Hi Jnesselrode
Re your query about safe time for standard beer bottles. The short answer is "very short" if you are just trying to kill the yeast. However, a side effect of pasteurising is that it also gets rid of undesirable pathogens which could spoil the cider.
Bottles exposed to 65C for ten minutes should reach the generally accepted carbonation level for cider.
Standard "beer" bottles are usually fill rated at 4 GV (Gas Volumes). According to Boyle's Law, pasteurising at 65C for 10 minutes should not generate more than 4 GV (60psi) in still bottled beverages or 6 GV in bottled beverages carbonated to 2.0 volumes.
There is some research from Washington State University that suggests that just one minute at 60C is enough to reduce yeasts to undetectable levels (see a post by Jaypkk 1 December 2020). However longer heat exposure might be needed to destroy pathogens, hence the commonly accepted longer time to give a "belt and braces" pasteurisation treatment for cider.
Frequent members of the forum will be aware that my answers sometimes get a bit long-winded because there are a lot of issues involved. This is no exception, so following is the long-winded version for those who want to understand a bit more about pasteurising cider.
While chemical pasteurising is favoured by some cidermakers (and it works), I have a bias towards Heat Pasteurising.
Heat Pasteurising is a function of time and temperature (i.e. a high temperature for a short time will give similar results to a low temperature for a longer time). This is based on a beer industry formula (del Veccio's formula) which calculates how much pasteurisation is developed at different time and temperature combinations. Pasteurisation starts once 60C is reached.
The conventional wisdom has been that although beer requires more pasteurisation than cider, only 50 PUs (Pasteurization units... a measure of pasteurisation) is required for cider. There are recent views are that anything over 30 PUs is enough, because cider generally has a low yeast and pathogen load compared with beer and other beverages like fruit juice which require higher levels of pasteurisation.
An issue with heat pasteurising sealed bottles is that as the temperature increases, C02 is driven out of solution thus creating pressure in the bottle. Andrew Lea has a good spreadsheet which calculates pressure for different volumes of C02 and temperature (google Andrew Lea Carbonation Table). As a guide, the Volumes of C02/Temperature range we are likely to work in when pasteurising is... 2.0 Vols/60C=74psi, 2.5 Vols/65C=109psi, which should give a comfortable safety margin when using "standard beer bottles".
Although standard beer bottles may be rated for a fill pressure of 4 Gas Volumes (60 psi), they are usually designed to industry standards that require them to withstand over 250 psi regardless of their size. Some data shows that the "worst case bottle" in a batch where not all bottles are tested is likely to withstand at least 50% test pressure, so the "fill" vs "test" rating of bottles has a high safety margin. Recycled bottles are usually rated at 75% of a new bottle.
In the case of stovetop pasteurising (see Pappers post at the top of the forum), the cool bottles are put into 190F (88C) water with the heat turned off. The water heats up the bottles while at the same time the bottles cool the water. The end result is something like equilibrium of around 70C (depending on how many bottles and how big the hot water container is), i.e the bottles don't get any hotter than equilibrium so really high pressure isn't developed in the bottles. I did some trials using this method a few years ago and found that a ratio of 4 volumes of hot water (2 gallons) to 1 volume of bottles (5 x 12 oz = 0.5 gallons) resulted in 70C equilibrium
My approach to pasteurising is similar but different. I use a sous-vide heater in a large bucket to hold the bucket temperature at a constant 65C (you could do this on a stove top). Just to monitor what is going on, I also have a bottle of water with a thermometer in the bucket with the cider bottles. This tells me what internal temperature the bottles reach so I can monitor the pasteurising level and so remove the bottles at the target PUs (usually around 25 PUs when they are removed from the bucket plus they will generate another 20 PUs as they cool down after being removed from the bucket, for a total approaching 50 PUs).
FYI, attached is a typical time/temperature chart from one of my recent batches which shows what happens. The combination of 10 minutes at 65C is more than enough for effective pasteurisation.
Hope this helps!
