refractometer question

[BrewKnurd]

If you have a dual scale refractometer, and 23 Brix is equal to 1.096, then the S.G. scale is suitable for wine, but not beer.

The gravity of the DME solution is fairly close to the 1.088 reported by some posters, so perhaps those refractometer scales are calibrated for wort, rather than wine.

This is exactly my understanding of how refractometers which are scaled like this (as mine is) are intended to work.

When using a refractometer calibrated for sucrose, you will get a higher Brix reading than you actually have, due to the refractive indices of wort and a sucrose solution of the exact same gravity being different. This error is usually between 2 and 6 percent on the high side.

So if you have a brix reading of 23, that would come out to around 1.097 if you used the value straight up. But if you divide by 1.06 you get 21.7, which is around 1.091. Admittedly, this is using the high end of the error, and still is higher than 1.088... but if the Brix scale is intended to measure sucrose and the SG scale is "calibrated" (and i put calibrated in quotes because it would be based on an assumed wort) to measure wort, then they should be offset by a bit.

http://www.byo.com/stories/projects-and-equipment/article/indices/29-equipment/1343-refractometers

 

[ajf]

Just out of curiousity, after you diluted to 23 were the volumes significantly different?

It was a very small sample, slightly over 4 oz, and I measured the water volume using a 1/2 pint jug with markings at 2, 4, 6, and 8 oz. I don't doubt that the volumes were slightly different, but a very small volume difference in a 4 oz sample could be significant. Both samples fitted in to my hydrometer test cylinder filled nearly to the top. If I'd known you were going to ask this question, I would have weighed the samples, but I didn't. I think I can safely say that the sample sizes were within 10% of each other.

-a.

 

[Dan]

If we're talking about Bobby's refractometers. My humble opinion is this:

Bobby_M does not put out products he has not researhced, proved and believed in. I did get my refracotmeter from him. It might be off, very slightly. Very slightly! But for the price he charged I' be a fool to complain. The thing works extremley well in my opinion.

I enjoy buyinj his products, especialy the one's he makes himself. Bobby's equipment is great in my opinion. He doesn't charge and arm and leg for his stuff and his products work extemely well.

The other day I was looking arournd for quick disconnets (QD's) for my brewery. I checked many places. What Bob sells f0r $4 cost 100% more on those sites.

From me... thankyou Bobby for not only the enormous amount of brewing info you have put out for free for homebrewers. But, Thankyou for great products and great pricing. Nobody ive seen selling beer stuf here has the heart, quality, or great pricing that you do.

Just my humble opinion.

Cheers Bro!

Dan

 

[ajf]

If we're talking about Bobby's refractometers. My humble opinion is this:

Bobby_M does not put out products he has not researhced, proved and believed in. I did get my refracotmeter from him. It might be off, very slightly. Very slightly! But for the price he charged I' be a fool to complain. The thing works extremley well in my opinion.

I enjoy buyinj his products, especialy the one's he makes himself. Bobby's equipment is great in my opinion. He doesn't charge and arm and leg for his stuff and his products work extemely well.

The other day I was looking arournd for quick disconnets (QD's) for my brewery. I checked many places. What Bob sells f0r $4 cost 100% more on those sites.

From me... thankyou Bobby for not only the enormous amount of brewing info you have put out for free for homebrewers. But, Thankyou for great products and great pricing. Nobody ive seen selling beer stuf here has the heart, quality, or great pricing that you do.

Just my humble opinion.

Cheers Bro!

Dan

I'm not talking about Bobby's instruments as I don't have one.

My experiment showed that there was a 7% difference between a sucrose solution and a DME solution, and if I use a calculator or lookup table such as
http://www.brewheads.com/brixsg.php
http://www.brewersfriend.com/brix-converter/
http://www.winning-homebrew.com/specific-gravity-to-brix.html
http://onebeer.net/refractometer.shtml
or articles such as
http://www.byo.com/stories/article/...y/1344-refractometers-and-mash-outs-mr-wizard
then I get a 7% error when using a refractometer to estimate the specific gravity of wort.
It is quite possible that some refractometers report a true Brix value (or close) when measuring wort, but they would be wrong when measuring must.

