Refractometer Creep?

[quickerNu]

I have just started using a refractometer. I have noticed if I set it down after taking a gravity reading, and look at it again 10 minutes later with the same sample on the glass, I have magically gained 3-5 points. Why? I figure even a boiling sample cools almost instantly since it is just a few drops. What reading should I trust?

 

[PberBob]

Just guessing - it might be drying out and getting a little more concentrated.

 

[Vale71]

That and the sample slowly cooling making the gravity actually increase. Always cool the sample to as close as possible to room temperature before measuring.

 

[dmtaylor]

That and the sample slowly cooling making the gravity actually increase. Always cool the sample to as close as possible to room temperature before measuring.

This. And, the refractometer is not as precise as a hydrometer anyway. I usually measure each sample twice, take two readings, then take the average. It typically varies by about 0.2-0.3 between readings and I want to be more exact.

 

[Alex4mula]

I think you need to cool to the calibration temp specified for it when which probably will not be room temp. Mine is 68F.

 

[Qhrumphf]

Survey says: evaporation. Even if it's cool, small sample drying up, sugars stay behind while moisture evaporates off, and a small amount of evaporation can easily drive up the reading significantly. Putting hot sample on cold refract it's pronounced.

Option A: collect sample in metal container and ice bath it to cool it down rapidly, then read. Best method for hydrometer but works for refractometer too.

Option B: draw refract sample hot into pipette, and ice bath that (or run under cold tap).

Side note, I've found, both with digital and analog refractometers (assuming ATC), I get the most consistent/accurate readings (compared against hydrometer) if I chill sample to the same temp as the refractometer (ie ambient temp and not the calibration temp, unless they happen to be the same). If it's warmer, or colder (ie if you're brewing outside in the summer or the winter), then the readings get wonky. The device corrects to its internal temp, not the actual sample, and relying on the sample and device to equalize temp is time for evaporation as above. Either the ATC doesn't properly temp correct and the reading is wrong, or evaporation skews it up and the reading is wrong.

 

[quickerNu]

Terrific explanation, thank you. In hindsight, I checked it outside (95-100 ambient), came inside, set it down and checked again. 30 degree ambient temp plus evaporation. I typically use a pipette and chill it, but I ran out.

 

[w8av]

This. And, the refractometer is not as precise as a hydrometer anyway. I usually measure each sample twice, take two readings, then take the average. It typically varies by about 0.2-0.3 between readings and I want to be more exact.

+1
I only use my refractometer to get an idea of where I need to be and make any necessary adjustments. I always keel in mind, as Dave said, that it is not as accurate as a hydrometer and use the hydrometer for more precise readings post-boil and post fermentation.

 

[mashpaddled]

Wort under the plastic plate of a refractometer is not evaporating over ten minutes enough to increase gravity by several points. If that were true the mash would evaporate before an hour went by.

 

[Bigdaddyale]

What's the proper procedure then? I'm going to start taking a sample and wait 5 min for the sample and Refractometer temperature to equalize then take a reading.

 

[tmurph6]

I find improper use of a refractometer is pretty common. The proper way to use it is to first ensure your wort is homogenous, which is really only necessary pre boil. Second is take a pipette of wort and drip onto the lens and cover. Wait 30 seconds for the sample to cool and take your reading. When you take your reading, please note that despite the SG scale being there, a refractometer measures in Brix only! The SG scale is an approximation and should not be taken as accurate across the entire scale. Lastly take your brix reading and use beersmith to convert to specific gravity. Also note though that refractometers are calibrated for clear sucrose solutions - which wort is not - this means you must use a correction factor to correct the brix reading before converting to SG. Beersmith by default uses 1.0254.

I suggest beersmith but you can really use any tool...

last tip, recalibrate your refractometer before each brew session. I find mine is off ever so slightly before each brew day, so getting it back to calibration using distilled water is good practice. I keep a jug of distilled water around just to do calibrations.

