Discordance In Vacuum Sealing for Coffee Storage

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thevitruvianman
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#1: Post by thevitruvianman »

Hi HBs

It seems that a lot of people seal their beans in vacuum containers to extend shelf life. My understanding of science, would disagree with this method along with CO2 release valves on bags (except to avoid explosion during shipping). We know beans need degassing to prevent volatile extractions and decrease the bicarbonate concentration which lowers the pH during extraction making an acidic shot. However, once beans have reached an appropriate level of degassing, I would think they should be stored in CO2 pressurized containers in the cold. Vacuum sealing, via Le Chatlier's principle, will increase the forward degassing reaction past the desired state, while pressurized CO2 would, in the right pressure and concentration, theoretically stop the degassing reaction (such a high concentration of reactants will make the reverse reaction occur at the same rate ad the forward reaction). Additionally vacuum sealing would, by the same principle, speed up the loss of volatile aromas that are reacting and releasing into the air. I understand wanting to avoid oxygen, but if that's the primary reason for vacuum sealing, pressurized CO2 would also prevent such exposure and seemingly prevent other reactions that take away from the freshness. What do you all think?

Jake
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HB
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#2: Post by HB »

I haven't read it in its entirety, but Vacuum storage harmful? poses many of the same question/concerns. That said:
thevitruvianman wrote:It seems that a lot of people seal their beans in vacuum containers to extend shelf life.
Really? I thought most people who frequent this site store coffee in the freezer in Mason jars filled to the top. Ken Fox's Coffee: To Freeze or Not to Freeze goes over this method in ridiculous detail.
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DaveC
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#3: Post by DaveC »

thevitruvianman wrote:Additionally vacuum sealing would, by the same principle, speed up the loss of volatile aromas that are reacting and releasing into the air. I understand wanting to avoid oxygen, but if that's the primary reason for vacuum sealing, pressurized CO2 would also prevent such exposure and seemingly prevent other reactions that take away from the freshness. What do you all think?

Jake
I completely agree. After extensive testing packing coffee in reduced pressure does not give optimal results. By definition any ridgid container from which the air is removed reduces pressure. I found the important thing was to remove as much of the air as possible, but without any pressure reduction e.g. a flexible bag with a valve. If I use one of these I remove air, but ensure the bag is still flexible, not a hard brick.

My preferred method nowadays is to pack coffee into a ziploc PTE pouch bag with a 1 way valve as soon as it's cooled. I expel as much air as possible and finalise the seal closure on the ziplock...then heat seal the bag. The later CO2 production and 1 way valve do a great job of eliminating any Oxygen that remains.

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aecletec
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#4: Post by aecletec »

I agree in principle and have found argon works well. Pressurised C02 is of interest to me also (we have had threads on this) but in practice vacuum sealing in a rigid container works well by reducing oxidation - not as well as argon.

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thevitruvianman (original poster)
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#5: Post by thevitruvianman (original poster) »

HB wrote:I haven't read it in its entirety, but Vacuum storage harmful? poses many of the same question/concerns.
I don't know how I missed that thread when I searched. Sorry about the redundancy. I guess I got caught up searching for bean storage containers with such features. I'm surprised inert gases have so much support. That helps with the pressure problem but you're still purging the degassing products from the container increasing the rate of reaction. I would hypothesize that longevity would be highest if you seal the roast ASAP (without the risk of bursting) and once the gas has purged the atmospheric oxygen out of the container as the pressure that would remain is all of the complex reaction products. It makes me think of homebrewing beer and having CO2 bubble out the water airlock on the carboy pushing oxygen out and preventing any more from entering. I wonder if a comparable jar size could be constructed for coffee beans. Hmmm
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Peppersass
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#6: Post by Peppersass »

I've been freezing freshly roasted coffee for over five years. About four months ago I started vacuum sealing and freezing beans. I use a chamber vacuum sealer. Some of the coffee has been vacuum sealed in plastic bags and some in mason jars.

So far, I've not found any degradation in flavor due to vacuum sealing. I haven't been doing it long enough to be sure, but in one case beans that had been vacuum sealed and frozen for over six weeks were perfectly fine, while prior to vacuum sealing I found that flavors begin to degrade after about four weeks in the freezer.

Perhaps more significantly, crema production does not appear to be compromised, which indicates there's still CO2 in the beans.

