Krausen when washing yeast

[skw]

I bottled my latest beer yesterday and decided to wash some of the yeast cake. I followed the instructions (sanitized jar, boiled and cooled water) and put the jar in a cool place (40s) overnight for things to settle. This morning I opened it and was surprised to find that it was not just under a lot of pressure but that there was krausen on top.

Does this mean that the bottles I just filled will also continue to ferment? The fermentation had reached a stable gravity when I bottled it and there weren't any sings of krausen on top of it (I typically give my beer enough time to get a crystal clear surface before bottling, even when gravity is stable already). Was this a stuck fermentation?

I don't have any mashing facts about my beer, it was 6lbs of extract on 4 gallons of water, OG ~1.068, FG ~1.015. That did sound about right to me.

 

[ColoHox]

Could you have contaminated it? Or was the pressure sucking into the jar and not out, due to the sealed temperature change?

 

[skw]

I'm pretty sure the pressure was pushing out, not in, judging from the krausen that sprayed out of it. Contamination, maybe? I would find it hard to see how that would happen, given that the only instruments involved were the jar and the spoon, both boiled in water for several minutes.

 

[ColoHox]

What yeast is it? 1.068 to 1.015 is pretty good attenuation. Maybe by mixing it up, the last few active yeast took it down a few points?
Even more strange is that it did it cold, right?

 

[skw]

Yeast is US-05, might have been slightly under pitched.
Mostly, I'm worried about bottle bombs. I'm wondering if the beer I bottled now is going to fermented more than I expected. Maybe I should open one every other day to check pressure?