Author Topic: stupid refractometer question  (Read 1345 times)

Offline homoeccentricus

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stupid refractometer question
« on: February 09, 2015, 10:21:55 AM »
Yesterday I brewed a strong porter, and had problems with the refractometer: I took several samples during the boil, cooled them, and read them with the refractometer, and had the impression that the boiling-off had little effect on the gravity. At the end of the boil I took another sample, and bang, spot on. I don't understand why that was so.

Is there a good technique for taking these samples? Would a sample taken from the top during the boil be less dense, and therefore give an inaccurate result?
Frank P.

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Offline BrewBama

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Re: stupid refractometer question
« Reply #1 on: February 09, 2015, 12:07:58 PM »
Interesting. I only take a sample on my lauter and sparge run, then one at the beginning (I call SG) and one at the end of the boil (OG).
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Offline majorvices

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Re: stupid refractometer question
« Reply #2 on: February 09, 2015, 12:12:40 PM »
It took me a while to wrangle getting my refractometer to work correctly. It is best to cool the sample a few degrees before putting it on the refractometer glass. Then press down the cover to make sure no air bubbles are messing up the reading. Then blow on the cover to bring everything to equal temp. If the sample is still too warm you will not get an accurate reading.

Offline HoosierBrew

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Re: stupid refractometer question
« Reply #3 on: February 09, 2015, 01:15:25 PM »
I take a sample a couple minutes after reaching boil for my first (preboil) reading, since the turbulence of the boil gives better mixing. I also take a post boil reading after cooling.  I place the preboil sample into a small jar with a lid, into the freezer for two or three minutes, and then take a reading.
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Offline Frankenbrew

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Re: stupid refractometer question
« Reply #4 on: February 09, 2015, 01:57:33 PM »
I cool my sample in the freezer, and then check it with my Thermapen before reading it. Refractometers are really temperature sensitive.
Frank C.

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Offline Wort-H.O.G.

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Re: stupid refractometer question
« Reply #5 on: February 09, 2015, 02:10:20 PM »
I take a sample a couple minutes after reaching boil for my first (preboil) reading, since the turbulence of the boil gives better mixing. I also take a post boil reading after cooling.  I place the preboil sample into a small jar with a lid, into the freezer for two or three minutes, and then take a reading.

+1

refractometer is great but you need to follow these guidelines to get consistent and accurate readings.

I like to take final reading after i transfer from kettle to carboy, when all the wort is cool and thoroughly mixed.
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Offline homoeccentricus

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Re: stupid refractometer question
« Reply #6 on: February 09, 2015, 02:42:22 PM »
The problem was that the boil-off was lower than I had expected, so I wanted to prolong the boiling time to reach the predicted gravity. So I took intermediate samples. Just a few drops, and I did wait a bit until the sample was no longer hot. So you are saying I really have to make sure the temperature goes down to 20C? So taking the temperature of sample with a Thermapen?  :P
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Offline Frankenbrew

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Re: stupid refractometer question
« Reply #7 on: February 09, 2015, 03:49:55 PM »
The problem was that the boil-off was lower than I had expected, so I wanted to prolong the boiling time to reach the predicted gravity. So I took intermediate samples. Just a few drops, and I did wait a bit until the sample was no longer hot. So you are saying I really have to make sure the temperature goes down to 20C? So taking the temperature of sample with a Thermapen?  :P

If you want to minimize the variables.
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Offline mabrungard

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Re: stupid refractometer question
« Reply #8 on: February 09, 2015, 03:52:34 PM »
Has anyone noticed that hot wort separates into a low gravity surface layer in the kettle? I experienced this many years ago and now I always collect my FG sample immediately after mixing (whirlpooling) to make sure that it is a uniform and representative sample.
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Offline HoosierBrew

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Re: stupid refractometer question
« Reply #9 on: February 09, 2015, 04:23:05 PM »
Has anyone noticed that hot wort separates into a low gravity surface layer in the kettle? I experienced this many years ago and now I always collect my FG sample immediately after mixing (whirlpooling) to make sure that it is a uniform and representative sample.

I've noticed that, Martin. That's why I started taking preboil readings a couple minutes after boil starts, to get better mixing.  And I stir constantly during cooling, when I take the postboil reading. Readings used to be all over the place, much better now.
Jon H.

Offline Stevie

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Re: stupid refractometer question
« Reply #10 on: February 09, 2015, 06:06:35 PM »
I have been having all sorts of refractometer issues. Two primary ones below.
1 - I keep it with my brew gear in the garage, so I need to remember to put it in my pocket at the start of brew day to warm up
2 - My pre-boil has been good, boiloff good, OG low???


I'm considering buying a digital version at some point. Those I know that have them, love them.

Offline Wort-H.O.G.

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Re: stupid refractometer question
« Reply #11 on: February 09, 2015, 07:10:53 PM »
I have been having all sorts of refractometer issues. Two primary ones below.
1 - I keep it with my brew gear in the garage, so I need to remember to put it in my pocket at the start of brew day to warm up
2 - My pre-boil has been good, boiloff good, OG low???


I'm considering buying a digital version at some point. Those I know that have them, love them.

my feeling is the OG is most difficult to get accurate reading, since you don't get a good mix of the mash and sparge runnings.
Ken- Chagrin Falls, OH
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Vienna IPA          O'Fest
Dort
Mead                 
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Amber Ale
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Ger Pils
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Offline 69franx

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Re: stupid refractometer question
« Reply #12 on: February 09, 2015, 08:48:59 PM »
i have had issues getting my hydrometer and refractometer to match up. I have tested both of them in distilled to calibrate, but not in a sugar solution. On brew days, I generally get readings 2-5 points lower with the refractometer at both stages of measurement: pre-boil, OG. I have been relying heavily on the hydro, because I had it first, but I will also need to spend more time soon to test them out at known levels to see which is correct, and to adjust the other
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Offline unclebrazzie

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Re: stupid refractometer question
« Reply #13 on: February 10, 2015, 12:04:39 PM »
I find my refractometer doesn't show much temperature dependency. Which is precisely the reason why I use it almost exclusively throughout the entire brewday. Only at the end, when I run the cooled wort into my primary fermentor, do I perform the ultimate SG with my hydrometer. I find this rarely differs more than one or two gravpoints from my refracto reading, and it gives me something compare my later hydro-readings with.

That being said, last brewday I had no less than 10 gravpoints of difference between refracto and hydro: 1050 on the former vs 1040 on the latter. No idea what happened there; I'm guessing recalibration is in order...
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Offline Scot (one T)

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Re: stupid refractometer question
« Reply #14 on: February 10, 2015, 02:36:32 PM »
I found this article helpful in for caring for and calibrating my refractometer:

http://ucanr.org/sites/viticulture-fresno/files/115503.pdf
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