Refractometer

[bford]

Where's the best how to use a refractometer video or tutorial? I just got mine in....

I brew small two gallon batches so wasting all the wort on hydrometer readings just isn't smart (not for profit) home business...

 

[dmcman73]

Where's the best how to use a refractometer video or tutorial? I just got mine in....

I brew small two gallon batches so wasting all the wort on hydrometer readings just isn't smart (not for profit) home business...

Digital or manual?

Either one to use is quite simple, just two different ways to read it. The important thing is that you calibrate it prior to each use using a drop of distilled water on the lens, it should read 0 on either the manual one or the digital one.

The digital one is easy to calibrate, place some distilled water on the lens, wait a few seconds for the temp to stabilize and press the "Zero" button. Once the display shows 0, wipe the lens clean of the water and then place a drop of your wort on it, wait a few seconds for the temp to stabilize and then press the read button.

For the manual one, flip the plastic cover up off the lens, place some distilled water on the lens and then flip the plastic cover down again, wait a few seconds for the temp to adjust then make sure it reads 0 or 0.000 while looking through the lens, if it does not there is an adjustment screw on it you will need to turn with a fine small screw driver (should come with one), you should be able to turn the screw as you are looking though the lens. Wipe it clean and then place some wort on the lens of the manual one the same exact way you did with the distilled water, wait a few seconds then look through the lens to read it. If your manual refractometer has both Brix (bx) and gravity readings, I would ignore the gravity reading and record the birx one. Those Gravity readings on them are never accurate and you'll get a more accurate reading using a Brix to Gravity calculator.

EDIT: I should note that the adjustment screw should be located under that small black plug on the body of the refractometer.

 

[bford]

Thanks... I have one of the manual versions...

 

[WissahickonBrew]

I will apply all of the tips mentioned so far in this thread, thank you one and all.

Does anyone have a suggestion related to the the light source for the reading? Is it imperative to go outside to get the better reading? Will fluorescent or incandescent lights throw the reading way off?

I am also wondering if there is a good formula to use when taking readings post fermentation to adjust for alcohol content? I am getting readings that seem way to low for what my recipe projected!

Thanks again all!

 

[balrog]

Is it imperative to go outside to get the better reading? Will fluorescent or incandescent lights throw the reading way off?

I wonder same thing, having just started using mine. I've noticed no perceptible diff between a daylight source reading and a tungsten lightbulb source reading, but I've not compared CFL, fluorescent or LED bulbs yet.

I am also wondering if there is a good formula to use when taking readings post fermentation to adjust for alcohol content?

I've Googled several.
http://www.brewersfriend.com/refractometer-calculator/
http://www.northernbrewer.com/refractometer-calculator/
http://seanterrill.com/2011/04/07/refractometer-fg-results/

And a lot of interesting reading for back-guessing OG when you have refractometer and hydrometer end SG readings:
http://www.woodlandbrew.com/2013/02/refractometer-summary-of-equations.html

 

[ajdelange]

The refractive indices for sucrose solutions (on which the scales of these refractometers are based) were measured by ICUMSA at 546 nm (green mercury line) and 589 nm (yellow sodium line) so that dispersion could be estimated and indeed the ICUMSA polynomial includes a term that allows one to calculate the RI for any temperature, wavelength and strength w/w and thereby construct a Bx scale. The important point is that the light used should be narrowband and preferreably in the yellow/green part of the spectrum. Using broadband light will result in dark to light border that is not sharp. Given the other inaccuracies associated with refractometers the additional error introduced by this blur may be insignificant. Note that the digital instruments contain an internal light source and the internal math will be tuned for the wavelength of that light source.

 

[Steve3730]

So overall its seems like refractometer best for during boil and pre pitch checks hydrometer still best for FG.

I brewed thus past weekend and cooling the cup of wort to check gravity took almost my entire boil time. Leaves little room to make corrections

 

[dmcman73]

So overall its seems like refractometer best for during boil and pre pitch checks hydrometer still best for FG.

