Jim Hughes "tagged" me in this post to blog about 5 characteristics of good coffee. I (like he) generally don't do these blog tag game things, but this one I can write about. But I may not pass the tag along.
I think I will focus on the process of making good coffee, instead of the characteristics of the finished product, as I think that will be more useful, but also the final product is so complex (hundreds of unique flavor compounds) that it would be difficult to describe. So, what follows are five characteristics of the process of making great coffee.
1 - Beans. Great coffee starts with great beans. There are many variables that factor into great beans, but I will focus on two: source and roast. A roaster must decide how to choose the beans to roast, and how to obtain them. Roasters that build direct relationships with farms that are aiming to produce a high quality product (generally called "specialty coffee") tend to also be the ones with the most care and knowledge of coffee and the coffee industry, and thus they tend to be the best roasters. If the roaster doesn't know why he is carrying/roasting a specific bean, move along. Second, the roast itself... this is critical, as coffee is useless without being roasted. The roast is an alchemic transformation of a green bean into a little package of potential flavor (think potential energy). The flavors in coffee come from the oils in the beans, developed in the roast. If you see those oils all over the surface of your beans, well they're not in the beans anymore, are they?
How do you pick a good roaster? Find one that is passionate about coffee and its potential flavors and complexity, that sources his beans directly from farms or at least goes and experiences these farms and builds relationships with the farmers, that knows why he has chosen a particular bean and how he roasted it, and that won't sell you a particular bean in more than one roast (good roasters generally feel that there is a "right roast" for each bean).
2 - Freshness. Coffee should be consumed within two weeks of the day it is roasted, in most cases. So buy from good local roasters, buy a little (e.g. 1 pound), and buy it often. Even more important - it should be ground immediately before use. Grinding should be the last step prior to combining the ground coffee with water. Coffee contains many volatile compounds which distribute flavor into brewing coffee, and one of the more important is CO2 (carbon dioxide). Roasted coffee loses much of its CO2 within the first two weeks post-roast, and once it is ground, it loses the vast majority of whatever CO2 it had within 60 seconds. So prepare your brewing system, prepare your water, then grind and brew.
3 - Grind. Coffee (the drink) is not made from whole beans, it's made with ground coffee. Coffee beans must be ground to the appropriate fineness for the type of brewing you are doing, and this will require some experimentation (generally, coarse for French press, finer for drip). Also, as mentioned above, you really want to grind as the last step before brewing. To grind with any consistency, you really need a burr grinder. Blade grinders just pulverize the same coffee particles over and over, so you get a very uneven grind.
Why does this matter? Because brewing coffee is really about extracting the flavors and oils from the ground beans. If you have an uneven grind, you will have "dust" bits along with some larger chunks... the larger chunks won't get completely extracted, and the dust bits will get massively overextracted. Overextraction means bitterness. This is why a lot of coffee is bitter (among many factors).
4 - Quantity and Time. You need to use the right amount of coffee for your brewing method, and unless you've spent some time working on your coffee, you're probably not using enough. Again, the problem is overextraction... if you stick a teaspoon of ground coffee in a 12-cup French press, you will overextract that coffee and end up with bitter (and probably "weak") coffee. Real coffee geeks speak in grams, but if you develop a fair approximation by volume, that's fine. Start somewhere in the vicinity of two tablespoons of grounds per 6-8oz of water, and go from there. Experiment. Your grind will be a factor here too, because a finer grind will extract more quickly.
Brewing time (in methods where you control this, e.g. French press) is also a major factor. This will require some experimentation, but generally 3-4 minutes is the right ballpark, if the other variables are in line.
5 - Water and Temperature. Use good water. Filtered water, spring water, whatever... just use good water. Then, use that water at the right temperature (in brewing methods where you control this). Boiling is too hot! You want to be around 200 degrees. Find a reliable, consistent way to control your water temperature.
Finally, I leave you with a characteristic that is NOT a characteristic of good coffee: bitter. Good coffee is many things, but bitter should not be a prominent one. Bitterness generally results from poor extraction (too hot, too long, too little coffee, poor grind).
Make some good coffee! FWIW, a French press and a Solis Maestro Plus grinder will get you on your way. Spend your money on the grinder, buy a cheap French press. Expensive drip brewers won't make good coffee unless every variable is right. Control the variables yourself.