Very different measured efficiencies between batches

[dude1]

With quite similar grain bills (crushed the same way) and a very predictible equipment (Braumeister), I get very different measured efficiencies in BeerSmith

They range from from 61% to 78%

I measure OG with a refractometer at the end of the chill when the wort is ready to be transferred to the fermenter, before pitching yeast, of course

Any idea why I get so irregular efficiencies?

Thanks

 

[Oginme]

How close are you to target gravity (pre- and post- boil)? How close are you in volumes (again, pre- and post- boil)? If everything else is the same between the two brews: volumes, grain bill, crush, mash time, vorlauf time, drainage, water retention in grain, etc. then the problem probably is with the flow of the mash liquor through the grain bed or differences in dispersing the grain into the mash water. a few good sized dough balls of grain can easily make a big difference in extraction efficiency.

 

[dude1]

Thanks

I find the same unpredictable swings in terms of pre-boil gravity as for OG.

Pre-boil vol is constant as I add water up to 24.5L
Post-boil vol is also very constant, about 20.5L

The only differences are between grain bills, but here again, I can't see a clear pattern between "Total grain" and the "Measured Mash Eff" of the Mash section

I will try to stir the mash better
You are right, when results are so unpredictable/unexplainable, the problem may come from dry grain balls

Thanks for your hints!

 

[dmtaylor]

How many pounds of grains are you using? The more weight of grain, the more wort that is permanently soaked up in the spent grains. This tends to reduce efficiency for bigger beers, and improve efficiency for small "lite" beers. Be sure to take this into account.

Who crushes your grains? Different shops will crush the grains to different extents.

Do you know your mash pH? If it's farther out than 5.2-5.5, then you're likely losing efficiency. This might hurt you for either very light colored beers, or very dark ones.