Coffee Grinders - Their maintenance, another key ingredient in the delivery of great coffee

I was reminded today following a visit to one of my customers just how important it is to have a programme that ensures that your coffee grinder is regularly maintained.

Today most if not all coffee shops have a coffee grinder alongside their espresso machine. We have a few customers in the food service business who even grind their own coffee for their filter and cafetiere coffee.

This is all great stuff when it comes to ensuring that the coffee is fresh, however coffee that is not correctly ground can itself be a problem.

The issue I came across today was the bluntness of the grinding blades.

As coffee roasters this is all second nature to us. We carry out regular tests to ensure that the particle size of our ground coffee is consistent. There are many commercial tests, however the one we carry out involves using a series of different sized sieves and establishing what weight of product remains in each sieve.

The result is then plotted on a graph using the mathematical technique of standard deviation and the theory is you get the classic "bell shaped" curve. In layman terms this reflects the spread of the different particle sizes and how much variation there is from the mid point.

This all sounds like very clever stuff, and it is, as an understanding of the average particle size directly impacts the flavour of the coffee.

Let me explain further; The water that infuses with the grounds needs to be in contact for a certain period of time in order for the coffee to give up its flavour. This fact is true of all coffee makers, however appears most critical in espresso based drinks.

The correct particle size will hold the water up just sufficiently to ensure a perfect extraction, however it is reliant on the spread of particle sizes being correct.

This is where the damage done by blunt grinding discs can be so disasterous for the final beverage.

When grinding discs become blunt, rather than "chopping or slicing" the coffee bean the blades break up the beans by crushing them. This has two effects:

1. The ground coffee will become much warmer during the grinding phase. This can result in a burnt taste coming through in the cup, as the essential oils are effectively cooked by the grinding process.

2. The spread of the particle sizes becomes much greater. This affects the ability of the ground coffee to "hold up" the water during the infusion process and means that it becomes increasingly difficult to deliver a good espresso drink.

It's always difficult to answer the question " how long will discs last?", however a ball park figure for espresso coffee grinders is of the order of 300 kilos. After this volume, wear should be carefully monitored, checks include "is the ground coffee becoming noticeably hotter?", or is it taking a lot longer to grind a given volume of coffee than it was when the blades were new?

Grinders are often the forgotten cousins of the espresso making process, however they are a vital element when it comes to delivering great coffee.