You are trying to calculate extract efficiency using a no-sparge method. Of course, that's going to suck! You leave 1/3rd of the converted extract in the grain using no-sparge (more or less). Your 42% is a red-hearing. You are trying to look
just at conversion (not total extract efficiency).
You do that by comparing your first wort gravity to ideal based on mash-thickness. Remember this chart?
http://www.braukaiser.com/wiki/index.php?title=File:First_wort_gravity.gifOk, so 3 cups for 1/2 lbs. = 1.5 qt/lb thickness. From the first wort gravity chart 100% conversion would yield a gravity of 1.082 (interpolating between 1.044 and 1.053 qt/lb).
You got 1.065. 65/80 = 79% conversion eff. That's lower than it should be (90+), but its not horrible.
As I said above, no-sparge is ~approximately 66% efficient sparging process. Here's the cross-check:
66% of 79% is (0.66 * 0.79) = 52% That's in the ballpark of your 42%. Errors get amplified pretty quickly when you start dealing with smaller quantities like this. Things like real grain absorption can really dominate the equation quickly.
A decent sparge should recover 80% of conversion. Which would equal about 63% extract efficiency. Low again, but not horrible. Its not really consistent with what you are reporting from your main brewing equipment.
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The experiment above was okay for isolating some of your mash. But, its quite a bit different from your normal mash setup. Different equipment, different conditions, etc. The results were different too....so, I'm not sure how much you can really learn from it. Seems like your crush is still a suspect. But, other than that....it didn't say much.
You changed too many key parameters to make too many more parallels to your primary mash.
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Like brewfun said above: you need to brew a calibration batch. 10 lbs of 2-row. Make it a SMaSH if you don't want to waste the grain/time.
Go back to my gravity readings post, and record everything I say to record.
Do you batch or fly sparge? If you fly sparge, record the data after every 2 gallons of sparge.
After you finish sparging, drain any remaining wort from the MLT. And refill with 10 qts of water, stir. Measure the SG of the runnings. compare to this chart:
http://www.braukaiser.com/wiki/index.php?title=File:Table_for_estimating_lauter_loss.gifMeasure all volumes very carefully, to the cup. Record all RAW readings, then do all temperature conversions.