In the following series of videos, barista and BH Coach, Julia Parera Deniz carries out a series of experiments looking into the performance of the French press under different brewing conditions. The videos are narrated by recording artist and member of the BH team, Debra Blaquiere.
Glass vs. Steel vs. Double-Wall French Press
In this video, we compare pyrex glass, vacuum insulated steel, and double-walled acrylic French presses to compare their temperature profiles. We used the same recipe for each brew. The only variable in the process is the material each brewer is made from.
At 10 minutes into the brewing process, and after plunging, we removed a sample of brewed coffee from each French press and measured each sample’s total dissolved solids (TDS) with a coffee refractometer. You can see the results of the experiment recorded in the chart below. The temperature of the glass French press was far lower after the water was added, and it dropped to the lowest temperature of all the brewers after 10 minutes of steeping. The brewer that remained the hottest for longest was the vacuum insulated steel.
You can see a direct correlation between a more slowly declining temperature profile and a higher TDS. The Vacuum steel brewer achieved a very high extraction yield of 25.67%. The acrylic brewer reached 23.16%, whilst the glass brewer reached 22.15%. All these yields are relatively high, but the hottest slurry produced a brew that was 16% stronger and more extracted than the coolest one.