title_body: What does the 'strength' mean (in numbers)?
upvoted_answer: Coming from Germany myself I have seen this rating only on a single brand of coffee. There is no standard for this (even though us Germans seem to like standardizations), but basically strength of the coffee is about the inherent bitterness and caffeine content you get out of it.
  
  The stonger a coffee the more caffeine and also the more bitterness you will usually get.