FLAT Drawdown Flow and Extraction Times
Once it is wet, the filter stitches to the dripper walls, eliminating the bypass effect. That is why different flow rates can be obtained depending on the dripper, opening a new world of possibilities for the barista to experiment with and select the dripper depending on the target extraction time.
As an example, the FLAT in a Kalita ceramic dripper (shown in the photo) has a very FAST drawdown time, while the FLAT in a Kalita glass dripper has a SLOW drawdown time. As a reference, in a continuous and constant pour, the Kalita glass can have a drawdown time 20% slower than the ceramic model depending on factors such as grind size, technique, and number of pours.
In the graphic above, it is possible to appreciate a great difference in the extraction time produced using the FLAT in combination with different drippers and grinds. The absence of a bypass makes the filter very sensitive to the dripper geometries. This phenomenon can be considered once the barista selects the dripper to be used with the FLAT to achieve target recipes and extractions.
As shown in the graphic above, the impact of grind size on extraction drawdown is significant when using FLAT filters, while waved filters are less affected due to air channels and bypass, resulting in more even coffee particle extractions.