Originally Posted by earwig
That helps a lot! Which is considered more accurate, before or after boil?
If you measure after the boil you are not going to get an accurate measurement.
To use more specific numbers, lets say you want to make a SMaSH using 10 pounds of 2-row pale ale malt and you want a preboil volume of 7 gallons.
The maximum yield of 2-row is 38 points/pound/gallon (see John Palmer
) so that means the highest pre-boil gravity you get is:
1.054 = (10 pounds * 38 p/p/g / 7 gallons)
Now if you end up with an actual pre-boil volume of 1.042 then your efficiency is:
1.042/1.054 = 78%
Your beer gravity will still be higher because you will concentrate the wort in the boil. If you go down to 5.5 gallons you will end up with 1.053.
My point here is that if you calculate efficiency AFTER the boil, you would be getting 98% efficiency (1.053/1.054) which is WAY off.
To really calculate efficiency you need to know exact volumes.
Hope that helps a bit.