Grind Size

Whatever type of coffee or coffee brewing equipment used the objective is usually the same.

It is a general principle of any material that the smaller the particle size the greater the surface area exposed for a measured weight of material. This means that the finer the grind of coffee, the greater the surface area of coffee exposed to the hot brewing water and consequently the more extraction of coffee soluble takes place per unit time.

Over-extraction can occur if the grind is too fine for a particular brewing method and under-extraction can occur if the grind is too large. The important thing here is the brewing method used, as different methods require different infusion times and consequently a different grind size.

The usual terms applied to coffee grind size are from the largest particle size to the smallest the following...

coarse - medium - fine - very fine(espresso)

Clearly coffee brewed in a simple coffee pot where hot water is merely added to the ground coffee in a pot a coarse grind should be used as the hot water is likely to be in contact with the coffee for a long time.

Inversely in an espresso machine the water is only in contact with the grind for  20-25 seconds (although under pressure) so a very fine (or espresso)  grind is needed for optimum flavour extraction to occur.

In a similar vein drip filter coffee machines require a medium to fine grind as the filter paper restricts the flow of hot water into the jug but even so the infusion time is quite short,

The cafetiere (or French Press) method requires a medium grind as the coffee may infuse for a while before the customer decides to end the infusion process by depressing the integral strainer to trap the used grounds at the bottom of the pot.

Most coffees sold these days are marked with a description of coffee grind size and the most suitable method of brewing.