KitchenAid 4KPES100, Coffeemaker, 88 manual Overextraction and Underextraction, Fresh Coffee Beans

Overextraction and Underextraction

Brewing great espresso takes an understanding of what actually winds up in the cup when coffee is exposed to water. Roughly 30% of a roasted coffee bean is made of water soluble compounds.

20% of those compounds dissolve fairly easily, while the remaining 10% take a little more work – which is a good thing, because that less-soluble 10% is acidic, bitter, and generally unpleasant. The goal of all coffee making is to extract the easily dissolved oils and compounds while leaving the rest in the grounds.

If ground coffee steeps in water too long, all the soluble compounds will be extracted, which makes for a very bitter brew. This is called overextraction. The opposite of overextraction is underextraction, which occurs when coffee is not exposed to the brew water long enough, leaving the essential flavours and aromas locked in the grounds. Underextraction results in coffee that is weak in taste.

Whether brewed coffee is overextracted, underextracted, or just right depends on several factors, including the ratio of coffee to brew water, the fineness of the grind, the brewing temperature, and the length of time the water is in contact with the coffee.

All these factors are either directly or indirectly affected by the barista’s technique.

Before Brewing: The Elements of Great Espresso

Before the espresso machine is even plugged in, you’ll need several elements to produce great coffee.

Fresh Coffee Beans

Great coffee can only come from fresh coffee beans, properly roasted. Many baristas recommend buying beans roasted no darker than a medium roast, the colour of which appears as an even chocolate brown. This roast preserves the natural sugars and flavour of the bean, which sets the stage for excellent espresso. A medium roast is the darkest a bean can be roasted without oils developing on the surface.

Darkly roasted beans – which appear dark brown or nearly black – look great, but the extra roasting overwhelms the more delicate coffee flavors and caramelizes any sugars. A heavy “roasted” coffee flavour, often bitter and sharp, will predominate with a dark roast.

To preserve the freshness of coffee beans:

Keep beans in an opaque, air-tight container and store them in a cool, dry place. Refrigeration is not recommended, as condensation tends to form on the beans whenever the container is opened. Freezing can help preserve beans stored for an extended period, but it will also impair flavour.

TECHNIQUES OF A BARISTA

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