title_body: Should I thoroughly clean the portafilter basket between shots?
upvoted_answer: There's a trade-off here. If you're working in a fast-paced coffee shop, you're likely to favour the faster option (knock out the coffee) over cleaning. Generally knocking out the coffee will get rid of >99% of the grounds from the previous pull, so the impact on the flavour of the next one will be so slight as to be unnoticeable. Usually the portafilter won't even have time to dry out, so the coffee won't dry on and clog up the portafilter.
  
  If you're making multiple coffees one after another, reusing the portafilter is probably acceptable.
  
  However if you're leaving the coffee machine alone, it's best to at least rinse out the portafilter before you (or the next person) comes to use it. Once the grounds/coffee start to dry, it'll clog up and be much harder to clean further down the line.