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-   -   Pre-boil efficiency higher than post-boil??? (http://www.homebrewtalk.com/f36/pre-boil-efficiency-higher-than-post-boil-80847/)

bearymore 09-17-2008 11:09 PM

Pre-boil efficiency higher than post-boil???
 
I brewed an American brown ale this weekend. When I measured the SG pre-boil, I got 1.057 on 7.25 gallons, implying an efficiency of about 67% (disappointing). After the boil, I got an SG reading of 1.068 on 5.7 gallons, implying an efficiency of 62%. For the pre-boil reading, I cooled the sample down to 65 degrees and corrected for the 5 degree difference from 60. I measured the post-boil sample at about 73 degrees and corrected for temperature.

When I sampled the pre-boil, I stirred the wort first and took the sample from about the middle of the kettle, so I wasn't measuring the first-runnings. After the boil, I ran about 1/3 of the wort into the fermenter and took a sample from the spigot at the bottom of the kettle.

What gives here? Did I do something incorrectly? What is my actual OG?

ajf 09-18-2008 01:04 AM

You have a difference of 5 - 6% assuming completely accurate volume measurements and ignoring the fact that the wort volume shrinks by about 4% when it cools. The shrinkage reduces the difference to 1 - 2% which can be explained by hop absorption, and wort left behind in the kettle. Your figures look pretty reasonable to me except for an OG of 1.068 which seems a tad high for the style.

-a.

MN_Jay 09-18-2008 01:01 PM

Edit: Never mind, I read the question wrong.

Bobby_M 09-18-2008 02:07 PM

First thing, how accurate would you say your volume meausurements are? If you were off +/- on both measurements by say 1/2 quart, it's enough to move the numbers by a couple %. The other varience as mentioned is losses to the system, tubing, spills, and wort locked into hop sludge, hot and cold break, etc. How much wort was visibly left in the kettle?

Having a brewhouse efficiency a few points lower than mash/lauter efficiency is extremely common. Mine varies by about 4% with extremely accurate volume measurement.

bearymore 09-18-2008 07:25 PM

Quote:

Originally Posted by Bobby_M (Post 856416)
First thing, how accurate would you say your volume meausurements are? If you were off +/- on both measurements by say 1/2 quart, it's enough to move the numbers by a couple %. The other varience as mentioned is losses to the system, tubing, spills, and wort locked into hop sludge, hot and cold break, etc. How much wort was visibly left in the kettle?

Having a brewhouse efficiency a few points lower than mash/lauter efficiency is extremely common. Mine varies by about 4% with extremely accurate volume measurement.

There were quite a bit of hops in this recipe, so a fair amount of hop sludge. Also there was some spillage as I transferred the wort to the fermenter. So I suppose all was normal.


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