Author Topic: High Pre-boil gravity  (Read 538 times)

Offline dzlater

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High Pre-boil gravity
« on: March 09, 2014, 03:31:05 PM »
    I have been figuring my recipes @ 80% mash efficiancy it always within a couple points, close enough for homebrew.  But my last few batches I have been ending up much higher.
  Looking at my notes (such as they are) I noticed it seems to occur on my low gravity beers, 1.045 and less.
   Today I did a beer the preboil was supposed to be 1.031 and I hit 1.041 which was actually higher then my intended post boil gravity. When I figure my efficiancy I get a 99%. I didn't even think that was possible.
I am using the same measuring stick to measure volumes that I have always used, so it's not that.  I was using a hydrometer and I recently got a refractometer. I calibrated the refractometer with distilled water
  The only thing different is that I switched from a false bottom to a hose braid in the mash tun.
The recipe was for 7 gallons preboil
6lbs pale ale malt
1.4 lbs crystal 60L
3.3 oz chocolate malt.
(the weird amounts is because I was using up the leftovers)
4 gallons mash
4 gallons sparge
I'm not sure what to use for mash efficiancy when figuring out a grain bill?








Dan S. from NJ

Offline HoosierBrew

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Re: High Pre-boil gravity
« Reply #1 on: March 09, 2014, 04:04:18 PM »
So is this the first batch where you used the refractometer ? How do you take your readings? I have a refractometer and hydrometer, and take refractometer readings a couple minutes after reaching a boil because you get a little better mixing (reduction of stratification) of the wort. I place a wort sample in a jar with a lid, into the freezer for a couple minutes before testing. I used to use an open container for samples, but the evaporation while cooling in the freezer gave me inaccurate, slightly higher preboil readings. Also, refractometers can sometimes give erratic readings, so I check my sample 2 or 3 times to be sure I'm getting a pretty consistent reading before feeling confident in it.

EDIT  -  I also calibrate my refractometer before every use.
« Last Edit: March 09, 2014, 04:13:29 PM by HoosierBrew »
Jon H.

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Re: High Pre-boil gravity
« Reply #2 on: March 10, 2014, 08:04:02 AM »
Does your refractometer have ATC? Readings would still need temp correction if not. Also, has there been a change in your crush? A better crush could greatly improve your mash efficiency. I'm not sure simply going from a false bottom to a braid would impact your efficiency by 10 points.
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Online denny

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Re: High Pre-boil gravity
« Reply #3 on: March 10, 2014, 08:48:04 AM »
Does your refractometer have ATC? Readings would still need temp correction if not. Also, has there been a change in your crush? A better crush could greatly improve your mash efficiency. I'm not sure simply going from a false bottom to a braid would impact your efficiency by 10 points.

Refractometer ATC corrects for the temp of the refractometer, not the sample.    I agree about the crush, but giving up the false bottom could be the cause if there was wort trapped under the false bottom that wasn't accounted for.
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Re: High Pre-boil gravity
« Reply #4 on: March 10, 2014, 10:24:49 AM »
1.041 must be a measurement error. Depending on the potential extract for those particular malt lots, that's probably a little over 100% efficiency. I would project a pre-boil gravity of ~1.033 (87% efficiency).

http://seanterrill.com/2013/10/05/batch-sparging-calculator/

More generally, efficiency won't be constant for different grain bills unless you also scale the pre-boil volume. If you're assuming 80% for a small beer, you may overshoot the gravity target.
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Offline dzlater

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Re: High Pre-boil gravity
« Reply #5 on: March 10, 2014, 01:41:51 PM »
It was my the first time using the refratometer.
You'd think I'd have been smart enough to compare it to my hydrometer on the first attempt.
It does have ATC.
The directions when calibrating to do it at temp. "close to or at 68f."
It doesn't say anything about the temp. of the sample.
I took the sample before the boil, after stirring well.
Used the little dropper thing that came with the refractometer.
I didn't let it cool off. That is how I've seen others do it.
I'm going to play around with it tonight, compare to my hydrometer.
I'll report back.

Dan S. from NJ

Offline dzlater

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Re: High Pre-boil gravity
« Reply #6 on: March 10, 2014, 02:30:03 PM »
I checked the refractometer against my two hydrometers.
Using 60f tap water
1.000 on hydro #1
1.003 on hydro #2 (this is the one that I knew read high 2-3 points.
1.000-1.001 refractometer.

I took some ice tea @ 60f and checked that
1.027 hydro #1
1.026 hydro #2
1.024 refact.

I boiled the tea and checked with the refractometer
and got 1.023
So the numbers aren't perfect, but not 10 points.
Dan S. from NJ

Offline HoosierBrew

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Re: High Pre-boil gravity
« Reply #7 on: March 10, 2014, 03:21:44 PM »
I would :      1.  Cool your sample before reading, check it a couple or three times to check for consistency.

                  2.  Take a wort sample after it comes to a boil, when you actually have pretty uniformly mixed
                       wort, unlike preboil.

                 I think you'll get more accurate readings.
Jon H.