As I said earlier, I think the most sensible thing to do is to check the refractometer reading against an hydrometer reading for what you use the refractometer for, and decide if any errors are acceptable to you.

One thing did surprise me was that I got a 7% difference, but when I calculated the Brix Correction Factor for Promash, I only got about a 4% difference. This could be because of an extract based sample with no specialty malts vs an All Grain sample. It could also be a measurement error on my part based on a sample of 1, or it could be because the refractometer has drifted over time. I will be taking more measurements to try and identify the cause of the difference.

-a.

 

[MalFet]

It's not really a question of Bobby's equipment so much as fundamental facts of physics. Bobby makes/sells great gear, but he can't change the nature of the universe (yet....).

We're trying to convert between an optical property of wort and a density property of wort, and that relationship is inherently complex. No scale will always be right, and any "built-in" calibration is going to be made on the basis of a very particular set of assumptions.

I've tracked my refractometer over a few dozen batches now and on average I've needed to bump my refractometer reading up by about 5% to match my hydrometer, though on any given batch that number has ranged from 3% to 7%. That's plenty good enough for me to monitor the mash, but certainly if you want a precise measurement of gravity you need to use a device designed for measuring density, not refraction.

 

[dbrewski]

OK now I am confused. I thought that the inaccuracy came from the calibration of the SG side compared to the Brix, but that the Brix side was still accurate for wort. Are we now saying the Brix side has up to 7% error? When I first used my old refractometer I compared it to a hydrometer reading and it matched. I just assumed from then on it was accurate.

 

[camiller]

...
But seriously there was some other thread going in here the other day where a couple of professional brewers were talking about these super accurate instruments...some kind of hydrometers but commercial grade, where you needed to use three of them to cover the whole range of potential gravities. I know +- a point or two will not matter to homebrewers, but it would be nice to know for sure where your tools are off a bit and a tool like that would do it. Does anyone know the name of those?

They're still called hydrometers, but if you buy them off of a laboratory supply company you'll have a wide diversity of ranges available to you.

If you're looking for some, cynmar.com has reasonable quality gear for cheap(ish) prices. If you're feeling very ambitious, you could always roll over to Fischer Scientific.

Williams Brewing used to sell a three piece set as well. Now they sell a "bottling" hydrometer with a scale of 1.000-1.040 and a "precision" hydrometer with a 1.000-1.100 scale. Most cheap hydrometers go 0.980-1.130.

 

[MalFet]

OK now I am confused. I thought that the inaccuracy came from the calibration of the SG side compared to the Brix, but that the Brix side was still accurate for wort. Are we now saying the Brix side has up to 7% error? When I first used my old refractometer I compared it to a hydrometer reading and it matched. I just assumed from then on it was accurate.

Short answer: yes, that's what I'm saying.

Long answer:

Brix is a unit that describes the concentration of sucrose in water. A 20 Brix solution is, by definition, exactly 20% sucrose by weight.

SG, on the other hand, is a measurement of density relative to water. A 1.080 wort will weigh exactly 1.080 times an equivalent volume of pure water, again by definition.

(Plato is an interesting hybrid measurement, but for our purposes you can just consider Brix and Plato to be equivalent).

What a refractometer measures is neither concentration nor density, but rather optical refraction. When you send light through a solution, it bends, and different kinds of solutions bend light to different degrees. What makes a refractometer useful is that the relationship between sucrose concentration and refraction is very predictable. A refractometer does not measure sugar concentration directly, but it measures something else that can be converted to sucrose density in a reliable and predictable way.

Unfortunately, we don't make sucrose solutions. We make wort that includes a wide mix of various sugars and other substances. All these different substances affect the refractive index of wort in different ways. A maltose solution refracts differently than a solution of dextrins, and both of these are different than sucrose. In most worts, the measurements are "pretty close", but there's no way to produce an exact conversion from optical refraction to concentration or density without knowing exactly the composition of the wort. That's not possible without serious lab gear and a test procedure far more complicated than using a hydrometer.

At the end of the day, there is always going to be an inherent uncertainty to converting between the optical properties and density properties of wort. On average, I find that bumping up my Brix reading by 5% or so gets me a value that is close enough to a hydrometer measurement that I don't worry about it. If you are trying to track density more precisely than that, you won't be able to do it with a refractometer. It's just a hard constraint on the nature of the universe.

