Why I stopped packaging our coffee in one-way valves

19/9/14 Nota Bene. This post was relevant to particular style of coffee (light to medium), roasted on a drum roaster (Diedrich IR5). Our current roaster (Loring Merlin) roasting a similar style of coffee leads some coffees – especially natural-processed coffees – to swell the bags up and occasionally burst. We currently cut open and vacpack these coffee bags again a couple of days after roasting. This is only the case for 1kg bags. 250g bags are not affected. We shall be ordering 1kg bags with valves in the future.


Yesterday I decided to do away with one-way valves on our roasted coffee bags when packing with a vacuum. It’s been something that I’ve been testing for many years now and time again I’ve come to the conclusion that they really don’t make that much difference to the coffee. Indeed, too often they provide an access point for oxygen to enter the bag and degrade the coffee.

Good for sniffing the beans, letting out aromas and bugger all else.

One-way valves are supposed to let CO2 gas out of the bag while preventing O2 getting into the bag. Oxygen is the main culprit behind the staling of coffee and packaging is an attempt to extend the vitality of the beans.

Coffee is supposed to de-gas (aka out-gas) after roasting. This gas is mostly CO2 and the amount claimed in Espresso Coffee: the science of quality – edited by Andrea Illy – is up to 10L of CO2 per kg of roasted coffee. If this were the case, fresh roasted coffee that is immediately packaged (best practice to minimise oxidation) would explode the bag unless there were a gas release valve.

One of the problems with the valves, even when working correctly, is that while they let out CO2, they also let out volatile aromatics. The claim in Espresso Coffee is that it’s a direct correlation: lose 50% of the CO2 and you lose 50% of the volatiles. And we at the more discerning end of the spectrum love our volatile aromatics. However, if this prevents bags exploding in the back of the car while negotiating midday traffic, it is an unfortunate, but fair trade off.

But I’ve never had a bag explode. I have read of roasters who have and this has kept me wary of doing away with the one-way valves before proper testing. However, we have roasted and packaged hundreds of thousands of kilograms of coffee. Sometimes the valves have been faulty and not allowed gas out. In the UK, these bags usually puff up, but haven’t exploded. In Malaysia, we use a vacuum sealer and quite often the one-way valves have not prevented gas entering the bags. The leak is audible. And it is in Malaysia that I’ve decided to do away with the valves. I also contend that, although CO2 is a by-product of the roasting process, there is no 10L CO2/kg roasted coffee released. Rather, I suggest that sealing the bags without using a vacuum results in trapped oxygen that reacts with carbon compounds within the beans producing CO2 gas. Ie 1kg of roasted coffee may produce 10L of CO2 gas if exposed to oxygen, but this amount of CO2 is not within the beans.

There is a theory that vacuum packing is not really necessary as if 10L of CO2 is produced, a kilogram of coffee packed right after roasting will push out most, if not all, oxygen through the de-gassing valve. This presumes that there is indeed 10L of CO2 hiding within the cells of the coffee. If it is in fact the oxidisation of carbon compounds that produces the majority of the CO2, then one is better of using a vacuum packer to remove as much of the air as possible without damaging the beans. The bags I’ve packed with a vacuum packer only puff up if the valve is faulty. Bags without valves puff up a little.

Part of the reason that I took so long to make this decision is that medium roasted coffee when put through an espresso machine while too fresh has voluminous, albeit short-lived, crema and it is difficult to get a good balanced brew. Indeed the taste can be quite carbonated. Presumably the extreme crema is a result of excess CO2 and the coffee needs to de-gas (we usually wait at least a week) before going through the espresso machine. However, if I take a bag without a one-way valve and vacuum-pack it the beans seems to go through exactly the same process of settling down. Perhaps there is some CO2 within the beans that needs to escape. But nowhere near enough to warrant using fault-prone valves. In fact, I’ve found that the beans taste better when vacuum packed without the valves. However, I’ve yet to do this blind.

Another reason for my tardiness is that every decent roaster seems to be using them. People I respect have spent hours glueing these valves into buckets (although there might still be a case for the valves here as the buckets cannot be vacuum-packed). So, every time that I’ve come to the conclusion that the valves aren’t worth it, I’ve been too cowardly to act, thinking that it’s better to be safe than order 25000 bags and find them exploding like Elektra machines en-route to the cafes. But (fuck it) I reckon I’ve tested this enough. And we’re ordering 60000 bags so, if I’m still here in a month, you’ll know it’s gone well.


83 thoughts on “Why I stopped packaging our coffee in one-way valves

  1. You can get rid of the one- way valve and the vacuum packing machine. Instead use Oxygen + CO2 Absorbing Sachet. Use a Simple Hermetic sealer, place the Oxygen Absorber (CO2 absorber ) pouch with the beans, now seal the bag. You will never have any problem of loosing taste or VOC or Flavours. Oxidation will start to arrest within hours, CO2 as it is liberated will be removed. VoC will remain as it is. So you do not face any bursting issues or loss of flavours.

  2. Coffee resting period:
    I have been told, and also found personally, that coffee needs to rest after it has been roasted for at least a day before the best flavor develops. Have you done any testing to see if this resting can be done under vacuum or does it actually need O2 to form the correct compounds for flavor?

    I was thinking of doing the following test: Roast 250 grams of coffee. As soon as it is cool put half in my chamber sealer, and leave the other half out. In 48 hours make two cups of coffee – one from each source and compare flavor. Have you, perhaps, done a similar experiment and can save me the trouble?

