We can think of several reasons for grinding your own coffee beans at home, not the least of which the aroma of freshly ground coffee.
Ground coffee will quickly go stale. The best time to grind your beans is just before brewing, grinding only the amount that you will use during that brew. Decide how much coffee you wish to brew, measure out the appropriate amount of beans and grind only that amount. The best ratio of water to ground coffee is 1:16.6 — for 720ml (25 oz) of brewed coffee that would be 43 grams (1.5 oz) of coffee.
Unless you always brew coffee using only one device or method, you will need to grind your coffee differently from time to time. Fine grind for some types of brewing, medium grind to coarse grind for others. This is easily accomplished when you grind your own coffee beans at home just as you prepare to make your coffee. One size does not fit all for ground coffee.
7 Grinds
We generally talk about 7 grind sizes: extra-fine, fine, medium-fine, medium, medium-course, course, and extra-course. These grind sizes span the gamut from Turkish/Espresso with a water contact time of 30 seconds to cold-brews with a water contact time of 12 hours or more.
Grinder
If I had to guess, I would expect that most folks use a blade grinder of some sort. While it is possible to achieve particular grind sizes using a blade grinder, a better choice for grinding your beans at home is a burr grinder. With a considerable amount of trial and error, some folks are able to approximate various grind sizes with a blade grinder – by pulsing the button, tracking the time, and eyeballing the grind consistency.
But, you can’t get serious about home brewing coffee if you’re still pummeling your beans with a blade grinder – they just don’t cut the beans into uniform sizes. Also, the whirling action of the blade gets too hot which can scorch your beans. Both of these issues make a difference in how your cup tastes. A burr grinder has a set of rotating “burrs” that crush the beans to the correct uniform size.