title_body: Pressurized vs non pressurized filter baskets
upvoted_answer: You will need to grind a lot finer with the non-pressurised baskets.
  With a pressurised filter basket, the resistance is mostly produced by the one tiny hole in the filter basket. For non-pressurised ones, the coffee needs to provide the resistance.
  If the grounds fail to provide enough resistance, the water will run through the coffee really fast, probably creating a bunch of channels which you can usually see as little holes in the coffee bed after the extraction. The problem with the channels is that most of the water goes through the channels (over extracting the coffee there) instead of evenly extracting all available grounds.