I made a four gallon porter, adding 1 pound of flame torched caramelized raisins (ala Lost Abbey) during the boil. After torching the raisins, I pureed them with a cup or two of hot wort, and dumped the slurry into the kettle. The raisins boiled for an hour or more. I also added 1 pound of Piloncillo sugar to the boil.
The wort fermented with WLP530 to give it a Belgiany flavor. Starting gravity was around 1.070 and two weeks later, it terminated at 1.010.
The resulting beer is has absolutely no raisin flavor - none. With a pound of raisins in a four gallon batch, a raisin flavor should be very apparent. For argument sake, Dog Fish Head Raisin Detre calls for 8 ounces and there is no mistaking it is a raisin beer.
I suspect the long boil is the root of the absent raisin flavor.
Does anyone have experience brewing with raisins and perhaps a similar experience? Did the boil kill the flavor?