In a commercial context, Espresso is all about making coffee fast—30 seconds per cup, compared to 4 minutes for filter coffee. That’s a big difference when you have 30 people waiting for service. It’s all achieved by pressure-speeding-up extraction.
When scaling your pressure to achieve different levels of extraction, using 9 bars will help you extract more with light roasts. When you need to extract less, 6 bars will help with dark roasts.
Angelo Moriondo: The Myth of the Selfish Barista – Barista Hustle
1884 Angelo Moriondo, the owner of the Hotel and Café Ligure in Turin, wanted to fix the problem of customers having to wait 4 minutes for a filter coffee to be made. Moriondo was not an inventor; he created the first espresso machine. Boiling water trapped steam and used steam pressure to push boiling water through the coffee at 1-2 bars; it was a quicker way to make coffee. The ‘express’ coffee machine (meaning instantly delivering coffee, thanks to steam pressure).
In 1949, Achille Gaggia made a massive leap in pressure with a spring lever, which now could generate crema. As a spring expands, it exerts less force, so the pressure profile declines.
1961 Faema E61 used an electric pump to provide a constant 9 bars of pressure.
2010 Pressure Profiling La Marzocco Strata came in, an electric gear pump that could do varying pressure at varying times through the shot.
The name Crema came from the marketing genius of Achille Gaggia in 1949.
The first-time high pressure was used in making coffee produced a bitter ‘coffee scum’, foam on top, which was initially scraped off and discarded. Gaggia made a negative into a positive. Calling the coffee “Crema caffè naturale” (natural coffee cream), because it made a creamy coffee.
Crema is formed by the CO2 trapped in freshly roasted coffee beans, which are hit with hot water under pressure, and the CO2 is forced to carbonate into the brewing yield in the puck (like a SodaStream). Once the coffee leaves the pressurised basket and exits the basket to the atmospheric environment (no more pressure on the coffee), the coffee is supersaturated and can’t hold onto the CO2 anymore, so it comes out of the solution where surfactants (surface active agent), such as melanomas (roast by-products), trap the CO2 in a bubble.
Incidentally, robusta produces about twice the crema of arabica. Robusta has less oil than arabica, producing a more stable emulsion. Oils weaken surfactants, like getting egg yolk into egg white when beating. Dark roasts produce more CO2 than light roasts.
Tiger striping in crema is just pieces of coffee on top of the foam (looks nice).
Crema indicates that the coffee was fresh and had been brewed with enough pressure to create crema. More crema gives a more roasted note, but removing it reduces bitterness.
Crema is not something that improves the taste of coffee; it just improves the appearance.
Why are espresso machines set to 9 bars? There is a flow peak covered in
Espresso Coffee: The Science of Quality 2004 by Rinantonio Viani, Andrea Illy
and Scott Rao Espresso Extraction: Measurement and Mastery.
You can experiment using a fixed dose of coffee at a fixed time of 30 seconds—varying pressures of 7,8,9, 10, and 11 bars. As pressure increases, more liquid gets through in a fixed time, and the flow increases until you cross the 9-bar threshold. The water pressure starts to compact the cake, making it harder to get through, and the flow decreases. So, 9 bars is about the peak flow for most espresso machines.
Pre-infusion occurs when water enters the basket and ends when the machine reaches peak brewing pressure. The aim is to gently wet all of the coffee at less than 3 bars before a big force of 9 bars hits it. This will improve the evenness of extraction and produce better-tasting coffee. Some machines use flow restrictors 0.6 – 0.8, which will take about 6 or 7 seconds before full pressure hits the puck.
Pre-infusion allows you to grind finer. One theory is fines migration; the puck swells up and traps the fines, preventing them from moving through the shot and sandbagging the basket holes.
The higher the pressure, the more likely you will get channels and uneven extraction.
Espresso channelling occurs when water flows unevenly through the coffee grounds during extraction. Imagine it as water taking a shortcut instead of flowing evenly through the entire coffee bed. Here’s how it happens:
Remember, addressing channelling ensures a better-tasting espresso!
RDT, also known as the Ross Droplet Technique, is a clever method used in coffee preparation. Let’s dive into the details:
So, next time you grind your beans, consider giving them a gentle mist—the Ross way!
Lever machines are great because as you wash way more of your puck, it becomes more susceptible to channelling. You decrease your pressure, which reduces the likelihood of channelling.
Espresso flow profiling is a fascinating technique that allows baristas to exert more control over the extraction process. Let’s dive into the details:
Flow profiling empowers baristas to create consistently flavorful espresso shots by thoughtfully managing water flow. ☕🌊1234
