As mentioned earlier, ground espresso coffee can be obtained in one of four ways: 1) by buying whole-bean coffees and grinding them at home just before brewing; 2) by buying whole-bean coffees and having them ground on a large-scale commercial machine; 3) by buying pre-ground, canned coffees; 4) by buying espresso "pods," little serving-sized paper bags of pre-ground coffee designed to fit in specially designed filters supplied with some home pump machines.
There is no doubt that buying fresh whole-bean coffees, storing them correctly, and grinding them just before brewing produces the freshest and most flavorful coffee of any kind, including espresso. The problem with applying this formula to espresso brewing is the precision required of the grind.
The little electric blade grinders so common now in North-American homes, used with care, will produce a grind sufficiently fine and uniform to produce decent, albeit thin-bodied, espresso on simple brewing devices that work by steam pressure only. However, larger pump or piston machines require a much more precise grind to operate to their full potential.
Whole-bean coffees custom-ground in a large, commercial grinder at the point of purchase are the next best alternative to grinding at home. Specialty coffee stores are preferable to supermarkets as a source for such coffees, since specialty stores usually maintain their grinding apparatus better than do supermarkets, and stock fresher beans.
However, if you do buy at a supermarket or fancy food store and set the grinder yourself, make certain to turn it to the setting indicated for "espresso." If there is no espresso setting indicated, turn to the finest setting and touch the grinder on for a second or two, catching a bit of the ground coffee. It should be a grit but not a powder. If you obtain a powder, back off one notch before grinding the rest of your coffee. Some commercial grinders offer two adjustments for espresso, a finer and a coarser. Set the grinder to the finest of the two adjustments if you have a pump or piston machine, the coarser if you are using a simpler machine that forces the water through the coffee with steam pressure.
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