Advanced Espresso

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Grinder Design

Æ 2.04 Warm Grinders and Temperature Stability

Although freezing beans might offer some benefits to extraction, it requires using single dosing for each espresso shot. That is not a practical approach for a busy cafe and, indeed, not possible when a barista uses a typical grinder designed for espresso, which relies on the weight of beans in the hopper to push the coffee through the burrs. With current grinder technology, for the main espresso offering in a busy cafe, the grinder used will inevitably get hotter the more it is used.

The resulting fluctuations in temperature cause inconsistency in dosing, shot time, extraction, and flavour. A pragmatic approach, then, is to stabilise the grinder temperature as much as possible, rather than to try to cool it at all costs.

Heat in grinders is created by the motor, the shattering of the beans themselves, friction between the coffee particles as they pass through the grinder, and friction of the particles against the grind chamber and burrs. The friction and shattering of the beans creates most of the heat, so isolating the motor from the grind chamber has a relatively small effect on reducing the temperature of the grinder. Cooling the motor alone, rather than the burrs or grinding chamber, has a limited effect in coffee quality but allows a grinder to make more shots in a given time before it overheats and malfunctions.

One approach used in modern grinder models that has greatly improved grinder consistency is to use fans to cool the motor and grinding chamber. This practice can reduce the temperature increase during busy times, making the grinder more consistent in dosing as well as potentially improving flavour and extraction. However, this technology works well only if the cooling system is connected to a thermostat: a fan that is turned on permanently, rather than only when a grinder is hot, can exacerbate swings in temperature during less-busy periods.

Taking this approach a step further, the Mythos series of grinders from Nuova Simonelli actually preheat the grinder chamber when the grinder is not in use,