Refractometer vs. Hydrometer

Hey all,

Hoping I can learn something today!

Expected my beer to be ready for kegging the other day and since I'm still green on the refractometer, I grabbed my hydrometer too, for good measure. I have the refractometer from Northern Brewer with the SG scale so the Brix to SG calculations are supposedly already done for me (supposedly?).

I calibrated my refractometer to zero with distilled water, checked the temp of the wort, was just about 60-61. Refractometer read 1.022 SG and hydrometer read 1.012. I was expecting about 1.012-1.014, so beer is now kegged!

But... what gives? I'm sure it's because I'm still learning the refractometer, but I know my hydrometer is pretty accurate because I recently tested it against my buddy's (who taught me to brew).

I'd really like to switch to the refractometer for the ease of checking -- especially since I want to play around with one gallon batches.

You need to run the adaption/conversion software once fermentation starts, when reading from a refractometer. This is a VERY well known item (for anyone using a refractometer at least).

Also, I have one of the refractometers with both scales on it (from Bobby_M) but didn't like it since I wasn't 100% sure the scales were properly aligned. So, I've since moved to highly accurate (lab/pro grade) refractometers for my readings (about $100 each). While most probably won't/don't care enough for that level of precision, I do.

I did read something about doing conversions after fermentation, but it only talked about brix to SG conversions, so I was confused & came here.

Does promash do this conversion, or is there a specific software I should be looking at? Or, website, java app, android, etc. lol

MKEbrew said:

I did read something about doing conversions after fermentation, but it only talked about brix to SG conversions, so I was confused & came here.

Does promash do this conversion, or is there a specific software I should be looking at? Or, website, java app, android, etc. lol

Click to expand...

found a couple online:

http://onebeer.net/refractometer.shtml

http://seanterrill.com/2012/01/06/refractometer-calculator/

within my past couple batches i've switched to using only the refrac after the boil.. previously i have done both a hydrometer and refrac just to be sure and my refrac has never been off much at all to warrant losing a couple of ounces each time i test.. i use the conversion in beersmith and it hasn't failed me yet, though i have also used similar ones like brewknurd mentioned with equal success..

Golddiggie said:

Also, I have one of the refractometers with both scales on it (from Bobby_M) but didn't like it since I wasn't 100% sure the scales were properly aligned. So, I've since moved to highly accurate (lab/pro grade) refractometers for my readings (about $100 each). While most probably won't/don't care enough for that level of precision, I do.

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So the reason for that is that they're attempting to account for the fact that refractometers are really designed to measure solutions of sucrose (pretty sure its sucrose). Wort is not primarily sucrose. So the refractive index of wort is not exactly the same as that of sucrose at a given gravity. So the SG scale on the dual scale hydrometers is an attempt to account for that.

I just couldn't trust the readings on the dual scale refractometer since if I used software to convert from brix to SG, it wouldn't match what the scale on the refractometer read. So, I picked up the higher quality refractometers and haven't had any issues since.

As for the conversion once fermentation starts, it's due to alcohol throwing off the readings. It's highly predictable, which is why software does it so well.

I use 4 dram vials to capture the wort, and then finished beer, for my readings. So, that's a total of 1oz (each vial holds .5 oz) to get both readings. Far less than you'll use for a hydrometer (unless you drop it into the fermenter).

BTW, the refractometers I have don't specify a type of sugar for their readings. You don't want to get one made for salinity (or urine) tests, but you don't need to worry about the type of sugar being used.

I've found that my refractometer reads pretty accurately if I use the android app I downloaded to my phone. I've checked against the hydrometer several times and it's always been right on. I haven't measured a very big beer though. And to be honest, once the beer has cooled, it's just as easy to grab a sample and use the hydrometer and I'm in no hurry to get it cooled down to testing temp at that point, unlike when I'm brewing and want to know my preboil and post boil gravities.

I'd use a hydrometer over a refractometer any day of the week.

stamandster said:

I'd use a hydrometer over a refractometer any day of the week.

