A range of immersion brewers use pressure as part of the extraction and filtration processes. This category includes, along with the AeroPress, the syphon and the more recently invented SteepShot brewer, because they utilise pressure to extract the coffee. Aerobie Inc. have estimated the amount of pressure that is achievable with a medium or high amount of arm action from a barista:
‘The AeroPress filter is 2.5 inches in diameter so the area of the filter is 4.9 square inches. If you press down firmly on a scale, it is relatively easy to get the scale up to 25 pounds and then, if you press hard on the scale, you can certainly get it up to 50 pounds. Therefore, if you press similarly hard on your AeroPress while brewing coffee, the firm pressing will be at 5.1 psi (25 lbs/4.9 sq in) and the harder pressing will be at 10.2 psi (50 lbs/4.9 sq in). Since a bar of pressure is 14.7 psi, the former is .35 bar and the latter is .70 bar. We have done taste comparisons between minimal and maximum pressure on an AeroPress and our taste buds can’t tell the difference.’
In this video, we install a pressure gauge into an AeroPress plunger. We fitted onto the device the same type of meter that we use to measure the pressure in an espresso machine boiler. We then compared the readings we obtained when plunging with different amounts of downward force.