poppalarge
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I've seen some people measuring the gravity of their wort with some kind of microscope device.
What is such a thing called?
What is such a thing called?
Gravity meter microscope thing
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Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:
Maybe you are referring to a refractometer ?
Like this one
http://www.austinhomebrew.com/product_info.php?products_id=1014
Like this one
http://www.austinhomebrew.com/product_info.php?products_id=1014
poppalarge
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That's the one.
How does it work?
How does it work?
poppalarge
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Sold!
gr8shandini
Well-Known Member
A refractometer measures the sugar content of the wort by measuring how far light bends (or refracts) when as it passes through. You can only take direct measurements prior to fermentation, though. Once you have alcohol in the mix, you need to use a formula to correct the readings. Since you're unlikely to miss your OG when extract brewing, you're better off just using your hydrometer. However, they come in really handy when/if you go all-grain since you'll want to take multiple samples of hot wort, and the few drops you'll need will cool really quickly.
By the way, if you search ebay, you can find them for much less than $100. More like 30 bucks. Just make sure you get one with Automatic Temperature Correction (ATC) as they don't cost much more and it's one less calibration you have to keep track of.
I should have mentioned, you have to have an accurate O.G. reading to get a reading after fermentation because a refractometer can't measure alcohol.
There are online calculators that you plug in the original reading and current reading (in brix) and it will spit out the current gravity reading.
There are online calculators that you plug in the original reading and current reading (in brix) and it will spit out the current gravity reading.
poppalarge
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Unibrow said:
And the same for FG ?
poppalarge
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gr8shandini said:
Gotcha. Thanks
In addition to getting one with ATC, you may want to look for one with a specific gravity scale as well as a Brix scale, even though it may be slightly more expensive. Of course if you only have the Brix scale you can just multiply the Brix reading by 4 to get SG, which works well for gravities up to about 1.050 or 1.060 - beyond that you can consult a table for the Brix to SG reading, such as this one:
http://www.fermsoft.com/gravbrix.php
http://www.fermsoft.com/gravbrix.php
FuzzeWuzze
I Love DIY
Like this?
Refractometer ~$100
Its only $30
http://www.amazon.com/dp/B003H7ILCW/?tag=skimlinks_replacement-20
I just got mine and calibrated it with my last brew, put my correction @ around 1.0285 or something...for the next few brews ill definately keep using it and updating the calibration to see if my correction value changes much...but i doubt it.
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That's the same one I have and from the same place, i got it in 3 days after ordering.
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1. Don't expect it to be useful for anything other than OG. I.e., after fermentation starts, use a hydrometer. If you insist on doing post-fermentation measurements, use Sean Terrill's calculator, not the one with Beersmith or any other.
2. The ones with SG instead of Brix are cool. I'd pay a few extra bucks to have this. See here. That's sold by our own BobbyM.
3. Cheers.
2. The ones with SG instead of Brix are cool. I'd pay a few extra bucks to have this. See here. That's sold by our own BobbyM.
3. Cheers.
What calibration are you doing?
All I do is get distilled water (sg 1.000) and take a reading then adjust the screw under the black cap until the refractometer reads 1.000.
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Same thing
for readings after fermentation i use this calculator,
http://onebeer.net/refractometer.shtml
If you do get one with a specific gravity scale as well as Brix, there is no guarantee that the specific gravity readings will be accurate. The same applies to using a look up table.
The refractive index is not a direct measurement of specific gravity, and needs to be converted. Unfortunately, the conversion depends on the type of sugars dissolved in the sample. If you are making wine, the sugars in the sample will be mainly sucrose. If you are making beer, the sugars will be mainly maltose. The conversion from Brix to specific gravity is different for samples containing sucrose than it is for samples containing maltose. The differences are small but noticeable, and both BeerSmith and Promash provide tools to account for these differences. Most of the conversion tables you will find on line are suitable for wine rather than beer.
Don't take my word for it. Check it out for yourself. Measure the OG of a beer with a calibrated hydrometer, and take a Brix reading with the refractometer.
Then make a table sugar solution with the same gravity as the measured OG of the beer, and use the refractometer to take a Brix reading. You will see that the Brix reading is different than the original Brix reading.
Check using an on-line look-up table, and you will almost certainly find that the look-up table closely matches the table sugar results.
