Re using a sous vide and cold crashing to cool down...
I have only been looking at pasteurising to produce a sweet carbonated cider. I was intrigued by the "convenient" dishwasher temperatures, but agree with the likelihood that too much heat for too long could cause problems.
For my tastes, letting cider "fully"ferment with SO4 (which sometimes finishes above 1.000), then adding AJ, sugar or whatever to about 1.004 or 1.005, then bottle and let carbonation take place, results in a nice dry cider with just a touch of sweetness. In fact I have bottled at 1.004 or 1.005 on the way down. No pasteurising needed for this.
However, some people prefer a sweeter cider than a fully fermented "dry" cider. So, I have just pasteurised a batch at 1.004 which was bottled at 1.009. I used a 1000W sous vide set to 70C to bring the bottles up to temperture and am really pleased with the outcome. The result was a sparkling and not too sweet cider with no "cooked" or "off' taste (unlike some of the alcopop ciders on the market).
Basically the process follows JimRausch's cooler pasteurising method, but with a set of "numbers" to tell me what was happening. The bottles were preheated with hot tap water to a bit over 50C, then brought up to 60C with the sous vide. (One pasteurisation unit (PU) is generated by 60C for one minute so that is considered to be the starting point for pasteurisation)
Bear with the following arithmetic, it is important. From 60C it took 5 minutes for the bottles to reach 65C then another 10 minutes to drop down to 60C once they were removed from the water. Pasteurisation units per minute isn't a linear relationship with more PUs per minute generated as temperature increases, so you do have to keep an eye on the bottle temperature as it is easy to "overcook" (e.g. a minute at 65C will result in about 6PUs, 67C will result in about 10PUs and 70C will generate 20PUs which is almost half of the target in a minute!).
When all the arithmetic was done (temperature and PUs generated each minute using the formula PU=t+1.393^(T-60)), I found that the outcome was 54 PUs. The target was 50PUs which is the currently accepted target (according to Jolicoeur and Lea), with 65C as the "guaranteed" pasteurisation temperature to kill the yeast (although there is some evidence that temperatures slightly below 60C may also work).
Breweries and the like will work on targets as low as15-30PUs with flash pasteurising, but for "craft" cidermaking, a temperature of 65C and 50PUs seems to be an easy target for effective pasteurisation with a good margin of safety as we generally don't have access to the precise process controls available to big operators.
I was going to see if fermentation would stop if I only achieved 30 PUs, but that target turned out to be a bit hard to stick to in practice as 30PUs are generated over the five minutes it takes to heat up to 65C, so the bottles would have to be rapidly cooled from that point to stop the "cool down" pasteurisation. It is easier to just let them cool by themselves and naturally achieve 50 PUs. Certainly, much of the pasteurisation takes place in the cooling down phase. It might be possible to heat the bottles more rapidly by adding boiling water (or even heating to only 63C) but it hardly seems to be worthwhile just to gain a few minutes or shave a few PUs off the result.
So, the above method "naturally" pasteurises cider without going to too much fuss (i.e heat up from 60C to 65C over 5 minutes then cool down in ambient air). It is worth noting that carbonation from 1.009 to 1.004 drop resulted in just over 2 atmospheres and when heated to 65C the pressure got as high as 5 atm (about 75 psi) which is below the supposed 100psi limit for beer bottles. At 70C it is 6 atm or 90psi (that is another reason why temperature control is important), still below bottle bomb pressure, but take care!
