Refractometer Wort Correction Factor

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VikeMan

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Let’s have a heart to heart about refractometer Wort Correction Factor (WCF). My hope, though not necessarily my expectation, is to convince people that WCF is primarily intended to account for differences between Worts, and not differences between Refractometers (as I’ve very often seen stated).

Refractometers measure the concentration of “stuff” in solution. They do this by measuring the refraction of light passed through the sample solution. The sort of refractometers we homebrewers use have been set up to measure Sucrose solutions, which just means that the scale printed on the instrument corresponds the readings produced by sucrose solutions.

But, sucrose is something that the solids dissolved in wort are mostly not. Instead, wort contains various sugars, unfermentable dextrins, proteins, lipids, etc. And each non-sucrose substance (most, anyway) has a refractive index that’s different from the refractive index of sucrose.

Thus, WCF. Dividing the refractometer reading by the WCF gives a better estimate of the true concentration of sugars/dextrins in the wort, accounting and correcting for the differences in refractive index.

But wait! Don’t different worts have different mixes of sugars, dextrins, etc., and so shouldn’t the WCF be different for each wort? You betcha it should. But as a practical matter, most people don’t have the time or inclination to experiment with, record, and analyze comparisons of refractometer readings vs. hydrometer readings to find the best WCFs for each individual recipe. So most folks grab a “default” WCF (1.04 or 1.03 are pretty safe) and use it. But it’s still a factor used to get a better approximation of the true gravity of the wort, accounting (in an average/default sort of way) for the previously mentioned differences in those refractive indexes. And it has nothing to do with the differences between one sucrose scaled refractometer and another sucrose scaled refractometer.

So where does the notion that WCF is intended to account for the differences between refractometers come from? I’m not 100% sure. About 10 years ago, Kai blogged about his wonky refractometer that needed a non-typical WCF. What he was really doing (reading between the lines) was adapting a typical WCF to account for his wonky refractometer, i.e. there were two factors disguised as one. I’ll take a minute to say that Kai has done as much for homebrew science as anyone, and far more than most. I don’t think he meant for people to think that WCF is essentially a factor to account for differences between refractometers, but I fear a lot of people may have taken it that way. So much so that it’s not hard to find spreadsheets intended for the recording of refractometer and hydrometer readings over many batches of wort, and then compute an average WCF “for your refractometer.” What these spreadsheets are really doing is computing an average WCF for the worts that particular brewer tends to make. That said, if the refractometer itself is inaccurate (or not calibrated), then Kai’s wonky-refractometer-adjustment will be embedded in the average computed. Perhaps the refractometer calculators should include two correction factors… one for wort (the WCF) and one for faulty refractometers. The latter could default to 1.0 for properly functioning refractometers. I’m only partly kidding.

But wouldn’t two different “sucrose” refractometers measure wort differently from each other? After all, they are sucrose refractometers, not wort refractometers, right? Well, no. Not if they are accurate and calibrated. As previously hinted at, the refractometer measures the diffraction of light, and doesn’t “know” that it’s referenced, via the printed scale, to sucrose solutions. Imagine two accurate and calibrated refractometers that both measure the same sucrose solution at, say, 15 brix (about 1.061 SG). Knowing how refractometers function, do we think that an equivalent single mash-derived WORT of about 1.061 SG would give two different measurements between these two refractometers? Of course not. But that’s what you’d have to believe if you also believe that two different accurate and calibrated “sucrose” refractometers need different WCFs from each other.


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dmtaylor

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For whatever it's wort ;) , my "factor" based on my experimentation here for an average wort or beer with my refractometer at my house with my process and my system is not 1.03-1.04, but rather 1.00. YMMV

I do feel the factor probably varies from instrument to instrument, and probably most importantly, from user to user. Every user is different, every eyeball different. I swear I can see different readings depending on light source, how far away my eye is from the peephole, etc. Any haze in the sample is also a factor. There will be inconsistencies between instruments, users, time & date, etc. It's gonna happen. As such...

Overall, a refractometer is never going to be as accurate as a hydrometer. It's super useful, and I can get repeatable results for both OG & FG within 0.002 for most worts/beers. However, it ain't perfect. Don't expect it to be.

