Previous articles have stressed that you can have the best beans and the best equipment, but the cup of coffee produced can still smell like fishy charcoal. Why? It's all to do with the "other factors." In this article, we look at one of these other factors: residual oils.

Downing his espresso in one gulp, our Technical & Quality Director Ewan Reid spins into scientific action: "Roasted coffee beans, especially high roasts like a classic espresso, are oily. The oils are a positive characteristic of the roasting process but can cause problems for the unwary." Ooh,scary!
Ewan continues, straight-faced. "If the barista doesn't take care to clean the portafilter and group head of the espresso machine regularly, the fresh aromatic oils from the coffee will begin to build up in these sectors." But hold on Ewan, won't that just mean that each cup of espresso we make will just taste better and better as the oils gather in the equipment?

"Not at all. The gathered aromatic oils will very quickly turn rancid and bitter, and that bitterness will taint every cup made." Not good.

The best way to avoid tainting your espresso is to have a proactive, preventative approach to the problem. How often you clean the machine will depend on the volumes of coffee made. Ensure regular backfiushing of traditional espresso machines, and take care to clean all the parts of the portafilter daily. If you have a bean-to-cup machine, put it through the cleaning cycle daily. Remember there is a range of foodsafe detergents available for weekly cleaning of the espresso equipment.

In short, the oils in espresso coffee represent a double-edged sword. Without them the coffee wouldn't have that amazing aroma and flavour; let them get the better of you and it's a recipe for disaster.

This article originally appeared in Fresh 7