DOES GRIND SIZE MATTER?
No matter how great your coffee beans are, you can ruin getting that perfect cup of coffee with the wrong grind size.
Too "coarse" of a grind and your coffee becomes under extracted and can taste weak or sour. To "fine" a grind, and it is over extracted and can be bitter tasting.
Here's a little simple science behind it.
Approximately 30% of coffee is soluble in water and coffee tastes best when it is extracted between 18 and 22 percent. Extraction yield is the amount of coffee that is dissolved in the water.
The grind setting determines the size of the coffee particles. Smaller grinds have more surface area, thus extraction happens faster. Coarser grinds have a larger surface area and extraction takes longer.
Think of sand particles (fine grind) versus stones (coarse grind). If you take the same amount of coffee beans and grind it on a "fine" setting you wind up with a lot of small grinds (ie. a lot of surface area) for the water to come in contact with and extract from. With the same amount of beans on a "coarse" grind you end up with fewer grinds, but larger size and thus a smaller surface area to extract from.
So, you need to determine how you will brew your coffee before you grind, because size matters!
HOW TO IDENTIFY YOUR GRIND SIZE
COARSE - Chunky pieces of coffee beans. Similar to heavy kosher salt.
MEDIUM - More like coarse sand with visible flakes and gritty texture.
FINE - Smooth texture, slightly finer than table salt.
VERY FINE - Finer than granulated sugar. Coffee grains are barely discernible.
MATCHING YOUR GRIND SIZE TO YOUR BREWING METHOD
Drip coffee makers with flat bottom filters (i.e. BUNN)
Drip coffee makers with cone shaped filters (KRUPS, Cuisinart, Chemex etc.)
Espresso machines extract fast at high pressure, and thus require a finer grind. Whereas the French Press method requires a coarser grind as it is immersion brewing where the grounds steep for 4-5 minutes.
A little tip to help you remember: Fast and Fine (fast extraction / fine grind) and then the opposite! Sorry, but we don't have a good tag line for coarse!