What just happened? 100% mash efficiency?

[MacKiwi]

So I'm in the middle of a brew day, and just finished sparging. While the boil is on, I often calculate my mash efficiency using this tool http://www.brewersfriend.com/brewhouse-efficiency/

My recipe has 5.7kg of Marris Otter, and 0.3kg of crystal 60. I've collected 37.5 litres in the boiler, at 1.051 (yes, temperature corrected). This tells me I had a mash efficiency of 100%! :shock: I normally only manage 80-82%...

So I double-checked the gravity reading (using a different hydrometer), and checked my volume again. And I don't think I added too much grain in the first place, as the bucket I use for weighing the grain is topped out at 6kg, so I can't add any more...

Is this even possible, or am I doing something daft???

I did a few things different with the mash which might contribute...
* It was my first decoction mash. Does boiling a portion of the mash help efficiency?
* It was the bottom of Marris Otter bin, so the grist was a bit more powdery than normal.
* I'm not using a pump (turned right down) for pumping runnings to the boiler, so I had a very long, even, consistent sparge.

 

[wigwamheed]

I can only presume its a variation in the grain? I would imagine the calculators for this sort of thing will be based on an average. Did you buy grain pure crushed? Maybe you got a higher % of endosperm in your mix than husk material? Not really sure just conjecture, wish this would happen to me :)

Meant to say pre not pure, damned predictive text

 

[MacKiwi]

The grain is the last of a 25kg sack of Crisps Marris Otter (from Mr Malt Miller). There's been a few other brews from this sack, and they were normal. I'm wondering if the "dust" at the bottom of the bin has a bit more sugar in it than the usual grain...

 

[wigwamheed]

I can only presume its down to the different ratio of husk to endosperm throwing of the calculations then, hopefully someone who actually knows will come along and enlighten us