 

[quickerNu]

Thanks tmurph6. I was growing frustrated with the amount of wort required to fill the standard hydrometer tube and finally purchased the refractometer. I have not seen those suggestions before. I will poke around in beersmith (2) and find that. Are you in Katy TX? I'm just up the road a way.

 

[tmurph6]

Thanks tmurph6. I was growing frustrated with the amount of wort required to fill the standard hydrometer tube and finally purchased the refractometer. I have not seen those suggestions before. I will poke around in beersmith (2) and find that. Are you in Katy TX? I'm just up the road a way.

No I’m in north Texas now, just haven’t updated my profile in awhile

 

[BrewMan13]

Also note though that refractometers are calibrated for clear sucrose solutions - which wort is not - this means you must use a correction factor to correct the brix reading before converting to SG. Beersmith by default uses 1.0254.

Quoting to emphasize; I used a refractometer for years before I even heard of a correction factor. Once I did, I measured hydrometer and refractometer side by side for a few batches and found that the refractometer was measuring 3 points higher every time. I have since broken it and see no reason to buy another. Cheers.

 

[VikeMan]

The SG scale is an approximation and should not be taken as accurate across the entire scale.

Yeah, the SG scale is arguably worthless (except for sucrose solutions). It shouldn't be taken as accurate at any part of the scale, which is why there's a correction factor in the refractometer calculators.

 

[balrog]

My first refractometer would hold zero w RO water for months
Gravity, coupled with a friction event, destroyed that one (sufficient but not limiting condition wherein said device was dropped into boiling wort), requiring a new one. That second one I have to zero every time. It's astounding. It's actually several stoundings all put together.

Point: yeah, check calibration.

 

[Birrofilo]

Yeah, the SG scale is arguably worthless (except for sucrose solutions). It shouldn't be taken as accurate at any part of the scale, which is why there's a correction factor in the refractometer calculators.

I insist this is not correct.

The correction factor is there because wort is different from a glucose-water syrup.

The refractometer doesn't know a bit about Brix or SG. It only measures Refraction Index, RI.

For each RI there is a certain known density, IF the liquid is a glucose-water syrup.

For each of those known glucose-syrup densities, there is one Brix correct value, and one SG correct value, and they both are equally correct.

If instead of measuring a water-glucose syrup you measure a wort, you are bound to have a certain error of measure, and this has nothing to do with whether the measure is express as Brix, or SG.

It is correct to say in any case that if you apply a Brix correction factor, that should be applied to the Brix measure (if you read in SG, convert this to Brix first).

 

[VikeMan]

The correction factor is there because wort is different from a glucose-water syrup.

The correction factor is there because wort is different from a sucrose solution. That's probably what you meant to say.

It is correct to say in any case that if you apply a Brix correction factor, that should be applied to the Brix measure (if you read in SG, convert this to Brix first).

Which is exactly why I say the "SG" equivalent scale on a refractometer is arguably worthless for beer wort. Why in god's name would anyone want to read the refractometer's SG scale, then convert to quasi-Brix, when the quasi-Brix number was already there in the refractometer display? No need to waste time converting an SG scale reading to quasi-Brix.

Also, if your refractometer is like every one I can recall seeing, the "straight" conversions from SG to Brix, and vice versa, will be very wrong over a large portion of its range. i.e. take a value, pop it into a reliable "straight" conversion calculator (not a refractometer wort correction calculator), like this one...
https://www.brewersfriend.com/brix-converter/Then compare the answer to the value on the refractometer's corresponding scale.

 

[Birrofilo]

@VikeMan

I have always given for granted that it's a glucose not sucrose solution that the refractometer is calibrated for. But I also guess there is little difference between the two. I'll have to check my refractometer's instruction.

What I mean is that the SG and the Brix values are equally exact, or equally wrong.

If you apply a "Brix correction factor" you arrive to a more exact measure of density, but then again wouldn't be more exact than a "SG correction factor" which would make you arrive to the same density.