I calibrate in plain water with each & every use, always, every time. I doubt most people bother with this. But I find that it matters. A lot. As does temperature. Don't get me started on temperature. You wouldn't like me when I get started on temperature.

My input on proper usage can be found here, along with a deep rabbit hole:


I've also argued with Sean Terrill (a10t2) on one occasion, and essentially got him to admit that Novotny's calculation (which is used by Brewers Friend) might be more accurate than his when SG >1.014, while we agree that his seems to be more accurate when SG <1.014. Again, YMMV. Another associated rabbit hole:



So there's my 2.5-cent summation of what I think I know about refractometers. Hope somebody might find some part of it insightful. If it raises eyebrows or questions, great. That's what we should be here for.
 
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CascadesBrewer

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Refractometers are very useful during the boil to assess gravity. That’s it.

That is my experience as well. I have taken a few readings of wort in the 1.060-ish range and I feel like I can get readings with my refractometer that match my hydrometer for my typical pre-boil and OG range. I have been using a correction factor of 1.02. Maybe I should look closer at that and play with a 1.03 or 1.04 factor.

When I have tried taking readings during fermentation, the line is always very fuzzy. Is this from yeast in suspension messing up the reading? I have tried taking FG readings, but they have not matched up with my hydrometer readings. I have only tried it a few times and not really dug into the issue, but my refractometer FG readings were a few points high after correction. It could be user error or it could be that the correction formula I tried is off.

I am also confused why I often need to recalibrate my refractometer every brew day. At first I assumed it was a fairly mechanical device and my initial calibration would stick, at least for months. It is often off several points between days. I believe that was the source of some of my original frustration with using my refractometer. I am now sure to calibrate with distilled water each day. It is a $20 model from Amazon that claims to have ATC.

I guess I am pretty happy with my process. I use the refractometer to verify my mash went well and that I am on track for my target OG and gravity. This lets me make corrections early on if needed. I then take "official" OG and FG reading with my hydrometer. I try to avoid gravity readings during fermentation, but sometimes I will take a hydrometer reading if I have questions/concerns about the fermentation. Using the refractometer would be handy for my 1 gallon batches.
 

balrog

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not 1.03-1.04, but rather 1.00. YMMV
For years I toiled with my secret, always thinking I was somehow in possession of a possessed refractometer, because I had a WCF of 1.00. I never told anyone. I was ashamed. I did not want to be ostracized, so I stuck my head in the sand and kept on going. (see what I did there? oh yeah. Ostrich jokes).

Anyway, then the day came that I took a refractometer reading in situ. Means I dropped the damned thing in the boil kettle. It did not survive. The beer was fine. The replacement, another $20-25 dollar one online, has caused me nothing but grief with it's wandering ATC-from-hell. Zero calibrate indoors, shifts up to 1.2 when taken into the 20F garage in winter. It is being replaced. It too, however, had a 1.00 to 1.02 WCF. But I am OCD Man and always use refractometer and std hydrometer and expanded scale hydrometer on ever reading. Yeah. I'm that guy. No, I'm not much fun to live with. But I couldn't quite pull the trigger on an EasyDens, or even the now $150 Milwaukee digital refractometer.

But, short story long, yes, I too typically have not seen WCF with my system of 1.04.
 
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VikeMan

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It is a $20 model from Amazon that claims to have ATC.

The replacement, another $20-25 dollar one online, has caused me nothing but grief with it's wandering ATC-from-hell. Zero calibrate indoors, shifts up to 1.2 when taken into the 20F garage in winter.

Couple of fun facts about ATC refractometers.

- The Automatic Temperature Correction corrects for the temperature of the instrument. It does not correct for the temperature of the sample. A lot of people know this and disregard it, thinking that the temp of the sample will "instantly" come down to the instrument's temp. Personally, I get more consistent results with hot samples if I give them some time to cool off.

- The ATC feature works within a fairly narrow range of temps, at least for the refractometers for which I've seen the specs. Like 50F-86F (for example).
 

balrog

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Couple of fun facts about ATC refractometers.

