Refractometer for ABV measurement?

I use a Milwaukee brand refractometer for my saltwater coral reef and would rather use one of these than a float hydrometer for cider making.
The one that I have is calibrated for salt water so is my assumption correct that I'll need a separate one for alcohol?

I'm not familiar with salt water measurements. What unit does it use? And what range does it cover? Most of the refractometers I'm familiar with show Brix, which can easily be converted to specific gravity (I believe Brix units are used more in the food industry, by fruit farmers and industry... Plato or SG would be better for us brewers). You'll want one that goes from zero up to 25 Brix or so (1.106 SG). Hope this helps.

I don't think salt and sugar have similar refractive indices, so I think you may need to get a refractometer calibrated for sugar. In other words, your hydrometer may be etched for specific gravity but if the refractive index of salt is different than the RI for sugar, the SG it suggests you have won't be accurate as the refractometer is measuring the angle that light is bent by the solution and is not in fact directly measuring the density - It is using that angle as an indication of the density of the liquid...

I'll get one for brewing then. Thank you.

You should be able to use the same one, assuming it has a scale somewhere between 0 and 30 brix. The amount that your fluid bends light depends on its density. You can use the same thing for DEF fluid or battery acid as well. It's all just measuring density. The only problem would be when you have a scale that wont work.

But I think salt water refractometers are designed to give you PPM readings based on the refractive index of salt water and not sugar water... So why would they provide Brix ...

Refractometers cannot get accurate direct readings once fermentation has started because alcohol has a different refractive index than sugar in solution. You can get reasonably accurate results by using correction calculators however. I suggest this calculator: http://seanterrill.com/2012/01/06/refractometer-calculator/

Brew on

bernardsmith said:

But I think salt water refractometers are designed to give you PPM readings based on the refractive index of salt water and not sugar water... So why would they provide Brix ...

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I was not aware that a salt water refractometer used a different scale. All of the refractometers i've seen use either brix or SG as their scale. However if you could convert from ppm to SG it would still be usable

doug293cz said:

Refractometers cannot get accurate direct readings once fermentation has started because alcohol has a different refractive index than sugar in solution. You can get reasonably accurate results by using correction calculators however. I suggest this calculator: http://seanterrill.com/2012/01/06/refractometer-calculator/

Brew on

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light bends in solution based on the density of that solution. This is a simplification, but it's true enough for our purposes. That's why we can use refractometers for brewing, measuring battery acid strength, measuring the amount of urea in DEF fluid etc.

javalin said:

light bends in solution based on the density of that solution. This is a simplification, but it's true enough for our purposes. That's why we can use refractometers for brewing, measuring battery acid strength, measuring the amount of urea in DEF fluid etc.

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Right, but again, the refractive index of sugar dissolved in water is different from the refractive index of alcohol in water or alcohol and sugar in water and so there needs to be a correction applied once fermentation has begun - which is why wine makers typically use a refractometer to check the amount of sugar in say, grapes (Brix) but use an hydrometer to check the specific gravity in the fermenting wine...

At around $20 on Ebay, is it worth doing conversions, etc? I have one that reads SG and potential alcohol.

Nobody here mentioned that refractometers are not particularly useful in measuring final gravity. There is a correction process, but it leaves a great deal to be desired. A hydrometer is very cheap, and very accurate.


H.W.

Owly055 said:

At around $20 on Ebay, is it worth doing conversions, etc? I have one that reads SG and potential alcohol.

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Do you have one of the ones with the correct, or the incorrect SG scale? There are both types out there. The SG value for 20°Brix should be 1.083.

Owly055 said:

Nobody here mentioned that refractometers are not particularly useful in measuring final gravity. There is a correction process, but it leaves a great deal to be desired. A hydrometer is very cheap, and very accurate.


H.W.

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Actually I brought that topic up in post #7.

Brew on

doug293cz said:

Do you have one of the ones with the correct, or the incorrect SG scale? There are both types out there. The SG value for 20°Brix should be 1.083.



Actually I brought that topic up in post #7.

Brew on

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I have one of each..........


H.W.

Owly055 said:

At around $20 on Ebay, is it worth doing conversions, etc? I have one that reads SG and potential alcohol.
A hydrometer is very cheap, and very accurate.

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I already have a hydrometer so I guess that I can use that for my last and final measurement and use the refracter for my many interim measurements along the way. This will conserve the must.

doug293cz said:

Do you have one of the ones with the correct, or the incorrect SG scale? There are both types out there. The SG value for 20°Brix should be 1.083.

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Owly055 said:

I have one of each......

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Are the ones available with the "incorrect" scale a defect or just used for something different?

So, I'm understanding that the one I get must show 20° Bx = 1.083 SG, is that correct?
Even then, the FG will need to be adjusted with the calculator right?

P.S. My saltwater refracter shows a scale of SG 1.000 - 1.070 and 0 - 100 PPM.

CMcPherson said:

I already have a hydrometer so I guess that I can use that for my last and final measurement and use the refracter for my many interim measurements along the way. This will conserve the must.





Are the ones available with the "incorrect" scale a defect or just used for something different?