The fact is, the refractometers that we buy are mostly used for wine work where Brix dominates and are normally calibrated in Brix. The calculator is therefore made for Brix calculation.

In this sense, I understand what you mean, that ultimately you don't use the SG scale, because you will have to correct the value with the Brix calculator.

My observation was due to reading often that the SG measure is less precise and one should only use the Brix value of the refractometer, because the Brix value is "native" and the SG value is approximate.

I now see that this is not what you were saying.

If we take this calculator: Refractometer Calculator - Brewer's Friend

And we use at OG the measure taken with refractometer in SG it's equally precise (or imprecise because the wort is different from the sugar solution) than the density taken in Brix with the same instrument. But the final density, to be used with this calculator, must be taken in Brix, because the calculator doesn't give us the possibility to use SG as the final density.

The "correction factor" is actually quite a misnomer. Sometimes I find it should be less than 1, sometimes more than 1 (when comparing OG taken with refractometer and hydrometer). I tend to ignore it. I accept the datum from the refractometer is approximated and I don't know in which direction. But yes, if you want to apply a "correction factor" and you want to use this calculator you have to work in Brix.

 

[VikeMan]

My observation was due to reading often that the SG measure is less precise and one should only use the Brix value of the refractometer, because the Brix value is "native" and the SG value is approximate.

I now see that this is not what you were saying.

Actually, that is part of what I was saying. I'll repeat:

Also, if your refractometer is like every one I can recall seeing, the "straight" conversions from SG to Brix, and vice versa, will be very wrong over a large portion of its range. i.e. take a value, pop it into a reliable "straight" conversion calculator (not a refractometer wort correction calculator), like this one...
https://www.brewersfriend.com/brix-converter/Then compare the answer to the value on the refractometer's corresponding scale.

Seriously, do this. Look into your refractometer, at 18 brix. Note the refractometer's SG scale value that corresponds with it. If it's like mine, it is just a hair less than 1.070. Now go to the calculator I linked, or any calculator you like. Not a refractometer correction calculator, but a straight brix to SG converter. Put in 18 brix and note the answer: 1.0741.

 

[Birrofilo]

Just to make myself clearer, both Brix and SG are measures of density.

If you apply a "Brix correction factor" of 1,04, that means you divide the reading in Brix by 1,04.

Your refractometer tells you 12,0 °Brix, and you divide that by 1,04 and consider 11,538461, or 11,54.

Your refractomer, if it has a SG scale besides the Brix scale, will tell you 1,048, or 48 points.

You apply a correction factor of 1,04 and you arrive to 48 / 1,04 = 46,153846 or 46,1 points, which is the same density.

 

[VikeMan]

I fully understand wort correction factors, trust me. What I'm talking about (in post #20) has absolutely nothing to do with wort correction factors.

Did you do what I asked? If so, what did you see?

 

[Birrofilo]

Seriously, do this. Look into your refractometer, at 18 brix. Note the refractometer's SG scale value that corresponds with it. If it's like mine, it is just a hair less than 1.070. Now go to the calculator I linked, or any calculator you like. Not a refractometer correction calculator, but a straight brix to SG converter. Put in 18 brix and note the answer: 1.0741.

My refractometer only has the scale in °Brix.

What you describe to me is either a quality problem of your instrument or of the equations at Brewersfriends.

The instrument should give you the same density reading, whether it is expressed in Brix or in SG. For each density, there is only one exact value in °Brix and only one exact value in SG. An instrument of decent quality must have the two scales aligned. Or it would be like a tachometer which gives you the right speed in mph and gives you a wrong speed in kmph.

If we get this table as exact, your instrument has a wrong SG scale. But that's only because it is a low quality instrument. For 18 Brix your instrument should give you a reading around 74 density points. Conceptually the two scales are exactly equivalent.

https://winning-homebrew.com/specific-gravity-to-brix.html

 

[Birrofilo]

I fully understand wort correction factors, trust me. What I'm talking about (in post #20) has absolutely nothing to do with wort correction factors.