    • I have done experiments with vacuum packing a kilogram of coffee, nitrogen flush with vacuum packing, and simply sealing another kilogram. In panel tests, we found that the vacuum packed coffees taste the same and the simply-sealed pack tasted a little different after one week. Nitrogen flushing wasn’t something that seemed to make a significant taste difference.
      Regarding flavour development, it’s quite possible that we commercial roasters are roasting coffee that tastes best after some resting and that we could roast differently to make the coffee taste great straight out of the roaster. It’s a bit of a mystery what’s going on in there within the beans.

      Do let me know how your experiment goes!

      • Thank you for the link to this article. The findings confirm my observations that lighter roasted coffee degasses less, but I didn’t know that medium roasted and dark roasted coffees degass similar amounts. It’s interesting that whole beans release more CO2 than ground beans.

  3. Could it be most of the dialogue centers around the widely used but imperfect packaging system… the bag?
    I’m MUCH smaller a producer than you all here. I pack in “Ball” glass jars. If I under pack the jar (1/2 full) the explosion upon opening is profoundly more (suprizing bordering on scary) than if I pack it tightly. Packed tightly there’s only a slight pop.
    I suppose it is because the physical mass of the beans eliminates the air thus inhibiting the off-gas. I’m now considering “gassing” my beans like they do with wine for the exact same reason. Preservation of VOC’s (flavor).
    Which brings me back to my initial, the container. Coffee bean bags look bad if inflated with gas but I believe that is exactly the environment they need to be in to preserve everything we love about coffee. Bags are easy to use,store, ship, an widely recognized as an industry standard and cheep too. BUT these considerations are not in the best interest of the coffee or the customer.
    Glass jars are impractical and expensive I know. But I can store my beans for weeks un opened with no appreciable flavor loss (subjective).
    I humbly ask any reader to try an experiment. Fill 2 Ball glass jars. 1 half full the other packed tightly. Wait a day. Open them and see. Then reseal them hand tight screw lid and wait how ever long you deem average beans will go stale. Open them and use.
    Also wine stores sell compressed CO2 in little cans
    Experiment with gassing your beans in a sealed container.

    Thanks for your time.
    Good luck

    • I have been sucking the air out of coffee bean bags and then taping the valve shut for years! I use a hand vacuum pump from a now defunct plastic bag vacuum system that has now changed over to a machine! Reading this, i guess I am keeping any Co2 in the bag. Is this considered good or bad?
      Also wine making stores (here in Canada) sell an inert can of gas to spray in a bottle or carboy to prevent the oxidation in the wine! Never seen it called Co2, they just call it an inert gas, supposed to sit on top of the wine and preserve it!

  4. I have read this entire blog and appreciate that you have taken the time to post your research and personal findings. A few things differ from my basic understanding so I have a few questions that I hope you can define for me.
    I roast my own coffee and have been a roaster for 7 years. I have an IR-12 manual machine. No automatic computer controlled profiles for me. I prefer to be right there, watch, see, smell and hear my roasts. I learn from them.
    I have had my own thoughts concerning the use of the “One Way Valve” in coffee bags and sell my coffee in my retail coffee shop in those types of valve bags.
    The contention that I have always subscribed to was that the bag valve allowed C02 to escape and it kept 02 from getting in. I believe that both C02 and 02 are each oxidizers and therefore both are destroyers of coffee thru oxidation. Like yourself, I have experienced the valve bloated bags after bagging fresh roasted coffee. I thought maybe the valves were tensioned tighter than other valve bags. I have also experienced no bloating or even less bloating bags after packaging fresh roasted coffee. I would agree that the valves are probably less reliable than perceived to be.
    So reading your results concerning the 02 / C02 I interpret that you do not perceive 02 and C02 to be balanced equally as oxidizers, with 02 having a greater effect on the beans in smaller quantities with C02 having the least effect as an oxidizer. This interest me because I have always considered both C02 and 02 to be equally effective oxidizers and the sole need for having the bag valve. The valve compensating for the expansion of C02 to minimize it inside the bag and the prevention of 02 getting into the bag for the sole purpose of oxidation, not bag expansion.
    I am not a chemist and I have never researched the potential of oxidation in either C02 or 02, so it is entirely possible that 02 is a much more highly potent oxidizer than is C02. I just haven’t thought of it that way.
    1. I prefer the extra crème on freshly roasted espresso and feel disappointed when it tapers off after 4 or 5 days. If C02 is the cause of this as you suspect then if C02 is retained inside the vacuum sealed bag without valve, then this crème should last beyond the 4 or 5 day period. Do you find this to be true?
    My next roast, which is tomorrow morning, I’ll be roasting espresso and I will use my vacuum sealer to test this theory. I will have same beans, same roast, a portion vacuum sealed in bag with no valve and a portion of beans not sealed.
    2. You say that your roasts are to just before second crack and that was your light/medium drop point. I’m just curious, what I consider a light roast is 439 degrees F, a medium at 442F at sea level. Do you find the same or are your roasts temps lower / higher than mine?

    • G’day Wes,

      CO2 is pretty stable and unlikely to degrade the coffee. I think that O2 is the big concern.
      If you’re looking to test things out, I’d have more samples. One bag of each is too low a sample to conclude very much. If you’re roasting with an IR-12, you could probably afford a few more test samples.
      Our filter roasts tend to be 209-212ºC, the lighter the roast, the longer the development phase to prevent woody, green flavours. It depends very much on the bean. Espresso coffee we usually roast to 216-218ºC, with one outlying bean to 222ºC. However, we also have some espresso roasts that come out at 212ºC. Bear in mind that these temperatures are for a Loring SmartRoast, with our temperature probes stuck in as far as they are and cleaned once a month, in our air-conditioned roastery with greens pre-cooled to 18ºC. Temperatures are not directly translatable. Moreover, we roast using profiles. We do roast initially by scent, but for consistency and the ability to manipulate flavour by extending or reducing the phases, I find profiles essential.