I brewed thus past weekend and cooling the cup of wort to check gravity took almost my entire boil time. Leaves little room to make corrections

I use mine for FG as well and it is spot on with my Hydrometer readings. I use and Android app call brewzor calculator. Once calibrated to your Hydrometer and Refractometer, it does a really good job in the conversion.

 

[LLBeanJ]

I have a cheapo $30 Amazon.com refractometer and had issues with repeatability when I first started using it. Due to that, I stopped using it for a while, but 4 or 5 brew days back decided to give it another try. After a little experimentation and some practice I found that I was able to get reliable results and now use it exclusively for OG readings. I still use the hydrometer for FG so I can drink the sample.

 

[ajdelange]

I use mine for FG as well and it is spot on with my Hydrometer readings. I use and Android app call brewzor calculator. Once calibrated to your Hydrometer and Refractometer, it does a really good job in the conversion.

Except when it doesn't. How do you know when you have one of those situations?

 

[phug]

So what we need then is a filter for a light source the provides the right wavelength of light. So someone needs a desktop background of precisely the right colour, with which to illuminate their refracto meter.

 

[fartinmartin]

Your getting way to deep with this light stuff, you are looking at a fuzzy break between light and something not as light, a different colour, any light does the job , even a flippin candle is good enough.

 

[ajdelange]

Get a magnifying glass and have a look at your monitor. You will see three 'leds' red, green and blue. The green, if they follow Rec. 709, should peak at about 530 nm and that's pretty close to the ICUMSA green wavelength. So use your 'Color Picker' to set G to 100% and R and B to 0 and you should have something reasonably close to what you need. If the shadow/bright demarcation line is sharp then that's an indicator that you are in good shape.

 

[FarmerTed]

Except when it doesn't. How do you know when you have one of those situations?

Every time I've take a sample into my lab, and measured the FG on an analytical balance, it's been within .001 g/mL on the density. That's good enough for me.

As far as light sources go, I just turn on the light above my stove, and do all my measurements in the kitchen.

 

[Steve3730]

Well its been great reading the discussion on the refractometer. I think pre pitch a refractometer is definitely worth it(and still helpful after) and digital sounds the way to go.

 

[WissahickonBrew]

What I took away from this interesting discussion is that initial calibration is the most critical part of the process. Don't worry too much about your light source. It works fine for post-boil and post ferm. :rockin:

 

[ajdelange]

Every time I've take a sample into my lab, and measured the FG on an analytical balance, it's been within .001 g/mL on the density.

You'll have to forgive my skepticism here unless you used a pycnometer. It is doubtful that you could measure the specific gravity of water that well let alone wort or beer. A class A 1 cc pipet is rated ± 0.006 cc which, as water weighs about a gram/cc implies SG standard error (by perfectly accurate weighing of water using conventional means i.e. squirt it into a weigh boat) of 6 points. As a practical experiment I made 10 specific gravity determinations on water and got 1.010 for the average with a standard deviation of 17 points (average is high because I blew out rather than wait 16 seconds for the pipet to drain for fear that evaporation would induce error in that time). There is thus somewhat of an aroma surrounding your claim.

Sean Terrell found that his cubic polynomial gave a standard error of 1.3 points. The 1 point you claim is thus 1/1.3 = 0.77 standard errors. Assuming that the error distribution is normal (and his histograms, despite an error in the way they are drawn confirms this at least in the center) the probability that you would see a deviation of 1 point or less is 44.7%. The probability that you would see a deviation of 1 point of less twice is 20%, the probability that you would see a deviation of 1 point of less three times is 9% and four times is 4%. Thus, while it is quite possible to have an unlikely event happen it is, well, unlikely. From this we have to conclude that 'every time' means 'a couple of times' and the aroma becomes stronger.


The point to all this being what the ASBC and EBC have known for years and published in their MOAs: It's OK to use a refractometer on fermented beer if it has been calibrated, for a particular beer, against a more reliable method such as a pycnometer (analytical balance) or densitometer. If you made the comparative measurements with a pycnometer I would still be skeptical but much less so.

