I used to freeze liquid beer yeast in glycerin in a frost-free freezer and it wouldn't last unless l kept the yeast inside a cooler within the freezer to shelter it from the defrost cycle. I'd expect greens would degrade over time as well, but not as fast as yeast.

Regardless of your freezer type, if you have a larger bag frozen now you'd like to subdivide, I'd just get everything ready and do it quickly and refreeze. To me that's prefereable than to keep opening one big bag multiple times. I wouldn't keep them in the fridge unless you will go thru them quickly.

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JohnB.
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#7: Post by JohnB. »

Brewzologist wrote:I store my greens vacuumed sealed in aluminized bags in deep freezer where there is no defrost cycling, and they last years with no degradation. But, in a frost-free freezer I don't think they'd last as long due to defrost cycling. I used to freeze liquid beer yeast in glycerin in a frost-free freezer and it wouldn't last unless l kept the yeast inside a cooler within the freezer to shelter it from the defrost cycle. I'd expect greens would degrade over time as well, but not as fast as yeast..
I've stored all my greens vacuum sealed in a frost free storage freezer since 2008 with no issues yet. I've roasted greens that had been in the freezer for over 10 years. The greens still smelled like fresh greens when I opened the bag, roasted normally & the coffee was great. Temps will rise some in the food compartment during a defrost cycle but the actual defrosting takes place on the coils which are outside the compartment.
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GDM528 (original poster)
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#8: Post by GDM528 (original poster) »

Taking over-thinking and over-analysis to the next level, so you don't have to (unless you want to):

Took a bag of vacuum-sealed greens out of the freezer and let them return to room temperature over 24 hours while still sealed. Then took a small quantity of the once-frozen greens and vacuum-sealed them again. I then froze, thawed, froze, thawed an additional seven times, to compare with the same greens treated in a saner manner (sealed bag at room temperature).

Each type was roasted with the exact same thermal profile. Batch sizes were matched, and the post-roast weight loss was measured:

Frozen/thawed once: 14.4% weight loss
Frozen/thawed 8x: 14.1% weight loss

The difference is within the measurement error, so I'm calling it the same weight loss.

No difference in the physical integrity of the post-roast beans, both ground up the same and the flow resistance for the shots was the same.

Post-roast whole-bean exterior color was indistinguishable, but after grinding there was a very tiny difference, with the 8x freeze/thaw being just a tiny bit darker:



Perhaps someone with a color analyzer can hold it up to the photo and measure the difference ;)

Tasted espresso shots with each sample:
The sample that was frozen/thawed 8x was slightly more acidic/brighter, with a bit more complexity than the 1x freeze/thaw sample - not what I would have expected when a roast goes darker. However, my impression is this did near-nothing to alter the overall characteristics of this blend of Brazilian greens. Not demonstrably worse or better, especially weighed against the hassle and dubious sanity of repeated freeze/thaw cycles.

This was a good opportunity to try out my prototype roasting gas analyzer (Humidity sensor on exhaust - other gas sensors ?), to see if there was any measurable difference during the roast:



Bean temperature curves completely overlapped between the runs. Volatile gasses (TVOC and "equivalent" CO2) readings were also essentially the same, given my previous repeatability measurements. There was a statistically significant difference in the moisture release readings, however. The moisture curve of the sample that was frozen/thawed 8x was less abrupt and reached a higher peak value for a total area-under-curve that was 7% higher than the 1x freeze/thaw sample. So, perhaps there's a link between roast color and total moisture release, even when the thermal profiles are identical.

My key observations:
1) Repeatedly freezing and thawing greens will subtly mess with how they subsequently roast. Not necessarily worse or better. I'm still gonna freeze greens for long-term storage, as those benefits are well established.
2) Roasting gas (moisture) analysis was able to identify a difference during the roast that bean temperature and weight loss couldn't detect, and I would have been more at a loss to understand/explain the difference in color and taste.

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JohnB.
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#9: Post by JohnB. »

I vacuum seal my greens in 1 lb batches before freezing. Frozen once/thawed once no matter how old they are.
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mkane
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#10: Post by mkane »

^^^same here but smaller batches. I've also quit buying some much.