You might think that a brew is at risk if you allow the grinds to steep in the bottom of a French press or a cupping bowl for too long. But this graph (below) taken from Barista Hustle’s Coffee Extraction app (developed by Professor Steven Abbott) suggests otherwise. As you can see, the expected extraction rate after 8 minutes is very low with a French press. Static immersion brews such as the French press and cuppings are less susceptible to overextraction than are other brew methods that combine long extraction times with extremely high temperatures. For example, boiling coffee for 10 minutes will lead to extremely overextracted flavours in the cup. But, with both French press and cuppings, a decreasing temperature profile as a brew progresses effectively safeguards it against overextraction.
The app in this video was developed by Professor Steven Abbott. It uses the results of scientific experiments and models to predict how the different variables in brewing will affect extraction and flavour. For a detailed explanation of all the functions of this app, check out this video from the Advanced Espresso course.
Let’s consider some traditional recipes for various immersion brew methods. Methods involving more turbulence, such as ibrik or syphon, usually require shorter time frames for the extraction process; static immersion brews, such as the French press, require longer time frames. For instance, you will see a cezve being prepared in a sand heater in a time frame of little more than 2 minutes, whereas with a French press, plunging no sooner than 4 minutes is a widespread convention that has existed for generations. Even in recipes as old as this one from The Encyclopedia of Domestic Economy, printed in 1855, the authors warn against boiling the coffee for any extended period:
‘The most valuable part of the coffee is soon extracted, and it is certain that long boiling dissipates the fine aroma and flavour.