title_body: The one-way valve, to squeeze or not to squeeze?
upvoted_answer: It doesn't actually matter!
  
  The valve on the bag is there to let gas out without letting gas in. The reason for this is that freshly roasted beans will continue to give off a bit of CO2 for a little while. Coffee that's packaged immediately after roasting will give off a bit in the bag, hence the need for a valve.
  
  Oxygen causes coffee to go off, which is why we keep our coffee in airtight containers to preserve it as long as possible. It's why the valve on the bag is designed to prevent air from the outside getting in.
  
  The CO2 that's accumulating in the bags is essentially inert, and won't cause the coffee beans to go off. It makes no difference whether you squeeze it out or not!