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I routinely take my pre-boil gravity after sparging to determine mash efficiency so that I can throw in DME or Dextrose for a lower than expected yield or add water for a higher than expected yield, all in an attempt to hit my target OG.

I batch sparge, and recently I realized that the force of circulation when collecting 2nd and 3rd runnings is not enough to fully distribute the collected sugar in the entirety of the wort.

When brewing today, I took a gravity reading directly after sparging, and then again after stirring for a solid minute. The pre-stir reading when cooled to 60F was 1.080. The post-stir reading reading when cooled to 60F was 1.050, so stirring definitely had an effect.

Unfortunately, with a pre-boil gravity of 1.050 compared to the projected yield of my grain bill, I would have achieved a mash efficiency of 96%. While this high of a yield would be great, it is not possible. I should be in the ballpark of 78-80%.

My thoughts are that either (A) I did not stir long enough and vigorously enough or (B) temperature variations in collected wort are preventing consistent absorption of the sugar throughout the wort.

It seems the best time may be just before boil when the wort's temperature is consistent and the process of heating has moved things around a bit.

Has anyone experimented with this and found the optimal time/process?

  • Are you drawing your sample from the base of the pot out of a ball valve? – brewchez Nov 4 '14 at 12:27
  • Yes, drawing the sample out of the ball valve of a 20 Gallon Blichmann Boilmaker. – Matthew Nov 4 '14 at 16:56
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It's best to measure as the wort comes to the boil for the reasons you mention - all the wort is at the same temperature and the convection currents have mixed the wort fully, so you get a much more accurate reading.

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Are you sure your calculating your 100% correctly? Or more importantly have you measured your collected volume precisely this can through off your calculation significantly too.

I batch sparge as well. Once I have all my wort collected I start my burner, give it a quick stir and take an immediate sample for preboil gravity. It doesn't take much of a stir to get the sugars homogenized through the wort.

Simply get the wort swirling then cut through it again with the spoon in the opposite direction. Both the temp and the sugars will homogenize fairly quickly. There isn't anything mystical holding it back.

I have checked using a refractometer and hydrometer recently. Due to the small sample size you'd expect the refractometer process to be more suspect due to insufficient mixing, whereas the hydrometer takes a large sample with better chance for a better sampling of the wort. Both measurements were the same when corrected for temp.

  • That is exactly how I did it...stirred vigorously to a whirlpool then cut back the other direction. As for volumes, I'm using the site glass on a 20 gallon Blichmann Boilmaker. I suppose it could be inaccurate. – Matthew Nov 4 '14 at 16:58
  • Then I guess I'd be focused on my first question about what is your 100% efficiency mark. – brewchez Nov 4 '14 at 17:20
  • I can't be certain that my 100% is accurate simply because I don't verify the max potential yield of each malt every time I brew a batch of beer...it's just too much work. I use estimates...37 ppg for 2-Row, etc. I'm sure they are inaccurate from time to time within a few points, but not likely so much that I would see a false 10-15% increase in efficiency. – Matthew Nov 4 '14 at 17:24
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A refractometer helps too, since you don't need to adjust for temperature and can use a very small sample. I normally rack the wort before I take a reading (and measure volume) which helps to evenly distribute the sparge and first runnings.

  • A refractometer in this case will only save me the time of waiting for the wort to cool. Ultimately, the issue here is a lack of even distribution of sugars throughout the wort. – Matthew Nov 4 '14 at 3:21
  • Taking a hydrometer reading of a cooling sample can produce variable results. If you don't mind the time, let it sit for an hour before you take your reading. – Wyrmwood Nov 10 '14 at 23:33

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