What causes this cherry-cough-syrup off-flavor?

Hello,

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:

CA Common:

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)

OG: 1.054
FG: 1.018

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!

Jonathan

Are you using tap water? If your local water system uses chloramine instead of chlorine, then it won't boil out, and you have chlorinated water in your beer, which I've read can cause cough-syrup flavors if there's enough chlorine/ chloramine. Try using campden tablets in your brewing water (cheap) or buying bottled water for your next batch (less cheap).

edit: 1/2 of a campden tablet will treat 10 gallons of water= cruch the tablet and mix it in, letting it stand for a few minutes before you brew.

Yeah, that could be it - I bought some tablets recently, but I don't remember if they made it into the batch I was talking about. I thought the next thing I'd do if nothing works is try a batch with only store-water...

Although, would chloramine affect darker/hoppier beers differentially?