- The Automatic Temperature Correction corrects for the temperature of the instrument. It does not correct for the temperature of the sample. A lot of people know this and disregard it, thinking that the temp of the sample will "instantly" come down to the instrument's temp. Personally, I get more consistent results with hot samples if I give them some time to cool off.

- The ATC feature works within a fairly narrow range of temps, at least for the refractometers for which I've seen the specs. Like 50F-86F (for example).
This is what I have found. Luckily my process is fairly repeatable, and taking a preboil reading has only once shown me in need of adjustment (an error in strike volume), so I typically zero in the house, take a sample preboil and take the instrument back into the house to sit before reading.
 

CascadesBrewer

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- The Automatic Temperature Correction corrects for the temperature of the instrument. It does not correct for the temperature of the sample. A lot of people know this and disregard it, thinking that the temp of the sample will "instantly" come down to the instrument's temp. Personally, I get more consistent results with hot samples if I give them some time to cool off.

I will play around with cooling hot samples to see the impact. I have read that a few drops of hot wort should cool quickly and not really impact the temperature of the instrument. My comment about ATC was more me wondering why one day a squirt of room temperature distilled water might read 1.000 and on another day it might read 1.003. The starting temp of my refractometer and distilled water should always be in the 65F to 75F range.
 

AlexKay

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To pick a nit or two, and to weigh in on the issue of "Refractometers! What are they good for?":

The key thing to consider is that the specific gravity, in and of itself, is not a particularly useful number unless you're trying to figure out how much your beer weighs. As brewers we're interested in the ABV primarily, and then in the concentrations of any remaining fermentable and unfermentable sugars. There are (the choice of several) equations that take the OG-FG difference and compute the ABV. These equations, like the refractometer equations, must take into account that in addition to the decrease of sugar, there is also an increase in alcohol. Like the refractometer equations, they also make assumptions about the sugar profile of the wort.

I don't know of any refractive-index-to-ABV calculators, but I also don't have any reason to think that the ABV calculated this way would be less accurate than one calculated from SG. (And if it is less accurate, is the difference in accuracy significant given our needs?) And for purposes of ensuring batch repeatability and predictability, I don't see any reason that a refractometer reading is inferior to a hydrometer reading.

Add to this the unique advantages of refractometers over hydrometers: they're much harder to break, use much smaller analysis samples, and they're relatively insensitive to the presence of CO2. I'd recommend a refractometer over a hydrometer for most brewers.
 

doug293cz

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To those of you saying you have 1.00 WCFs: are you reading a Brix scale, or an SG scale? I suspect that refracts with SG scales may have built the WCF into the scale, especially if the refract is sold specifically as a brewing instrument.

Brew on :mug:
 

dmtaylor

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Using the refractometer would be handy for my 1 gallon batches.

This is the main reason I did so much investigation with how to use the thing properly. I typically brew 1.5 to 2 gallons. If I felt compelled to take hydrometer samples for OG and FG, I'd be wasting a huge percentage of the batch.

I'd recommend a refractometer over a hydrometer for most brewers.

Not sure I recommend a refractometer for most brewers, because the vast majority of people won't bother to learn to use it properly, so it leads to endless confusion. It is a very useful tool IF the user understands how to use it.

To those of you saying you have 1.00 WCFs: are you reading a Brix scale, or an SG scale? I suspect that refracts with SG scales may have built the WCF into the scale, especially if the refract is sold specifically as a brewing instrument.

Brew on :mug:

SG scales on refractometers are very iffy at best, and misleading since the thing can't even measure SG but only Brix. I record only Brix values and use only Brix values in the conversion calculations.
 

balrog

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To those of you saying you have 1.00 WCFs: are you reading a Brix scale, or an SG scale? I suspect that refracts with SG scales may have built the WCF into the scale, especially if the refract is sold specifically as a brewing instrument.

Brew on :mug:
I only ever use the brix scale, converting to SG with the likes of BrewersFriend calculator.
 

doug293cz

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SG scales on refractometers are very iffy at best, and misleading since the thing can't even measure SG but only Brix. I record only Brix values and use only Brix values in the conversion calculations.
Refractometers don't directly measure Brix either. They respond only to index of refraction. The scale inside is just a physical representation of the correlation between index of refraction and concentration of sucrose in a water solution using the Brix scale.

