GC7 Said:

Dave

I do not see the logic in your conclusion regarding rigid canisters.  In fact, your two statements seem contradictory.

A vacuum is simply the absence of oxygen or other gasses within a space.  Your beans in the bags could in fact be exposed to far MORE oxygen then a cansiter that has a better vacuum and seals to maintain it. The space above the beans is meaningless it seems to be if there is little to no oxygen.

Your second statement that you are not sure how good a pressure drop is for coffee is the definition of vacuum it seems to me.  If there is less of a pressure drop in the bags it means there is MORE air or oxygen.

I'd really like to hear a coffee experts take on the vacuum issue.

Posted June 16, 2008 link

christiang Said:

But here's my question. I'm wondering what people think about this for roasted coffee, especially coffee I'm not roasting myself?  

What I've been doing is bagging up small portions of coffee 2-3 days out from the roaster when I first get it. I'm the only drinker in my house and I usually only go through about half a pound every two weeks (not considering company).  So my theory was that I could preserve the freshness so that by the end of a couple of weeks, I might have coffee closer to a few days out rather than 2 weeks out.  I've been thinking about doing the same with modified canisters - a series of small canisters with valves - preferably glass so I can avoid having all that plastic touching my coffee. I've also been vacuum bagging up small single doses and popping them in the freezer ala George Howell - (http://www.terroircoffee.com/content/view/217/) and Ken Fox (http://www.home-barista.com/store-coffee-in-freezer.html).

Posted June 27, 2008 link

DavecUK Said:

Each point in order

OK well that's up to you

Thanks for that bit of information about the nature of a vacuum...but you need to do a little more physics

Again need more Physics, in a canister your not changing the volume of the storage container...in a flexible bag you are!

Good luck, because the explanations for the whole degassing thing seem a little confused, so I don't know how useful their take on vacuum packing is going to be

A I always say...no one has to vacuum pack coffee in flexible bags straight after roasting, or at any other time...you clearly don't want to do this and that's your right. I and quite a few other people find it makes a huge difference if it's done correctly and the coffee is handles correctly. It's not about keeping it longer, but keeping it better. So even though your not convinced (and I don't really care that your not), hopefully people will spend a few dollars trying it. If it works, then they have gained more than they spent, if it doesn't work for them, the amount of money invested is very small.

P.S What would happen to a sealed balloon in a rigid canister as opposed to a flexible vacuum bag as you removed the air?

Posted June 28, 2008 link

raisin Said:

Also, vacuuming does arrest the CO2 outgassing that normally progresses during the first few days of air exposure, so this will all proceed as new once opened. This means that you need to plan ahead, and "decant" the vacuumed beans before consumption to optimise extraction.

Posted June 29, 2008 link

GC7 Said:

At this point, the gas -- mostly in the form of carbon dioxide -- has been generated by oxidation of carbohydrates. About half is retained inside the beans, causing high pressure and the beans to double in size. Entrapped carbon dioxide is very important in maintaining storage life of roasted coffee, because under normal circumstances un-ground, roasted coffee beans would be very susceptible to oxidation. The protective cushion of carbon dioxide is largely liberated during grinding, and is the chief cause of ground coffee losing its pleasing aroma and flavor. "

I'll try to find more but it seems from this that it is trapped CO2 as a result of the roasting process and it is not produced post-roasting.

Posted June 30, 2008 link

1. Why does ground coffee still "degass", there was a roaster I knew packing coffee in portions and he used to have to leave the beans a week before he could grind and pack them. If the CO2 was held pressurised in a bean, grinding should liberate all this "trapped" CO2
   
   
2. If the CO2 was somehow "trapped" within the bean...then storage in a low pressure environment (vacuum) should make it "degass" faster...but it doesn't?
   
   
3. Why does vacuum packed coffee stop producing CO2 for a few days, then on exposure to Oxygen, it starts producing CO2 again...doesn't make sense if all this CO2 is "trapped" as a result of roasting.
   
   
4. Why if you freeze coffee doesn't it "degass"?

cv Said:

I'm not so clear how vacumn packing slows down the outgassing. Seems to me the opposite would be the case, don't freshly roasted beans when vacumn packed in bags actually re-inflate the bag?

Posted June 30, 2008 link