What you need to know about pressure to make the best-tasting espresso
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.
A brief history of espresso
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.
What is Crema?
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.
More pressure is not better.
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.
The use of different pressures: Pre-infusion
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.
WHAT ARE CHANNELS?
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:
- Uneven Flow: Water should pass through the entire coffee puck evenly when brewing espresso. However, sometimes, it finds a weak point in the coffee bed and creates a channel. Water flows faster through this channel, leaving other puck parts under-extracted.
- Over- and Under-Extraction: The coffee extracted near the channel becomes over-extracted, while grounds away from the weak point remain under-extracted. This combination results in a cup that is both weak and sour yet overly bitter.
- Causes of Channeling:
- Poor Coffee Grounds Distribution: Uneven distribution of coffee grounds in the portafilter can lead to channelling.
- Grinding Too Fine: Extremely fine grounds can cause water to find easy paths.
- Saturation: Inadequate wetting of the puck can create channels.
- Low Dose in the Basket: Too little coffee can lead to channelling.
- Fixing Channeling:
- RDT: Use water spray on the beans before grinding to reduce static electricity.
- Distribution Tools: Use tools like side tamping or self-leveling tampers.
- Puck Screens: help distribute water more evenly.
- Pre-Infusion: Allow a brief pre-infusion before full extraction.
- Inspect the Spent Coffee Puck: Look for signs of channelling.
Remember, addressing channelling ensures a better-tasting espresso!
What is RDT?
RDT, also known as the Ross Droplet Technique, is a clever method used in coffee preparation. Let’s dive into the details:
- What Is RDT?
- The Ross Droplet Technique involves adding one or two water droplets or lightly spraying a fine mist of water over your coffee beans before grinding.
- The goal? To reduce static electricity during the grinding process.
- Why Is Static a Problem?
- When you grind the coffee, static charges build up due to friction between the beans and the grinder burrs.
- These static charges cause freshly ground coffee to cling to everything it touches—your grinder, countertop, and even the air.
- How Does RDT Solve It?
- By adding a minimal amount of water to the beans, the grinder environment becomes more conductive.
- This allows the static charges to dissipate, preventing coffee grounds from behaving like magnets and sticking together.
- Benefits of RDT:
- Better taste: See Moisture-controlled triboelectrification during coffee grinding – ScienceDirect
- Consistent Grind: RDT minimizes static cling, resulting in a more uniform grind.
- Less Mess: Say goodbye to coffee grounds clinging everywhere!
- Ross’s Legacy: Named after David Ross, who introduced this technique in 2005, RDT has become a game-changer for coffee enthusiasts.
So, next time you grind your beans, consider giving them a gentle mist—the Ross way!
Puck Degradation
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
Espresso flow profiling is a fascinating technique that allows baristas to exert more control over the extraction process. Let’s dive into the details:
- What Is Flow Profiling?
- Flow profiling aims to control the flow rate of water during espresso extraction.
- Unlike pressure profiling (which focuses on varying pressure), flow profiling adjusts the rate at which water flows through the coffee puck.
- How Does It Work?
- Imagine placing an adjustable valve between the espresso machine’s boiler and the coffee grounds.
- By manipulating this valve, you can fine-tune the water flow during extraction.
- Why Is Flow Profiling Important?
- Consistent Extractions: Similar to pre-infusion, flow profiling enhances consistency. It prevents sudden, forceful water streams that can lead to uneven extraction.
- Channeling Mitigation: When water rushes through the coffee puck, it seeks paths of least resistance, causing uneven extraction. Flow profiling helps prevent this by intentionally saturating the grounds.
- Ramping Pre-Infusion: A common technique involves starting with a restricted flow and gradually opening the valve during the initial 10-15 seconds of extraction. This ensures even saturation before ramping up pressure.
- Ramping Down: Toward the end of the shot, coffee grounds become less resistant. Flow control allows precise targeting of weight output without changing the grind. Unique flavors can be explored.
- Machines with Flow Profiling:
- Notable machines, such as the Lelit Bianca and the La Marzocco GS3, use flow profiling to effectively control the flow rate.
Flow profiling empowers baristas to create consistently flavorful espresso shots by thoughtfully managing water flow. ☕🌊1234
