Technical Review Information
Machine: La Marzocco GB5Extraction pressure: 9 bar
Extraction temperature: 93.5 degrees Celcius
Extraction volume: 30 mL +/- 1 mL
Filter Baskets: Synesso ridgeless
Grinder: Mazzer Robur Electronic
Dose: 20 grams +/- 0.2 grams
Baristas: Will Priestley and David Seng
Methodlogy:Every dose was weighed to 20 grams +/- 0.2 grams. It was then distributed and tamped. The shots were extracted to 30 mL and timed. This was repeated 5 times for every tamper.
The Espro was tamped until it bottomed out at 30 pounds.
The Dema.RAL was set to a tamping depth of 5 mm using digital vernier calipers.
The Pullman was tamped manually relying on the barista's muscle control for repeatability.
The results of the testing are published in the table below
Scientific Notes
For the purposes of the article, 15 kg was referred to as a force. Scientifically, this is not correct, kilograms is the S.I. measurement unit for mass. In physics, the concept of force is used to describe an influence which causes a free body to undergo an acceleration and is measured in Newtons (N). In our case, a tamper of 58 mm in diameter is pushing loosely held ground particles of coffee closer together to make them more compact. At 15 kg, the associated force of tamping is F = 15 kg * gravity = 147 N (Newtons) where gravity = 9.81 m/s^2. The following calculations detail the force of the pump acting on a 58 mm diameter filter basket and how it compares to the 147 Newtons of tamping force.
As you can see, 0.56 bar of tamping pressure is dwarfed by 9 bar of pump/brewing pressure. To put it in simpler terms, pump pressure is 16 times greater than the pressure of a 15 kg tamp in a 58 mm filter basket!
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