Brewing water temperature is important because it influences flavor, brew strength and flow rate. Sensory evaluation shows that both acidity and body increase when coffee is brewed at a higher temperature, and bitterness and astringency decrease with lower temperatures. The rate at which each chemical component in coffee is dissolved is also related to temperature. Check out the following table, which shows the increase in concentration of some of these compounds as temperature increases. (expressed in mg/L)

The “ideal” temperature is determined by a number of variables, the most important of which is your taste. But most professionals prefer temperatures in the range of 185-204 degrees for espresso preparation. The following are a few established facts regarding the relationship of temperature to espresso quality.

• Excessively low temperatures produce sour, under-extracted espresso
• Excessively high temperatures produce bitter, acrid and woody flavors
• Higher temperatures result in more solids extraction and body
• Higher temperatures result in slower flow rates

But remember, espresso preparation (coffee preparation) relies on many variables. So just because you produce a sour, under-extracted espresso, that doesn’t mean temperature – or temperature alone – is the culprit.

Managing Brewing Temperature

Thankfully, good commercial espresso machines can be incredibly reliable in temperature management. Multiple-boiler machines – which have one boiler dedicated to steam wands and one to brewing water – are now commonly outfitted with a PID (proportional integral derivative) controller and can produce consistent brewing temperatures shot after shot. Think of PIDs as a precision thermostat.

But baristas should be mindful to purge the group head prior to engaging the portafilter and producing a shot. This purge not only clears the dispersion screen of any debris, but it also preheats the group head to ensure greater temperature stability.