Gonna brew a stout today ... probably the Oatmeal stout from last year's state fair comp and I'm thinking of trying an experiment .. that is, adding a can or raspberry puree (I'm only going to do 5 gallons).
So the question is, when to add? My first notion was in secondary ... racking onto the puree out of primary. I've seen additions from late boil to secondary ... but thinking like Oskar, it seems to me that boiling would drive off the aromatics.
It turned out okay, but was a bit astringent (partly due to very high carbonation). Did well at the OC Fair, but then it was in a category with only 4 other beers...
Add the puree after primary fermentation has slowed. It's a canned product and sterile so no worry of contamination. The primary fermentation can even drive off the aromatics as they are scrubbed by the C02.