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Jasonscheltus
Post subject: storage: freshly better understood.  PostPosted: Oct 12, 2009 - 10:36 AM



Joined: Feb 10, 2008
Posts: 363

So I've never understood why coffee stored in a one-way-valve bag acts so differently to coffee stored in a tin-tie bag once opened.

I've experienced huge variation between the two. Basically concluding that once a one-way-valve bag is opened, the coffee inside will stale quicker than coffee store either in a tin-tie (no valve and not sealed) or in a Monmouth crate.

And I'm pleased to say now I know why. (This might not be new to y'all).

CO2 diffuses from the roasted coffee bean because of the pressure difference between the inside of the bean and the atmosphere. From Illy, that the roasted bean will release CO2 until the pressure is the same on the inside of the bean and the outside.

What I hadn't thought of, was that the one-way-valve will release gas only at a certain pressure i.e. it will take a certain pressure to force gas from the bag, through the one-way-valve. This means that the beans inside the bag are at equilibrium at 1.3 ATM or 1.2 or whatever, but NOT atmospheric pressure.

So once the beans are exposed to the actual atmospheric pressure (1atm) there is still a pressure difference and CO2 is expelled out at a greater rate than beans that have been adjusting at the "real" atmospheric rate.

Happy for y'all to call bullshit on this. Just an idea, and I really would like you to let me know what you think.

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JulieJayneOffline
Post subject: Re: storage: freshly better understood.  PostPosted: Oct 12, 2009 - 08:35 PM



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Jasonscheltus wrote:
...What I hadn't thought of, was that the one-way-valve will release gas only at a certain pressure i.e. it will take a certain pressure to force gas from the bag, through the one-way-valve. This means that the beans inside the bag are at equilibrium at 1.3 ATM or 1.2 or whatever, but NOT atmospheric pressure.
Yes, but I suspect that the pressure is much higher than expected. For that reason, we seal but don't use a valve, and reccommend that coffee is consumed within a week.

But what you suggest does make sense. Sealed, stored coffee will stale faster, than unsealed stored coffee. But the unsealed coffee is already much staler.

The only good advice is to drink coffee, not to store it.

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brucebOffline
Post subject: Re: storage: freshly better understood.  PostPosted: Oct 12, 2009 - 09:07 PM



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JulieJayne wrote:
The only good advice is to drink coffee, not to store it.


Exactly! I roast 400g batches, which gives me about 320g roasted coffee which I dump into the grinder(s). I use between 50 and 60g per day so they last 5-6 days. I don't worry about light, air, temperature because they remain fresh for 6 days and then at the latest they are gone. I try to roast 2 days ahead of the time the previous batch is going to run out. Easy days!

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EspressoSquirrelOffline
Post subject: RE: Re: storage: freshly better understood.  PostPosted: Oct 12, 2009 - 09:22 PM



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maybe i missed something, but i don't think the lack C02 is what makes beans taste stale, the removal of C02 is important, thats why we don't have beans straight after roasting (if you can wait)
the valve bags release the C02 on purpose, the aim is to have as little in contact with the beans as possible, the closest you can get to a vacuum

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Jasonscheltus
Post subject: Re: storage: freshly better understood.  PostPosted: Oct 13, 2009 - 09:42 PM



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JulieJayne wrote:
Jasonscheltus wrote:
...What I hadn't thought of, was that the one-way-valve will release gas only at a certain pressure i.e. it will take a certain pressure to force gas from the bag, through the one-way-valve. This means that the beans inside the bag are at equilibrium at 1.3 ATM or 1.2 or whatever, but NOT atmospheric pressure.
Yes, but I suspect that the pressure is much higher than expected. For that reason, we seal but don't use a valve, and reccommend that coffee is consumed within a week.


Surely that means the pressure inside the bag would be even greater than if it did have a valve, increasing the rate at which CO2 is expelled from the bean once the bag is opened?

I'm saying "CO2 expelling from bean" instead of "staling" because I think staling is a combination of loss of CO2, oxidation, UV treatment and heat treatment etc. etc. Staling is pretty complicated.

