Although I recently admitted to my failings as a true coffee connoisseur, my palate remains resolute in its hatred of oxidation. Or, having puzzled over the chemical processes involved, I should say that I hate the change in flavors and aromas caused by reduction-oxidation, but that takes too long, and efficiency matters in the kitchen. Furthermore, while my math skills may be passable and I find physics fascinating, chemistry has, at least since the 7th grade, given me a headache: Something about all that rote memorization and what I always took to be an unhealthy and mind-numbing emphasis on the “what” at the expense of the “how”.
In any case, suffice it to say that the taste and smell of a food (for the avoidance of doubt, coffee is closer to the bottom than the top of the Food Pyramid, at least in my kitchen) changes by virtue of the food’s contact with the air we breathe, and most of these changes are not for the better. Oxidation creates that nasty metallic taste, the perception of acridness and overcooked-ness. This process is particularly acute in two of my favorite beverages, wine and coffee; fortunately, water, by my accounting the only other liquid truly essential to the sustenance of life, seems a bit more stable when left to its own devices.
In the case of coffee, the important thing to know is that the process of oxidation begins immediately, and the engine for this process is heat, although it is also deleteriously influenced by the piercing of the shell of the bean (the excellent if slightly more technical discussion I base this on may be found here): As soon as the bean is roasted, its taste and smell begins to degrade, in ways both subtle and profound: The compounds responsible for “good” flavors fade away, and the concentration of those responsible for “bad” flavors increases. The good news is that Mother Nature is also a coffee lover and, as is her wont, designed the bean in a particularly clever way: First, the external structure of the bean itself traps and protects many of the desirable features of coffee’s flavor profile inside; second, even after grinding, some of the aromatics remain inside the coffee by virtue of the bean’s naturally occurring oils and waxes known as lipids.
So what’s a deeply entrenched caffeine addict to do?
- Buy your beans in smaller amounts, as frequently as practical, and as close as possible to the date on which the beans were actually roasted. Clearly, this gives a huge edge to your local micro-roaster, and not because it’s “free trade”, or “local”, or even because they buy better beans (all of which may, or may not, matter to you), but because the chemistry itself dictates that locally roasted coffee will taste better. Funny how often this basic lesson seems to come up so frequently in food and cooking, and how much better suited to good eating (albeit more time consuming) is the old-school model of grocery shopping, in which we would buy our daily bread from a baker, our vegetables from the produce stand of a farmer who grew them, the fish from a fishmonger who just caught it. Easy rule: If you can’t figure out when it was roasted, you probably don’t want to buy it.
- If you’re going to store your beans for any length of time (and we do this as a matter of course – there is idealism, and there is keeping the family sane and the parents well-fueled at all times), try to get them in vacuum packs (to reduce air contact), and store them in the freezer (to mitigate the deleterious effects of temperature).
- Grind it when you’re going to drink it, and only brew what you’re going to drink. I don’t know about you, but I just don’t buy the argument that grinding your own beans is messy and time-consuming; and since the actual science tells me that I can drink better coffee simply by grinding my own, that seems to me a pretty cheap and easy way to consume a superior product. If you must brew a larger quantity first thing in the morning, then at least transfer it to an airtight carafe or thermos or whatever in order to slow down the nasty effects of heat and air on your beverage.
There is, as ever in the kitchen, an object lesson in all this: Simply by buying my coffee fresh and close to home, by preparing it when I actually want to drink it, and by only making the quantity that I actually want to drink, I will drink better coffee.