Is it possible that I actually got 99% efficiency?

I brewed NB's Dead Ringer IPA kit on Friday of last week. The three previous batches to this one I had been getting terrible efficiency on. It was from a LHBS that I hadn't previously used and I always had good efficiency prior to getting from them so I'm sure it's their crush.

Anyway I was really looking forward to getting good efficiency again with this batch.

Grain bill:
11 lbs 2-row
1 lb Caramel 40

I mashed in a 10 gallon Igloo cooler at 148* for 60 mins. I lautered all of the wort out and then dumped 170* water back in until the grains were covered by about an inch of water. I stirred the mash up, let it sit for 10 minutes, lined my spaghetti strainer with paper towels, started lautering and pouring enough water into the strainer to keep the grains covered. When I ran out of water, I just left the ball valve open and when it was done, I had 7.1 gallons of 1.044 wort at 146*. Corrected for temperature, that's 1.062 at 60*.

The OG of this beer is supposed to be 1.064 but that's AFTER boiling off almost 2 gallons of water. I boiled for 90 minutes and came up a little short of 5 gallons (4.9) and my OG was 1.074.

How is it possible that I got this much efficiency from this batch?

Looks like 82% to me.

11 lbs 2-row x 37 ppg = 407
1 lb C40 x 34 ppg = 34
= 441 total

Actual:
4.9g x 74 OG = 363

363 / 441 = 82%

Not 100%, but still solid.

Also note: your preboil / postboil readings don't match.
7.1g x 62 OG = 440
4.9g x 74 OG = 363
Those 2 numbers should match if the only change is boiloff (i.e., no losses to splashing, added sugar, etc)

TyTanium said:

Also note: your preboil / postboil readings don't match.
7.1g x 62 OG = 440
4.9g x 74 OG = 363
Those 2 numbers should match if the only change is boiloff (i.e., no losses to splashing, added sugar, etc)

Click to expand...

I did my efficiency calc based on pre-boil volume and gravity, which would explain why I got 99% (440/441).

I didn't add any sugar (fermentable or otherwise) or any water prior to taking the post-boil gravity. What would cause this? Is my hydrometer not reading correctly? I have a thermapen so I know my temp numbers are accurate.

FWIW I'm happy with 82%.

I'm usually a good 5-10% higher based on my pre-boil calcs. I attribute it to a few things:

Thermal expansion...measuring volume of hot wort instead of cold. So your 7.1 measured gallons might be high by a quart or so
Temp correction...I also use a thermapen, and the correction charts are systematically high for me, especially when I'm correcting a sample over 100F. So I put my sample into a small mason jar into an ice bath to cool it quickly; it's much more accurate for me when 60-80F.
Hop absorption...are you filtering/straining into the fermenter? Hops, especially whole hops, absorb quite a bit. I use 0.15 qts per oz as an absorption factor

I wouldn't trust a hydrometer reading at much above room temp. The "corrections" don't seem to be correct most of the time.