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Old 01-10-2013, 04:09 PM   #1
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Default Refractometer Questions

SWMBO ordered me the standard brewer's model w/ ATC from Brew Hardware.

As I was reading the instructions last night, I have questions about calibration and use of this instrument.

Calibration must be done with 68 degree distilled water ( I get that)

But the directions also mention that the refractometer should be calibrated at the temperature that it will be used.

I brew outside (in Northern Vermont) and this weekend when I brew my first AG the temperature is supposed to be in the 40's or 50's (we are currently having a not normal stretch)

So I need to calibrate this thing outside?
If so, i am positive that the distilled water for calibration will not be 68 degrees.

The directions also mention that sample and air temperature should be the same.

I thought the whole point of a refractometer with ATC was to be able to check gravity of runnings on the fly as I am doing it.

HELP me understand all of this....



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Old 01-10-2013, 04:16 PM   #2
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You want to calibrate to whatever your ambient temperature is when you brew.

The ATC does not adjust the refractometer for the temperature of the liquid, but rather for the temperature of the ambient air. Realistically, that's not a problem, simply because the few drops of liquid applied to the stage will reach ambient temperatures within a few seconds.

I just keep a little dropper of water in my brewkit and calibrate at the beginning of each brew day. Give your refractometer enough time to acclimate to the outside, and that's all you really need to do.



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Old 01-10-2013, 04:56 PM   #3
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Right, the ATC is to compensate for ambient and therefore instrument temp. The lower range of automatic adjustment, based on calibration at 68F is about 50F (essentially I read that as, the ATC will work by swinging about 20F up or down from the temp at which it was calibrated). IOW, if you calibrate while the instrument (and roughly the sample as well) is at 50F, then it will be accurate when measuring samples while the instrument is at 30F-70F. The reason you want to try to get samples down to NEAR the ambient temp is so that the sample affects the instrument temp very little and so you don't get drift while the instrument and sample are reaching equilibrium. The other reason to chill down a sample while it's in the pipet is to avoid concentrating the sugars due to evaporation. The sample is what, .1mL on the prism and has a great surface area. If it's at 200F, you could reduce it down to .09mL before you drop the cover.

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Old 01-10-2013, 05:18 PM   #4
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Default Thanks...

Thank you both (it is always nice to have the person that you bought the refractometer from answer a thread.. Thanks Bobby once again proving why I will keep doing business with you.

I like the idea of keeping a small dropper bottle of distilled water right with the refractometer.

So once calibrated to the ambient air temperature, i can test runnings at mash temperatures and it should all be OK.

AND... The most accurate reading will be when sample is cooled to the same temperature as I calibrated at??

Follow up question that comes after some research online.

It seems that an adjustment needs to be made when these refractometers are used for beer (something to do with sucrose versus maltose in the wort)
What is this all about??

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Last edited by brewkinger; 01-10-2013 at 05:21 PM. Reason: additional question
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Old 01-10-2013, 05:48 PM   #5
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The major challenge is compensating for the presence of alcohol once fermentation has begun. It's a bit of black magic, but the best compensation method I've found is on Sean Terill's website. You need to know the original brix and then enter the current apparent brix and it will calculate it for you. Many people have found some fluctuation in accuracy but that's the tradeoff for only having to pull a 1mL sample out of the fermenter. I only use my refractometer post fermentation when I have a beer that is prone to stalling out and I want a roundabout answer on how it's doing. When a beer is ready for the keg, I just detour some of the racking over to my test tube and put the hydrometer in because I want to drink a 3oz sample anyway.

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Old 01-10-2013, 06:09 PM   #6
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There is some small amount of disparity between sucrose and wort for refractive index, as well, though it's relatively negligible...on the order of 3-4%. In all likelihood, that's not going to be your least accurate measurement.

But, I'm a bit obsessive about this stuff, so I do make the adjustment. Different people report different calibration facts, but I find that I can multiply my Brix reading by around 1.04 to get a more accurate measurement.

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Old 01-10-2013, 06:35 PM   #7
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Could you just keep the refractometer in the house so you don't need to recalibrate?(assuming it's close to where you brew)

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Old 01-10-2013, 06:44 PM   #8
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Quote:
Originally Posted by brewn4fun View Post
Could you just keep the refractometer in the house so you don't need to recalibrate?(assuming it's close to where you brew)
That wouldn't really change anything. If you want to keep your instruments calibrated, you have to recalibrate them periodically. Generally, it's wise to calibrate them to real-use circumstances.

You could certainly keep the refractometer inside, but then you'd want to calibrate it to the inside temperature.
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Old 01-21-2013, 04:05 PM   #9
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Thanks again for all the advice on this topic.
First AG went well.
As circumstance would have it, brew day yesterday in northern VT turned out to be "lovely"
Snow squalls, ambient outside temperature somewhere around 36 when we started and around 8 degrees when we finished.
Wind gusts of upwards of 50mph.
Power went out 5 minutes before we started and came back on about an hour before we finished. (thank goodness I have a generator to keep SWMBO happy)

Bottom line was water heating, mash in and boil all were done outside.

Once I was mashed in, we took the cooler inside and put it up on shelf because I figured that it would maintain temp a lot better inside than out.

So I calibrated refractometer to inside temps of 66 degrees and all testing of wort was done inside.

My question is (and I think I know the answer, but I want to verify for my own piece of mind)
The fact that the runnings were around 150 degrees does not matter?

Because the droplets that I place on the window cool quickly?

I ask this only because my first AG experience and the numbers that the refractometer gave me resulted in 73.8% efficiency for my first time.

1.081 first runnings
1.054 second runnings
1.043 pre-boil / 7.25 gallons

So I am essentially just double checking that I made no mistakes and the efficiency is real.

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Old 01-22-2013, 05:38 PM   #10
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Just started using a refractometer... your single post explained more than 2 weeks of research did. Much appreciated...

And great question, Brewkinger!



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