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Why?? Is it because of the cost difference? Hydrometers can give off readings pretty easily. Plus, more people post about then breaking than almost anything else in brewing. Refractometers won't roll off the counter on you (and then shatter). Plus a hydromter reading is easily buggered by foam in the tube, or presence of any carbonation/bubbles in the sample. Then there's the vast difference in how much of a sample you need for the readings.

I wish I had a refractometer when I made my first batches of mead. It would have saved me a significant amount of must during the process.

Golddiggie said:

BTW, the refractometers I have don't specify a type of sugar for their readings. You don't want to get one made for salinity (or urine) tests, but you don't need to worry about the type of sugar being used.

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Well sure, you probably don't need to worry about it, because we're talking about error in the range of a few percentage points, so its not a big deal for most people.

That said, whether or not your refractometer specifies, it was designed to convert a refraction measurement into a gravity. That requires that it know specific gravity as a function of refractive index. Since this changes for various sugars, the accuracy will indeed be affected as you deviate from whatever sugar (or theoretically blend of sugars, although I don't know if anyone's making those) it was designed to meaure.

The refractometer correction for the presence of ethanol formula is pretty straightforward, just work it out in your head:

SG=1.001843-0.002318474(OB)-0.000007775(OB^2)-0.000000034(OB^3)+0.00574(AB) +0.00003344(AB^2)+0.000000086(AB^3)

where SG = Specific Gravity, OB = Original Brix, AB = Actual(current) Brix

camiller said:

The refractometer correction for the presence of ethanol formula is pretty straightforward, just work it out in your head:

SG=1.001843-0.002318474(OB)-0.000007775(OB^2)-0.000000034(OB^3)+0.00574(AB) +0.00003344(AB^2)+0.000000086(AB^3)

where SG = Specific Gravity, OB = Original Brix, AB = Actual(current) Brix

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No way I can do that in my head. Besides, there's enough software options that will do it for you far faster.

Golddiggie said:

No way I can do that in my head. Besides, there's enough software options that will do it for you far faster.

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I came up with 42.

Golddiggie said:

No way I can do that in my head. Besides, there's enough software options that will do it for you far faster.

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Humor is lost on some people...

BrewKnurd said:

I came up with 42.

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Right, 6 x 9.

camiller said:

Humor is lost on some people...

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Not when it's actually funny... That wasn't even close. Never did like math much.

Right, 6 x 9.

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Sure, now you make a reference I get... :cross:

Golddiggie said:

Why?? Is it because of the cost difference? Hydrometers can give off readings pretty easily. Plus, more people post about then breaking than almost anything else in brewing. Refractometers won't roll off the counter on you (and then shatter). Plus a hydromter reading is easily buggered by foam in the tube, or presence of any carbonation/bubbles in the sample. Then there's the vast difference in how much of a sample you need for the readings.

I wish I had a refractometer when I made my first batches of mead. It would have saved me a significant amount of must during the process.

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Lol... it breaks? Yeah... sure you got me. And wort can get infected!

It's cheaper and who cares if the sample is a couple oz's? Besides there's times you won't be able to use the refractometer to read your gravity. You can ALWAYS read gravity with the hydrometer (unless it's broken )

stamandster said:

Lol... it breaks? Yeah... sure you got me. And wort can get infected!

It's cheaper and who cares if the sample is a couple oz's? Besides there's times you won't be able to use the refractometer to read your gravity. You can ALWAYS read gravity with the hydrometer (unless it's broken )

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Actually, I see the exact opposite being true. Try taking a gravity reading during your mash with a hydrometer. You'll have to cool it down to closer to 60F in order to get anything close to an accurate reading. You'll also need to chill down several ounces of wort to get the reading (not a couple). That takes TIME that you might not really have. Do the same thing with a refractometer with it's <1ml sample size needed. Have a refractometer with ATC and you get a reading immediately.

I have yet to see ANY instance where you could use a hydrometer and not refractometer.

BTW, unless you have at least one hydrometer in reserve, if you break yours on brew day, and the HBS isn't either close, or open, you'll not get gravity readings. Sure, you can also store a sample, if you want to waste almost a full bottle worth in the process.

Personally, I see the refractometers I purchased as being a 1 time event. You cannot say that with hydrometers. If you use them, eventually you'll break them. The only thing I could see replacing the ones I have now is if I can score a digital one for a good rate.

