Efficiency - 5 gal vs. 10 gal batch - WTF!

[Vintage63]

I have been working diligently on getting my brew system dialed into the right efficiency so I can be a more consistent brewer. I have measured the liquid that remains in all my transfer lines and counter flow chiller, etc.

The last 3 brews have been 5 gallon batches (5.5 gallons going into the fermenter and 5 gallons being kegged). Each of those brews came in at 65% total efficiency.

So, I figure I'm pretty damn close to 65%. I get a new recipe going for this weekend and set it up exactly the same as I did for the previous 3 batches.

This time though, I am doing an 11 gallon batch and splitting into 2 fermenters (5.5 gallons each). Using BeerSmith, I scaled the recipe and made sure I had 65% in as total brew house efficiency. You know, because that's what the last 3 batches came in at.

Brew day goes off with no problems. But, my total brew house efficinecy comes in at 80%. WTF!!

I had 65% on the last 3 brews, do everything the same and get 80% this time. This is really throwing off my OG and becoming frustrating. I should have been in the 1.057-1.060 range but came in at 1.070.

Should I be making adjustments between 5 gallon vs. 10 gallon batches? What else should I be doing that I am not?

Thanks for the insight!

 

[ajf]

Assuming I don't screw up, I get about 85% mash/lauter efficiency, but only 75% brew house efficiency. At least some of this drop is caused by dead space and wort trapped in the equipment, and this will be a constant irrespective of the batch size. This would increase your brew house efficiency a little bit for a larger batch, but I don't think it would cause a 15% jump.
Do you fly sparge? If so, the increased grain bed depth could cause a noticeable increase in efficiency, and no matter what sparge method you use, the dead space in the MLT will be a constant which will increase your efficiency a bit with the larger batch.

-a.

 

[Vintage63]

Thanks ajf. Yes, I do fly sparge. I sparge at about 1 qt. per minute and use a float switch to keep about 1-2" on water on top of the grain bed.
Here I thought doing the same thing every time and accurately measuring all my brew house losses would help!
WTF is wrong!!

 

[octopus]

You should be able to back calculate what your mash/lauter efficiency was for both batches. This would provide some insight. I think you will be surprised how much trapped wort will affect your total efficiency as was previously posted. Good luck!