      • Thanks Michael,
        I feel that you are correct in the stability of the C02 because I know of other people who have used the canister method of preserving coffee and they tell me it works great for them evacuating the 02 and not worrying about the C02. He uses an AirScape. It was actually those conversations that convinced me to do more research on the subject and brought me to this article you have written.
        I have a friend who is a retired chemist and I’m going to ask him about his thoughts on the 02 / C02 oxidation issue. I’ll try to remember to report back here on what he tells me. I am going to bag up samples and hopefully I will have those results as well. As for roasting profiles, procedures and processes, I concur, profiles are essential. Typically my roasts are blends that I have developed and usually they follow close to the same profiles. Each bag of green that I receive can be a little different than the last. The GrainPro bags have improved the quality of the greens and the way I profile those beans.
        One point of interest between your temps and mine is that your temperature spread, excluding the 222C bean, between your light filter roast and your espresso roast is 7C where as mine is 4.5C (439F & 447F). Of course I know depending on beans, etc. But I thought it was an interesting point. I roast my bean blends all together at once, I do not separate varietals, roast then combine later.
        I now have fresh roasted beans of two different blends sealed in non valve bags. I can see the bags starting to bloat. In a few hours I will take the bags to the vacuum sealer then evaluate from there.
        Have a fine day… in the UKay !

    • if C02 is retained inside the vacuum sealed bag without valve, then this crème should last beyond the 4 or 5 day period.

      Because the co2 is in the bag you wont get hi crème. It should be inside the roasted beans to get high crème. Obviously you loose that in 4 to 5 days because co2 escapes from the beans via degasing process. So use it from 2 to 4 days of roasting for high crème.

      • Mike.. sorry for the delay… exactly what you said… only he said it in terms like, “Well, seeing as Co2 is used to extinguish a fire…” ummm… Well anyway, I then created two bags of vacuum sealed coffee and left them. Both bags, with no valve and being vacuumed soon began to grow in size like a balloon… One of the bags developed a leak and deflated, the other bag grew pretty large and kept it’s size until last week, when I opened the bag and we brewed he coffee. It was good, still had decent cupping and aroma. So now I have changed my approach. Co2 is not as harmful as I had brought myself to imagine! Imagine that!

  5. Hi agoodkeensavage,

    I have a question I was hoping you could help me with. I know one-way valves are supposed to let CO2 gas out of the bag so they don’t explode, but would it be possible to flush the bag with a mixture of N2 and CO2 gas? I’m wondering if this would lead to a chemical equilibrium of CO2 so as to slow down the coffee degas?


    • The nitrogen flush is just to displace the oxygen in the bag. Most of the nitrogen is then sucked out – some air remains, but less oxygen than if we’d just vacuumed. I don’t see any benefit in using N2 over CO2 or a CO2/N2 mix, but it is to flush out oxygen, not to slow down degassing.
      Nitrogen and argon are inert and used in applications where the gas isn’t vacuumed and there are compounds present which the CO2 will react with – such as water (2-5% of roasted coffee).
      The benefits of flushing at all vs just vacuuming are debatable and in my experiments, I haven’t noticed any difference in coffee quality.
      I’m not sure that preventing degassing is desirable (flushing and vacuuming is to reduce oxidation), as excessive CO2 is a right pain in the jacksie when brewing – we usually wait a couple of weeks after roasting before brewing. If you wanted to slow down the degassing, I imagine you would need to pressurised container and Henry’s law reckons, in this case, a CO2 flush would be preferable to N2 flush.

  6. Hello Agoodkeensavage and mates in this forum

    Good Day!

    I recently bought some KGs of coffee beans (meidum roasted) and it is pack in a one way valve too. I also bought a vacuum plastic bag and decided to draw all the air out of the bag. After a few days I noticed that the vacuum plastic bag has puff up but not to the extend of exploding. I am just wondering

    1) I am assuming that it is CO2 since most of the air in the bag has been drawn out
    2) Should I remove and re-vacuum pack again.
    3) What is the danger if I just leave it as it is? Does it affect the coffee beans drastically or accelerating into the stale stage of coffee.
    4) My objective is to keep the coffee longer and with min oxidization.

    Any comment or advices is greatly appreciated. Thank you!


    • The CO2 shouldn’t accelerate the staling of the beans. Every time you open the bag, you’ll introduce oxygen, which is the real killer, so if the bag isn’t about to explode, I’d leave it until you want to drink coffee.
      Vacuum is good if you’re using the 2kg in a day, but if you’re drinking it all yourself, I recommend freezing the coffee, vac packed, in individual portions. Each time you wish to brew, you just need to take a bag out, thaw, then brew as normal.

      • Can you point me in the direction (in your website or elsewhere) of information as to why there’s a difference between drum roasting and air roasting? Considering getting into this myself, but don’t have a lot of background. Intend to start with a small popcorn popper for my own personal use and experimenting in small quantities, then doing larger batches on a grill top, rotisserie style basket. Not sure whether the latter counts as drum or air, for this purpose. Thanks, -Aaron-

      • G’day Aaron,

        I’ll take a stab at this. Roasters apply heat energy to the coffee beans by three forms: contact, radiation and convection. Contact heat is the energy conducted by touch. Radiation is the heat energy that emanates from every thing that is over 0ºK. Convection is heat on the move and the difference between drying your clothes on a line on a hot day and on a hot and windy day. Although most of the heat energy in a drum roaster is convection, there’s much more contact heat energy than with an air roaster, which is nearly all radiation and convection energy.
        In terms of your beans, there is a temptation to roast quickly with air-roasters, which leads to underdeveloped coffee. However, this is not necessary and it’s possible to mimic the flavours obtained in a drum roaster using an air-roaster with lots of control like the Loring roasters.