I agree that the Brix scales in refracts tend to be much more reliable than the SG scales, but that is the fault of the instrument manufacturers for implementing the scale incorrectly

It is fairly easy to create calibration solutions for a Brix refractometer, since Brix is just the weight percent sucrose in a water solution. For example you can make a 20 Brix calibration solution by mixing 20 grams of sucrose with 80 grams of distilled water.

Brew on :mug:
 
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VikeMan

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It is fairly easy to create calibration solutions for a Brix refractometer, since Brix is just the weight percent sucrose in a water solution. For example you can make a 20 Brix calibration solution by mixing 20 grams of sucrose with 80 grams of distilled water.

I wonder how many people might find that a reference 20 Brix (or whatever) solution doesn't measure exactly 20 Brix on their refractometer's scales. We calibrate at the zero point with water, but that doesn't necessarily guarantee that the instrument's scale is accurate in wort or beer "OG and FG" ranges. Makes me think we might want to be calibrating with sugar water instead.
 

balrog

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I wonder how many people might find that a reference 20 Brix (or whatever) solution doesn't measure exactly 20 Brix on their refractometer's scales...Makes me think we might want to be calibrating with sugar water instead.
Oh I am so totally gonna do this.
Also makes me want to try with Domino, Dollar Store brand, grocery store brand, etc.

And check with my hydrometers as well.
 

CascadesBrewer

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I wonder how many people might find that a reference 20 Brix (or whatever) solution doesn't measure exactly 20 Brix on their refractometer's scales. We calibrate at the zero point with water, but that doesn't necessarily guarantee that the instrument's scale is accurate in wort or beer "OG and FG" ranges. Makes me think we might want to be calibrating with sugar water instead.

I gave it a try with a solution of 40g of Domino Cane Sugar and 160g of Distilled water. With my refractometer calibrated back to a 0 reading with distilled water I got a reading of about 19.9 Brix with the solution. With my hydrometer (which I verified read 1.000 with distilled water) I got a reading of 21 Brix (on the "Balling" scale, or 1.082 on the SG scale, which would be 1.083 if temp corrected from 70F to 60F). Hmmm....makes me wonder if my hydrometer scale is off a touch and I have been putting my trust in the wrong instrument!
 
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VikeMan

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I got a reading of 21 Brix (on the "Balling" scale, or 1.082 on the SG scale, which would be 1.083 if temp corrected from 70F to 60F). Hmmm....makes me wonder if my hydrometer scale is off a touch and I have been putting my trust in the wrong instrument!

I think 20 Brix = 1.083.
 

doug293cz

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I gave it a try with a solution of 40g of Domino Cane Sugar and 160g of Distilled water. With my refractometer calibrated back to a 0 reading with distilled water I got a reading of about 19.9 Brix with the solution. With my hydrometer (which I verified read 1.000 with distilled water) I got a reading of 21 Brix (on the "Balling" scale, or 1.082 on the SG scale, which would be 1.083 if temp corrected from 70F to 60F). Hmmm....makes me wonder if my hydrometer scale is off a touch and I have been putting my trust in the wrong instrument!
No problem with your hydrometer's SG scale. A 20 Brix/Plato solution of sucrose actually has an SG of 1.083.

Brew on :mug:
 

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I have a cheap Chinese-made Refractometer that has the WCF of 1.000000000. Strangely, it's as exact as my fancy British Hydrometer. I mean, even in its SG scale, which is usually regarded as rubbish. No need to convert anything. If it says 1.050, no need to take out the Hydrometer, which will show exactly what the cheapo Refractometer says.
Most times.
I think it's a sort of a manufacturing fault turned lucky. Slightly misplaced scale print or whatever.

Sometimes however it strays wildly.
Now I got an idea that might be because of the difference in wort composition.
 
