I test French press brewers much like I test standard drip coffee makers. I begin by hand-washing and hand-drying each product. Then I grind enough coffee beans to meet a specific brewing ratio. For French press brewing, that's 4 ounces of ground coffee to 32 ounces of water.
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We test French press coffee makers the same way we test standard drip machines.
Brian Bennett/CNETI then add hot water (203 degrees Fahrenheit, 95 degrees Celsius), or nearly boiling water, to the brewing chamber, stir the grounds and let them sit for 4 minutes. After that I drop the coffee plunger for each press and pour a sample cup. Next, I draw a sample of the brewed coffee and measure its percentage of total dissolved solids. I use a pocket reflectometer for this test. From there, I can calculate the extraction percentage for each batch of coffee I brew.
Ideally, the extraction percentage of brewed coffee should be in the range of 19% to 22%. Though this number alone doesn't guarantee delicious joe, it's a strong indicator of it. Ultimately, the truth lies in a proper taste test.
Coffee extraction percentage
Bodum Chambord French Press 21%Bodum Brazil French Press 19%Mueller French Press 27%Hamilton Beach French Press 23%Coffee Gator French Press 19%Veken French Press 20%Frieling French Press 19%Kona Press 17%SterlingPro French Press 18%OXO Brew Venture French Press Coffee Maker 21%