title_body: How do I know when to stop pulling my shot?
upvoted_answer: I generally judge when to stop my shot based off when blonding begins to occur. This is when the espresso changes to a noticeably lighter, yellowish color. At this stage, only bitter flavors are being extracted from the coffee, and any more extraction will only degrade the flavor of your shot.
  
  It takes a bit of practice to notice blonding, and can be made more obvious by using a bottomless portafilter. I also suggest using a stopwatch to determine how long it takes before blonding occurs, so you can see how consistent the rest of your process is.