Originally Posted by steve25
how much higher will o.g. be after boil, compared to out of mash tun?
it depends on how much volume you have before and after the boil.
if you measure 1.040
gravity in 7
gallons of wort in the kettle, your wort contains a total of:40 * 7 = 280
If you boil this down to 5 gallons, those 280 points will be spread out in 5 gallons, so the gravity after the boil will be:280 / 5 = 56
Leaving you with 1.056
gravity on the 5 gallons.