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Much higher OG than excepted

Hello folks,

So, I will try and give all the details up front, including grain bill and mash info, but the general story is that I ended up with a much higher OG than calculated via the recipe and via Beersmith.

Both the recipe and Beersmith anticipated a pre-boil gravity of 1.055, which is exactly what I hit.
Post boil was estimated at 1.068 (including Lactose). I measured 1.080.
I am not worried about the beer, but I do want to learn about what may have caused me to miss the gravity estimates. I have been brewing All Grain for only a few months and have yet to have the experience of overshooting my gravity.

Below is the grain bill/etc, as well as answers to some of the questions I would expect.
Much thanks in advance!

5 gallon batch - Sweet Stout
Pre boil vol - 6 gallons
Mash - 3.75 gallons of water, 11.5 pounds of grain at 152f for 60 minutes. Mashed out for 10 minutes. Fly sparged 3.5 gallons.
8.5 lb Maris Otter
1 lb Crystal 80L 6 row
1 lb Chocolate malt
.5 lb Black Malt
.5 lb Roasted Barley

Pre Boil gravity estimate 1.055 - gravity measured 1.055 (temp corrected)

1 lb Lactose (added at begining of boil)
.5 oz Cluster (60 min)
.5 oz Styrian Goldings (60Min)

OG estimated 1.068 - OG measured = 1.080

Yes, the gravity reading was temp corrected to 70 degree calibration
Yes, I have calibrated my hydrometer
Yes, I tripled checked my gravity reading
Yes, I recognize that the lactose is not fermentable

Just doing a few quick google searches, it appears that a lot of brewing software are under-calculating the gravity contribution of lactose at least based on actual observations. Some brewing software calculate it as low as 1.030pppg and others claim they observe it to be closer to 1.045pppg. This could account for some of the discrepancy.

I usually get 10-14 points of concentration from my boil. So if my pre-boil gravity is 1.044 then I will more than likely end up with a SG around 1.056 after my 60 minute boil. It looks like your system would be similar going from 1.055 to 1.068. That being said it would appear that the gravity of the lactose wasn’t accounted for.

I could be way off but this scenario makes sense in my head.

Were your volumes accurate? I did not see where you stated your proposed and actual final volume. I am not great at math, but it is a pretty easy calculation to go from 6 gallon preboil at 1.055 to 1.080 at xx gallons. If you ended up with only 4.6 gallons and you expected 5.3, you boil off was more that you thought.

Nothing in the process should change the ratio unless the formula did not account for the lactose

Good point, I failed to mention that. I ended with 5 gallons into the fermentor. I

Interestingly enough, I took my first gravity reading today since fermentation began. Came in at 1.028. Eek. Obviously, that is a fair amount of movement from 1.08, but it certainly is still high.

Just threw in the Cacao nibs. We will see how that changes the flavor…

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