So, I'm understanding that the one I get must show 20° Bx = 1.083 SG, is that correct?
Even then, the FG will need to be adjusted with the calculator right?

P.S. My saltwater refracter shows a scale of SG 1.000 - 1.070 and 0 - 100 PPM.

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The conversion between BRIX and SG is absolute 19.98 = 1.083. If it's wrong, it's wrong... period!

H.W.

CMcPherson said:

I already have a hydrometer so I guess that I can use that for my last and final measurement and use the refracter for my many interim measurements along the way. This will conserve the must.





Are the ones available with the "incorrect" scale a defect or just used for something different?

So, I'm understanding that the one I get must show 20° Bx = 1.083 SG, is that correct?
Even then, the FG will need to be adjusted with the calculator right?

P.S. My saltwater refracter shows a scale of SG 1.000 - 1.070 and 0 - 100 PPM.

Click to expand...

The best ones don't have the SG scale at all- just brix which is what you're measuring anyway.

Then, do some quick rough math on the go. Like today, I had a brix of 13 preboil. 13 times 4 is 52. So my preboil was 1.052. It's really close to that, in lower numbers. And anybody can multiply anything times two, and then add them together (multiplying by 4) in a few seconds. That's exactly what that "SG scale" does- just multiplies the brix number.

Then, after that you can sit and do the correction formulas to get the exact number it would have been in gravity. Plus, you can use your "wort correction factor" when you calibrate your hydrometer and refractometer together for a more accurate reading.

Refractometers are meant to read the refraction of light through a sucrose solution. The SG scale on the refractometer is notoriously inaccurate, especially in higher gravity worts/musts, so it's just better to either pretend it's not there, or to get one without in the first place.

The handiest thing with a refractometer is you can check the reading of your fruit before picking or pressing. That's one of the main reasons for a winemaker to have one.

Yooper said:

The handiest thing with a refractometer is you can check the reading of your fruit before picking or pressing. That's one of the main reasons for a winemaker to have one.

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I didn't even think of that!

My 0 - 100 PPM scale is meaningless I guess?

I have looked at A LOT of posts here on homebrewtalk about this topic trying to figure out how to use a refractometer since I am a new brewer. Yooper is very often part of the discussion and everyone talks about the deficiencies. I can't find the most interesting thread where a guy tested several of his brews with an old hydrometer a newer hydrometer and a refractometer. Here is what I read, but take it with a grain of salt since it is not my personal experience.

Refractometer - Positives - A couple of drops of product is used for testing. Super easy to use. Ignore the other scale that isn't Brix. Do ALL calculations using Brix and then convert to SG using the various online beer calculators. This tool is great for multiple readings during the boil to verify you hit your target OG assuming you let it cool off between tests. This tool is great to get accurate OG readings. Negatives - After alcohol enters the equation you must go down deep rabbit holes and really understand what exactly you are doing to get fairly accurate results, though never as accurate as a hydrometer. Plus the added complexity contributes to user errors. Many if not most brewers will not use a refractometer for FG readings. Those that do will use it to identify if fermentation has stopped and a minority of users will do the calculations required to calculate their FG readings for purposes of calculating ABV. Also, as Yooper mentioned in this post big beer readings become more difficult to measure OG accurately.

Hydrometer - Positives - Stable, accurate, easy to use, already in beer brewer units, reliable. Some say they enjoy the snapshots in time when they taste their beer at different parts of the process. Negative - Every time you use it, you lose beer before it is completed. Sanitize your testing equipment and you can dump it back in. Some brewers are still concerned that the extra handling (dumping back) will create opportunity for infections.

Thank you very much AZ for taking your time to help.
The more that I consider this, it seems like trying to make things easier by using a refractometer will end up adding to my learning curve.

I'm trying to brush up on my basic chemistry... I'm not gonna add math equations to the picture.

CMcPherson said:

Thank you very much AZ for taking your time to help.
The more that I consider this, it seems like trying to make things easier by using a refractometer will end up adding to my learning curve.

I'm trying to brush up on my basic chemistry... I'm not gonna add math equations to the picture.

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You don't need to know or understand the math equations in order to use them. There are lots of calculators available. Pick one that's highly rated, and that you like. Some brewers like to understand how the math works, and others couldn't care less.

Brew on

My hydrometer is gonna be used making my turkey brine tonight.

doug293cz said:

You don't need to know or understand the math equations in order to use them.

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You sound like a Civil

OP is correct that the PPM scale is useless - it's intended to correlate the objective degree of light refraction relative to a "pure water" reference, to a measurable degree of other-stuff-in-the-water, based on fairly specific assumptions of what that other stuff is. Since your Other Stuff here is mainly sugars, whereas the Other Stuff a saltwater aquarium refractometer scale would be designed assuming is (chemically unrelated) aqueous ion solutions, you couldn't safely assume any relationship at all (except that they'd probably not be inversely correlated).

Brix is apparently defined in terms of sugar solution density, so I'd be mildly surprised if a saltwater-oriented refractometer had a Brix scale, and suspicious of it if it did. Getting one designed for brewing probably is your best bet, but it might be worth correlating the Brix readings between them to see if you can still use yours as a backup if you drop it or something.