Hi Rick... just got back from a couple of days away so I missed your question about the purpose of pasteurisation. Sounds like you are having fun!
Originally when Pasteur came up with the idea of pasteurisation, it was to inactivate spoilage mechanisms in wine etc, which don't have a big yeast load. This still applies to other beverages such as milk, juice, etc.
In the case of beer, cider and the like where fermentation has taken place, the idea is also to inactivate or kill the yeast so that fermentation doesn't continue in the container (otherwise there is the potential for BOOM!)
Without getting too technical about this, the "magic temperature of 60C" was developed from empirical research by an Italian scientist DelVeccio and others in the 1950s. They came up with a formula PUs=time in minutesx1.393 raised to the power of celsius temperature -60 (i.e. PU=t x 1.393^(T-60)). This is easy enough to calculate with a spreadsheet but even easier just plugging numbers into on-line calculator (google... calconic pasteurisation calculator). So, by monitoring temperature and time it is easy to track your pasteurisation level. (or working out that so many minutes at whatever temperature will give you the desired result).
Breweries still use this approach to pasteurise beer and to tailor it to minimise energy costs. Typically they will heat beer to 72C for 30 seconds which is the equivalent of 60C for 15 minutes (i.e. 15 PUs). For beer 15-30 PUs is enough, but for craft cider which has a higher yeast load, the accepted target is 50 PUs. As I said above, it is actually quite difficult to under-pasteurise cider because even just two minutes at 70C will get to around 50PUs and stop the yeast in its tracks. By the time the bottles cool down a lot more PUs will be generated from the residual heat.
Cheers.