Which tool is essential for steaming milk and incorporating air?

The steaming pitcher is essential for steaming milk and incorporating air because it is specifically designed to hold milk while allowing the barista to control the aeration process. The shape of the pitcher facilitates the creation of a whirlpool effect, which is critical for achieving the desired microfoam texture. The spout of the pitcher helps in precisely pouring the steamed milk, which is particularly important for latte art.

While other tools such as a cleaning towel can be used to maintain hygiene and a frothing thermometer can help monitor milk temperature, they do not serve the primary function of steaming and aerating the milk. Measuring cups are useful for portioning ingredients but lack the design necessary for effectively frothing milk. Therefore, the steaming pitcher stands out as the vital instrument for achieving properly steamed milk with the right texture for espresso drinks.