title_body: Is it necessary to allow a shot of espresso to rest before adding it to a drink?
upvoted_answer: Not necessary in my opinion.  In fact, i prefer to add it as soon as possible.  The activity you describe is the crema dissipating.  I prefer a lot of crema...  if you wait 30 seconds, there should still be decent crema integrity.  By the way, Starbucks trains their baristas to add the shot within 10 seconds of brewing.