Author Topic: ATC Refractometers  (Read 9347 times)

Offline tygo

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ATC Refractometers
« on: May 23, 2010, 06:26:00 PM »
Just picked one of these up and the directions say that the automatic temperature correction will handle samples up to 50F - 86F.  Obviously a sample pulled right from the kettle is going to be higher than that.  So how is that handled?  Should I let it cool a little before dropping it on the prism?

It wouldn't take long for a little bit of wort to cool down to below 86 but my impression when reading people describe using these things is that I could take the sample directly out and drop it on.
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Offline a10t2

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Re: ATC Refractometers
« Reply #1 on: May 23, 2010, 09:21:37 PM »
The ATC range refers to the temperature of the refractometer, not the sample. Once the hot wort hits the room temperature lens it'll cool down very quickly.

It's probably a good idea to have some way to cool the sample down immediately anyway, though. Otherwise evaporation will skew the readings, IME.
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Offline richardt

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Re: ATC Refractometers
« Reply #2 on: May 24, 2010, 06:26:25 AM »
One or two drops of wort (regardless of temp) quickly cools down when it hits the much cooler glass plate of the refractometer.
Then you flip the clear plastic cover plate on top of it (which is also cooler). 
This takes all of 2 seconds.  There's no evaporation taking place once your cover plate is on.
Now you can take all the time in the world reading it
Just multply your brix reading by 4 to get a rough estimate of your SG.

There's no need to worry about evaporation nor the need to rapidly chill your drops, IMO.
Just use the plastic dropperettes to sample a few drops onto the refractometer, flip the cover plate, and read it.
Then flip the cover plate off and LICK the refractometer!  It's a great way to assess for astringency or process problems, esp during sparging.
Congrats on the refractometer--it's a useful tool.

Offline tygo

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Re: ATC Refractometers
« Reply #3 on: May 24, 2010, 06:55:33 AM »
Thanks, that all makes sense.  I actually got one that has both a Brix and SG scale so at least I don't have to do any math.  I'll be taking the new toy for a spin this weekend.
Clint
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Offline Kaiser

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Re: ATC Refractometers
« Reply #4 on: May 24, 2010, 08:18:48 AM »
you should check the calibration with water before you use it. Though mine is an ATC meter its ATC seems to be broken since the calibration changes with temperature.

Kai

Offline hopfenundmalz

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Re: ATC Refractometers
« Reply #5 on: May 24, 2010, 08:22:39 AM »
Be sure to calibrate with distilled or RO water.  If you have a really high mineral content in your tap water like me, your cal will be off.
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Offline tygo

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Re: ATC Refractometers
« Reply #6 on: May 24, 2010, 10:18:51 AM »
I calibrated it at room temperature (70 or so) with distilled water but I'm planning to recalibrate it outside in the garage immediately prior to using it.
Clint
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Offline Kaiser

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Re: ATC Refractometers
« Reply #7 on: May 24, 2010, 11:34:17 AM »
I calibrated it at room temperature (70 or so) with distilled water but I'm planning to recalibrate it outside in the garage immediately prior to using it.

Also, the ATC works based on the temperature of the unit itself and not necessarily the temperature of the prism. The latter determined the temperature of the sample. I can see how they can have different temperatures if the refractometer was stored in a cold room and the moved into the warm outside air for measurements.

Ideally you want the unit to acclimate to the temperature of the area where you will be measuring.

Kai

Offline nyakavt

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Re: ATC Refractometers
« Reply #8 on: May 24, 2010, 12:12:15 PM »
There's no need to worry about evaporation

This has not been my experience.  I use the refractometer for lots of things on the hot side, including pre-boil OG measurements and mash gravity measurements.  The reading would be way too high (pre boil gravity > post boil gravity, or mash gravity much greater than predicted) with just a drop on the lens compared with a cooled hydrometer sample, and also when pouring a bit onto an open dish to cool before sampling.  Then a couple of times I took a hydrometer sample to chill in the freezer and checked with the refractometer right away and after chilling - the hot sample was 2 Brix higher.  I also could not get any consistency when taking two readings in a row.

For the last dozen or so batches I've switched to cooling the sample in an airtight container, either a small screw top test tube or a 10 mL syringe.  The results have been much more consistent to each other, as well as matching the hydrometer sample and the predicted mash gravity.  There could be other factors at work here (like stratification of sugar concentration in the MT or kettle) that affected my readings, but I've seen enough to convince myself that this evaporation is a real concern and must be addressed, even with small samples that are quickly covered.

Offline richardt

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Re: ATC Refractometers
« Reply #9 on: May 24, 2010, 06:38:58 PM »
Short version:  I respect the fact that you’ve given this a lot of thought and are dedicated to improving the accuracy of your measurements.  I merely disagree with the premise that your refractometer readings are off because of evaporation.  Instead, I think it is due to sample stratification.  After all, don’t we wait 15 minutes or so for the hot and cold break to settle before transferring?  Why wouldn’t sugars and proteins of various shapes, sizes, and weights be any different?

