Low OG with All Extract brew

Btaz said:

I have a brew that was supposed to have an OG of 1.080. When I measured it I got a reading of 1.077 after the correction (1.076 at 66 degrees). I took several measurements, spinning the hydrometer each time and consistently got the same result. I have a slight boil over, but other than that there really isn't anything I can figure out how I didn't get the expected OG. On top of that, using brewer's friend extract calc I should be at 1.085 (5.25G water, 12 lbs LME).

Any ideas where I might have messed up?

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BansheeRider said:

Partial or full boil?

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whoaru99 said:

A quick calculation shows that adding 0.25 gallon to make up for a boilover on a 5 gal batch of 1.080 will reduce the gravity to almost exactly as you're reading it. Calculated 1.076.

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Btaz said:

This is probably it. It is a 5.25 gallon batch. I had 4G to boil and ended up adding about 1.5 gallons to get to the full volume. I'm curious, how did you do the calculation?

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Btaz said:

Full boil starting with 4 gallons of water. Probably only boiled off/boiled about 0.25 gallons.

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chickypad said:

So not a full boil then (that's why Banshee was asking). If that's the case it could also be a mixing issue. Even if you feel like you mixed well it's very hard to get the top off water to perfectly mix with the dense wort and it can throw you off.

For the calculation G1 x V1 = G2 x V2 where G is gravity in pts, V is volume in gal:

5 x 80 = 400
400 / 5.25 = 76, or 1.076 at 5.25 gal

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Btaz said:

Thanks for the idea. I think the math isn't quite right since the OG was supposed to be 80 with 5.25 gallons of water the whole time, but when I follow along the same idea I think the boil over accounts for the difference.

LME * Water * X = OG where X is the factor that converts the LME to Water to an OG.

Initial Plan: 12 * 5.25 * X = 80
X = 80/(12*5.25) = 1.2698

Since I estimate I lost a quarter ounce during the partial boil (now that I know the terminology correctly) I take a ratio of my initial LME to account for the loss. I later added enough water to get back to 5.25 so that inputs stays the same.

Actual Execution: (3.75/4*12)*5.25* 1.2698 = 75

Given that I'm at about 77 now I must not have lost a full quarter gallon. For curiosity sake:

(Y/4*12)*5.25*1.2698 = 77
Y = (77/(5.25*1.2698))/12*4 = 3.85

So I *only* lost 0.15 gallons in my boil over and the other 0.1 gallons was likely just the water boiled off. That probably explains my low OG.

any ideas why the Brewer's Friend Extract Calc would over estimate the OG to be 85 with 5.25G water and 12 lbs LME? I've found the other calculators to be pretty good, but this seems abnormally off to me. I wonder if there are issues at higher gravitys.

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