confused about boil amounts

[wadwrich]

I have been looking at AG recipes. I am confused because although they are all trying to achieve 5.5 gal. batches, there are boil amounts ranging from 6 - almost 8 gallons. Why is that? If liquid evaporates at a certain rate when boiling, wouldn't you get different amounts at the end of a 60 min. boil if you boiled 6 and then say 7.5 gallons? How would you get 5.5 gallons at the end from both of them? Do they evaporate at different rates depending on how much grain was mashed?

 

[histo320]

Boil off rates vary from place to place and even brew to brew for most people. The mash does not have anything to do with the amount of boiloff whereas temperature, humidity, and altitude do.

Most people attempt to have 5.5 gallons at the end of the boil so that when they bottle/keg they have a full 5 gallons.

In the Summer I start the boil with 6.25 gallons, in the winter I start with 7.25, due to more boil off.