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Blackdirt_cowboy

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I don’t know what to make of all this. My refractometer measures in brix. I’ve been using it for years. I constantly test it against my hydrometer and it always gives the same readings. Even when I check after fermentation and run it through the calculator on brewers friend, same reading as my hydrometer. I’ve come to rely on my hydrometer 100%. I feel like I need to take my refractometer with me to go play the lottery.
 
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VikeMan

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1.081. I did that in my head! (See above, my simple method :))

But... 20 "real" (i.e. sucrose solution) Brix does equal 1.083, with no correction needed, which is what we were discussing when I posted the 1.083. I assume your method is intended to include an implied WCF, for wort?
 
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But... 20 "real" (i.e. sucrose solution) Brix does equal 1.083, with no correction needed, which is what we were discussing when I posted the 1.083. I assume your method is intended to include an implied WCF, for wort?

Oh dang, you're right! Implies a wort correction factor of 1.025. I did that so long ago, I forgot about it. Thanks for that.
 

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I got 2 hydrometers and recently used all 2, just before bottling.
1 said 1.000,
2 said 1.002
So I decided to mark them and just make sure I use the same one for all measurements.
It's the same story with my refractometers. They give different readings as well. I use the one that reads from 0 to 20 brix as it is just easier to read (the other is 0 to 40)
Only tricky thing is that I've gone from contact lenses to glasses. Definitely more difficult to read wearing glasses
 

Srdjan Ostric

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Let’s have a heart to heart about refractometer Wort Correction Factor (WCF). My hope, though not necessarily my expectation, is to convince people that WCF is primarily intended to account for differences between Worts, and not differences between Refractometers (as I’ve very often seen stated).

Refractometers measure the concentration of “stuff” in solution. They do this by measuring the refraction of light passed through the sample solution. The sort of refractometers we homebrewers use have been set up to measure Sucrose solutions, which just means that the scale printed on the instrument corresponds the readings produced by sucrose solutions.

But, sucrose is something that the solids dissolved in wort are mostly not. Instead, wort contains various sugars, unfermentable dextrins, proteins, lipids, etc. And each non-sucrose substance (most, anyway) has a refractive index that’s different from the refractive index of sucrose.

Thus, WCF. Dividing the refractometer reading by the WCF gives a better estimate of the true concentration of sugars/dextrins in the wort, accounting and correcting for the differences in refractive index.

But wait! Don’t different worts have different mixes of sugars, dextrins, etc., and so shouldn’t the WCF be different for each wort? You betcha it should. But as a practical matter, most people don’t have the time or inclination to experiment with, record, and analyze comparisons of refractometer readings vs. hydrometer readings to find the best WCFs for each individual recipe. So most folks grab a “default” WCF (1.04 or 1.03 are pretty safe) and use it. But it’s still a factor used to get a better approximation of the true gravity of the wort, accounting (in an average/default sort of way) for the previously mentioned differences in those refractive indexes. And it has nothing to do with the differences between one sucrose scaled refractometer and another sucrose scaled refractometer.

So where does the notion that WCF is intended to account for the differences between refractometers come from? I’m not 100% sure. About 10 years ago, Kai blogged about his wonky refractometer that needed a non-typical WCF. What he was really doing (reading between the lines) was adapting a typical WCF to account for his wonky refractometer, i.e. there were two factors disguised as one. I’ll take a minute to say that Kai has done as much for homebrew science as anyone, and far more than most. I don’t think he meant for people to think that WCF is essentially a factor to account for differences between refractometers, but I fear a lot of people may have taken it that way. So much so that it’s not hard to find spreadsheets intended for the recording of refractometer and hydrometer readings over many batches of wort, and then compute an average WCF “for your refractometer.” What these spreadsheets are really doing is computing an average WCF for the worts that particular brewer tends to make. That said, if the refractometer itself is inaccurate (or not calibrated), then Kai’s wonky-refractometer-adjustment will be embedded in the average computed. Perhaps the refractometer calculators should include two correction factors… one for wort (the WCF) and one for faulty refractometers. The latter could default to 1.0 for properly functioning refractometers. I’m only partly kidding.

