How to tell if I have mold in my beer?

I've been brewing beer for almost a year now using Brewhouse Beer Kits.
I started a Canadian Light Lager a little while ago and it has been ready to bottle for a few days and I have noticed what may appear to be mold in the carboy.
It is clinging around the edge of the carboy on the surface and is white. I spoke with the manager at the beer supplies store who told me that it could be hops residue but I can't figure out how to tell the difference between that and mold.
Any suggestions?
Thanks

J.

If you can post a picture we can look at it, he's probably right that it is leftover krausen and hop residue. It is really rare for mold to grow on beer, BUT the good news actually is that if it is moldy, the beer below may be perfectly fine and drinkable. You would just rack the beer slowly and carefully under the beer, leaving the mold behind.

A little taste and sniff test will tell you if the beer is fine or not. Remember nothing pathogeninc can grow in beer...so even an "infected" batch (which is totally different from mold, btw,) could be perfectly drinkable...some people do make beers purposely infected for the funkiness (like flander's red.)

SO don't be quick to count it out...it may be perfectly fine.

Best way is to cuture an agar plate. Incubate. The cells will grow into easily identifiable colonies...which you can take a sample of...and prepare a slide...and look at the micro organism under a microscope.

This beer turned out to be one of the best ones I've brewed. Just rack from underneath

Thank you so much guys.
I really appreciate it.
It turns out that it is mold, minimal though. So the batch should be okay.
Take care and all the best in brewing

J.

No problem. Its kind of scary when you see that for the first time, on a batch you worked so hard on.