I keep being told at my local coffee shops that espresso that sits dies within 15 seconds unless it is mixed with milk. But when you drink a cup of espresso you don't slam it like a shot. None of my local barista's can actually explain what this means or the taste difference, so can anyone clarify what this means and how it happens.

Maybe they mean that the crema cant hold up to latte art, etc?

Sounds like another myth... many have seen the video where James Hoffmann made latte art after scraping off the crema from a shot.

The places available here are not doing latte art, but every shop says it, from the chains to the drive thru huts to the mom and pops. I even went to Starbucks today thinking that even though I don't like their coffee maybe the large chain would know more about it. They spouted the same line about it "dying" but couldn't explain what it actually meant either. The girl actually said that that is why espresso comes in a shot, lol.

These rules are usually intended to promote consistent behaviour from employees. A hard 10 second rule works much better than more vague training advice like "try to use shots as quickly as possible", "don't save shots for the next customer", and so on. The 10 second rule stays in the minds of every Starbucks employee, ensuring every drink is prepared with freshly made espresso. It's an excellent quality control measure.

That makes sense and was kinda what I was thinking since no one could tell me what it meant. Thanks.

Sounds like a myth.

James Hoffmann on Room Temperature Espresso



But this is a much better answer (hadn't read it when I was digging up these other sources):

Bob_McBob wrote:These rules are usually intended to promote consistent behaviour from employees. A hard 10 second rule works much better than more vague training advice like "try to use shots as quickly as possible", "don't save shots for the next customer", and so on. The 10 second rule stays in the minds of every Starbucks employee, ensuring every drink is prepared with freshly made espresso. It's an excellent quality control measure.