title_body: Does the caffeine content differ in "ristretto" shots?
upvoted_answer: Well first off what is your definition of ristretto? It's very frequently misunderstood to mean simply a short shot of espresso, when really it's all about your coffee to yield ratio. Ristretto styled shots range somewhere in the 1:1 to 1:1.5 range (arguably). For example if you put in 18 grams of coffee, and then yield out 20 grams of espresso (1:1.1)- then you are somewhere in the land of ristretto. 
  
  What does this mean as far as caffeine goes? There is no difference at all. Whether you are pulling a normale or a ristretto shot, you still want an extraction somewhere around 20% of the original coffee mass. This means that you are extracting the exact same amount of coffee, but simply putting that into a smaller amount of water.
  
  The other thing to look at is that caffeine is one of the first compounds that is extracted in the extraction process. So even if you decided to pull the shot a bit short and under extract it, you should still have the same caffeine content.
  
  I'm sorry I have no sources or citation. I hope this helps!