title_body: When are beers better "hard" poured rather than "soft" poured?
upvoted_answer: Beers served on nitro have only about 25-40% of the dissolved carbon dioxide compared to regular beers served only on CO2.  For stouts, the figure is usually closer to 25% - 40% is for lagers served on nitro. 
  
  With only 25% of the carbon dioxide, there is less concern of creating too large a foam. Plus the nitrogen causes the foam to be made of very very small bubbles, which readily turn back into beer. You can see this as the cascade (video) after the beer has been poured hard into the glass.
  
  If the beer served on nitro has more than 35% CO2 then it's a good idea to reduce how hard you pour - as the percentage of CO2 increases, so does the size of the foam with a hard pour.