Any food oxidizes when it is exposed to the air, coffee beans are no different. Once the beans are ground they react to the air much faster due to the increased surface area. If these grounds are not covered then the effects of this will be noticed very quickly. This is why the coffee lover grinds their own beans in their own home. By grinding at home you can grind what you need, ensuring the best freshness.
However that's not to say that it's the right option for you. Grinding take a lot of time and is quite messy. If you want a cup of coffee few people have enough time to grind their own beans. However if you want to grind your beans then you should make sure you pick the absolute best that your budget allows.
There are three different types of coffee grinder, some of these are fairly inexpensive while others are ludicrously expensive.
You can have a mashing action grinder which can be something like a mortar and pestle. You can use these to crush the beans up to produce the grinds. This however produces an uneven grind size, you shouldn't use this method unless you have no choice.
You can also purchase grinders that use a blade. Now these don't technically grind, they chop like a blender! The blade spins round and chops up the beans into smaller and smaller pieces until they are small enough to use. This method is quite quick, however the grains produced are too big and are often uneven in size.
It's important to get even sizes of grinds because otherwise the uneven surface areas can cause different amounts of coffee to be exposed to the water. Chopping also creates heat which wastes some of the aroma which would otherwise be going in to your coffee.
The best option is to use what I like to call a burr grinder. This uses a motor driven plate that has small teeth on it. This grinds the beans so that they are regular sized and small. If you can afford a good model you can even adjust the size of the granules that are produced by the machine.
It is important to be able to adjust the size of the grounds so that you can get the perfect cup of coffee. You should also be able to control the speed which reduces the amount of aroma lost by the friction.
There are two types of these grinders, real coffee lovers opt for the conical grinder. These are noisier, however they have lots of control over size and speed.
You can get a good conical grinder to go as slowly as 500 RPM. Many others spin at 10,000RPM or some even higher. It's good to have this extra bit of control so that you can fine tune and get as little heat as possible. If you are brewing Turkish style cups then you need very fine grains, which is again where the variable size comes in.
You should also take a look at the standard of construction of the unit that you are buying. Also consider how easy it is to clean, and how much noise it creates. You should opt for a model that comes with a cleaning brush and make sure you can remove the grinding plates.
Nice optional extras include auto shutoff functions, and also being able to see the beans and grinds while the machine is working. This is good because you can see exactly how well it is working. The color of the grinds can change slightly depending on the fineness of them so opt for clear containers rather than stylish black ones!
If you need some extra advice then read some reviews so that you can buy the perfect grinder for your needs.