I just brewed a partial mash version of BierMuncher's Black Perl Porter. This was my second time brewing this beer; the first time went perfectly. This time, however, I'm getting some ridiculous gravity readings for the OG, and I just wanted to check with you guys that they couldn't possibly be right...
The gravity-contributing ingredients are (5 gal batch):
- 1.0 lb 2-row
- 2.0 lbs Munich
- 1.0 lb Caramel 20L
- 1.0 lb Chocolate
- 1.0 lb Flake oats
- 4.17 lbs Extra light DME (boiled 10 min)
- 8 oz Malto-Dextrine (boiled 20 min)
- 4 oz Lactose (boiled 15 min)
My target gravity was 1.074.
All of the grains were mashed using DeathBrewer's stove-top method. At the start of the boil I had 3.875 gallons of wort at 1.047 (~11.75% brix), which makes 182 gravity-gallons (a.k.a. "total gravity units" in Ray Daniels' Designing Beer book). My target of 5 gal at 1.074 was 370 gravity-gallons. So my deficit was 188 gravity-gallons, which at roughly 1.045 gravity per pound of DME per gallon of water implied I should add 4.17 lbs of DME during the boil in order to achieve my target gravity (my original recipe called for 4 lbs, so I was only slightly off).
I realize now, that when I did this calculation, I totally forgot to account for the gravity that would be contributed by the 12 combined ounces of malto-dextrine and lactose, which I hadn't yet added. So I should expect my OG to be higher than the 1.074 target, but not by a whole lot, right?
Well, after topping off to 5 gallons and aerating thoroughly, I drew my sample of wort and read its gravity first on the refractometer: 24.75% brix! This works out to about 1.110! I was like WTF, so I double checked with a hydrometer, and it confirmed, about 1.105 to 1.110 specific gravity.
Is it just me, or shouldn't it be physically impossible to achieve a gravity that high with the ingredients I added, no matter how great my efficiency was? There is not much hops in this recipe (1.5 oz), and in any case, I strained almost all of the hop trub out. What other kinds of factors/errors could lead to such crazy gravity readings? Is there a proper way to take a gravity reading that I'm possibly not following, which could lead to this?