BIAB Efficiency 102.8% <--- How's that possible?


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May 10, 2013
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I'm a BIAB brewer and new to Brewer's Friend. I'm trying to understand the efficiency data-entry and the results I'm seeing.

Here's a batch I just brewed that produced efficiency numbers which I don't understand.

Thanks in advance for any guidance anyone can provide!

Conversion: 102.8% <--- How's that possible?
Pre-Boil: 87% 31.7 ppg
Ending Kettle: 91% 33.1 ppg
Brew House: 67% 24.5 ppg

Here's the values I plugged in that produced those efficiency results

Mash Complete:
Volume: 8.5 gal <--If I use the pre-boil volume I get a conversion of 93.7% which seems more reasonable
Gravity: 1.045

Pre-Boil Gravity
Kettle Volume: 7.75 gal
Gravity: 1.045

Boil Complete
Kettle Volume: 6.75
Orig Gravity: 1.054

Fermentation Complete
Final Gravity: 1.012

Water Gallons Quarts
Total mash water needed 8.51 34
Grain absorption losses -0.74 -3
Starting boil volume 7.77 31.1
Boil off losses -1 -4
Kettle dead space -1 -4
Hops absorption losses -0.02 -0.1
Misc. losses -0.25 -1
Amount going into fermentor 5.5 22
Total: 8.51 34

Amount Fermentable PPG °L Bill %
10 lb American - Pale 2-Row 37 1.8 90.9%
0.5 lb Belgian - CaraMunich 33 50 4.5%
0.5 lb American - Chocolate 29 350 4.5%
11 lb Total 
Amount Variety Type AA Use Time IBU
0.5 oz Northern Brewer Pellet 7.8 Boil 60 min 14.73

Mash Guidelines
Amount Description Type Temp Time
-- BIAB Temperature 150 F 60 min

Other Ingredients
Amount Name Type Use Time
20 g Pumpkin Pie Spice Spice Boil 5 min
1 each Whir-floc tablet Fining Boil 15 min

Fermentis / Safale - English Ale Yeast S-04
Attenuation (avg):72%
Optimum Temp:59 - 75 °F
Fermentation Temp:70 °F
Pitch Rate:0.35 (M cells / ml / ° P) 99 B cells required
That all looks pretty good.

Higher than 100% efficiency just means you mashed slightly more grain than the recipe called for, or the ppgs in the recipe editor were slightly lower than what was actually purchased. Grain ppg does vary slightly year to year. Not all scales are accurately calibrated at LHBSs.

As for the Pre-Boil: 87% 31.7 ppg vs Ending Kettle: 91% 33.1 ppg, that is just due to rounding errors in measurment, but in theory should be exactly the same, unless the pumpkin spice had some sugars in it?

If I use the pre-boil volume I get a conversion of 93.7% which seems more reasonable
93.7% conversion would be low. It is possible there was some stratification which threw off that reading.