fixing boil off % for my brewery

[butterman]

I know that at the end of the day fixing boil off % is a matter of recording brewing data & is largely a matter of experience but I have a new Herms system that I have only brewed with once in the upper reaches of summer weather. For my 50 litre pot at a rolling boil I calculated that I then had in the region of a 12% boiloff per hour.

My question to experienced brewers is what can I expect with my next brew in autumn (fall) now that the the ambient temps have dropped quite significantly. In other words is the ambient temp a significant or insignificant factor for boiloff %, such that it it is necessary or unecessary to seasonally make adjustments to the boil off % in my software.

Thanks

[BDawg]

In my experience, colder temps reduce the liveliness of the boil a bit, all other things being equal. That translates to lower roll and lower boiloff. However, there is so much play in the flame levels on my burners that that is easily compensated. Yours may or may not have as much variability so you need to find that out for yourself. If you are already backing the heat down and have a lot of room to spare, then this will not be a problem. If you max it out in the summertime just to hit your roll, then it will be more apparent as the temp dfops,

Another issue you may run into in very cold brewing is propane tanks freezing up. Running the heat for long periods may cause the tank to freeze up due to all that gas expanding. You should have more than 1 tank ready to swap out when the flame drops due to this freezing effect. I found it to sometimes happen when ambient was below 0C/32F. Obviously, the colder it is, the more this can be a problem. It can range from lower gas flow right down to complete stoppage.

Hth

[BDawg]

One other thing-
Boiloff is better measured using volume per time, not percentage. The reason is that the amount of liquid boiling off is constant based on your boil pot geometry, etc. A percentage means that less and less is boiling off as time passes, but this is observably incorrect. Setting the measurement tobliters per hour will be more accurate.

[spiderwrangler]

I feel like humidity would have an effect, but it may not be enough to really translate to anything measureable.

[Bugeater]

The volume per hour boiloff rate is much more useful than % per hour. If you have 12% boiloff on a 50 liter batch, it will be 24% on a 25 liter batch even thought you will have the same volume boiled off in both cases. You will seldom have that much a difference in starting volume however this is a consideration when you have a difference of a few liters from batch to batch. If you know your exact starting volume and your boiloff rate in liters/hour it is very easy to adjust your boil time to end up with your desired final volume.