(As a side note: If 2-3% measurement error is too much, what are you trying to track? Efficiency? ABV? Attenuation? In all these cases, there are other inherent limitations on measurement that introduce as much or more error than a refractometer will. In any system, your data is only as precise as your least precise measurement. For most people, that least precise measurement won't be gravity.)

 

[BrewKnurd]

OK now I am confused. I thought that the inaccuracy came from the calibration of the SG side compared to the Brix, but that the Brix side was still accurate for wort. Are we now saying the Brix side has up to 7% error? When I first used my old refractometer I compared it to a hydrometer reading and it matched. I just assumed from then on it was accurate.

The real point is that no refractometer can accurately measure the density of all worts, because wort is not consistent, and you're not directly measuring density. Sucrose is easy, because sucrose is always sucrose, so there's a more reliable correlation between refraction and density. Different worts will have different compositions of sugars, color components, etc, and therefore two worts of the same density can have different refractive indices, and will therefore read differently on a refractometer.

What I do is take a preboil sample and then measure with both my hydrometer and my refract. Usually the offset is a few gravity points. I then use the refract through the rest of the boil, applying the offset. This is a simplification, as the offset wouldn't stay constant, but i figure its close enough.

EDIT: What MalFet said.

 

[dbrewski]

OK, I get it. No I don't need to take 99.99% accurate readings, I'm just trying to understand if and where the measurement is off. Sounds like an adjustment is in order.

These things should come with disclaimers.

 

[MalFet]

OK, I get it. No I don't need to take 99.99% accurate readings, I'm just trying to understand if and where the measurement is off. Sounds like an adjustment is in order.

These things should come with disclaimers.

Indeed. That's why I wish someone would make a refractometer that only displayed refractive index. That way, people would at least realize that there's a conversion involved.

All that said, though, I love my refractometer. It's not one of Bobby_M's (I got it before he started selling them), but it looks to be nearly identical. I use a refractometer throughout my mash and boil, and then compare it against a hydrometer reading taken as I go into the fermentor. If you keep good notes, you'll have a pretty good sense after just a few batches of how much correction is necessary.

 

[zeus53219]

I have a Extech RF11 refractometer only in Brix scale. In the instructions it does state to use a Brix Correction Factor of 1.04 with Wort/Maltose, 1.01 with Sucrose and 1.00 with Sugar in Fruit Juice/Fructose. So if I have a brix reading of 23 measuring wort, that would come out to around 1.093. If I was measuring must, it would be 1.097. Guess refractometers are a little like women, they are all a little different, but once you know how to read them right, you achieve good results.

 

[ajf]

I've tracked my refractometer over a few dozen batches now and on average I've needed to bump my refractometer reading up by about 5% to match my hydrometer, though on any given batch that number has ranged from 3% to 7%. That's plenty good enough for me to monitor the mash, but certainly if you want a precise measurement of gravity you need to use a device designed for measuring density, not refraction.

What are you putting in your beers? or how are you converting from Brix to SG ? I need to reduce the refractometer reading by about 4% to forecast a reasonably accurate SG reading

-a.

 

[MalFet]

What are you putting in your beers? or how are you converting from Brix to SG ? I need to reduce the refractometer reading by about 4% to forecast a reasonably accurate SG reading

-a.

Apologies, ajf. I missed this message somehow. It was only when looking for this link for someone else that I noticed your question.

Nope, I definitely multiply by 1.05. In other words:
(Brix refractometer reading) * 1.05 = (reasonable prediction of hydrometer reading)

It could be that we just have differently calibrated screens in there from the get-go. If that's the case, it looks like Kaiser and I got our refractometers from the same batch:
http://braukaiser.com/blog/blog/2012/03/23/dont-trust-your-refractometer-blindly/

This is the lesson here, it seems: all measurement tools are different, so it pays to calibrate!

 

[ajf]

Well, the good news is that using a Brix Calibration Factor, the readings from the refractometer (in whatever units they are actually displayed) seem to be able to give a fairly accurate representation of S.G.
I wonder however how much the Calibration Factor varies according to the grain bill, and how much the boil with or without hops affects it? I know, that whenever I have brewed a lager using Pilsner malt and used the refractometer to estimate the S.G, I seem to get higher efficiency than if I brew a pale ale using M.O. I can see I need to do some more experiments, and possibly develop some brewing software where the correction factor is somehow linked to the ingredients.