But wouldn’t two different “sucrose” refractometers measure wort differently from each other? After all, they are sucrose refractometers, not wort refractometers, right? Well, no. Not if they are accurate and calibrated. As previously hinted at, the refractometer measures the diffraction of light, and doesn’t “know” that it’s referenced, via the printed scale, to sucrose solutions. Imagine two accurate and calibrated refractometers that both measure the same sucrose solution at, say, 15 brix (about 1.061 SG). Knowing how refractometers function, do we think that an equivalent single mash-derived WORT of about 1.061 SG would give two different measurements between these two refractometers? Of course not. But that’s what you’d have to believe if you also believe that two different accurate and calibrated “sucrose” refractometers need different WCFs from each other.


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Does the cloudy stuff at the bottom of the fermenter affect reading? In other words, should the sample be clear? My feeling is that it does and gives you a higher reading.
 

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I have a feeling that solids would make for a "fuzzier" line, but I have never tested fresh from boil kettle cloudy vs wait an hour clear, in order to see a difference. Another good test.
 

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I'd like to see how others do with their refractometers and the cloudiness of their samples...

I've found that it makes a big difference. Whenever I pull a sample from my mash wort to check with my refractometer I let it sit in a small dish or shot glass for a while, 10 minutes or so at least. I've found that the very first reading, and the 10 minute later reading, are different from each other. And I've once pulled a much larger sample to check with a hydrometer, and the hydrometer matched the 10 minute reading nearly perfectly.

I do not however recall if the initial vs. 10 minute readings were higher / lower (which was which) or by how much they were off. Sorry. I did the test and left thinking - "wow, note to self, it matters, so make sure to be patient before grabbing the reading".
 

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I have spent a lot of time learning the use of my refractometer, it gets used for virtually all of my readings during brew day.
I can't remember the last time I used my 'old school' hydrometer - probably to verify the calibration of my refractometer and Tilt hydrometer.
As others have said, I find that when measuring hot wort I have to let the sample cool in the refractometer for at least a minute or two before the reading is stable (and that is using an ATC refractometer).
The only screwy numbers I get are trying to measure mash gravity, but once the grain is cleared the pre-boil gravity is correct.
I haven't spent the time to build various wort correction factor tables, but when comparing the hydrometer readings to the refractometer over various types of worts and running the numbers through the refractometer calculator - I have found that the standard default grab of 1.04 gives me numbers that are withing my acceptable error factor.
The corrected readings I get from my refractometer usually match up to the estimated numbers in Brewsmith within a point or two.
I couldn't live without my refractometer any more on brew days - it makes the process so much easier.
 

CascadesBrewer

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As others have said, I find that when measuring hot wort I have to let the sample cool in the refractometer for at least a minute or two before the reading is stable (and that is using an ATC refractometer).
Do you put drops of hot wort on the refractometer and then let that sit for a minute+, or do you cool the wort sample first?
 

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Do you put drops of hot wort on the refractometer and then let that sit for a minute+, or do you cool the wort sample first?

I put the hot or boiling drops right on the refractometer and just let it sit for a minute or two.
The reading is pretty stable after that.
The refractometer reads low when the sample is hot, so I just let it sit until the reading stops climbing.
 

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The refractometer reads low when the sample is hot, so I just let it sit until the reading stops climbing.
If you don't mind, next time you do this, see if the droplets show any haziness / particulates floating around. When hot and later when cold - i.e. did they move off to the side.

Maybe everyone knows but hydrometers measure density, refractometers measure how light moves through. Particulates make little difference (maybe none) to hydrometers, but have huge effects on refractometers.
 

balrog

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(maybe none) to hydrometers
I've been on the receiving end of some lively discourse on this topic but I've never tested it myself, as the hydrometer sample is oft times settled mostly by the time I finish pitching and setting up the ferm chamber. Example
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I wonder whether for my wheat-centric and no-boil batches whether my data show difference between hydrometer and refractometer consistent with particulates causing (statistical) effect? Something to look into.
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1665091188901.png
 
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VikeMan

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Copied from a post by a soil scientist on a different brewing forum:

"Particles in suspension will alter hydrometer readings. Soil scientists exploit this principle when they use specially calibrated hydrometers to evaluate soil particle size distribution."
 
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