Gusher bug?

[BDawg]

Sanitize a new cap.
Sanitize the bottle (ie, spray the whole thing outside with starsan or better yet, dip it in solution for a minute.).
Take one of your bottles that seems to be showing signs of this gushing.
Crack the cap slowly to release the pressure.
wait for the foam to rise up to the top.
Cap it with the new cap, on top of the foam.
Warm that puppy up above 70F and keep it warm for 2 or 3 weeks.

A gusher bug will show signs of infection - off flavors, acid, wild yeast flavors, etc.
An under-fermented beer will likely regain full pressure or more but have no off flavors.
Over-primed may show flat to a modest carbonation level but no off flavors.

If you can get the most experienced palate you know to taste it, you will likely get better unbiased feedback.

I'd look here to see if there's someone on there you know or lives near you:
http://www.bjcp.org/apps/reports/proctors.php

HTH-

[Klickitat Jim]

Wow, only one national or higher in eastern Washington. I'll have to work on that

[brewinhard]

Do you happen to see any noticeable ring or line (bumps or dots) in the neck of the bottle where the beer/air interface is? This can be a telltale sign of wild yeast or bacterial growth indicative of an infection. Check some random bottles with a flashlight.

[Noetikon]

A gusher bug will show signs of infection - off flavors, acid, wild yeast flavors, etc.
An under-fermented beer will likely regain full pressure or more but have no off flavors.
Over-primed may show flat to a modest carbonation level but no off flavors.
HTH-

Good tip! I'll try that. I do bottle condition for 2-3 weeks at 70+ degrees and have not noticed any obvious off-flavours yet. But I'll try this method.

And there is no tell-tale ring around the neck.