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JulieJayneOffline
Post subject: Re: RE: Re: storage: freshly better understood.  PostPosted: Oct 13, 2009 - 11:02 PM



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EspressoSquirrel wrote:
maybe i missed something, but i don't think the lack C02 is what makes beans taste stale, the removal of C02 is important, thats why we don't have beans straight after roasting (if you can wait)
the valve bags release the C02 on purpose, the aim is to have as little in contact with the beans as possible, the closest you can get to a vacuum
Valve bags... do not release the CO2. Unless you purposely squeeze the bag. Fresh roasted coffee can sit in a sealed valve bag for a week or more before the valve opens. Depending on roast level, volume in the bag etc.

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brucebOffline
Post subject: RE: Re: RE: Re: storage: freshly better understood.  PostPosted: Oct 14, 2009 - 06:01 AM



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We can do nothing but postpone the inevitable and we can only postpone it for a short time.

The staling process is not caused directly by loss of CO2, but it is accompanied by it. Beans start to degenerate or stale the moment they are roasted. For espresso, as we all know, the large part of the CO2 generated by roasting must be allowed to escape before use. What happens after that is just degradation. Bags with or without valves, cans, freezers, nitrogen gas, argon gas, etc. can do nothing but slow the process down for a few days.

If there was a way to stop staling the coffee industry would be using it. The coffee industry knows the secret. They know that they are selling stale coffee, but they also know there is no satisfactory way to stop the staling process and they know that the majority of coffee drinkers don't know what fresh coffee even tastes like. They know that people want to buy a can or a bag, preferably of pre-ground coffee and use it as they need it. They cannot be bothered with trying to obtain fresh coffee.

Staling is the result of a series of events, but in the end is irreversible and cannot be stopped. Oxygen (or air) and higher temperatures can accelerate the process, but there is nothing that can completely stop it. Even cryogenic temperatures won't help because the process immediately takes place upon thawing. The sugars, oils and acids in the beans undergo autocatalytic reactions that will occur no matter what you do to try to stop them. Roasted coffee is not a storable consumable. Trying to store it is like trying to store fruits and vegetables. You can get away with it for a short time, but no matter what you do they will lose flavour and go bad.

Here is a useful writeup on this subject, not from the chemist's viewpoint, but more from that of the coffee drinker.

Edit: Corrected lost text and added link.

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Jasonscheltus
Post subject: RE: Re: RE: Re: storage: freshly better understood.  PostPosted: Oct 14, 2009 - 09:19 PM



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bruce, what about canned tomatoes?

seriously though - I'm not trying to work out how to sell stale coffee. I'm just trying to understand the way it behaves. You say it doesn't work, I'm interested in why it doesn't work.

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brucebOffline
Post subject: RE: Re: RE: Re: storage: freshly better understood.  PostPosted: Oct 14, 2009 - 09:54 PM



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It's not a secret. I'm just not good at explaining it. The chemical processes that cause staling are inexorable and irreversible. That's not at all unusual in organic or biochemistry. There are many processes that march forward no matter what you do to try to stop them. Try to make an insalate caprese out of canned tomatoes. Even if you use fresh mozzarella di bufala it won't taste like a salad of fresh tomatoes.

Tom (of SM) says that the valve in the bag lets the CO2 force the air out of the bag. He says that is a big advantage for storing beans. In my experience the advantage is minimal. Staling is not just caused by the presence of air, although the air accelerates the process. No matter what container, no matter what temperature, no matter what gas surrounds the beans, after 14 days at the latest they are stale. With higher temperatures, sunlight and unlimited access of air they will be stale some days sooner.

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I just bought a 65 pound bag of Yirgacheffe. I'm working on my tenth cup today. Wooooooooooooooo
 
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crphillipsOffline
Post subject: RE: Re: RE: Re: storage: freshly better understood.  PostPosted: Oct 24, 2009 - 09:04 AM



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What do people reckon to storing beans in a pressurized vessle.......what effect do you reckon this would have on how long you can keep them fresh? Better or worse than a vaccuum?

I personally roast enough to last 3-4 days.....i chuck them in the hopper and use them and then roast some more......i've got my roasting down to a fine art now where i know exactly what time and temp for which beans. It's amazing the difference it makes if you roast the bean that little bit too dark or too light......an extra minute in the roaster can make the difference between a good shot and an excellent shot.

My advice.......drink it....don't store it:-)

By the way......just about to place an order with Bella Barista for some green beans......can anyone recommend and good coffees to go for?

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