Shaking in place for the first half of the rosetta.
Forming the base of the rosetta requires the shaking technique. Shaking and fishtailing are closely related, except fishtailing is a gradual reversing motion and shaking occurs in a fixed position.
After the cup is half full and you have tilted it towards the north, the spout should be positioned at the bull’s-eye — right above the middle of the cup. As you shake the pitcher, you oscillate it on the east–west axis, on either side of the bull’s-eye.
Here, rapid eddies can be produced. The combination of a strong eddy flow and the shaking technique can amplify the results of a single swipe of the pitcher — a swipe of perhaps 1 centimetre — to more than 15 times its initial length. For this reason, the alternating east–west line should be thickly drawn. A 30-mL/sec flow rate is needed to generate this combination of thick lines and a fast eddy flow.
The figure below, which depicts a sine wave, uses the terms ‘crest’ and ‘trough’ to describe the passage of the wave along the x axis. The wavelength in the shaking technique is zero. (It’s fishtailing that has the wavelength, as we will describe in the next lesson.) That means you’re moving the pitcher from side to side but not backwards. The trick to getting smooth, thick lines is finding the balance between the flow rate, the amplitude, and the wave speed.
Barista trainers debate as to whether it is better to oscillate by allowing the pitcher to pendulum from the handle through a shake of the wrist or via a lateral motion from the elbow. You can achieve good results with either of these approaches. It all depends on your chosen pitcher grip.