title_body: Inconsistent Espresso
upvoted_answer: No tamping
  
  Start tamping your coffee. Without tamping channels form a lot easier, making your shot pour a lot faster and making your coffee taste sour and bitter at the same time. If you still manage to get 11 bars of pressure somehow without tamping, I'd assume your coffee is ground way too fine anyways, making it even more likely to form channels since they offer less resistance than the puck itself.
  The fact that the first shot flows slower than the second one probably boils (no pun intended) down to a colder brew head. If you're not doing this already try flushing your brew head and portafilter to get them hot (so hot you barely manage to hold it for a few seconds) before pulling a shot.