The science and technology behind a silky smooth espresso.
Espresso is a brewing method for coffee that, through the filtering of ground coffee through highly pressurized water, generates an intense, deep and syrupy caffeinated beverage. Standard filter coffee is brewed using a drip method – heated water is simply poured over coffee grinds and allowed to filter through them under gravity alone, absorbing their oils and essences. However, espresso is a considerably more complex brewing method that involves many stages of preparation and production. These variables, which can have a dramatic impact on the finished product, include water temperature, pressure level, filter type, tamp level (how much the ground coffee is compacted before brewing!, fineness of the bean grind, type of grinder, freshness of the beans and type of bean roast.
For the espresso machine brewing process, the beans, which have been grown and roasted, are first ground into incredibly fine, uniform grains using a grinder. Next the grains are compacted by a tamper (a weighted device used to compress the grains) into the coffee machine’s portafilter, a basket device used to control the flow of water filtered through the grains. On home espresso makers, this filter is usually the pressurized variety, which is designed to automatically compensate for poor/uneven grind and tamps. The espresso machine’s pump then draws water from its tank into its boiler for heating to the correct temperature. Advanced machines use a ‘roller coaster’ technique, where the ideal temperature is maintained in a constant process of water heating, temperature checking, boiler disconnection, temperature checking and water reheating. This means that the water temperature constantly fluctuates either side of the ideal, resulting in a faster ideal temperature pick-up time when water is required for an espresso.
Finally, the water is pressurized and forced through the filter and coffee grains. The heat and pressure of the water extracts and emulsifies the essences of the ground coffee, producing a thick, syrupy liquid topped with a layer of crema – a fine-celled foam imbued with the taste and aromatic properties of the bean.
Espresso machine facts
According to the Specialty Coffee Association of America, we’re in the ‘third wave’ of coffee – it was mass produced, mass marketed and is now being refined.
Espresso is simply a unique method for brewing coffee. Any bean can be used with any level of roast, each giving a flavour dependent on origin and processing technique.
It’s often thought that a shot of espresso contains more caffeine than a cup of filter coffee. In fact, its reduced size means people consume roughly two-thirds less.
Due to its intense and deep flavour, the espresso is used as the base for many other coffee beverages, including the Corretto, Bicerin, Guillermo and Ristretto.