title_body: Why do some grounds float and others sink when brewing by pour over
upvoted_answer: Bean density varies dramatically with roast level.  The more roasted a bean is, the less dense it becomes.  My guess would be that less dense beans would have more of a tendency to float and more dense beans would have a tendency to sink.  However, I imagine that there are other factors as well.  Grind size would affect the mass vs surface size of the grounds and have some say as well.  Age could also be a factor since freshly roasted beans still contain/give off some amount of gas.  That degassing time can also vary with roast level and bean variety, so just time since roast may not always be a consistent measure.  Overall I'd guess there are four plus factors affecting the "float" of your grounds.  And that's not to even say anything about the content of the water itself.