Evaporation Rate

Okay, maybe this is a dumb question but here it goes: why does more wort evaporate during a 60 minute boil if the final volume is 10 gallons as opposed to 5 gallons (with the evaporation rate remaining constant)?

The evaporation rate is a percentage of the batch size, therefore 10% per hour would boil off 1/2 gal if you have a 5 gallon batch or 1 gallon if you have a 10 gal batch.

Cheers!
Brad

I have always found this to be strange, if all of my parameters remain the same ie rate of boil, boiler size, ect. but only the volume changes, then you will still lose the same amount from the boil. I always thought that loss was from the rate of boil and the size of the vessel, after all isn't the loss from the surface area and the rapidity of the boil.

I get the same loss wether I boil 20lt or 40 lt.

Andrew

Yeah, it doesn't make sense to me either, but I'm not particularly gifted in this area. I'm going to start measuring by after boil volumes to see what the figures are.

I understand Brad's explanation above, but I don't understand why the evaporation rate should be a percentage of the batch size...