Green Coffee Storage
People in the coffee trade used to say that raw coffee was eternal, and we used to agree. The revised estimate is that green coffee lasts about a year from processing (assuming a six-month rotation of stock). We are unlike most green coffee sellers in that we do not have old stock; we are careful to make sure the coffee you receive is as fresh as possible. If we sell out of the previous crop year (something we always want to do) and new crop has not come in, we will not have that coffee until the new season. It is helpful to think of coffee as produce with a seasonal cycle, just like apples, peaches or asparagus. Coffee is not nearly as time sensitive as peaches though!
Green coffee should be kept cool and dry at room temperature and away from direct sunlight. The refrigerator is too moist and the freezer is too dry. The general rule for green coffee storage is this: if it's comfortable for you, then your coffee is happy too. Keeping the beans in a cupboard or pantry in your kitchen is usually sufficient, but the best storage conditions for green coffee probably exist in your basement or another part of the house that is not subject to large shifts in temperature and humidity. You can store it in the ziplock bags for a few months, or for longer in a fabric bag that allows better air movement. If you live in a dry region, keep your beans in an airtight container or bag to keep the moisture from evaporating. There are bugs or larvae that might be attracted to the burlap or cotton, but almost nothing will eat green coffee. Green coffee can get moldy if it gets wet, so keep your beans dry and throw away any coffee that gets soaked.
If you have a home vacuum sealer you may consider vacuum packaging any coffees you want to store long-term. It is not necessary, but it will protect the flavors of the bean, especially in very humid or very dry environments.
There is a difference between “aged coffees” and old coffees. Aged coffees are put through a specific process of rotation, not just left to sit in a bag, so all old coffee is not "aged." Aged coffees display unusual (and often desirable) qualities, such as reduced acidity and interesting flavor notes. Not all coffees age well, but some are greatly improved. Particularly bright coffees lose their character after about a year and taste flat, but more earthy coffees can age well. Older coffees usually display a "baggy" quality - they start to taste like the bag they are stored in, or like paper or cardboard. Yum!
Finally, some coffees store better than others, both for transport and for the home user. Typically, very high grown coffees tend to hold up the best and retain their flavor characteristics longest. Bright, floral coffee can lose those volatile compounds faster than other coffees that are perhaps less sparkling to begin with.
For some thoughts on roasted coffee storage and grinding/brewing.
Coffee Storage for Transport
For decades now, green coffee has been transported from origin in 60 kg or 70 kg (132 to 152 pound) natural fiber bags - jute, sisal or burlap. Coffee keeps a reasonably long time in these bags (about a year) and they are very durable. In the past few years, however, the specialty coffee industry has been experimenting with alternatives, primarily packaging in multi-layer plastic bags (GrainPro) or vacuum packaging in Mylar bags and shipping in cardboard boxes. This is an investment for mills and adds some labor and cost, but both methods extend the flavor-life of the coffee. b
Vacuum packing at origin is fairly rare because of the cost. We see it with Cup of Excellence auction coffees, Brazil Daterra, Panama Esmeralda, and some Kenyas. It is an expensive process, adding roughly 10 cents a pound. Buyers of top-tier specialty coffee will cope with this increase, but for middle-tier specialty coffee, where cost is more of an issue, the technology is less feasible. Vacuum packaging requires more handling too, as the vacuum sealed blocks of coffee seem to work best in the 25 to 50 lb. range, not 132 to 150lbs. like the bags.
The GrainPro bags are a multi-layer plastic bag (a vapor barrier sandwiched between two layers of polyethylene) made to prolong the storage life of dried grains and seeds. They provide a moisture and vapor barrier, protecting against "ingress of water vapor, while retaining low O2 and high CO2 levels created by the respiration of the commodity" (quoted from the GrainPro literature). The use of these bags has been suggested for some time, and the results of an interesting study conducted by Andrew Miller and Luke Harris were published in Roast Magazine in the July/August 2008 issue. Their study on four different coffees found that coffee flavor was better preserved by warehouse storage in GrainPro than in jute.
GrainPro adds 3-6 months to the shelf life, conservatively speaking. Vacuum packing has longer-term benefits if they are multi-laminate bags, up to 9 months. A lot of this is still developing as the industry starts to adopt these materials.