  7. Dear agoodkeensavage,

    Many thanks your useful posting. May I have 2 questions ?

    1. After roasting we used vacuum packs, but the bags is swelling , how can I vacuum pack minimizing the loss of the aroma and preventing the swelling of the bag ?
    2. which the material of bags that we should use in vacuum pack to prevent the swelling ?
    3. the volume of machine (kg/m3) we should use ?

    please advise.

    • Hello Le Van,

      Some beans degas more than others. Darker roasts, giling basah and natural processed coffees tend to swell up quite a bit: lighter roasts and fully-washed less so. Also the air-roasted coffee from the Loring seems to produce greater quantities of gas than drum roasters. We store our coffee for a couple of weeks before distribution and so can keep an eye on the bags that are swelling too much. These bags are cut open and vacuum-sealed again.
      The effect of the material of the bags on gas production is not something that I’ve looked into. However, I feel that it’s unlikely to make a difference. Interesting idea though. I use 3ply laminate.
      I don’t measure vacuum strength, we just suck a the air out. The guys at Coffee Collective advise not to vacuum too hard as it may increase likelihood of damage to the bags.

  8. I have one way valve glass jars, and it works perfectly. I only roast about 200 grams of beans per jar, which allows me to consume the beans as fresh as possible after letting it degas for a few days. It allows me to put the hot beans directly after roasting in the jar without having to let the bean cool like you would with plastic bags. I think this also preserve a lot of the aroma you might lose otherwise.

  9. I have just got back from holiday from Austria where (like Germany) all coffee is tightly vacuum packed into brick-like packets.

    So I went into my local Tesco supermarket (a large UK supermarket chain) and I suddenly realised that nearly all the pre-ground coffee being sold was in attractive loose foil packages (still sealed of course).

    Only a couple of brands (Douwe Egberts and Lavazza) were in German-style brick packages.

    THEN I noticed that the pricing of the loose packages that filled most of the shelf was about 15% higher than the ‘bricks’! Lavazza was cheaper than Tesco own brand!

    The ‘bricks’ must be more efficient to transport and stack – is the loose packaging a marketing ploy to charge more for the same stuff?


    • The pre-ground coffee that is tightly packed in bricks needs to be completely degassed before packing. You could replace the term completely degassed with staled.
      That doesn’t mean that the coffee in “loose packages” is fresh-roasted. Generally, if the bag doesn’t have a roasted on date, it won’t be fresh-roasted, and you’re unlikely to come across such bags at the supermarket. Freshness is one of the things that makes coffee good. Staleness makes all coffee bad.

      • Staling needs to be defined: for me it’s the degradation of volatile aromatics and the rancid flavour of the oils. I presume that this is due to oxidation, but I haven’t conducted any experiments to be assured of this.
        Degassing quickly would require a means to quickly degas the beans while preventing oxygen from coming into contact with the coffee.
        I don’t know that a complete lack of CO2 is a good thing. There may well be taste or extraction benefits from some CO2 left in the beans at the time of brewing. However, it would be interesting to find out. I note that in videos of transparent portafilter extractions, the bubbling that I had expected from CO2 didn’t seem to take place. Maybe complete and rapid degassing followed by vacuum packing would be a good thing. How would you do it?

  10. Hi,
    I’m new for this business. I have ordered for 1000nos of one way valve bags. But now i confused, that whether this bag is worth and good for keeping coffee as fresh. So please tell me one better option to keep coffee powder fresh.

  11. Thank you for this write-up. I am new to espresso (less than a year). Those opinions that seem reliable are often a bit too technical. Here is my situation–would love to hear some advice.

    I buy 1lb bags and they arrive within 48-72hr of roasting. 1lb lasts me, give or take, 15 days. Originally, I packed them in pint mason jars (~180g of beans) and pumped air out each time. Several people told me that I am ruining the beans as it sucks out more than just oxygen. Currently, I use half-pint jars (~90g of beans) and simply tighten by hand. 1lb is about 5 jars and each jar is about 5x16g shots. I only have time for 1 shot per day Mon-Fri (4-6 on the weekend). By the time I get to the 3rd jar they make a popping sound (CO2 I am assuming). It’s very hard for me to comment on smell/taste as I’m simply thoroughly confused by searching for “the” bean to stick with and by the fact that the same bean (at the same age) behaves differently from batch to batch…

    Some say that trapping CO2 after initial degassing of 48-72hr actually preserves the quality of the coffee. Some say let it degas 6-7 days. Some say to pack the 1lb in 6 jars instead of 5, so that there’s room in the jar for CO2 to mix with O2. Others suggested that I leave the beans in their resealable bag (with the degassing valve) and only jar 90g at a time–”active” jar so to speak. Should I buy small degassing containers? (not even sure whether those exist)

    In NYC, beans are very expensive whether you buy in store or ship. Thank you in advance for saving me some $$$ and frustration!

