RDT: Spray or Drop or the Spoon Method Not every grinder has low retention, it’s important to make sure you’re getting out what you put in.
Make sure the puck is absolutely dry. Dosing funnel helps with distribution as well.
Distribution. The objective is to have an homogeneous and even bed of coffee to avoid uneven flow. To remove the clumps, use a needled tool to stir and move around the coffee inside. Go deep, it’s important to reach the base. Go higher slowly until out of the coffee.
Paper in the bottom of the puck? It reduces the oils, increases flow and yields higher extraction. It’s hard to get by those papers, it’s easier to cut actual paper filters. It’s very optional, it yields a different profile.
Puck screens? Thick disks of metal mash that stays on top of the coffee bed. They help distributing the water. It also allegedly prevents the expansion of coffee towards the top. It apparently increases the yield. They’re hard to clean, so it’s a bit of a nuisance.
Tamping. It’s done before the puck screen, but maybe after too. Make sure the pressure is as vertical as possible. Doesn’t have to be infinitely strong, just feel until coffee is not squishy anymore. There are tampers with auto pressure relievers but it’s not that valuable.
Pre-infuse at 3 bars until first drops, then push to 8~bars, stay there until the end. Very simple, very forgiving. If using a darker roast, pre-infusion can be shortened.
A profile for extracting sweetness out of lighted roasted coffee that are usually very acidic. Requires a slightly finer grind. At pre-infusion stage, go to 5 bars and go back to zero (stop pushing). After about 20 seconds, resume pushing at 8~9 bars.
A profile for prioritizing clarity over body by going very long (ratios above 1:5) for lighter roasts.
Roasting generates co2, that is trapped inside the grounds. Hot water at high pressure can disolve a lot of CO2. Basically carbonated water. When coffee comes out at atmospheric pressure, it starts to bubble out the CO2. Foam is just air bubbles trapped in a liquid, protected by sulfactant (a surface active agent) that wraps around the bubbles makes the bubbles strong. It’s hydrobhopic at one and and hydrophilic at the other and. Broadly speaking, the likely sulfactand are melanoidines which are byproducts of proteines in pyrolisis.
Robusta has more CO2 and less oils (lipids), and oils take the place of the sulfactant and the bubbles aren’t as strong.
Flecking / Tiger Stripes are tiny particles of ground coffee that made through and get stuck in the foam.
Crema provides feedback. Lack of crema indicates that something gone wrong, be either stale coffee or extraction was too quick etc. Skimming off the crema changes texture and reduces biterness and roastiness, but it’s a mater of personal preference. The crema isn’t that relevant for texture, as espresso is already very bodied. A great looking crema is nice, but it doesn’t make sense to pursue more crema.
Grind size: Finer grinds opens more surface area thus more extraction. Ratio/Extraction Yield: how much espresso you’re pulling out of the original dose. Temperature: higher temperature means higher extraction. 90~96 C Pressure/Flow Rate: higher pressure increases extraction.
How to get a head start just from the coffee description?
Variety: Catura, Catuaí, Gueisha, Maragogipe etc. Processing: Natural, Washed, Honey etc. Roast Level: Light, Medium, Dark.
heirloom is dense, hence difficult to extract, hence we need more extraction. Finer grind size, bigger ratio, more temperature. Maragogipe is less dense and is bigger and more spread out. It’s more soluble, so it needs less extraction.
Start by entering the zone: 1 to 2~3 ratio in about 20~30 seconds. This is achieved with big and intuitive changes in grind size and . Until entering this zone, dialing by taste is unproductive.
First and foremost consider the roast level to decide on the ratio. Darker roasts extract easier.
The reference intervals for Espresso brews are:
(Source: https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0219906)