Sorry for yet another somewhat long winded reply to a problem but there are a couple of issues that you might consider. I have a fair bit of empirical data on time, temperature, and pressure from my "experiments" with heat pasteurising which might help with your issue. If you have access to Jolicoeur, Section 15.2 has a good coverage of temperature and pressure issues when pasteurising.
I can't tell you what went wrong, but your temperature targets etc all seem to be in the right order for a successful heat pasteurisation. Based on my experiences (successful and unsuccessful, with a few bottle bombs along the way), you might think about the following...
- How strong are the bottles? From the pic they look like fairly standard bottles with grolsch type caps. I have used bottles similar to these from the local brewing shop but I don't think they are any stronger than "standard" beer bottles which I usually salvage.
- What was the carbonation level? As a rough "rule of thumb" I have found that pasteurising bottles with 2 atm of carbonation at around 70F (fairly "normal" room temperature) will generate over 5.5 atm (80psi) of pressure at 149F as the CO2 gas is driven out of the cider. This (149F) is the "recommended" pasteurisation temperature according to both Jollicoeur and Lea. This is based on anything over 140F generating pasteurisation units (PUs) and aiming to accumulate 50 PUs in total during the process. With my Sous Vide, it takes about 5 minutes for the bottle temperature to go from 140F to 149F which generates 15 PUs (PUs vs temperature isn't linear since the higher the temperature, the more PUs are generated per per degree).
Removing the bottles and letting them cool back down to 140F takes about another 10 minutes or so, generating a further 35 PUs. There are some suggestions that around 25-30 PUs are enough for cider but I am happy to go conservative and work on 50 PUs.
The point of this is that you can expect the initial bottle pressure at room temperature to more than double by the time the bottle temperature is 149F, taking the pressure towards the 100 psi limit for "ordinary" beer bottles. So, how high was your starting carbonation?
- Was the yeast completely stopped? At 115F it is unlikely that you would have stopped the yeast even though some pasteurisation can occur below 140F. The remaining yeast may have continued generating CO2 possibly to the point where your bottles became overcarbonated, especially as you have added honey for sweetness. The yeast would continue gobbling this up. Also my data shows that at 115F the pressure would have increased by 60% above the 70F pressure. If you inadvertently started at, say 4 atm (easy to do if the yeast was still working away after bottling and before pasteurisation) you could have reached over 6 atm (100 psi). My last batch took about a week from bottling for the pressure to reach 2 atm, which is when I pasteurised.
So releasing pressure and re-pasteurising sounds like a good option. I find that I am quite happy with only slightly (perlant or petillant) carbonated cider. You still get good mouthfeel at 2 atm without it being too fizzy.
- How much carbonation do you have after releasing the caps? Obviously the trick is to retain some carbonation, but I don't know how to reliably keep the carbonation level where you want it when you release the caps. Possibly the simplest way is to decant one of your bottles into a plastic soda bottle and use it for the squeeze test (most soda is carbonated to around 2.5 atm which makes the soda bottle quite firm). By trial and error, releasing pressure at room temperature will give you an idea of what works. As doublejef suggests, warmer bottles will degas more, but on the other hand, cold bottles will retain more CO2 in solution to be released for carbonation after you reseal the bottles.
Good luck!
