I know different people try different things to preserve roasted coffee beans, including freezing them or vacuum sealing them. But do any of these actually work? I have a very rare and expensive coffee bean that I'd like to take out once a month or so on special occasions, and I'm trying to see if there's anyway to do this without buying the coffee new every time.
Coffee beans, once roasted, are perishable; they don't "keep". Within roughly five days of roasting staleness is detectable (taste/quality is adversely affected). There is one way to preserve freshness: consume freshly roasted beans within roughly a week. Don't freeze; beans absorb moisture and lose flavour— ick. Vacuum packs aren't the answer, either. To remove all gases from packaging would require a system using pressure, 29" Hg, that no one, not even coffee giants, can afford. The best practice is to just buy beans (roasted on the day you purchase, ideally) in quantities you'll use within a week to 10 days.
What I usually do is to place the degased beans (30hours after roasting) in a nitrogen atmosphere. I did a couple of experiments to check whether this is working, namely mass-spectrometry on the brewed coffee. Although this does not directly link to the taste, it confirms my theory that the nitrogen atmosphere conserves the solubles in the coffee for a longer period of time. In a good atmosphere (>0.1ppm H20 and >0.1ppm O2) and no ambient light, the flavor, in my opinion, can be conserved for up to six months.
The problem with vacuum is that you actually extract part of the flavor by helping the beans to degas further.
Right after the coffee is roasted, you should not consume it right away but degas it for one or two days. Degassing improves the flavor for a while, say up to ten days, then the overall quality of the bean began to get worse. There is nothing you can do to reverse it, as coffee is alive. However, you may slow it down by using vacuum packs or freezers.
I have just edited and added the "storage" tag. There are many discussions under this tag on how to store green beans, roasted beans and ground beans. Please take a look.
I am a coffee roaster. The coffee industry has played a shell game with us when it comes to the question of preservation and freshness. They have led us to believe that it has to do with the off-gassing. It absolutely does not. There are lipids and other such oils and fatty compounds in the coffee. These are what go stale. These can be preserved by freezing the coffee in air tight containers. Technical specifics can be found in Michael Sivetz's book "Coffee Technology". Freezing/unfreezing/re-freezing isn't a good technique. If you can manage - break up your supply into the amounts you'd normally use and store them like that individually...in the freezer. Small glass jars that seal air tight work perfect.
I was able to get some non-freshly roasted beans from Germany one time. Sold to me for cheap because it wasn't freshly roasted. I kept it since October 2015, and just last week (June 2016) I was still drinking some of it. It's flatter, but the acidity is still there. (Owing to the fact that those were some rather high-level green beans). It was just in the same bag it came with, and some loose plastic clip to keep it closed.
It took me so long to finish it because i'm always preoccupied cupping and road-testing beans that I roast for my kiosk business. (The irony of being a coffee business!)
In fact, in an Intelligentsia video/speaking occasion somewhere, they mentioned how when they cupped some old and new coffees side by side, the 6-month old roasted still scored better, and it's really just evidence of the excellent quality of green coffee.
Coffee is a weird product in that it never actually befits "special occassions". For special occassions, you bring out wine, beer, cocktails. The best and absolutely superwordly experiences of drinking high quality coffee are those nights when you come home tired from work, and find a sliver of excitement in a cup of fruit-bursting pure joy COFFEE.
I place my freshly roasted beans into an empty wine bottle and then vacuum pump it for storage. The special rubber stoppers have a one-way valve in them which allows air to be removed and held under a partial vacuum. The advantage of this method is two fold. First, the container is as full of beans as I can get it which minimizes the space available for air (oxygen is the bad guy). After pumping out the air with the little hand pump, it creates a partial vacuum which extracts additional oxygen from the bottle but also promotes the accelerated off-gassing of carbon dioxide. I know the beans are emitting CO2 because for the first day or two I can continue to pump out gas from the bottle. After that, the bottle holds a vacuum indefinitely.
I've stored freshly roasted beans like this for at least a couple of weeks with no noticeable loss of flavor. After I open the bottle and begin to use the beans, I can re-seal it; although the more space there is in the bottle, the more oxygen will remain in the bottle even after I pump it out. After using a couple of days worth, I more often transfer it to a zip lock baggie that I can roll up and extract air from.
Longer storage than a couple of weeks I can't comment on because I don't roast coffee that far in advance. I prefer my coffee as freshly roasted as possible.