It’s the concentrated essence of coffee. A pure expression of the flavors locked in the bean. Coffee with its amplifiers turned up to eleven.
We call it espresso.
After one sip of a well-made espresso, one might wonder how such intensity of flavor is even possible. Baristas know that extracting the best flavors from good coffees takes finely ground coffee, the right amount of hot water, and very high brewing pressure.
The modern espresso machine which creates those conditions is the result of over 100 years’ worth of innovation and refinement. Knowing how these machines work helps professional baristas make better espresso. This same understanding can help the Barista at Home choose and use the right espresso machine in their own kitchens.
Brewing under pressure
One hallmark of a well-made espresso is the silky-smooth caramel-colored emulsion of coffee oils, sugars, and carbon dioxide gas called crema. To get it, and the full flavor of an espresso, it takes high brewing water pressure – about 9 bars worth.
Innovators had long used steam and other mechanical means to increase speed and brewing pressure. It wasn’t until after World War II, however, that a spring-and-lever-driven design was able to achieve pressures high enough to produce crema.
Levers and pistons have now mostly been replaced with electric-motor-driven pumps. Lever machines remain a unique option for mobile espresso bars and the adventurous barista at home.
Controlling the brew water
One key feature of a brewed espresso is its diminutive size. A double espresso typically has a volume of 2 ounces or less. Producing that volume consistently requires controlling the water flow through the ground coffee. In most espresso machines, this water flow is started and stopped by pairing the aforementioned electric pump with a solenoid-driven brew valve.
This combination of pump and valve can be operated in a few ways.
The simplest arrangement finds both wired to an on-off switch. This semi-automatic style puts control of the brew water directly at the barista’s fingertips. It’s simplicity usually means lower price. The barista does need to monitor the espresso carefully though: watching the stream of coffee while it brews into a shotglass or familiar ceramic cup, possibly guided by a small scale.
Other machines automate the process a bit more by stopping the shot for the barista. This volumetric system uses a small flowmeter to measure the amount of water dispensed, then stops the flow at the programmed volume. This type of system works reliably but is typically a bit more expensive than semi-automatic versions.
The boiling point
Brewing water isn’t the only thing under pressure in an espresso machine. Most are built around a steam boiler which contains both superheated water and pressurized steam. The steam is useful for steaming milk for various espresso beverages, which we’ll discuss in a future episode of Barista at Home.
To make great espresso, brewing water must be heated to about 200⁰F. One good way to do this heats brewing water by passing it through separate chambers inside the steam boiler called heat exchangers. This popular approach relies on careful design and barista skill to produce appropriately-hot water. It’s mechanically simple, inexpensive, and works well.
Another great approach heats brewing water directly using one or more dedicated coffee boilers. This multiple-boiler style of machine often uses a digital heater control to ensure that brewing water reaches the coffee at exactly the right temperature. This degree of control is appreciated by many baristas. Like many premium features, this control comes with a premium price tag.
A hot shower
Once brewing water is heated, it flows to one or more brew groups. This highly-specialized component serves several important functions.
Since the group is water’s last stop before reaching the ground coffee, the group can fine-tune brewing temperature. Clever Italian engineers have long counted on this, which is why many groups are heavy and made of brass.
Even extraction is essential for espresso quality. For that reason, espresso machine groups use internal channels and stainless steel screens to create a uniform shower of water.
Brew groups also feature pliable gaskets to keep pressurized brewing water contained, as well as grooves which securely hold while still allowing the barista to remove a closely-related component…
As the name suggests, the portafilter is a portable filter. It’s purpose is to hold the ground coffee during the extraction process.
The “filter” portion is a small stainless-steel basket, its bottom perforated by dozens of tiny holes. This basket is held in a sturdy chrome-plated brass housing. Many feature spouts on the bottom to direct streams of brewed espresso into waiting cups. All have a handle to enable the barista to easily remove it to dispose of spent grounds and reload with fresh.
Portafilter baskets come in a variety of sizes. 1 ounce single espressos might utilize a basket designed for as little as 7 grams of ground coffee, while “triple baskets” meant to produce larger volumes may accommodate well over 20 grams. Baskets do have an optimal fill level, so skilled baristas will select a basket which is appropriate for the amount of espresso they plan to make. Most professional baristas choose a “double basket” which is ideal for 16-20 grams of ground coffee and between 1 and 2 ounces of brewed espresso.
Better coffee through science
A well-made espresso: good coffee, finely ground, plus the right amount of hot water, brewed under pressure. 100 years of science has never tasted so good.
Want to learn even more about using science to make better coffee? Stay tuned for next month’s edition of Barista at Home. Can’t wait that long? Call Dilworth Coffee at (866)849-1682 and ask to talk with Brady about Brewology.