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Pre-Boil Gravity Calculation

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BlindFaith

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I posted this issue on the beginner's forum as well, but I thought I could get a more knowledgeable response here. Ok, I brewed a Founder's BS Clone with no real issues as my pre-boil gravity came out at 65 points. My OG, at about 85 F, reads 73 points. I have been using the formula of V1*C1 = V2*C2 to calculate my OG based on my volumes (V1 and V2) and pre-boil gravity (C1). This time my OG should have been 83 points, according to the formula (which has never been wrong before), but it is 10 points low. What gives? There is no top off, so it isn't an aeration problem. I aerated and checked again anyway, same thing. I just calibrated my hydrometer, but I also have a refractometer and it shows the same. I took a hydrometer and refractometer pre-boil sample just to be safe and they both read very close at around 65 points. I am confused.....

6.3 gallons pre-boil
Just under 5 post
 

momobono

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Hmm. I just ran it through the brewer's friend calculator just to check it, and you're right on target with your calculations. One thing I can think of is maybe your pre-boil gravity reading was off somehow? A cold pre-boil would be a high reading, giving you the idea that you had more sugar than you actually did. That would throw the calculations off from the start. Did that 1.083 OG target come from the recipe you built, or are you solely relying on the equation for that number?
 
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BlindFaith

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The 83 points came from the calculations based on my pre boil SG. My reading must have been off somehow, but inaccurate readings are usually low due to bad mixing. It was just a weird occurrence that happened. My efficiency was low, but it will be good beer. The wort tasted great.
 
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