 

[fartinmartin]

It can't just be me LOL ! And again. LOL

 

[dmcman73]

You'll have to forgive my skepticism here unless you used a pycnometer. It is doubtful that you could measure the specific gravity of water that well let alone wort or beer. A class A 1 cc pipet is rated ± 0.006 cc which, as water weighs about a gram/cc implies SG standard error (by perfectly accurate weighing of water using conventional means i.e. squirt it into a weigh boat) of 6 points. As a practical experiment I made 10 specific gravity determinations on water and got 1.010 for the average with a standard deviation of 17 points (average is high because I blew out rather than wait 16 seconds for the pipet to drain for fear that evaporation would induce error in that time). There is thus somewhat of an aroma surrounding your claim.

Sean Terrell found that his cubic polynomial gave a standard error of 1.3 points. The 1 point you claim is thus 1/1.3 = 0.77 standard errors. Assuming that the error distribution is normal (and his histograms, despite an error in the way they are drawn confirms this at least in the center) the probability that you would see a deviation of 1 point or less is 44.7%. The probability that you would see a deviation of 1 point of less twice is 20%, the probability that you would see a deviation of 1 point of less three times is 9% and four times is 4%. Thus, while it is quite possible to have an unlikely event happen it is, well, unlikely. From this we have to conclude that 'every time' means 'a couple of times' and the aroma becomes stronger.


The point to all this being what the ASBC and EBC have known for years and published in their MOAs: It's OK to use a refractometer on fermented beer if it has been calibrated, for a particular beer, against a more reliable method such as a pycnometer (analytical balance) or densitometer. If you made the comparative measurements with a pycnometer I would still be skeptical but much less so.

When I first used a digital refractometer I was a bit skeptical so for the past 4 brews I made, I used a hydrometer along side with the digital refractometer. The first thing I did was check the calibration of my Hydrometer with distilled water (every brewer should be doing this) to determine if mine was at 0 or +/- of it. Next, I calibrated my refractometer using distilled water to zero it out (this is done on digital and those "manual" ones).

I then took a sample of wort prior to pitching and measured it using both my hydrometer and refractometer. I took those values and plugged them into a app called brewzor calculator in it's refractometer calibration settings, since this was the first time I was using it, this only needed to be done once.

I then selected the "Unfermented wort" setting, plugged the Brix value in and the conversion from Brix to SG was spot on between the refractometer and hydrometer.

When I checked it after a few weeks in, I again measured with my hydrometer and the refractometer, again, checking the calibration with distilled water on both. I then took a sample and measured using both. This time in the brewzor calculator I selected Fermenting and entered the Brix value from the refractometer and the converted value it came back with for Gravity was again, spot on with my hydrometer.

I did this for 3 other brews, I only calibrated the brewzor calculator once on the first batch and each time, the calculated value for SG from the brix reading was spot on, I think one of my brews was off by +/-.002. I brewed a stout, wheat, holiday ale and a pumpkin ale.

 

[FarmerTed]

You'll have to forgive my skepticism here unless you used a pycnometer. It is doubtful that you could measure the specific gravity of water that well let alone wort or beer. A class A 1 cc pipet is rated ± 0.006 cc which, as water weighs about a gram/cc implies SG standard error (by perfectly accurate weighing of water using conventional means i.e. squirt it into a weigh boat) of 6 points. As a practical experiment I made 10 specific gravity determinations on water and got 1.010 for the average with a standard deviation of 17 points (average is high because I blew out rather than wait 16 seconds for the pipet to drain for fear that evaporation would induce error in that time). There is thus somewhat of an aroma surrounding your claim.

No, it's not that hard to get a fairly accurate measurement by taking replicates with a syringe, weighing volumes to 0.1 g, and then comparing to masses of equivalent volumes of water. Taking the average weights of the beer compared to the average weights of water gives a density, and the standard deviations on the masses gives an estimate or the error. It works fine for me.