Finally, if you want to know why I prefer Promash to BeerSmith, try using the help button to explain it. I have BeerSmith v 1.4. The help may have been improved with version 2.x
-a
The refractive index is not a direct measurement of specific gravity, and needs to be converted. Unfortunately, the conversion depends on the type of sugars dissolved in the sample. If you are making wine, the sugars in the sample will be mainly sucrose. If you are making beer, the sugars will be mainly maltose. The conversion from Brix to specific gravity is different for samples containing sucrose than it is for samples containing maltose. The differences are small but noticeable, and both BeerSmith and Promash provide tools to account for these differences. Most of the conversion tables you will find on line are suitable for wine rather than beer.
Don't take my word for it. Check it out for yourself. Measure the OG of a beer with a calibrated hydrometer, and take a Brix reading with the refractometer.
Then make a table sugar solution with the same gravity as the measured OG of the beer, and use the refractometer to take a Brix reading. You will see that the Brix reading is different than the original Brix reading.
Check using an on-line look-up table, and you will almost certainly find that the look-up table closely matches the table sugar results.
Finally, if you want to know why I prefer Promash to BeerSmith, try using the help button to explain it. I have BeerSmith v 1.4. The help may have been improved with version 2.x
-a
gr8shandini
Well-Known Member
ajf,
I don't disagree with anything you say, but in the end, the inaccuracies you mention are "in the noise." For example, what's the accuracy of your hydrometer at anything other than 1.000? What's the accuracy of the thermometer you used to measure the temperature of the sample? How much error is there in your readings due to things like parallax, judging the meniscus, not having completely degassed the sample, etc.? I don't know the answer to any of these, but as a wild guess, I don't think anyone can expect to get better than within +/- 0.002 of the actual SG with a hydrometer. Similarly, a refractometer isn't all that easy to read and even though mine has lines for every 0.1 Bx, I can't really say I can read it better than the nearest 0.25 Bx. So that's a 0.001 error on top of whatever the accuracy of the refractometer is.
But the real question is, what kind of difference is noticeable to a taster? Since you're really only tasting FG, I would say that I can tell the difference between a beer that finishes at 1.005 from one that ends up at 1.015. But could I tell a 1.010 from either? I doubt it. So it looks like there's at least a 5 point spread in what I can discern in the finished product (YMMV, of course). I don't know what the magnitude of the errors you mentioned are, but I'm guessing they're much less than that.
Also, keep in mind that the yeast pretty much have the final say in how your beer turns out. Even with the best instruments and strictest process controls, the major brewers still have to blend batches to get a consistent product. I like to do what I can to be scientific about my brewing, but it often helps to remember that most of the time we're measuring with a micrometer and cutting with an axe.
I don't disagree with anything you say, but in the end, the inaccuracies you mention are "in the noise." For example, what's the accuracy of your hydrometer at anything other than 1.000? What's the accuracy of the thermometer you used to measure the temperature of the sample? How much error is there in your readings due to things like parallax, judging the meniscus, not having completely degassed the sample, etc.? I don't know the answer to any of these, but as a wild guess, I don't think anyone can expect to get better than within +/- 0.002 of the actual SG with a hydrometer. Similarly, a refractometer isn't all that easy to read and even though mine has lines for every 0.1 Bx, I can't really say I can read it better than the nearest 0.25 Bx. So that's a 0.001 error on top of whatever the accuracy of the refractometer is.
But the real question is, what kind of difference is noticeable to a taster? Since you're really only tasting FG, I would say that I can tell the difference between a beer that finishes at 1.005 from one that ends up at 1.015. But could I tell a 1.010 from either? I doubt it. So it looks like there's at least a 5 point spread in what I can discern in the finished product (YMMV, of course). I don't know what the magnitude of the errors you mentioned are, but I'm guessing they're much less than that.
Also, keep in mind that the yeast pretty much have the final say in how your beer turns out. Even with the best instruments and strictest process controls, the major brewers still have to blend batches to get a consistent product. I like to do what I can to be scientific about my brewing, but it often helps to remember that most of the time we're measuring with a micrometer and cutting with an axe.
Hum...I did research 2-3 years ago saw the prices and said **** it. Now its that time of the year when the fat man comes. I now have a request. Thank you sir!!
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FuzzeWuzze
I Love DIY
You need to do that yes, but you also need to calculate your Brix correction factor as it will be different for everyones set of gear..
