I must say, I find this thread both amusing and scary at the same time. Amusing in that folks are worried about bottle bombs from yeast, but not about heating pressurized glass bottles. Scary because glass is inherently unpredictable, and frankly, I'm a bit surprised that more explosions haven't occurred.
Pappers, while I appreciate the information and detail which you have provided, I'm not convinced that your method is safe at any reasonable carbonation level. You have admonished people to not to pasteurize over-carbonated bottles, but at what level is it over-carbonated?
If you take any brewing calculator (see Brewheads
) and punch in a few numbers it may be informative. Take 3 volumes of CO2 and a temperature of 190 F and see what the pressure inside the bottle becomes (135 PSI). That's enough pressure to blow Champagne bottles. Even Champagne bottles can explode - visit any Champagne producer and you'll invariably find some broken glass. Beer bottle are definitely not designed for that (what do they test them at 60 PSI maybe?). At 2 volumes you get 98 PSI.
So back to the calculator. If you have 2 volumes of CO2 and the temp in the pot drops down to 160 when you put the bottles in and stays at that level, you'll only get 75 PSI. Honestly, I don't even want to go there, but at least it is a lot lower.
Now yeast themselves will only ferment up to around 7-8 atmospheres of CO2 pressure (even Champagne yeast). So they aren't going to produce a pressure above about 98-110 PSI at room temp. So if you are worried that the yeast are going to explode bottles at 98-110 PSI, then why on earth would you heat bottles so that they range from 98-135 PSI. I cannot understand the logic.
The only rationale that I can put to it is if the yeast are left alone, that 98-110 PSI will be there at all times where in the pasteurization process, the bottles only stay at that pressure for 10 minutes and are then able to cool down back to reasonable pressures, so that if they survive the boiling, you should be okay. However as you reach in to grab a 190 degree glass bottle with 100 PSI in it, I'd only do it wearing some heavy duty mitts and some safety goggles.
The fact that you've been fortunate thus far does not guarantee future safety. I've had some commercial bottles explode in a small outdoor fridge when it lost power and the temp was above 100F, so putting bottles with any level of carbonation in 190F water is potentially dangerous. I would strongly encourage anyone considering this approach to rethink the effort. It's a heck of a lot safer to force carbonate to 2 volumes of CO2 if you want to keep something sweet.