How Flow Rate Influences Line Width
In making latte art patterns, the requisite flow rate and the width of the milk stream exiting your pitcher are not static. Even the simplest designs require two or three flow rate adjustments. To ensure a precise metric to which you can compare your own flow rate, we took precise measurements from Shinsaku and developed a flow profile for each design we will examine.
Shinsaku’s filling flow rate measures 10 ml/sec on average, whereas his painting flow rate accelerates to almost three times that rate. (We will discuss painting and filling in the next lesson.) As Shinsaku pours faster, his lines get wider. To estimate a percentage increase in the width of flow, imagine a hose with a certain volume of water passing through it. If you double the amount of water flowing through the hose, then the hose will need to be wider. Assuming his flow speed doesn’t increase, a 100% increase in the volume of milk leaving Shinsaku’s pitcher works out to roughly a 42% increase in line width.
A simple design such as the monk’s head (just a white circle surrounded by a ring of crema) calls for only one flow rate change, so it’s a good place to begin. The filling flow rate of 10 ml/sec is steadily maintained until the halfway point.
As you begin to position the design on the surface of the drink, an immediate acceleration of flow is needed. The flow rate doubles to 20 ml/sec until the liquid reaches the top of the cup. If you have managed to portion your milk judiciously, there should be just the right amount to reach the top of the cup without overflowing. This also alleviates the need to decelerate at the end of the pour.
Hitting the Accelerator
The acceleration of milk flow out of a pitcher is created by the difference between the angle of the surface of the milk and the bottom of the spout of the pitcher.