THE HOME BARISTA'S GUIDE TO ESPRESSO just under "Frothing Milk". Closer to the bottom of the page under "First things to learn" - last paragraph.
The milk in the pitcher should whirlpool or form a standing wave of turbulence in order to fold foam into liquid. With a one hole tip, angle the entry, and keep it close to the edge of the pitcher to rotate the milk into a whirlpool. With a multi-hole tip, point it straight down and keep it near the center of the pitcher—the hole dispersion pattern on a properly designed tip will create a whirlpool or a standing wave of turbulence for you. If your multi-hole tip does not do this, change it for another, or block some holes and convert it to slower, single hole use.



