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Old 02-02-2012, 05:03 AM   #1
BootsyFlanootsy
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Default Missed OG by 10 points!!!! Over-sparge to blame?

Made a 5gallon batch tonight. OG was supposed to be 1.062. Preboil gravity was 1.044 which by my calculations with a 60min boil should have given my a post boil gravity of 1.057, ( this is before the addition of 12oz's of invert sugar at 15mins, which theoretically should have brought me up in the ballpark of my calculated OG),. However I wound up with an OG of 1.052!! WTF?!?

So I started thinking, I miscalculated my sparge water addition. I should've only added 4.61 gallons, but would up adding about 5.25. I overcollected by about a gallon.


My initial guess is this could be a big part of the culprit.


Curious what those more learned in the ways have to say about this...

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Old 02-02-2012, 05:06 AM   #2
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What was your preboil volume? What was your final volume post boil?

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Old 02-02-2012, 05:20 AM   #3
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sorry, pre-boil was 6.5. post-boil was 5.

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Old 02-02-2012, 05:24 AM   #4
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seeing that my pre-boil gravity was 1.044, I calculated 6.5 x 44=286. then 5gallons post boil so 286 divided by 5 = 57 giving me 1.057 OG - my late addition of invert sugar. putting me right close to the mark... at least in theory.

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Old 02-02-2012, 05:29 AM   #5
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You either had a poor sparge (not extracting enough of the sugars), poor mash efficiency or bad hydrometer readings. Did you take the gravity of the final runnings of your sparge? Gravity by refractometer or hydrometer? If hydrometer, did you correct for temperature?

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Old 02-02-2012, 05:37 AM   #6
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yeah Hydrometer. No, I didn't take a gravity reading until both the first runnings and the sparge were combined.

Guess it's time for me to bone up and buy a refractometer.

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Old 02-02-2012, 05:47 AM   #7
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According to the formula:
preboil GU x preboil volume = postboil GU x postboil volume

your calculation of SG=1.057 before the sugar addition is correct...

Are you sure you measured your preboil and postboil volumes accurately? How are you measuring the gravity? Maybe your refractometer is not reading consistently (I recently noticed mine isn't, much to my surprise), or alternatively your hydrometer sample wasn't cooled to 60F.

Edit: while writing I see you measured with a hydrometer... note my comment about my refractometer above... maybe it's not reading consistently because it's a chinese $15 job.

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Old 02-02-2012, 05:59 AM   #8
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Rough estimate with BeerSmith, when starting with a 1.044 gravity with 6.5 gallons, your final gravity with 5 gallons minus the 12 oz sugar would be 1.054. Are you sure your volumes are correct?

A 60 minute boil with 6.5 gallons typically won't get to 5 gallons. Is your process repeatable to go from 6.5 to 5.0 gallons in only 60 minutes? I typically only lose 1 gallon in an hour, but everybody's set up is different.

Using the same calculation with the sugar added and 5.25 gallons post boil gives: 1.044 preboil, 1.052 post boil.

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Old 02-02-2012, 01:12 PM   #9
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If I had to guess I'd say you had less than 6.5g preboil and slightly more than 5g post-boil. 6 gal preboil and 5.1g post-boil would come out 1.051.

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Old 02-02-2012, 06:37 PM   #10
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tre9er-


you are spot on sir. I just ran the numbers and that is precisely what happened. OK, this is very valuable to know, thanks everybody!

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