When instructing a new barista, I'm quick to remind him or her that brewed coffee only has two ingredients: Coffee and water. I issue this reminder to hammer home the idea that while seemingly simple on paper, this coffee thing is actually profoundly difficult to master and perfect. That is to say: You will screw it up more often than you get it right. It's just the way it is.
Additionally, to say that coffee is only two ingredients is a bit misleading, because so many other things go into the perfect cup. How coarse or fine are your coffee grounds, how hot is your water, how long do the water and coffee stay in contact?
And that's not even taking filters into consideration. But we should! Here's why.
Any time coffee is made using a filter of some sort, that filter plays a huge part in the quality of the flavor and extraction. The perforated-metal portafilter your morning espresso is pulled through, for instance, might have accumulated a build-up of old oils on the bottom during a busy drink rush, for instance, and those oils will start to go rancid and contribute off flavors over time: By noon, the drinks that pass through that residue might be fully tainted, overwhelmed by an astringent or sour, almost metallic flavor.
What about paper filters? They're disposable, so they should always be clean, right? Well, sort of: Despite their box's tamper-evident packaging, paper filters come with a host of taste contaminants all their own. From the basic papery flavor they can contribute themselves (just the nature of the beast, sadly) to the slightly dirty or woody taste that can come from any dust that might settle inside them, paper filters are a subject of much discussion and disagreement among incredibly discerning coffee lovers: To rinse or not to rinse?
(And this isn't even remotely getting into the bleached vs. natural filters debate—we'll save that for another time.)
Personally, I suggest flushing paper filters out with hot water before brewing, to ensure not only that the dusty stuff doesn't end up adding a musky note to your coffee, but also so it doesn't clog the filter's fine pores, which could slow your coffee extraction.
If you're using a filter cone, such as a Melitta, Chemex, or Clever dripper, the easiest and quickest way to rinse and preheat your paper is to place it in the cone as normal and simply pour four to five ounces of hot water through it, saturating the entire surface.
The preferred methods, however, are to dunk or soak rather than simply rinse with poured-in water. While the former flushes dust and microfibrous gunk out of the filter completely, rinsing might cause it to settle in the bottom of the cone, where it could still potentially flavor your cup.
To prevent that dusty tragedy, take the filter and, holding it open from the bottom fold, dip it upside down into a dish or bowl full of hot water. Alternately, to save time you can soak several filters at once time in a hot-water bath, using one and setting the other clean ones aside to try for future brews.
Do you rinse your filters before brewing? Do you find it makes a difference, or is this just my coffee-geek paranoia rearing its ugly, undercaffeinated head?