Gravity Confusion

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tgolanos

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I brewed a German Pils this afternoon. Before starting, I entered my recipe into Brewer's Friend to get all of my numbers (expected BG, OG, FG, strike water amount & temp, etc) and hit everything spot-on. Pre-Boil gravity was 1.036 for a conversion efficiency of 80%. At this point, it seemed all was well. Boil went well, too, so now I'm just letting it cool enough to pitch my yeast.

However, now comes the interesting part. I took a sample to measure the OG, cooled it to my hydrometer temp but only measured 1.038- 0.002 points higher than my BG. I did add some top-off water to counter my boil-off so my first thought was it hadn't mixed well yet. I took another reading 30-45 minutes later, and it was still 1.038.

Any ideas of what went wrong here? Am I missing something glaringly obvious? Recipe is below for reference. Any help would be much appreciated.

Batch Size: 25L (20L post boil into fermenter, 5L top-off)
Boil size: 30L/8 Gallons
Estimated BG: 1.036
Measured BG: 1.036
Estimated OG: 1.043
Measured OG: 1.038

Ingredients:
3.25kg/7.2lbs Pilsner Malt (Castle), 37ppG
0.80kg/1.8lbs Pale 2-row (Joe White), 38ppG
0.25kg/0.55lbs Carapils (Weyermann), 33ppG
0.10kg/0.22lbs Melanoidin (Weyermann), 37ppG

Double milled all of the grains myself while heating my mash water. All the grains looked crushed and there was even some flour. Mashed in 18L/4.7 Gallons of water at 66°C for 60 minutes, dunk-sparged in cold water for 10 minutes, then squeezed. I did notice a tear in one of my grain bags - I do split-boils in 2 kettles because my stove can't handle full volume - so I couldn't squeeze that one as much as I had hoped. Combined my runnings, measured BG, and began boil.

Hops:
30g Perle at 60 minutes
15g Perle at 30 minutes
15g Saaz at 5 minutes

Cooled the worts in water/ice baths until they reached 30°C and poured them into the fermenter. Took samples to measure OG and let the wort continue to cool.
 
36 X 30 / 25 = 43

You post boil diluted to 25 liters should have had a gravity of 1.043 if your preboil of 30 liters had a gravity of 1.036.

Your measurements are skewed somewhere. Either volume, gravity or both.

Did you leave wort behind in the kettle with trub and hop debris?
 
You boiled of 10 liters (2.6 gallons) in one hour on your stove top, split boil?

Is that typical for your setup, because it seems excessive, indicating one of your volume measurements were off.
 
36 X 30 / 25 = 43

You post boil diluted to 25 liters should have had a gravity of 1.043 if your preboil of 30 liters had a gravity of 1.036.

Your measurements are skewed somewhere. Either volume, gravity or both.

Your maths gives me the exact Gravity I was expecting. I'm wondering now if I mis-read my hydrometer when I took the BG sample. I did stir the mash less than I normally would because it was holding heat so well this time. I guess my thought was to not lose heat at the expense of stirring properly.

Did you leave wort behind in the kettle with trub and hop debris?

No. I strained all the wort into my fermenter, catching as much trub and muck as possible.

TexasWine said:
You boiled of 10 liters (2.6 gallons) in one hour on your stove top, split boil?

Is that typical for your setup, because it seems excessive, indicating one of your volume measurements were off.

10L boil-off (give or take a bit) is fairly normal for me. It's excessive, sure, but it usually doesn't present a problem since I always accommodate my recipes for that.
 
If you removed the hops and trub prior to the fermenter, you left the absorbed wort behind, it can be substantial.

If all your measurements are not true and precise.your efficiency calc goes wonky fast and is just an estimate.
 
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