Extraction
In order to make great coffee, it can help to understand how coffee is brewed, a process often referred to as extraction. Here’s how it works:
There are lots of delicious chemical compounds inside roasted coffee beans. There are also some things that don’t taste fantastic. Brewing is the process of extracting those compounds out of the hard structure of the beans. This is basically done by dissolving the compounds into the water, then filtering that solution so that the structure of the beans, made of cellulose, is left behind.
The trick to good extraction is know the order that certain compounds are extracted, which basically follows the size of the molecules from smallest to largest. Here is the order:
Aromatics, fruitiness, acidity, caffeine (which is bitter)
Roast notes, AKA results of the Maillard reaction
Sweet flavors
Bitter flavors
So, the goal here is to extract the good stuff (items 1-3 on the list), and stop the extraction before there is too much of the bitter stuff.
There are two major implications of this:
If every coffee ground was a uniform sized ball, water could penetrate them evenly and dissolve what’s inside evenly. Of course, that is not the case. Still, the more similar the particles are in size, the easier it will be to make great coffee. In essence, a “better” grinder is defined by its ability to output consistently-sized grounds. A “spinning blade” grinder will typically produce a wide variety of particles: some “boulders” which are too big to get any sweetness out of, some perfectly sized particles, and some “fines,” which get fully extracted so contribute a lot of bitterness. As a result (particularly with drip methods), the coffee can be both under-extracted (sour) and over-extracted (bitter) without enough perfectly extracted coffee (sweetness) to make it work. Burr grinders have a much “tighter distribution” of ground size, so it’s much easier to target the center of the distribution and have the out lying particles fit into the overall extraction in a balanced way.
Knowing how to extract more or less allows you to improve your coffee from one batch to the next, and to make predictions about how to adjust if, for example, you are making a batch for four people instead of one. So, how do you increase extraction? Well, think about dissolving something in water, like really chunky salt. What would you do to make it dissolve?
Use hot water (Hotter water dissolves things much faster.)
Use lots of water (a small amount of water will become saturated so it will not dissolve things as well. There is less “space” in the water.)
Make the salt chunks smaller (This increases surface area.)
Stir it like crazy (Agitating the water exposes the salt to more water over time.)
Finally, you can just wait, as dissolving takes time
One coffee roaster I know describes these ideas as “adding energy to the system,” which speeds up extraction. He would also note that roasting is adding energy to the system, and indeed, darker roasts extract more easily than lighter roasts.
For coffee brewing, you can use this list to make an adjustment in your process by adjusting the variables that you can control in your particular brew method.
If you want to increase extraction (most commonly due to too much of a sour flavor), use hotter water, use more water (though this can also dilute your coffee), grind finer, add agitation, or extend brew time. It’s best to only adjust one factor at a time, though in “percolation” methods (anything where the water passes through the coffee constantly) adjusting grind size will also affect brew time, as will agitation.
If you want to decrease extraction (often because the coffee is too bitter), use cooler water, less water, a courser grind, minimize agitation, or decrease the contact time between grounds and water.
For more on this topic, read about Dialing In to maximize the flavor of any bean.