    • The style of coffee that I’m familiar with is low to medium roast, high quality greens and vacuum packed in good quality trilaminate bags. What I say relates to this style of coffee only.
      Get rid of your jars. You cannot vacuum all the air out and a good bag with a good squeeze is a better, cheaper and a far less fussy option. If the beans come in good bags with a zip lock leave them in it. If you feel the need, suck out as much air as you can through the one-way valve.
      sucking air out of a bag
      However, I maintain, bags without valves are just as good, perhaps better, especially if they’ve been vac-packed.

      • Thanks for that! Ok no jars. My coffee does come in a decent bag. 1lb yields 28 shots for me–exposing the entire batch to oxygen 28 times over the course of 15 days seems unnecessary, no? I dose 16g into the grinder and am not comfortable with any other method.

        My understanding is that your contention refers to the point of sale and storage post sale. What’s your take on actual operational use? Let me know if you can recommend a good brand of bags for coffee storage.

  12. I would attribute at least some of the outgassing to water and brewing. When I put plastic wrap over a carafe full of room-temperature water and grounds I’ve just stirred in for cold brewing, the top bulges, and I suppose at espresso temps an even greater vapor pressure would arise. Water exposure, as opposed to oxygen, seems a better explanation for the frothiness of crema too: As crema forms beneath the basket, it’s exposed to oxygen, but the crema forms and froths so fast and in such a small space, I think it must be the sudden decrease in pressure that’s the immediate cause, and the ultimate cause is the brew temperature. The higher temperature raises the vapor pressure of the volatiles, but they remain dissolved until the brew exits the pressurized liquid/solid environment inside the brew head.

  13. I would attribute at least some of the outgas-able content to contact with water and brewing. If When put plastic wrap over a carafe full of room-temperature water and grounds for cold brewing, it soon begins to bulge. I suppose at espresso temps the amount of outgassing would be more. My sense is that crema forms as the shot enters the relatively low pressure and airy environment below the basket. I guess that could reflect either contact with oxygen or the lower pressure, but it happens so fast and in such a small space I’m going to guess it’s the pressure: Heat raises the vapor pressure of the volatiles, which remain mostly dissolved in the pressurized liquid/solid environment within the basic, but they evaporate like mad as they exit, fluffing the crema.

  14. Hi everyone – great comments. I experienced first hand an exploding coffee can the other day which not only scared the shit out out of me but also nearly deafened me – and I’m ex military! In hind sight though, I love my coffee and will not stop opening up this superb blend that we buy – albeit a little more carefully now. I can assure you all though that if you are unlucky enough to have ‘one let’ go in your hands, it is seriously more than just a ‘little pop’ – more like a fucking hand grenade went off next to your head and it really does have the potential to injure if you’re unlucky enough to get an eye in the way of a bean missile or an underlying heart condition. Cheers all. Dave

    • A coffee can is a different beast to a coffee pack. By definition a can cn sustain a much higher pressure and that means that it is dangerous if the coffee was canned really fresh. That hardly ever happens for just that reason. Illy even have a sticky tape valve on their cans to avoid this situation.

    • G’day Dave,

      A vacuum packer and a coffee bag are pre-requisites for no valves to work. Also we roast our coffee to much lower levels than most – I haven’t tested the effect of roast level on outgassing, but darker roasts are supposed to give out more CO2. My contention is still that you need O2 in the container to produce most of the CO2.

  15. Pingback: Degassing Process ~
  16. It seems there is a disconnect here in what people mean by “releasing x litres of CO2”. I’m assuming that’s litres of CO2 at standard temperature and pressure. If the reaction causing the release of CO2 is a normal reversible reaction, then as the bag pressurizes it will slow down and eventually stop producing CO2. So, assuming the bag is strong enough, the amount of CO2 produced will be precisely enough to generate equilibrium pressure in the volume provided.

    Put the coffee in a small, strong container and a large, strong container twice the size and you’ll find that one produces twice the amount of CO2 according to the ideal gas law.

    Stating that coffee produces some specific amount of CO2 in a pressurized environment is impossible without stating the equilibrium pressure of the reaction and the volume of the container.

  17. After 34 years of developing breathable films and packages th cellophane (15 years), Bopp-bi-oriented polypropilene and Bopet-bi-oriented polyester used on Lettuce, Salads, sugar coated bakery, peanuts, cheese, cigarrs, cofee and snacks packaging. My opinion is that the perfect packaging film is the PVDC coated cellophane because keep the aroma inside and do not let the oxigen get in, while the moisture content of the film (around 14%) makes the CO2 became absorbed and released by moisture transfer.
    After reviewing the newest options on films, i had discovered recently that Bopet has a natural aroma barrier and absorbs water up to .5% which make it the closer to cellophane PVDC coated.
    I know about valves because the first ones were developed for Brocoli and Couliflower packaging for the same reason of CO2 release by Apio Inc. on late 80S when i developed the first antifog CO2 breathable for ´produce packaging. Since then i considered funny to have hermetically sealed bags with a hole. Later on cofee bags became more funny because they used aluminum foil armored bags hermetically sealed with a hole.
    My conclusion on explosive bags is altitude changes during transportation, that happen frecuently on light weight salads and potato chips bags (Ask Pepsico and Dole)
    If somebody wants the perfect bag without a hole send me a message, i work in Tampico Mexico for the largest Bopet maker of the world as preretirement job before moving to teach packaging to the new comers.
    Sonrian mas y seran felices.