Long version:   Three key parts to evaporation are heat, humidity and air movement (source:  http://en.wikipedia.org/wiki/Evaporation).  As I see it, plunging a dropperette beneath the surface of the liquid to draw a sample of wort (regardless of temp), promptly placing a very small sample mass of just one or two drops on the cooler refractometer surface (which has a much larger mass and serves as a heat sink), and placing the cover plate over it pretty much removes all three parts necessary for evaporation.  There’s even less kinetic energy to drive evaporation as the liquid cools, the humidity probably does decrease (but you’re reading within a few seconds, so it should be negligible), and the air movement is nil (as the cover plate prevents exposure to air movement and may limit humidity changes since there’s practically no exposed surface area to permit it).

The refractive index is dependent on
1.   The material/media in which it is traveling
2.   The frequency of light
3.   The temperature
(source:  http://en.wikipedia.org/wiki/Refractive_index)

As you mentioned, I think it is quite possible that you may be noticing temperature and specific gravity stratification of your pulled samples.  This sample inhomogeneity may be yielding slightly lower readings if you’re pulling smaller samples from the upper and/or outer portions of the larger sample.

Assuming you’re doing the readings in the same place regardless of your sampling method, the frequency of light isn’t changing (whether you’re consistenly brewing outside or in the kitchen).  If you’re doing one reading outside with one method and another reading inside with a different method and using a different light source—give it some thought and eliminate that variable.

Temperature gradients can cause fluctuation in refractive index within a single medium to generate a refractive effect, e.g., mirages and looming artifacts (source:  http://micro.magnet.fsu.edu/primer/lightandcolor/refractionintro.html).  I don’t know if there’s enough of a temperature gradient with a refractometer to create this refractive effect to a significant degree that we’d notice it.  My bias is that a temperature gradient is not playing a role with the refractometer readings.  IMO, even the chilled specimens are more likely to be causing specific gravity stratification in the time it takes to chill the sample, which I perceive as having a greater effect on one’s refractometer readings than temperature gradient effects would.

And, like Kai said earlier, it is best to acclimatize your refractometer to ideal conditions.  Thanks for letting me participate in such an interesting discussion.

Offline a10t2

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Re: ATC Refractometers
« Reply #10 on: May 24, 2010, 11:53:10 PM »
Instead, I think it is due to sample stratification.

I really can't believe that there's any stratification in a kettle full of boiling wort.
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Offline jimbo44

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Re: ATC Refractometers
« Reply #11 on: May 25, 2010, 12:24:32 AM »
I simply pull of a pipette full of wort (about four drops) and run the bulb under cold water for about 5 seconds.  then I drop a couple on the refrac and look.  I have broke a refrac with 212 water.  also be gentle when you flip the lid down.  really hot wort and an impact can break the prism.  It doesn't happen every time, but if it happens once, thats one to many.  Side Note:  I use beer smith and there's a nice conversion tool for measuring fermenting wort.  I have ran some tests and that can be off by more than three points.  That can really start to add up, so I suggest always using a hydrometer once it is fermenting.
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Offline tygo

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Re: ATC Refractometers
« Reply #12 on: May 25, 2010, 03:55:19 AM »

Ideally you want the unit to acclimate to the temperature of the area where you will be measuring.

I can definitely see the logic of this.  If the ATC range is 50-86F though I can see situations where the ambient temp outside in the garage where I brew would be higher than that range.  In those cases I assume that will affect the accuracy of the reading?  I guess if it's higher than 86 outside I should take the reading inside.
Clint
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On Tap: Lucifer's Hammer Golden Strong Ale, Dopplebock, Old Fuzzynut's Ale

Offline tygo

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Re: ATC Refractometers
« Reply #13 on: May 25, 2010, 03:56:37 AM »
I simply pull of a pipette full of wort (about four drops) and run the bulb under cold water for about 5 seconds.  

Are you using the plastic pipette that came with the refractometer?  Will that hold up to boiling wort?

Using this method it seems like evaporation wouldn't really be significant since you're cooling it down quickly inside the pipette.
« Last Edit: May 25, 2010, 03:58:22 AM by tygo »
Clint
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Offline richardt

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Re: ATC Refractometers
« Reply #14 on: May 25, 2010, 06:26:40 AM »
Instead, I think it is due to sample stratification.

I really can't believe that there's any stratification in a kettle full of boiling wort.

I agree--there shouldn't be any stratification in a kettle when the wort is boiling.

However, when the wort has been chilled down to yeast pitching temps (60-80 F) during the 15-30 minutes of whirlpooling and using the immersion chiller, then stratification has probably occurred (as evidenced by the improved clarity of the wort and the sedimentation of the break material and trub.

Personally, I tend to perform my refractometer readings during lautering (T <170 F) and at the end of the boil/post chill (T 60-80 F).  I'm not putting hot wort (T =212F) on my refractometer.  I really don't see the need to check the SG during the boil--I trust my BeerSmith brewsheet and want to follow the hopping and boil schedule as accurately as possible--that's what is going to determine what the beer tastes like.