Use whichever you like, just don't be fooled into thinking that a refractometer is any less useful. If anything, it's far more.

Golddiggie said:

Actually, I see the exact opposite being true. Try taking a gravity reading during your mash with a hydrometer. You'll have to cool it down to closer to 60F in order to get anything close to an accurate reading. You'll also need to chill down several ounces of wort to get the reading (not a couple). That takes TIME that you might not really have. Do the same thing with a refractometer with it's <1ml sample size needed. Have a refractometer with ATC and you get a reading immediately.

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The ATC actually refers to the ability to compensate for ambient temperature, not the sample temp. Since its only a few drops, as you mention, its pretty much at the refractometer temp almost instantly. What ATC does for you is if you have the refractometer outside where its 90 degrees, the ATC compensates for the fact that its not at 60 or 70 or whatever ambient temp it was designed to work at.

Golddiggie said:

I have yet to see ANY instance where you could use a hydrometer and not refractometer.

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Any time you want to directly measure the specific gravity rather than approximate it based off of a correlation of varying accuracy.

Golddiggie said:

Personally, I see the refractometers I purchased as being a 1 time event. You cannot say that with hydrometers. If you use them, eventually you'll break them. The only thing I could see replacing the ones I have now is if I can score a digital one for a good rate.

Click to expand...

Purchasing a hydrometer has been a one time thing for me.

I use both. And what I have found is that they disagree by varying amounts throughout a brew day, and from one batch to the next. Therefore, if I really want to know the gravity, I use the hydro, because it will be right. The refractometer will be close enough for most purposes.

I've noticed that the main complaint about a refractometer, is that it makes measurements based upon sucrose content. What do you think a hygrometer does? The Plato system and SG of a hygrometer are based upon that same sucrose content NOT maltose, etc. If it's a problem with one, then it's a problem with both. Personally. I like my dual scale SG/Brix Refractometer.

Runner said:

I've noticed that the main complaint about a refractometer, is that it makes measurements based upon sucrose content. What do you think a hygrometer does? The Plato system and SG of a hygrometer are based upon that same sucrose content NOT maltose, etc. If it's a problem with one, then it's a problem with both. Personally. I like my dual scale SG/Brix Refractometer.

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Hydrometer, not hygrometer.

And no, SG is not based on type of sugar. Specific gravity is specific gravity, and it is entirely independent of the type of sugar. Now, if you want to complain that calculating the alcohol based on a change in specific gravity is dependent on sugar type, that's fine. Its also dependent on things like the specific metabolic pathways favored by the particular yeast. But measuring the gravity is not in any way dependent on the type of sugar. You could use a hydrometer to measure the specific gravity of any fluid that had a SG in the proper range.

Calculating the sugar content based on that gravity would be dependent on type of sugar, tho, and maybe this is your point.

BrewKnurd said:

Hydrometer, not hygrometer.


Calculating the sugar content based on that gravity would be dependent on type of sugar, tho, and maybe this is your point.

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I did express myself poorly, and the main point I wanted to make WAS that even with a SG reading you wouldn't know exactly what sugar (or other substance) was affecting the SG. My comment about degrees Plato does apply, though - it's based upon Sucrose, as is the refractometer.

Runner said:

I did express myself poorly, and the main point I wanted to make WAS that even with a SG reading you wouldn't know exactly what sugar (or other substance) was affecting the SG. My comment about degrees Plato does apply, though - it's based upon Sucrose, as is the refractometer.

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Well, sure, but its also an empirically derived scale based on specific gravity. So in that way, degrees plato is similar to the refractometer results, in that you're taking one measurement (either S.G. and refraction, respectively), and using that to estimate another property (sugar content or S.G., respectively).

I agree that no matter what, there are assumptions going on in this measurement. But a refractometer adds an additional layer of assumption. In addition to assuming that your S.G. is correlated to your fermentable sugar content in a certain way, it also assumes that your refractive index is correlated to your S.G. in a certain way.

I imagine that in certain situations, the error introduced by the SG to sugar content and the refraction to SG correlations offset and the refractometer is in fact more accurate at determining what you really want....