  18. I am a home roaster and total amateur. But I fresh roast and vacuum seal immediately in mason jars. Now if this tremendous about of CO2 were for real, by now probably several times over I would have suffered death by exploding glass jars. But this has never happened. I will admit that if opened and resealed the jars can gas up after a week or more but still no more than a popping sound when opened. It appears to me, no cupping expert, that flavor does not suffer and preservation is enhanced. But I will admit prying the jar open to overcome vacuum tightness with the blunt end of a beer can opener can be annoying. But if killer CO2 were an issue, I wouldn’t have pry the lid off, it would fly off, wouldn’t it? The great C02 myth is bogus and tight vacuum sealing largely prevents large CO2 accumulation. I notice vacuum sealing is also used for maximum fresh when shipping green beans from the mill/farm. Combined with freezing this all drastically extends the life time of green and roasted coffee.

    • Hi there, Question: Your mason jar idea is, to me, brilliant but I have some questions:
      I plan on roasting multiple kinds of beans then letting them degas overnight, then storing them in mason jars… now… I plan on opening one of the mason jars every other day (if not daily) to use the beans and then resealing the jar- that way, which ever bean I didn’t use that day, can stay fresher longer. So open the jar, reseal the jar, open the jar, reseal the jar, switch to a different bean, open the jar, reseal that jar, etc. It’ll be a hassle but I think the shelf life and longevity of the flavor will be worth it. Did you find that to be the case? How long have you kept the beans in the jar? are you able to use this method often and still have the same freshness results? or would constantly opening the jar and then resealing it allow the beans to grow stale? The reason for all of this is that I would like to reduce how often I have to roast. So would this also be a good method for long term storage? Say… a couple of months? I have been seeking this information for a VERY long time and no one seems to have the answers. lol. You are the only one that I have noticed to use this method for daily coffee grinding consumption so I hope you might know the answers /crosses fingers

      • For quality’s sake I reckon you’re best to roast a little often. However, rjduwors is on the right track, freezing is your best option if you want to extend shelf life. This might not work for all roast types – I suspect that water-quenched beans may suffer in the freezer – but it works well for ours. I recommend storing the beans in air-tight, single portion packs and defrosting fully in the pack before grinding. I wouldn’t do this commercially, rather it’s my recommendation for customers who want to extend the shelf life at home.

    • Hello Everyone, I am a home roaster and an avid do-it your selfer. I came up with a great system. I bought a few Kingston, low pressure, one way valves and mounted them on the metal disc of ball jar lids. I use o-rings to get a tight seal. I roast my beans, and put them in ball jar and seal them up tight!! If and when the pressure builds, I get a wonderful puff of amazing roasted coffee aroma!! I’ve also made my own valves using some stock brass cylinder, steel balls and a light spring. Happy roasting!! Mark Vinci markvinci@aol.com

  19. This is quite interesting as one could in theory use a substrate more suited to the application than a valve.
    “Cellophane” for arguments sake (PVDC Coated) has a O2 transmission rate of 1cc/M2/24 hours however CO2 is probably double that as it seems to migrate through film faster than O2.
    The material is not really suited to Vac pak apps without being laminated to say Polyethylene.
    One would suppose that the volatile (presume aromatics) components in coffee will probably have a reasonably larger molecule than say CO2 (don’t know if true) but many moons ago I was involved in a packaging project for perfumed stationery and we discovered that Cellophane (PVDC coated) let almost no perfume through however Polypropylene allowed quite a strong odor to be noticed outside the sealed pack almost immediately and I have also seen occasions where essential oils (like in cloves) have migrated through polyprop bag and lifted the print. Cello is a good barrier to fats and oils so this does not happen.
    It also needs to be recognized that UV can have an affect here as well.
    Here is a data sheet link for cello (white opaque) if interested but have a care Polyprop bags are often sold as Cello bags! Cello, like paper has “deadfold” Polyprop will not stay folded and if burnt Cello smells like burnt paper, polyprop a bit like candle wax.

    Click to access UK-CELLO-A310-XSB-0207.pdf

    • hmmm…i think it was some 18years ago that most retailers kicked out all the packaging that contained PdvC/PvC. Today it is still not acceptable, moreover since there are barriers like SioX, Alox, Evoh and PvoH available. Only a few products that have been unable to find an alternative still ise the XS version of Cello. XS in the old days was used for twist wrap and also for products that had to “breathe”. One of which was a classical product in The Netherlands, “Indische Cake” from Lindemulder & Beuving.
      Please do not compare this with a valve, its like comparing an apple with spareribs…

      • sorry to break the sad news but PVDC is still quite common to RCF, BOPP, PET and other packaging film applications where high barrier &/or sealants are required.
        Much BS attributed to PVDC .
        Possibly applications such as BWK (bleached white kraft paper) for wrapping cheeses, butter & greasy products need to claim more attention as these carsonagenic products (BWK) have a high affinity for fats and oils unlike PVDC.
        Common app for PVDC is sealant layer for lidding to PVC (shock horror!) thermoformed trays which is probably one of the most common material in this app.
        Most thermoformed trays are either HIPPS, PP, PET & PVC. Makes you wonder doesnt it?
        Kinda nice to think about when you next microwave your polyethylene perathphalate (PET) quickie meal ………. mmmmm…..yummy!
        Please give me a break, I have been in this game (flexible packaging) for over 35 years + 7 years in New Guinea growing Rubber, Coffee and Cocoa (yep a plantation manager) so somehow I think I know just a little bit about this.
        Not particularly interested in the green rhetoric, just a suggestion for a possible solution.
        Might be worth researching MAP packaging, plenty of neat stuff there but do not look too closely at the materials.
        A clay pot with a wax bung seems a solution? All natural but the CO2 foot print is probably a downer!