-a.

 

[MalFet]

It's an interesting question. I just brewed two batches back to back, and the grain bills couldn't have been more different. First was 1.084 with all base malts and roasts. The other was 1.040 with MO and lots of crystal. Both required a 1.05 conversion, but a few weeks ago I brewed two other batches and I needed 1.03 and 1.07. It's very weird. I'm not sure how much of the variation is ingredient based versus just measurement error.

 

[ajf]

I agree that it is interesting. I was going to run a series of experiments, making a large number of small (1 liter) batches. I think I shall add refractometer readings for each batch, taking refractometer and gravity readings both pre and post boil; and see if I can see any patterns. The advantage of the 1 liter batch size is that I can weigh everything accurately to the nearest gram, which should minimize measurement errors.

On your two batches where you needed unusual correction factors, could you provide me with the grain bills, so I can see if I get similar results?

Thanks for your useful comments.

-a.

 

[Yooper]

I agree that it is interesting. I was going to run a series of experiments, making a large number of small (1 liter) batches. I think I shall add refractometer readings for each batch, taking refractometer and gravity readings both pre and post boil; and see if I can see any patterns. The advantage of the 1 liter batch size is that I can weigh everything accurately to the nearest gram, which should minimize measurement errors.

On your two batches where you needed unusual correction factors, could you provide me with the grain bills, so I can see if I get similar results?

Thanks for your useful comments.

-a.

GREAT idea! I'll be following your experiments. My correction factor is 1.052 for my hydrometer and refractometer to match with wort.

 

[MalFet]

On your two batches where you needed unusual correction factors, could you provide me with the grain bills, so I can see if I get similar results?

That's the thing, they weren't really unusual. I see a pretty even distribution in the range 1.03 to 1.07, depending on the batch. If I run with 1.05 I end up with something that is always close enough for my purposes, but I wouldn't say that 1.05's are more common than 1.03's or 1.07's.

The most recent 1.03 was 90% 2row and 10% special b, 1.065 OG. The 1.07 was a 82% Belgian Pilsner, 6% acidulated, 6% aromatic, and 6% malted oats for an OG of 1.054.

It's possible that I'm just having measurement errors, but I use a lab grade hydrometer, adjusted for temperature, and my ATC-refractometer seems otherwise reliable. I brew indoors, so my ambient temperature is pretty much 70º all the time.

Keep us posted if you find anything!

 

[ajf]

Thanks MalFet.

I have an adequate supply of US 2 row, Maris Otter, and German Pilsner, and a good supply of specialty malts. I have also bought a 1 L vacuum flask for doing small mashes in. I have an accurate finishing hydrometer, but so far, nothing accurate that can measure a gravity > 1.020.

I ordered a couple hydrometers that should plug that gap. While waiting for them to arrive, I will try a few small batches to determine the thermal mass of the vacuum flask, and boil off rates etc. I shall also write a simple program which accepts inputs of measured specific gravity and Brix readings from the refractometer, and calculates a Brix Correction Factor based on the formula Specific gravity = (Brix/(258.6-(Brix/258.2)*227.1))+1.

The Brix reading will be divided by the correction factor before applying the formula, so with my refractometer, the correction factor will be > 1, and with yours, the correction factor will be < 1.

Then I will be able to start some tests.

Each test will consist of brewing ~ 1 L batch, measuring the pre boil volume, gravity, and Brix, then boiling for 45 minutes +, and measuring the post boil volume, gravity and Brix. I will then perform a fast fermentation test using bread yeast on the stir plate to determine the limit of attenuation.

I shall start using a mash thickness of 1.25 qt / lb, and a mash temp of 154 F and using just one of my base grains. Then I can repeat the test using a different mash temperature to see what effect the mash temperature has on attenuation. Then, using a single temperature, I will try mash thickesses of 1, 1.5, 1.75, and 2 qts / lb to see if I can detect any differences caused by the mash thickness, and using a low temperature, I will try some longer mashes to see if I can detect any difference caused by the mash time.

Having done this, I shall try a sub-set of those tests using various specialty malts, and then some typical mixtures of base and specialty malts to see if there are any noticeable anomalies.

