steam up

Short definition from Wiktionary

Verb

1. 1
   To become steamy.
2. 2
   To become coated with condensation.
3. 3
   To bring (a steam boiler) up to working steam pressure: to build up a head of steam inside (a boiler).
4. 4
   to build up a head of steam.
5. 5
   To cook by steaming.