What is the main reason to purge the steam wand after use?

Purging the steam wand after use is essential primarily to remove milk residue and prevent bacterial growth. When milk is steamed, it can leave behind deposits in the steam wand that can quickly become a breeding ground for bacteria if not cleaned properly. By purging the wand, you clear out any leftover milk and ensure that it is sanitized before the next use. This practice not only maintains hygiene but also ensures optimal performance of the steam wand for creating quality foamed milk in the future.

Maintaining the temperature of the steam, preparing for the next shot of espresso, and ensuring consistent steam release are important considerations, but they are secondary to the critical health and cleanliness aspect of preventing residue build-up and contamination that purging directly addresses.