    • Many of the bags do expand to resemble balloons. None have exploded. I’ve had a couple that have stretched to the point that they’ve breached the seam and deflated.
      I’m still monitoring the experiment and don’t want to preempt the conclusions. However, as you asked, it seems to depend on roast level: the darker the roast the greater the expansion. Briefly, the taste of the coffee is consistently good. The coffee seems to last longer, but this needs further testing.
      I’ll do a post in the future on this.

      Caveat: all our coffee is roasted before second crack and all is zero defect, or close to it. I’ve yet to try roasting coffee with defects or over second. It is all vac-packed as soon as it comes out of the roaster. We don’t use the nitrogen flush.

      • The answer to the balloon problem, is partly, to use slightly larger bags in the first place. The standard 250g bags are actually too small… often based on american 8oz sizes, and wiht no excess capacity, because it is assumed that there will be a valve to release the pressue. I have one hard roasted coffee. Hard roasting means that the coffee beans expand more. Filling the 250g bag with this coffee, it comes to the brim, whilst other medium roasted coffees have room to spare.

  20. Hi I am from Ecuador, Sudamerica. We have a roastery with my husband, we only roast good quality and very good quality coffee. We are interested in keeping the freshness as long as its possible, the problem is wen you sell your coffee to the supermarket is almost impossible to control the time it gets to the consumer. We want to sell boutique coffee from few producers that have exceptional coffees. So we bought a vacuum machine. I made some experiments with valved bags as well as bags without valves, and also with coffee just roasted as well as coffee that has degas for few days (like 5 day degassing before packaging).
    My findings were: If I roast and vacuum pack the coffee immediately, in the bag with valve or without it, it begins to inflate. If I roast and wait 5 days for degassing it is possible to pack it in either of the two bags (with o without valve). So it seems that the rate of degassing is grater than the capacity of the valve to expel de CO2 out of the bag.
    My concern is about the coffee losing its aromas during the degassing period out of the bag before packaging. I am looking for some information about vacuum packed coffee and I don’t really find the information I need. Could you help me on these please, how can I vacuum pack minimizing the loss of the aroma and preventing the swelling of the bag.
    The fine thing i that the valve works if I don’t use vacuum, the bag doesn’t swell with just roasted coffee. And if I vacuum pack the degassed coffee in the valved bag, it also works, so the valve isn’t fake.
    Could you give me an advice, please…

  21. Fantastic, I am not alone. I have been retailing fresh coffee for 8 years and have tried bags with and without valves. My experience says that valves fail far more often than is accepted. Either they don’t open when they shoud or they allow air in. I much prefer to vaccuum without a valve, and no they don’t explode… ever. oh and Arthur, I am in the Netherlands.

  22. As far as I’ve read, I understand you’re using valve+vacuum packing, what’s the purpose of that?
    Vacuum and valve are meant to do the oposite.
    If you don’t puncture the valve then it doesn’t de-gas. Then the valve is useless.
    If vacuum is resisting with beans, then keep with it. In my case, vacuum works only for ground and for bean I need valve.

    • albeit many professional roasters can not conceive using a valve inside a vacuum pack, here is the explanation: during packing you can choose to remove the oxygen by flushing Nitrogen or CO2 inside the bag, or removing the air by creating a vacuum. After the vacuum, the beans start to vent CO2 slowly. to avoid exploding bags, they have inserted a one-way valve on the filling machine. This procedure saves gas flushing, but uses energy in the vacuum chamber.
      Most bags will appear a bit brittle afterwards, making it look like a fawlty bag. In Italy its not considered an issue since the majority of the consumers know very well what happened, but these bags will not sell in most other countries.

      • The problem is that for these bags to sell you have to educate the customers. In a single shop that can be done, but when you try to expand you come up against the coffee establishment that does not want to listen.

  23. i am also interested in the valve findings. i do my own roasting now and will never go back to commercial roasts. before i bought a valve tin from sweet marias i was using a jam jar partially open the first 24 hours. now i have the tin. i have also been scared to test the theory and have never done away with de-gassing. being a pour over brewer i have come to the conclusion that coffee really only lasts a few days. i have tested many roasts including my own and bloom from infusion only happens a few days after roasting. this has also confirmed many roasters like jjbean lie about their roast dates. this could be because of increased demand and they shipping older coffee to keep up but stamping current dates.

    to the person who roasts but does not like to…..wtf? quality is night and day. sometimes i open a jar/tin i have roasted just to smell the aroma. that same aroma has never come out of a commercial bag. you also have to contend with roasters never roasting all the different roasts. ex. etheopean being roasted passed city plus when its best flavours are just before city+.

    • Hey Jason,
      So have you noticed a taste difference between coffee stored in the Sweet Maria’s tin vs. coffee in the jam jar? My husband and I home roast and I contend that we do not need to pay extra for the tins since we are drinking the coffee within 2 weeks (usually within 1 week) and the *free* glass jars we have suffice for that length of storage. (Plus I just ruined 2 of the tins by rinsing them out which I did not realize was a big no-no. doh!)

      Of course he is much more the connoisseur so maybe it’s just my dull taste buds that can’t tell a difference.

  24. Hi Roger,

    a blond roast releases some 3L of CO2 within a weeks time, whilst a dark roast may vent up to 15L in the same amount of time. Variations are possible, depending on the blend, temperature etc.
    Most of the CO2 has gone after 1 week. The flavour/taste of the beans must remain intact for a period of 6-12 months, depending on the OTR of its packaging material.
    If you witness variations within a blend, it may also well be that the blending itself is not a perfect match. Than again, some roasters tend to wait a couple of days before packing. This period of time may fluctuate, causing a variation on taste as well.

    If you have trouble sleeping, due to an overdoses of coffee, I can advise you to read “Espresso, the chemistry of Quality” written by Andrea Illy.