Tools that dont ask for it are using the 'generic' 1.04 brix factor thats middle of the road and works for most people. Calculating this correction factor and calibration is built into Beersmith(how i did it).
Since i dont always feel like my hydrometer is making the best measurements i'll be recalibrating this over the next few brews to see if i stay around 1.0285 or not...only a few points of misreading of the hydrometer can throw this off by a bit which makes the refractometer less useful.
All I was saying is that the conversion form Brix to Specific Gravity depends on whether you are making wine or beer.
If you are making beer, using a dual scale refractometer, or a conversion table will generally result in an estimated S.G. value that is 3 - 4% higher than the true S.G. value.
I have two hydrometers; a triple scale one that reads about 3 points high that I can get readings accurate to within about 2 - 3 points if I use a magnifying glass, and a finishing hydrometer that gives a reading accurate to 1 point with my reading glasses.
I can read my refractometer to within 0.25 Brix (1 point) without any problems.
Using the refractometer tool in Promash, I can translate 19 Brix to a S.G. of 1.075. This was confirmed against the S.G. reading from a narrow range hydrometer which has since got broken.
If I use a lookup table or calculator, I get a predicted S.G. of 1.079.
I'd much rather use a tool that gives accurate results, than something that has been proven to be inaccurate.
-a.
FuzzeWuzze
I Love DIY
Are you applying a known Brix correction factor that you have calibrated your refractometer against? That may be where your losing your accuracy if you are just using the standard 1.04 correction factor most tools assume instead of calculating your own for your hydrometer and refractometer setup.
I'm not losing any accuracy, but I would if I used a look up table to convert Brix to S.G.
I'm using Promash instead of Beersmith, and I did calculate to Brix correction factor. I find it interesting that you are using Beersmith, but quote the details on said factor from Promash.
-a.
gr8shandini
Well-Known Member
Well, there's no question that you like to be precise and have the gear to do it. But I guess what I was getting at is that, for the average home brewer, being 2 or 3 points off is "good enough." Especially as you'll be consitently off in the same direction. Finally, I'd hazard a guess that most of us are actually more accurate using an uncalibrated refractometer than trying to correct it using a reading from a $6 LHBS hydrometer.
Bottom line, I am making beer, Not a rocket to the moon,
If my reading is within a few points, and yes it is, I am perfectly happy.
FG reading? I am more concerned about if my fermentation is complete, steady brixs readings tell me that. did it finish at 1.010 or 1.012 ? I don't really care, it finished and I will be happy to drink it. Semi accurate O.G. and an online calculator get me in the ballpark,
One advantage I have over hydrometer readings, i can get a sample through the airlock hole with along pipette and don't have to take the lid off my bucket.
If my reading is within a few points, and yes it is, I am perfectly happy.
FG reading? I am more concerned about if my fermentation is complete, steady brixs readings tell me that. did it finish at 1.010 or 1.012 ? I don't really care, it finished and I will be happy to drink it. Semi accurate O.G. and an online calculator get me in the ballpark,
One advantage I have over hydrometer readings, i can get a sample through the airlock hole with along pipette and don't have to take the lid off my bucket.
Brix/Plato is not intuitive or mathematical. It's a quaint, legacy measurement that will go away some day.
Specific gravity is the standard method in chemistry to compare any liquid to the density of water.
gr8shandini
Well-Known Member
That's odd seeing as the Brix/Plato scale was invented as a way to make SG intuitively meaningful to brewers - http://en.wikipedia.org/wiki/Brix
In short, if your wort is 12*P, it's 12% sugar by weight. That gives most people a lot better idea of what's going on than knowing that it's 1.048 times heavier than water.
Good point. I still like the units that makes mathematical sense.
gr8shandini
Well-Known Member
I'm failing to see how it doesn't make mathematical sense. One is a ratio of the weight of a solution to the weight of water and the other is a ratio of the weight of sugar in solution to the total weight of the solution. I'm an engineer and we've probably got hundreds if not thousands of such non-dimensional units, so I guess I'm just used to using the one that's most convenient for the application.
That said, I'm still trying to retrain myself to "think" in Plato since most recipes you encounter for homebrewers are listed in terms of SG. Now that refractometers have become more reasonably priced, I think it would be nice if our community started posting both. Especially for all-grain recipes where the use of a refractometer is practically mandatory.
