Thoughts on off-gassing technique?
Posted Mar 21, 2015, 10:15 PM UTC
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Maybe start off with the beer homebrewer's motto: Relax, don't worry, and have a homebrew.
I suspect that this whole discussion should be considered "theoretical," not because there aren't observable data, but because home roasters should, in theory, finish drinking the coffee before light or staling factors set in.
For practical purposes, if you are storing a quantity of coffee, all the evidence I've read has said "light is bad, oxygen is bad, building co2 pressure is bad." If you're talking about a lb of home roast, it is going to be gone before anything but full open air storage is going to hurt it. And if you haven't done actual tests... I haven't... evilbadro has a point.
Because it seems interesting, I will try a series of non-scientific experiments with storage over the next couple of weeks.
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I had the idea of cutting the one way valve from a bag of coffee I just finished and using it as the lid on a mason jar. I'm guessing it should work but has anyone tried this before? I plan on switching over to the metal mason jar lid after 12-24 hours once the initial de-gassing phase is over. Thoughts???
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Well, you could keep using that one-way valve if you wanted to. It's not going to let any air in, much like the seal of the metal lid, but it also allows for any off-gassing that happens to push any remaining O2 out through the valve as the jar fills up.
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Unless you are having problems with a particular bean, this should not be necessary. The coffee will last longer if you just put it in airtight jars immediately after roasting. You can tweak the rest period for espresso a bit by sealing or not sealing the jar immediately. The point of this being that espresso works best in a window of more or less 7-10 days. If you don't want to wait 7 days, you may get better results on day 5 by letting the beans off gas more before sealing them. On the other hand if you don't think you will use all the beans by day 10 you may get better results on day 11 or 12 by sealing the beans immediately after roasting.
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I just crack my jar once a day!
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I'd really be more worried about the non-opaque container. Light will damage your coffee just as much as air.
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Never thought about that. I've moved them to the cupboard! Thanks for the heads up.
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I agree here, the three things you want to keep your coffee as fresh as possible is a dark, dry place and limit the air to the beans.
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Light will damage your coffee just as much as air.
No, over the length of time before skillfully roasted coffee goes stale (about three weeks) light does nothing. Green coffee should not be exposed to light because over months it will degrade but it is not a concern for roasted coffee.
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And he has a jar of green coffee sitting next to a window. I don't see your point.
e: Also, light is heat, heat damages coffee, therefore light damages coffee.
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My point is very simple. Light isn't going to do anything to coffee over a month green or roasted. Don't store green coffee in clear plastic bags for six months and expect the coffee to be as good as if you had stored it in those bags inside a dark bin. Light is not heat. Direct sun might heat things up but roasted beans don't need to be obsessively stored in the dark.
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Read the scaa staling report. Opaque containers retain freshness an order of magnitude longer than those with a window.
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Light is bad for both green and roasted. It's the main trigger of oxidation, especially in dark roasted arabica. In the case of green bean, light will heat up the bean during the day (causing moisture evaporation), and then it cools at night (causing evaporation). Bad.
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Light is not the main trigger for oxidation. The partial pressure of oxygen in the container is the main factor for oxidation. In an airtight container off gassing of CO2 lowers the partial pressure of oxygen, retarding oxidation. As I said earlier, I am not advocating leaving beans in direct sunlight, but in a normal room with a clear jar it is preposterous to suggest that ambient light will have any influence on temp. Furthermore typical diurnal temperature variations will not cause any moisture issues at all inside a sealed jar.
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You're saying that pressure causes oxidation? This doesn't sound right to me. According to this man, "light catalyses the main trigger for auto-oxidation reaction." Do you have anything to back up your statement about ambient light? I'd be interested in seeing it because packaging requirements for coffee dictate light proof containers.
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Is this really necessary? Maybe I'm not roasting right, but I barely get much gas when opening my tightly sealed ball jar after 24 hrs.
Edit: I typically shoot for a light city roast.
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I'm not sure, really. I'm pretty new to roasting (finished my 4th roast today) but when I haven't been home to open the jar every now and then, I get a pretty noticeable pressure build-up which I can only assume slows the off-gassing process.
My roasts so far have been closer to FC/FC+ so I'm not sure if that makes a difference. I still have a lot to learn hence why I was asking for people's take on this.
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Interesting, thanks for the reply. Perhaps if I waited 3+ days after roast to first open, I might hear that "woosh" from the pressure buildup, but I almost never can wait beyond 24-36 hrs.
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I roast to a City/City+, and I crack my jars twice a day for the first three days. The gas is noticeable every time.
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i'm sure it matters to some extent but for home roasters with small batches i think it's got to be pretty far down the line in priorities. just keep them in simething air tight in the cupboard and dont worry about it
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So I'm guessing the pressure buildup is dependent on the amount roasted vs available space in its storing container? I roasted 90g and place them in an 8oz ball jar and rarely get the "woosh". I think it did happen though when I went 5+ days before opening once.
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yeah im just using jelly jars and 95 to 100 grams the WHOOSH is more like "pfft" . like i said I'm sure it matters but your roasting process is going to be what really matters
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I've done the same. My main concern was the foil crinkling and folding all weird allowing for gaps for outside air to get in.
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The amount of CO2 formed depends on how deep you roast. It can get as high as 1-2% of the roasted bean weight. Releasing it minimizes aroma loss and oxidation. Most of it's released within the first few hours after you roast, and then it slows, but continues for a few weeks. Valve bags are popular but glass has a better barrier, and I only work with small batches that are cupped within 2-3 days. So, I let them breath for an hour or two after roast, and then store in small glass swing-top jars, right up to the top. The lid pops right off from pressure inside. The CO2 is only released if it has the headspace, otherwise it remains inside the bean's cell walls.
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To clarify, the CO2 is not staying within the bean's cell walls. If it were, no pressure would develop and there would be no pop or whoosh upon opening the jar. Reducing the headspace does mean that more oxygen is displaced by beans when the jar is first sealed. Less oxygen and more beans to release CO2 means a lower partial pressure of oxygen within a sealed jar as CO2 is released. Because the concentration (partial pressure) of oxygen is the most significant factor in staling, reducing headspace will mean longer shelf life. Incidentally, sealing the beans up immediately after roasting will also extend shelf life as all the CO2 off gassing in the initial few hours will also contribute to reducing the partial pressure of oxygen in a sealed jar.
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The CO2 generated during the roast is trapped inside the bean cells because it's released only when the internal pressure is lower than external. When a barrier is used, like a sealed glass container, the external pressure eventually becomes higher than the internal, and CO2 is no longer released, with some of it still trapped in the cells. This is also true for the other volatiles, including some aromatics, which is a surely a good thing to have retained until grind.
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You can use the old bag and re-seal it with an iron... Trick is to cut as little as possible each time to maximize usage.
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For small quantities, such as produced by home roasting, there is essentially no concern with off-gassing. I've put 6oz of just roasted beans into a tightly sealed ziploc bag, and 4 days later, there is not even a hint of pressure in the bag.
Ziplock are hardly airtight though. Not sure if this is the best example.
I agree that I wouldn't trust a ziploc bag to be airtight for some critical purpose. But to demonstrate coffee bean off gassing, we only need to witness a "hint of pressure", and I believe that a ziploc bag is capable of this job. Demonstration.
your ziplock are clearly better than mine!
That could very well be. I use 4-mil Uline industrial poly bags. ;)