Grind size and choosing the right grinder

Grind size: 

Different grind sizes are used for different coffee brewing methods to avoid over or under extraction of coffee. Under extraction is when enough flavours are not extracted from your ground coffee. This happens when the grind size is too coarse. Over extraction is when too much flavour is extracted from the ground coffee. The coffee tastes bitter and unpleasant. This happens grind size is too fine. Grind size affects the following: contact time, extraction rate and flow rate.  Grinding the coffee finer increases the surface area. A finer grind reduces the rate of flow, resulting in an increased contact time. The larger surface area, thus, increases the rate of extraction. It boils down to (yes, that's a coffee reference) personal preference. You really have to experiment to figure out the grind size that suits your palate.

Choosing the right grinder

Grinders can change the taste and quality of your coffee. It is therefore important that you choose the right grinder. There are essentially two types of grinders, Blade Grinders and Burr Grinders.

Blade grinders typically contain two blades at the centre. When the blades rotate, the coffee beans are chopped and ground. These are similar to the blenders/grinders  in your kitchen.

Burr Grinders contain two revolving abrasives called burrs. The coffee beans are fed into burrs in small quantities. The rotating burrs grind the beans through friction and feeds the ground coffee into a container. The distance between the burrs can be changed to get different grind sizes.

Burr grinders win over blade grinder in uniformity of and control over grind sizes. To get a reasonably uniform grind size in blade grinder, you have to grind the beans in spurts (inching) instead of grinding all at one go. Blade grinders however beat the burr grinders in cost (they are cheaper than the burrs) and ready availability. 

If you are coffee connoisseur, you should pick up a burr grinder.