Efficiency pre-boil vs. post-boil

[cluttered_table]

I brewed a 2.5 gallon batch of Palmer's Oak Butt Brown, increasing the grain bill by 10% to allow for batch sparging:

4.125 lb standard 2-row
1 lb Cara Red
0.25 lb Caramunich III
0.125 lb chocolate malt

Total 5.5 lbs. Mashed with 7 qt water for 60 min at 155 F, then added 1.75 qt top-off to make first draining 50% of pre-boil (6 of 12 qt).

Drained 1.5 gal at 1.0812 (1.078 + 0.0032 temp correction). By my math, that's 61.5% efficiency, about what you'd expect for no sparge.

Sparged with 3 qt and drained at 1.0488 (1.045 + 0.0038 temp correction).

Sparged again with 3 qt and drained at 1.0291 (1.025 + 0.0041 temp correction).

Total collected 3 gal, combined gravity 1.0601 (91% efficiency??).

60 min boil, 8 qts in fermenter, plus approx 0.75 qt lost to hops and hot break in kettle. Gravity post-boil was only 1.0656 (corrected for temp). I know I boiled off more than I planned, but did I really lose that much fermentable sugar?

Thanks.

 

[KAMMEE]

You don't boil off sugars, only water vapor. So, you condense the wort by boiling. You went from 1.061 to 1.066, thats concentration of sugars... not thinning of the wort. Looks like you're fine.

 

[cluttered_table]

You don't boil off sugars, only water vapor. So, you condense the wort by boiling. You went from 1.061 to 1.066, thats concentration of sugars... not thinning of the wort. Looks like you're fine.

But the volume was reduced from 12 qt to 8.75 (8 in fermenter + 0.75 loss).

12/8.75 = 1.371, so if sugar stays and water goes during the boil, gravity should have been closer to 60 * 1.371 or 1.083.

I'm starting to question my gravity measurements of the wort, pre-boil. I pulled a sample of each draining, and put it in a white bowl to cool. [The white bowl made it easy to see the color get lighter in each draining.] In the 10 minutes or so the hot (170 F) wort was cooling in the bowl, water could have evaporated out, concentrating the sample wort and skewing the readings up.

 

[Yooper]

Keep in mind that if you checked your SG at mash or boil temps, even with temp correction tables, they are notoriously inaccurate. You really need to cool the sample to under 90 degrees or so in order to use the temperature adjustment tables with any accuracy.

I blame your hot temp OG readings as the fault here. I'm sure that's the issue. The readings are just not correct, that's why they don't add up.

 

[BendBrewer]

Do the math.

(3*60.1) / 5.5

(2.75*65.6) / 5.5

See how your efficiency didn't change?

 

[cluttered_table]

Do the math.

(3*60.1) / 5.5

(2.75*65.6) / 5.5

See how your efficiency didn't change?

I think you may have mis-read my numbers:

Volume at start of boil was 12 qt (3 gal), gravity was 1.0601.

Volume at end of boil was 8 qt (2 gal) in fermenter plus 0.75 qt (0.1875 gal) left in boil kettle. That 0.75 qt was estimated from 1 cup of hot break muck plus about 2 cups wort-logged whole hops. [At the end of the boil I whirlpooled and let set covered for 10 minutes, then siphoned off to two smaller covered pots for cooling in the bathtub.] Gravity was 1.0656.

I started with 12 qt and I ended up with 8 qt plus 0.75 qt non-recoverable, or 8.75 qt. That means 3.25 qt evaporated over the course of 60 min, which seems about right.

(12/4)*60.1/5.5 = 32.8
(8.75/4)*65.6/5.5 = 26.1

I read (and corrected) SG for the 3 drainings at temps between 84-90 F, having let the samples cool in bowls from a starting temp of about 160-170 F. It may be that evaporation during cooling is to blame, which makes more sense than me hitting 91% efficiency on my 11th homebrew batch ever. Next time I will seal the samples in a jar or the like and cool them quickly.

I'm pretty confident with the pre-boil volumes out of my MLT, based on several calibration batches. The initial water is carefully measured tap-temperature, and the wort going into the fermenter is carefully measured at 70-75 F.

 

[johnnybrew]

Use this site to calculate your efficiency. Very easy.

http://www.brewersfriend.com/brewhouse-efficiency/