The first tank will be at around 45 degrees Celsius and the second one at around 75C.

Calculating the PUs onces the bottles are at the right temperature will not be that difficult and the coils will turn on and off to keep the temperatures at the required degrees since once i submerge the bottles, the water in the tanks will lose heat.

The biggest question, (since I am filling the bottles at around 4 degrees Celcius) is how can I calculate the time it will take for the cider in the bottles to reach that temperature of , let's say 65-68 C.

Is there a formula that can give me the required time to reach a certain target temperature (for the cider) or even an estimate once the bottles are in those tanks?

My thermodynamics laws are a bit rusty and I can't seem to find an equation that gives me the time required, assuming that the water in the tanks will remain almost constant since the coils will turn back on every time the water loses it's target temperature.

Thanks for the help!