Note: the actual volume of a pipette or syringe doesn't matter if you compare the mass of the beer to the mass of an equivalent volume of DI water (using the same instrument), so if there's 0.6% error in the volume reading of the instrument, that gets cancelled out.

I've also run nmr's on beer samples, and the water/alcohol ratio comes out extremely close to that predicted by the refractometer. So, again I'm pretty happy with just using a refractometer.

 

[ajdelange]

No, it's not that hard to get a fairly accurate measurement by taking replicates with a syringe, weighing volumes to 0.1 g, and then comparing to masses of equivalent volumes of water. Taking the average weights of the beer compared to the average weights of water gives a density, and the standard deviations on the masses gives an estimate or the error. It works fine for me.

OK. I find I can measure 30 mL liquid mass into a 35 mL syringe with a standard error of 0.21% in the mass. Easy enough to do with water but with fermented beer? It's enough of a PITA to get the gas out prior to shooting a sample from a syringe into a U-tube meter but if it can be done for the digital meter it can be done for anything. I guess I just questioning the 'not that hard' statement. If I'm going to divide the average of a bunch of beer readings by the average of a bunch of water readings to get an SG the SEMs will RSS and I'll need, with .21% CV, about 9 measurements of each to get me to 0.001 SEM in the SG estimate. Is that approximately what you do?

Note: the actual volume of a pipette or syringe doesn't matter if you compare the mass of the beer to the mass of an equivalent volume of DI water

That is, of course, the principle on which a pycnometer works. Using a pycnometer you only fill the bottle once with DI water and once with beer because you fill it to precisely the same volume even though you don't know what that is. Temperature error is also taken care of because the 'plug' contains a thermometer.

so if there's 0.6% error in the volume reading of the instrument, that gets cancelled out.

Not quite. The bias portion of the error (the 30 cc mark is misplaced on the body of the syringe) gets canceled out. The random error (the rubber gets slightly deformed from being pushed back and fort, the bubbles...) get averaged down by taking multiple readings.

So I am less skeptical now that I understand that what you do is pretty close to what you would get with a pycnometer or density meter on the SG measurement. I am still skeptical that you can get such an improbable result compared to Terrel's. A possible answer is that his SG measurements weren't very good. So I guess I need to ask directly: How many comparisons did you do before drawing this conclusion?

So, again I'm pretty happy with just using a refractometer.

I guess when all is said and done that's what really counts.

 

[dk21]

Interesting discussion. I have a refractometer and like the idea of it, but I've gone back to using a hydrometer. Why? While my spot checking was close enough, I found that the longer I let it sit at the temperature I calibrated at, the more the reading changed. I'm not sure if that's due to the fact that I have a run of the mill, cheap one or not. It's also really difficult to read accurately because all of the measurement ticks are so close together. A digital one would help with that, I suppose.

 

[FarmerTed]

So I am less skeptical now that I understand that what you do is pretty close to what you would get with a pycnometer or density meter on the SG measurement. I am still skeptical that you can get such an improbable result compared to Terrel's. A possible answer is that his SG measurements weren't very good. So I guess I need to ask directly: How many comparisons did you do before drawing this conclusion?



I guess when all is said and done that's what really counts.

I've done it with 4 or 5 beers, and maybe run proton nmr's on 3-4 of those (using a low-res permanent magnet instrument). The idea is similar to a pycnometer; we have one somewhere at work, but I don't want to have the conversation with the person who manages it what I am using it for.

 

[fartinmartin]

I suppose a pricknometer measures inches, is that length or girth ?

 

[natefrog255]

I brewed my first high gravity beer and realized I didn't have a high gravity hydrometer. WIth shipping costs at NB it was just $9 more to get a refractometer from Amazon, so I bought that instead. I use that for pre-pitching readings and then the hydrometer for post, sounds easier. We'll see what happens. I saved some post boil wort, so I'll tr to do a reading.

Is it essential to calibrate? I don't have distilled water on hand.

 

[FarmerTed]

Just use the same water that you used on brew-day to calibrate it.