A famous South Korean cafe, Rodier, was using a rotary WDT tool, D**. However, while the coffee stream seemed to be stable, the EC logs were coming out with a very typical brewing shape. After thinking long and hard about what could be the cause, I checked the WDT tool and saw that it had a lot of very thick needles in the center.

I disable the tool, and immediately the center extraction starts disappeared. The EC logs also returned to their normal appearance.

"I only use the manual WDT tool these days. It tastes better and is more reliable.”