I certainly know you know. What I meant is that one can work in Brix and in SG in the same way. Ultimately it is density, just like "speed" is "speed" however you measure it. kmph or mps or mps can be transformed into each other measure. If your instrument had a precise SG scale, you could use that in the same way as the Brix scale.

 

[VikeMan]

My refractometer only has the scale in °Brix.

Ok.

What you describe to me is either a quality problem of your instrument or of the equations at Brewersfriends.

There's nothing wrong with Brewers Friend's calculation. Since you don't have an "SG" scale on your refractometer...

Anyone who has a "dual scale" refractometer: Would you mind taking a look at 18 Brix in your instrument and reporting what it aligns to on its "SG" scale?

I don't have the equipment to take a picture of the display in mine, but here's a random picture from the 'net that shows the same erroneous equivalence.

I've also seen a few pics (of other refractometer's scales) with better "alignment." (Though it's not strictly speaking an "alignment" issue, given that 0 brix does in fact equal 1.000.)

 

[Birrofilo]

I suspect the reason for the misalignment of the SG scale is that the producer did not want to use smaller characters for the SG value and couldn't use thinner lines. Imagine you have to "squeeze" the Sg values so that the 1,075 is roughly where 18 Brix is. You have to compress all the values on the right and they would touch each other or even stumble on each other, and the lines (one line for each SG point) would touch each other.

The producer wanted to make a single line for each SG point and this was not possible with that available space.

That's why the SG scale is misaligned (I mean "not coherent") with the Brix scale.

The producer should have made a SG scale with, let's say, a line every 3 SG points (3, 6, etc.) but that would have given the impression of an "imprecise" instrument, therefore he made an imprecise instrument which gives the impression of precision.

(This entire last paragraph can be imagined as being said by Sir Humphrey of "Yes, Minister").

 

[Qhrumphf]

The last few non-digital refracts I've used have been accurate WRT where Brix and SG line up (and somehow close enough to 1 correction factor to take at face value). But many of them are not, as in the picture above. Whatever the reason, there's a lot of poor quality refractometers on the market.

 

[VikeMan]

The last few non-digital refracts I've used have been accurate WRT where Brix and SG line up (and somehow close enough to 1 correction factor to take at face value). But many of them are not, as in the picture above. Whatever the reason, there's a lot of poor quality refractometers on the market.

Thanks. Mine was not cheap. But it is pretty old.

I would recommend that anyone contemplating paying any attention to the SG scale on their refractometer verify its accuracy first. I've seen a bunch with scales just like (or very close to) mine. And if it is indeed more prevalent in cheaper models, well, that's what most homebrewers are using. So brewer beware.

 

[tracer bullet]

I grab wort samples into a small aluminum dish, and let them sit for a minute or so. It gets close to room temp by then and allows any little itty bits of grain or hops to settle out a bit as well. Then I measure.

It helped me get pretty stable readings where as before w/ hot wort stuck straight onto the thing I'd get #'s that didn't make sense.

 

[moorejl57]

I spent quite a lot for my analog refractometer (VEE GEE BTX-1) because, well, who doesn't like expensive toys. The main difference I see between this one and a cheepie on Amazon is that it is very heavy, has a very clear scale with good contrast and holds it's calibration like a rock. I bought it in 2014 and have needed to calibrate it only twice. It has a lot of thermal mass in the body and prism and seems to cool down the sample in about 30 seconds for a stable reading. Since it is hard for me to read it better than about 0.2 Brix, I take it as a approximate reading and I am happy with that. I mostly use it during the boil to know when I have hit my starting gravity.

 

[balrog]

My $25 refractometer requires i measure sample, then immediately clean water, repeat. It is a very temperature-finicky thing. Luckily I can live with that. When it's the dead of winter, brewing in the less-than-toasty garage, it can be quite tricky. At this point in my brewing career, my process rarely causes massive issues with SG.

It's just a tool for measuring, and all such devices require calibration and proper use.