Why did I get geysers?

My current batch of bottle carb'ed hard cider gushes geysers and makes a serious foam head when poured. I'm trying to figure out where I went wrong.

I have a pressure monitor that I made from a gauge and PET bottle cap. I let the bottles carbonate until the pressure was 25 psi at 75°F, which according to ZahmNagel's chart should be 2 volumes of CO2. Then I put them into the fridge. I assumed that 2 vols is a safe level, but I wasn't expecting gushers.

Is there something basically wrong with my assumptions, or is 2 volumes too much?

This is how I monitor the process:

 

How much time between putting them in the fridge and then opening them to discover the problem? 2 volumes is pretty low, should not be a problem at all. Are you confident in your bottle sanitation?

 

If the idea was to arrest the yeast by chilling the beer after the chosen pressure was reached, I don't think that's reliable...

Cheers!

 

Did you have a gauge on one when it was in the fridge?

 

I put them in the fridge Weds to have them cold for Turkey Day. They'd been carbing for almost 3 weeks (Nottingham is slow). And yes, I'm quite anal about sanitation.

 

No, but the PET bottle for that batch hasn't been opened so I'll put it in the fridge and see what happens. It's currently saying 17 PSI @ 67°F, which really isn't much.

 

this is probably true.

My guess is they were still fermenting in the fridge. Not being cold for very long co2 was fully equal or in solution since it hadn't been cold for long.