How is Estimated Original Gravity Calculated?

It seems this value is typically 4-5 points higher than normal?  For example, my extract 5.25 gallon recipe uses the following grains.  Beersmith gets 1.061 but I get 1.057?  Efficiency is grayed out so I'm assuming BS uses the Yield pct for each grain?


2 lbs Briess Pilsen DME: Potential=1.044, yield=95.65%
      points=(.9565*44) * 2 / 5.25 = 16.03

6 lbs Briess Amber LME: Potential=1.038, yield=81.7%
      points=(.817 * 38) * 6 / 5.25 = 35.5

1 lbs Weyermann Caramunich II: Potential=1.035, yield=75.74%
      points=(.7574*35) * 1 / 5.25 = 5.05

By my calculation, total points should be about 1.057?  What am I missing?

Mark

Mark,
  You don't multiply the yield by the potential (they are actually just two expressions of the same underlying value).

  So your example would be:
    44 * 2/5.25
    38 * 6/5.25

And finally the last one (Caramunich) is a steeped grain which typically yields only about 15% efficiency (you don't extract much by steeping) so this would be:
  35 * 0.15 / 5.25

If you do the math and total those up you will be very close to the BeerSmith 2 number.

Brad

Great, thanks.  If I chose 2-row barley and mashed it then I would multiply by the efficiency correct? 

Mark

If you mash it - (such as partial mash or all grain) it will use your overall brewhouse efficiency to calculate the OG.

Brad