I'm a first-time poster, but I've searched a lot for the answer to this problem. I've noticed in some of my beers that, after I bottle (I don't taste this in the sample I take on bottling day), I get an unpleasant flavor that is sort of like cherry cough syrup. It seems to be mostly in the nose, and I really get it when I burp.
The flavor has appeared prominently in an ESB and a CA common that I made (both half-batches, all grain on the stove-top). It has been conspicuously absent on the light summer ales I've made during the same time. That made me think it could have something to do with hops or the specialty grains I use for color and flavor in the darker beers.
Here's an example of the process that resulted in the off-aroma/flavor:
4.25lb American 2-row
.5 lb Munich Malt
.5 lb Crystal 60L
Northern Brewer .5 oz (60)
Northern Brewer .75 oz (15)
Northern Brewer .6 oz (1)
I fermented it at 60 degrees (I have a chest freezer with temperature control, and I stick the thermometer onto the side of the carboy). Left it in the primary for 3 weeks, then transferred to bottling bucket. Used PBW and Star San on everything. Beer came out beautifully clear and perfectly carbonated. Taste is great except for this one thing.
Thanks for your help!