I just hope my readings are fairly consistent.

If anybody has any other suggestions or comments, I'll be happy to consider them.

Please don't hold your breath until the tests are finished. Even if nothing goes wrong, it will take a long time to complete the tests, but I will post the results as I get them.

-a.

 

[mattd2]

I didn't get really accurate measurements but... I did an IPA on the weekend, ended up at:
1.071 Hydro
1.070 Refract
18° Brix Refract - converts to 1.074 with an only calculator.

So far I am leaning towards trusting my Refract's SG scale... so far

 

[FATC1TY]

I didn't get really accurate measurements but... I did an IPA on the weekend, ended up at:
1.071 Hydro
1.070 Refract
18° Brix Refract - converts to 1.074 with an only calculator.

So far I am leaning towards trusting my Refract's SG scale... so far

Why is that?

Have you calibrated your hydrometer in proper temp distilled water?

 

[mattd2]

Why is that?

Have you calibrated your hydrometer in proper temp distilled water?

The hydro measurement is probably just due to my "quick" effort at reading it. There was a fair amount of foam to read through and I was 95% sure it was on 71, but 100% sure it was not 74.
I will continue to take an initial og with both a hydro and refract (and try to be more scientific about it) until I am sure which way to lean.

 

[diS]

By reading all of this calibration factors it seem that only my refractometer gives lower reading.. as I can remember my calibration factor is around 0.96.
I tested it with 2 samples in different batches and get the same result.. both hydrometer and refractometer are calibrated in distilled water.

 

[MalFet]

By reading all of this calibration factors it seem that only my refractometer gives lower reading.. as I can remember my calibration factor is around 0.96.
I tested it with 2 samples in different batches and get the same result.. both hydrometer and refractometer are calibrated in distilled water.

Maybe we're just doing the algebra slightly differently, or maybe I'm just misunderstanding you. My refractometer produces lower readings than my hydrometer does, and I need to multiply my refractometer's reading by around 1.05 to match my hydrometer. Is that what you're seeing too?

 

[brewswellwithothers]

If I might suggest another variable to the discusison of grain bills, the Mash temp. We already know that different mash temps give more/less dextrins and effect the body and attenuation of the beer. Perhaps this is where the Brix conversion is getting the swings from 1.03 to 1.07.

 

[ajf]

Maybe we're just doing the algebra slightly differently, or maybe I'm just misunderstanding you. My refractometer produces lower readings than my hydrometer does, and I need to multiply my refractometer's reading by around 1.05 to match my hydrometer. Is that what you're seeing too?

Brewing Software such as Beersmith and Promash divides the Brix reading by the Brix Correction Factor before converting to S.G. Because of this, I would like to keep the division, but dividing by 1/1.05 is exactly the same as multiplying by 1.05.

If I might suggest another variable to the discusison of grain bills, the Mash temp. We already know that different mash temps give more/less dextrins and effect the body and attenuation of the beer. Perhaps this is where the Brix conversion is getting the swings from 1.03 to 1.07.

Already covered in post 50.

-a.

 

[brewswellwithothers]

@ ajf

I read all the posts but must have missed that part, glad to see that was included and thank you for running those tests. I am interested in how these tests turn out, as I am still getting used to my equipment and all grain. I've done 3 batches so far, 2 with a Refractometer way out of calibration; and last one with a replacement Refractometer properly calibrated. This last batch I was able to hit my numbers spot on with expectations; and my final pre-fermenter readings with Refractometer and hydrometer matched pretty well.

 

[diS]

Maybe we're just doing the algebra slightly differently, or maybe I'm just misunderstanding you. My refractometer produces lower readings than my hydrometer does, and I need to multiply my refractometer's reading by around 1.05 to match my hydrometer. Is that what you're seeing too?

Seems its just inverse calculation, I am dividing refractometer reading with calibration factor where Calibr. factor = Brix refractometer reading : Brix hydrometer reading.

 

[MalFet]

Seems its just inverse calculation, I am dividing refractometer reading with calibration factor where Calibr. factor = Brix refractometer reading : Brix hydrometer reading.

Right, that's fine. In that case, we're both seeing error in the same direction. Kaiser's refractometer did the same thing.