YOU JUST PURCHASED A BAG OF COFFEE AND YOU NOTICE THAT JUST A LITTLE
BIT ABOVE THE MIDWAY POINT
OF THE BAG THERE IS A SMALL HOLE! IF YOU SQUEEZE THE BAG, YOU HEAR GAS
ESCAPE THROUGH THE HOLE
AND, HOPEFULLY, YOU SMELL SOMETHING WONDERFUL. WHY ON EARTH IS
THERE A BELLY BUTTON ON THE
BAG? YOU ALREADY KNOW THE SIMPLE ANSWER: TO LET OUT AIR. OF COURSE,
IT IS MORE COMPLICATED
THAN THAT. THAT HOLE IS PART OF A BIGGER DISCUSSION OF COFFEE
FRESHNESS AND HOW BEST TO STORE
ROASTED COFFEE TO MAINTAIN FRESHNESS.
Presumably, since we know the major factors that cause coffee to stale— gas
evolution, high temperatures, oxidation, and humidity—we ought to able to
control them to extend the shelf life of the coffee. By teasing some of the data
available in the myriad of research on the topic, we can make some general
statements that will help. However, without direct research to support our
hypotheses, and the ones of the coffee industry at large, some of our conclusions
will have to be educated guesses.
Let’s address each staling factor individually, starting with gas evolution. Since
smaller coffee pieces allow the release of more gas, keeping the coffee as intact
as possible will help. Thus, grinding coffee ahead of time is a poor practice.
Rather, grinding should occur just prior to brewing. The other potential way to
slow down gas evolution (and all chemical reactions) is to decrease the storage
temperature; cooler temperatures slow down chemical reactions and chemical
mobility. Thus, storing coffee in the refrigerator or freezer will accomplish this.
Unfortunately, I can’t find any sensory data that explores specific taste changes
when stored at cooler temperatures.
Coffee geeks abhor the idea, but, at best, they have some personal, anecdotal
evidence to support it. Freezing coffee could run the risk of creating crystals that
could shatter cells, much like grinding. Freezing could also lead to freezer burn,
which probably isn’t a flavor anyone wants to introduce to a coffee. Arguably, the
biggest reason not to store coffee in the freezer is the risk of condensation
forming on the beans as the beans come out of the freezer. This water may then
lead to a deterioration of the quality by hastening the natural staling of coffee
when the coffee is out of the freezer or by allowing ice crystals to form on the
coffee if it is returned to the freezer. Refrigeration doesn’t run the risk of crystal
formation, but the condensation is still an issue.
Ultimately, individual drinkers
will have to decide this on their own, at least until some new research surfaces.
Preventing or minimizing oxidation reactions is as simple as keeping oxygen away
from the roasted coffee beans. Of course, with the atmospheric concentration of
oxygen at about 21 percent, that isn’t so easy. Simply putting just-roasted coffee
in an oxygen-impermeable container and sealing it doesn’t solve the problem
since the air trapped in the container is full of oxygen. Besides, even if coffee were
sealed up in a container, the container would likely explode as a result of the
pressure build-up from all the volatile compounds being released! So, either the
air has to be completely sucked out of the container before it is sealed or all the
air must be replaced with a gas that is completely inert, like nitrogen.
I have no knowledge that any company packages just-roasted coffee and then
evacuates the air before sealing it, though it seems like a worthwhile strategy.
Many larger roasters do flush bags with nitrogen before sealing them. Some
research supports this as an effective means of extending the acceptability of the
coffee farther from the roast date than by using normal air.
Lastly, controlling the amount of water coffee is exposed to is fairly simple. If the
coffee is packed in an oxygen-impermeable container, then the container is also
likely to be water impermeable. After the container in opened, keeping the coffee
in an air-tight container that is waterproof should help minimize exposure to any
humidity in the air, although, if the air was full of moisture when the coffee was
sealed or closed in a container, then the container won’t offer any protection.
So, what’s the story with the bag and its belly button? The bags that have them
are made out of oxygen-impermeable materials. Generally, they prevent many
gases from passing through. Thus, as mentioned before, if freshly roasted coffee is
sealed in a bag, it is liable to explode. The belly button, more formally known as a
one-way valve, is a crafty device that allows gas to exit the bag but prevents any
gas from entering. It is a release valve; the carbon dioxide and other volatile
compounds can escape but oxygen cannot enter.
The one-way valve is a fantastic tool but it has its limitations.
For one thing, unless
the air trapped in the bag while sealing it is replaced with something inert,
preventing oxygen from entering is irrelevant; the bag is already full of it (though
the valve still prevents the bag from exploding). Secondly, once the bag is opened
by the consumer, any internal protection is lost and the consumer must
repackage the coffee as best as possible.
Ultimately, we aren’t able to prevent the staling process from occurring. At best,
it can be delayed. However, if coffee is drunk within a few weeks of roasting, the
need to delay staling is most likely unnecessary. After all, the freshly roasted
coffee will still be pretty fresh!