Further, when I vacuum seal in a plastic bag, the bag collapses tightly around the beans. It stays that way for about four weeks, and then the bag starts expanding. No doubt, this is CO2 degassing from the beans. After a couple of weeks there's a significant amount of CO2 in the bag. My conclusion is that freezing retards degassing but doesn't prevent it. I also conclude that the act of vacuum sealing isn't sucking the CO2 out of the beans, or at least not a substantial amount of it.

That's my experience, FWIW.

The theory that putting the beans in a vacuum will suck all the CO2 out assumes that the gas can freely diffuse out of the beans, and the only thing slowing it down is ambient air pressure. That seems unlikely to me. I would think the CO2 could easily mix with the ambient air if there's no resistance preventing it from doing so. Isn't it possible that the CO2 formed during roasting is trapped inside cell walls or other membrane-enclosed spaces that resist rapid diffusion, and that it takes time for those membranes to break down and let the gas out?

Further, I question whether volatile aromatics that would get sucked away by a vacuum sealer make it into the cup anyway. Anything that would get sucked away by the vacuum probably dissipates very rapidly after grinding. That's why we need hot water to release aromatic compounds.

Finally, it's not clear whether there's any relationship between loss of CO2 and staling or loss of flavor, other than both taking place over time.

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thevitruvianman (original poster)
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#7: Post by thevitruvianman (original poster) »

So with my university membership, I have access to a lot of scientific journals, and for the first time I started looking up coffee roasting and kinetics ones instead of my typical genetics searches for my research. From what I had read, it seems like my original thoughts of a reaction taking place are wrong except for the oxidizing reaction of oxygen molecules making the beans stale. So previous threads relating to Le Chatlier's principle are irrelevant. But we can all agree oxygen is bad and removing it prolongs freshness. So what we are concerned with is the diffusion of CO2 produced in the pyrolysis reaction (fancy for heat breakdown of sugars) though once the beans are cooled the reaction stops and we are left with micro and macro pores in the bean holding concentrated CO2 and essential aromatic compounds. I'd like to discuss the three storing methods using a simplified analogy:

Imagine one of these pores is a large room with small, high up windows and the concentrated CO2 is a supply of 100 baseballs. Now the room is filled with people that are trying to throw these baseballs out the windows which is a fairly difficult task. The peak freshness would be when there are say 75 baseballs in the room, but the people in the room will keep throwing them regardless of the supply left. Additionally there are people outside the building that will try to throw whatever is around them back into the building. Now consider some storing methods:

Just freezing: the bean pores would contract and CO2 would move slower, so in our analogy the windows are smaller and the people move slower, so the people won't be able to throw the baseballs out as quickly. As pressure increases, there are more people to throw things on the outside of the room. And lets say oxygen molecules left in the container are water balloons that the outside people have and can throw into the room making things gross.

Vacuum Sealing: There are no people to throw anything on the outside of the room, so we don't get any nasty water balloons. However, without people to throw baseballs back into the room, the supply will still diminish. Though as pressure increased when the bag started to fill back up, some people would then be outside and able to start throwing baseballs back in again.

Pressurized inert gas: There are many people outside the building throwing wiffle balls into the room. Their presence does not matter in the room and there are so many people throwing so many of them that they often collide with the baseballs being thrown out and knock them back inside. But over enough time, baseballs will still escape the building past the desired 75.

Pressurized CO2: There are just as many people as the inert gas but they are also equipped with baseballs. This setup would maintain the inside baseball content much longer than the other methods. Especially when combined with the cold.

With these thoughts, I would still think that pressurized CO2 is the best solution. And the thought occurred to me that dry ice is readily available in grocery stores, so I would venture to say the best storing method would be putting a chunk in the jar with the beans you're going to freeze and leave the lid loose. Once the chunk has sublimated (and pushed out the atmosphere/oxygen) seal the container. This could be dangerous depending on how much pressure builds up, but as long as the container doesn't explode, I would venture to say this could be the best method. But this is all in theory.
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JohnB.
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#8: Post by JohnB. »

I've been vacuum sealing & freezing (-10°F) my roasted coffee for 7 years now with excellent results. I've only had the issue with the bags expanding that Dick mentioned happen a few times but maybe that's due to the temperature of my freezer. I've removed bags that had been left in the freezer for 6 months or more that were still tightly sealed around the beans. Left on the counter for an hour the bags expanded (beans degassing?) & the beans produced normal crema & nice shots using a normal grind setting.
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