Coffee has its own Cain and Abel: siblings with opposed personalities sharing the same DNA. Aging is coffee's Abel—the positive, naturally occurring chemical and physical processes that, over time, optimize roasted coffee's aromas and flavors. An opposing process, staling, is coffee's Cain: negative (yet, still natural) changes to aroma and taste, bent on ruining aging's good and vital work—literally killing quality, if given the opportunity. Whether Cain wins comes down to how coffee is preserved after roasting.
The sermon stops here, its purpose to introduce a discussion about coffee packaging—a complex topic that raises lots of questions. The critical factor in coffee packaging is roasting—specifically, the chemical changes that occur during and after the roasting process. Understanding roasting dynamics creates the foundation to understand packaging, and the strengths and limitations of bags and cans. What's more, all bagging methods aren't created equal; same goes for canning. I'll sort out the specifics in a bit.
A green-hued coffee bean picked at the farm is a very different thing from its later, roasted self—what we picture as "coffee." Green coffee beans are essentially composed of water, minerals (mainly potassium), carbohydrates (sugars, mono/poly/olyglycerides), amino and chlorogenic acids, proteins, lipids (mainly triglycerides), caffeine, and a host of other substances like trigonelline, enzymes, and polyphenols—some in minor quantities, but still fundamental. Many of these team up during roasting to create aromas. Other kinds of aromas, called volatiles, with names like 3-isobutyl-2-methoxypyrazine, are present in the raw beans themselves, in large amounts. I'll refrain from giving the full list.
When coffee is roasted, almost everything about it becomes something new. Small, hard, green, and barely aromatic raw beans become bigger, brown, fragile, and fully aromatic.
The wonderful, warming coffee aroma we know isn't present in these raw beans. It emerges through the magic of fire during the roasting process: through coffee's physical and chemical reactions to high temperatures. What takes place is known as the Maillard Reaction.
During any chemical reaction, nothing is destroyed or created, it is often said; rather, everything is transformed. When coffee is roasted, almost everything about it becomes something new. Small, hard, green, and barely aromatic raw beans become bigger, brown, fragile, and fully aromatic. Volatile and non-volatile aromas melt into one another, creating thousands of new aromas. And the process generates lots of carbon dioxide.
That carbon dioxide—up to 10 liters per kilo of coffee for dark-roasted coffee, owing to the long roasting time—naturally releases from the beans over a period of weeks after roasting, rapidly over the first few days, then more gradually over the remainder of what's called the degassing period.
Carbon dioxide is a friend of coffee: part of its Abel side, since it preserves and even enhances quality. Carbon dioxide that escapes from beans forms a barrier against coffee's biggest enemy, its main Cain: oxygen, and the oxidation process it fuels. Oxidation is part of staling, and it degrades quality by altering coffee's essential oils and aromatic components, ultimately creating a rancid taste akin to butter left out too long.
Other post-roasting, staling-promoting enemies of coffee include moisture, high temperature, and light. Moisture and heat do their dirty work quickly, accelerating oxidation and degradation of aromas. Light has a similar, albeit less aggressive effect.
As blood brothers, aging and staling are a part of the same process, with a complicated, delicate relationship. Right after roasting, for up to roughly five days, coffee beans contain too much carbon dioxide to be brewed properly. [Corby's note: When I was researching The Joy of Coffee, I found that three days past roasting was the ideal time to brew beans.] Its aromatic components are unstable. Preparing espresso with young and carbon dioxide-rich beans creates far too much crema (yes, too much of the silky foam isn't a good thing), because crema is primarily composed of carbon dioxide. Overly young coffee, as I call it, is less aromatic and less flavorful—under-developed, like a Polaroid picture before everything comes into focus. The taste strikes some as sour.
Conversely, beans not properly preserved or used too long after roasting lose too much carbon dioxide; in the process, too many volatile aromas escape. The result is degraded, weakened coffee in the cup.
All of which, finally, brings us to packaging, to bag vs. can. How best to ensure aging triumphs over staling? The answer is: It depends.
NEXT: How packaging and proper storage can extend coffee's shelf-life