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Original gravvity way lower than estimated

I just started an Imperial Stout and I use iBrewmaster. It calculated the OG at 1.094 but it came out at 1.078, pretty big difference and I am trying to figure out why. I double checked ingredients. Only thing I can think of is I had it in the system as a 5.5 gallon boil going down to a 5 gallon batch and I only boiled 4.5 gall then added water to bring it up to 5 gallons before taking the gravity reading. But either way it should still be the same right? Here is the recipe

Imp stout
Style: Imperial Stout OG: 1.078 (I changed it to the actual one, it was estimated 1.094)
Type: Extract FG: 1.018
Rating: 4.0 ABV: 7.86 %
Calories: 254 IBU’s: 55.18
Efficiency: 70 % Boil Size: 5.57 Gal
Color: 35.4 SRM Batch Size: 5.00 Gal
Preboil OG: 1.088 Boil Time: 60 minutes

Fermentation Steps
Name Days / Temp
Primary 14 days @ 68.0°F
Secondary 14 days @ 72.0°F

Grains & Adjuncts
Amount Percentage Name Time Gravity
6.00 lbs 42.11 % Briess Golden Light LME 60 mins 1.038
5.00 lbs 35.09 % Briess Golden Light LME 30 mins 1.038
1.00 lbs 7.02 % Briess Caramel 120L 60 mins 1.032
0.50 lbs 3.51 % Brown Malt 60 mins 1.032
0.50 lbs 3.51 % Briess Caramel 20L 60 mins 1.033
0.50 lbs 3.51 % Chocolate Malt 60 mins 1.034
0.50 lbs 3.51 % Briess Caramel 40L 60 mins 1.034
0.25 lbs 1.75 % Briess Roasted Barley 60 mins 1.033

Amount IBU’s Name Time AA %
3.00 ozs 51.35 Cluster 60 mins 7.00
1.00 ozs 1.76 Northern Brewer 2 mins 8.50
1.00 ozs 2.07 Centennial 2 mins 10.00

Amount Name Laboratory / ID
3.00 pkg California Ale White Labs 0001

Amount Name Time Stage
8.00 oz Malto-Dextrine 15 mins Boil

It is notoriously difficult to mix top off water into wort thoroughly, especially with later extract additions. Depending on where you take the sample from, you can get wildly different numbers after topping off.

Almost all of your gravity is coming from extract, which you really can’t screw up. I’d say you made good beer, and I’d move forward assuming the calculated OG was correct, not the measured OG.

One other thing - I don’t know how iBrewmaster works, but it looks like it’s assigning gravity numbers to your specialty grains. If you just steeped them, you will only be getting negligible sugars from these.

I topped off and then airated for about 20-25 min so I think it would have blended somewhat but maybe not. That could account for it I guess. I can also change the gravity reading to 0 for all the steeped grains. Would that be it?

That’s actually stirring it up way better than I was giving you credit for.

When I punch your recipe into BeerSmith, I’m only getting an estimated OG of 1.085. Without the specialty grains, your recipe would yield 1.075. I’m guessing you just didn’t get very much out of the specialty grains, which is totally normal. Your OG could very well have been 1.078, which I think is perfectly fine for this recipe.

What temperature did you steep the specialty grains at, and for how long?

I started them when the water hit 165, turned off the flame and let them sit for 20 min with a lid on.

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