I should have just re-read
Palmer instead of using an online calculator. My last batch yielded 7G of wort at 1.068 using 17lbs of malt. (7 x 68)/17 gives me 28 ppm. Using 16 lbs of 2 row at max of 37 ppm and 1 lbs of Oats at 32 ppm my mash efficiency is 76%. Not sure what
Brewsfriend is measuring when you select "Conversion".
Maybe this will help:
Source:
Brewer's Friend
Simplistically,
Conversion Efficiency is the percentage of starch in the grain that is converted to sugar in the mash
. It's actually a bit more complicated as it's based on specific gravity, and everything soluble (sugars, dextrins, proteins, lipids) that comes out of the grain into the wort adds to the SG. All the soluble stuff that comes from the grain in the mash is defined as extract, which is ~90% carbohydrates (sugars, dextrins, soluble starches.)
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The rest of this post is not about the definition of conversion efficiency, but rather about how percent extract potential is related to SG potential.
When you mash, some fraction of the grain is converted to soluble extract, and maltsters put this on their datasheets as a percentage. This percentage is called the extract potential. The value is based on doing a test mash (specifically a "Congress mash") done with a very fine grind, and the grain weight is based on the fully dried weight of the grain (0% moisture content.) So, what is listed on the datasheet is Fine Grind Dry Basis (FGDB) Extract Potential. Base grains typically have a FGDB potential near 80%.
When potentials are listed in SG format (e.g. 1.037) this is determined by the SG of the wort created (at 100% conversion) when one pound of grain is mashed with enough water to create one gallon of
wort. Note that the mash water volume is less than 1 gallon, as some of the final wort volume is due to the extract dissolved in the wort.
If you dissolve table sugar (sucrose) in water, 100% of the sugar dissolves, so sucrose has an extract potential of 100%. If you dissolve one pound of sucrose in 0.954 gal of water you will get 1.000 gal of sugar solution (wort) at an SG of 1.0462, or 46.2 pts/lb. Thus 46.2 pts/lb is used to represent 100% FGDB extract potential. To determine the pts/lb extract potential of a grain, you multiply the percentage extract potential by 46.2. Thus if a grain has a FGDB extract potential of 80%, then the pts/lb is:
0.8 * 46.2 = 36.96 [which rounds to 37]
Therefore, 80% extract potential is an SG potential of 1.037.
Brew on