So the temp strip on my bottle of QF doesn't appear to work...

[Burnt Toast]

I heat it in the microwave for 10s, stopped, then another ten (it bubbled slightly at the end), but when I removed it, even though the bottle was quite warm, the temp strip read black.

Sounds like youve overheated (bottle temp over 100 dg). Simply let the bottle cool down until you see the green indicator on the temp strip.