    • Hello Arthur,

      Thanks for your reply.

      I usually find the flavour/taste of commercially roasted beans (as well as those I occasionally roast myself) starts to fade by 7 to 10 days after opening a valved bag. That’s one of the reasons I chose my current roasted coffee bean vendor. They put the date of roasting on the bottom of the bag (I hope they’re being truthful). I then calculate 2 to 3 days after that date before opening the valved bag. (When I roast my own, I seal it in a foiled valve bag and wait 2 to 3 days as well.) Either way the flavor-fade factor stays the same. By 7 to 10 days after opening, the coffee just doesn’t taste the same.

      I buy only a pound at a time, so there’s no real loss (if I roast my own, I can’t roast more than 6 oz. so the fade occurs only with the last few cups. Then I have to roast more, which I don’t really like to do – one reason why I prefer to buy roasted beans over green ones). But, of course, a pound of beans lasts longer than 6 oz.

      But I’m starting to think the variations in bitterness might have something to with the age of the green beans used by the roaster. I don’t buy blends, so if they’re blending them they’re not telling me they are.

      As far as coffee keeping me awake, for some strange reason it has the opposite effect with me (as long as I don’t drink more than a 4 oz. cup at a time – not much by typical American standards, but when you think about how a latte or similar specialty coffee is mostly milk with an ounce or two of espresso, perhaps the 4 oz. cup of black coffee I drink is nearly the same). Had a cup late last night and drifted off to sleep faster than if I had skipped it.

    • G’day Arthur,
      I’m interested in the research that lead to the 3L for a blond roast, 15L; dark. Do you have the reference?
      I must take issue with the 6-12 months claim for flavour. If what we’re after are the fruity, flowery, herby aromatics, they don’t last much longer than a month if vac-packed and kept in a climate controlled store.
      Also, ‘Espresso, the Chemistry of Quality’ was edited by Illy. He co-wrote some of the papers that are included in the collection.

      Thanks for your input,


      • Hi Michael,

        these data has been assembled over the past 20 years. It was measured mostly in Northern en Southern Europe at both small and big roasters to whom we supply valves/packaging/filling machines.

        Your comments on the flavour claim are accepted. I know of a famous Scotland based roaster who states on his packaging a line like: these beans have a shelf life of 12 months, but the gates of heavenly taste close after 6 months…



  25. Googled coffee and one-way valves and found your site. Although, your interest seems to focus primarily with the chances for exploding coffee bags, I thought you could provide some information regarding taste. My interest is in determining taste parameters (specifically, bitterness in cup) from roasted beans that have stayed sealed in bags with one-way valves for a range of one to ten days from day of roast to day of grinding and brewing a cup.

    I like to wait 48-72 hours after roasting before opening the bag. Unless I roast my own, I cannot guarantee this specificity from most roasters. Still, I have noticed variations in flavors, as well as bitterness, between what commercial roasters claim are identical roastings. As my technique for grinding and brewing provides a given flavor and bitterness for a one-pound bag of medium roasted Colombian Supremo beans until the bag is empty, there should be little variation using a subsequent one-pound bag from the same roaster. However, I continue to notice these variations in flavor and bitterness and I am beginning to think the amount of time in the sealed bag with a one-way valve may have something to do with it.

    Any help you could provide would be appreciated. Thanks.
    Roger Baronat

    • I was looking at three cases: 1. bag with working valve. 2. bag with faulty valve. 3. bag without valve.
      I can only conclusively say that all case 2. samples tasted slightly fermented/funky. Bear in mind that I’m testing these in a very humid country. During blind testing I couldn’t detect a difference between samples 1. and 3.
      So far as bitterness in the cup, all samples would provide decent acidity and bitterness depending on extraction.
      Variations in the roaster’s coffee may come from the different sources of the beans. Colombian Supremo means they are all beans above a certain size from Colombia. Terroir and varietal doesn’t come into the equation. If you’re after consistency, you need the beans to be all the same varietal, from the same estate/area, picked at the same stage of ripeness and possibly at the same time of day (witness Clouds of August).

  26. Thanks for sharing! It’s absolutely an interesting story.

    please can you revert to what type of valve you have used? Was it the original Goglio valve or a copy? I would love to send you some bags with the Goglio valve to test.

    I am curious to know your findings,

    for now, I do hope the 60.000bags without a valve do ok and will not explode in the market. I have heard of people who save money on the valve and puncture the bag with a needle…

    • I don’t honestly know who makes the valves. Perhaps the Goglio valves are less prone to being faulty than those I’ve been using. However, my contention is that if the bags are vacuum sealed they do not require the valves at all. Puncturing the bag would somewhat defeat the vacuum, eh?
      We’re still using the valves in the UK as we don’t yet use a vacuum packer there.

      • The UK market does not respond well to vacuum packs. Lavazza is one of the few to be put on shelf if I am not mistaking.
        Personally, I prefer the vacuum packed beans but they are quite difficult to find in the shops since the majority considers the visual appearance to be substandard.
        Most common type of valve in the UK is made by Whipf, a fairly good copy when compared to the original Goglio type. The Goglio valve however tends to close when there is still a little overpressure inside the bag. This will avoid air re-entering the bag. Puncturing the bag is possible when you are certain it is going te be used in a weeks time….

        Finally, I am amazed/shocked by the fact that in my country (The Netherlands) most of the specialist coffee shops (real coffee, not the smoking type…) sell their special blends (250gr at +/- E 6,=)in paper bags, or alu bags that are taped…what a waste…

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