help me understand somthing - Home Brew Forums

 Home Brew Forums > help me understand somthing

09-17-2012, 12:25 AM   #1
slider67
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Aug 2012
UMR MM 282.3, MO
Posts: 38
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Hello

brewed my 3rd batch up today.
--5.5 lbs. British Golden Promise
--4.75 lbs Rahr Pale Ale
--0.5 lb Flaked Barley
--0.25 lb German Munich Malt
--0.25 lb Briess Caramel 20
--0.25 lb English Chocolate Malt
--0.25 lb English Medium Crystal
--0.125 lb Roasted Barley
--0.1875 lb Belgian Special B

mashed at 151 for 60 mins.

o.g. is supposed to be 1.060
preboil volume of 7.25 gallons was at 1.045 taken with a hydro and refrac.
with calculations thats right were it should be pre boil so no dme needed

after the hour long boil i carried 5.25 gallons to the fermentor
and came up with a gravity of 1.056 4 point short

where did the 4 points go?

its not that im worried just trying to understand, my calculations seemed right,

Thanks
Tim

09-17-2012, 01:18 AM   #2
TromboneGuy
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Jul 2011
Wichita, KS
Posts: 278
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Unless I'm doing this wrong...

7.25 x 40 points = 290 points
290 / 5.25 = 55 points (more or less)

So it sounds like 1.056 is about spot on.

EDIT: doing this on my phone, remembered the numbers wrong.

7.25 x 45 = 326
326 / 5.25 = 62

So, yeah. Did you lose some volume to trub and hops in the kettle? Because that would do it.

09-17-2012, 01:24 AM   #3
TromboneGuy
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Jul 2011
Wichita, KS
Posts: 278
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Losing even about 12 oz. would make up the difference.

09-17-2012, 01:28 AM   #4
ArcLight
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May 2011
Millburn, NJ
Posts: 1,385
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>> 1.045 taken with a hydro and refrac.

Did you cool down the wort to room temperature? Else the heat will throw off your measurements.

>>and came up with a gravity of 1.056 4 point short

Same question for the amount in the fermentor. Did you adjust for temperature?

09-17-2012, 02:14 AM   #5
slider67
Recipes

Aug 2012
UMR MM 282.3, MO
Posts: 38
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yes i left the trub and hops in the kettle when i racked it to the fermentor,

and all the hydro readings were room temp, plus all were done with a refractometer also, both were callibrated and each reading was spot on with both insturments

this is how i figured my preboil gravity

(post boil gravity 60)x(post boil volume 5.5)/ pre boil volume 7.25 = 45.5

so im still confused how leaving the trub and hops can make you lose points
shouldnt the total post boil volume be the same gravity.

i should also point out that my post boil volume was a little under 5.5 gallons

Thanks
Tim

09-17-2012, 02:19 AM   #6
ArcLight
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May 2011
Millburn, NJ
Posts: 1,385
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>.so im still confused how leaving the trub and hops can make you lose points
shouldnt the total post boil volume be the same gravity.

They absorb wort that contains sugar. This sugar is now lost.

09-17-2012, 05:45 PM   #7
MachineShopBrewing
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Nov 2009
Montrose, MN
Posts: 1,053
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Quote:
 They absorb wort that contains sugar. This sugar is now lost.

You only have two possible explanations- Either you measured the gravity wrong, or you measured the volume wrong. Sugar does not get lost. There are no other options.

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09-17-2012, 06:32 PM   #8
billl
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May 2012
Raleigh, NC
Posts: 2,331
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Just a note on precision.....

Just because we can type decimal places into a calculator doesn't mean we have the ability to measure that precisely in a bucket or carboy or hydrometer etc. Your margin of error on a hydrometer is 1 point. That is about 2% here for each gravity measurement. Your volumes are being measured to the nearest quarter gallon, but lets say you can estimate to 0.1 gallons. That is another 2% for each volume measurement.

Compare that to your calculation. 7.25*45/5.5= 59 points. You measured 56 or 5% off. You've got 4 separate measurements with a margin of error of 2% each. None of your measurements even need to be "wrong" to fall within that margin. It could easily just be the inherent uncertainty of trying to measure volumes from gallon lines on a bucket and OG marker in 1 (or 2) point increments.

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09-17-2012, 06:45 PM   #9
helibrewer

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Nov 2011
Santa Rosa, CA
Posts: 3,820
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^^^ This. Sugar is not lost, just diluted (by adding volume) or concentrated (by evaporating volume).
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09-17-2012, 06:55 PM   #10
slider67
Recipes

Aug 2012
UMR MM 282.3, MO
Posts: 38
Liked 1 Times on 1 Posts

Thanks for the replies fellas, i agree the meassuring could have been off, just as well of missreading a point or to on the hydro, the first 2 brews i did both came out a few points higher, both pre and post boil.

so i was just trying to figure out why this one was spot on preboil but short post boil, that clears a lot of things up.

Thanks
Tim