refractometer question

[ajf]

Fascinating.

1. How does your gravity go down during the boil?
2. Your BCF calculations appear to be a bit different than mine. I come up with Brix 18.35, SG 1.079, BCF 0.9606
   and Brix 15.9, SG 1.067, BCF 0.9715
3. When taking gravity readings, I take a reading (accurate to ~ 0.0005) at a temperature between 60F and 80F, and then apply temperature compensation. Using 5 decimal places instead of 3 for the temperature compensation seems to provide much more consistent results.
4. Isn't it a pain to cool the pre-boil sample to a reasonable temperature for a hydrometer reading.

So, I did a small experimental batch mashing 100% M.O. at 154F for 60 minutes. (I tried for 150F but missed.)

The results were:
Pre-boil

• Brix 7.25
• SG 1.02801
• BCF 1.0261

Post-boil

• Brix 12.6
• SG 1.05029
• BCF 1.0115

Once again, the post-boil correction factor was less than the pre-boil, but the pre-boil BCF was noticeably smaller than the 5 g batches mashed at a lower temperature.


-a.

 

[william_shakes_beer]

The brix scale is a measure of the amount of sucrose in a solution. Wort contains very little sucrose, but relatively large amounts of maltose and maltotriose. The conversion from brix to S.G. is different for a wine must (almost 100% sucrose) and beer wort (mainly maltose and maltotriose). Because of this, it is not possible to have a S.G. scale on the refractometer that is accurate for both beers and wines. Most refractometers with a dual scale have an S.G. scale calibrated for wine, but there may be some where the S.G. scale is calibrated for beer. Even if you have one that is calibrated for beer, the calibration will change slightly, depending on what went into the wort.

-a.

Interesting. I didn't think of that, but it makes sense. When I was shopping for my refractometer I saw them made for many substances, including saline, beer, wine, and urine!!! I guess mine's OK because its called a "brewfractometer" It has always read very close to my expected OG, so I assume its accurate. (how's that for reverse logic)

If I had a beer refractometer and a wine refractometer, both correctly calibrated for their respective substances, would they both read 1.00 in distilled water?

 

[ajf]

If the 1.00 refers to Specific Gravity, then yes. That would be the only point on the scales that would be correct for both wine and beer, and that should correspond to 0 Brix.

-a.

 

[luke2080]

Fascinating.

1. How does your gravity go down during the boil?
2. Your BCF calculations appear to be a bit different than mine. I come up with Brix 18.35, SG 1.079, BCF 0.9606
   and Brix 15.9, SG 1.067, BCF 0.9715

-a.

The reading on that Brew Day was the "End of Mash" - not pre-boil. It was my mash reading before I started the sparge. I had taken an actual Pre-Boil reading as well, but didn't validate that with the hydrometer, so not useful for seeing the correction factor.

That is weird you have the different BCF for my numbers. You are using an actual "mathematical formula" - right? I'm trusing BeerSmith - plugging in the Brix and SG, it gives the BCF and when you use ther refractometer tool, it uses that adjustment until you change it. I wonder if BS has an error in that calculation, and what impact it has.

 

[luke2080]

Isn't it a pain to cool the pre-boil sample to a reasonable temperature for a hydrometer reading.
-a.

Such a pain. Looks like I'll have to do it over the next 5-6 brew days at least. Hopefully get some sort of consistent pre boil and post boil BCF, so I can have 2 different BCFs to use.

Realizing it is different for each grain bill, but I should find some good average to use for my refractometer. I've been recording everything in BeerSmith, despite spending half my days making complex Excel models for work. May be time to start really recording data. Will be nice to finally reach the day where I only use the Refrac - and am comfortable with the results.

 

[ajf]

The reading on that Brew Day was the "End of Mash" - not pre-boil. It was my mash reading before I started the sparge. I had taken an actual Pre-Boil reading as well, but didn't validate that with the hydrometer, so not useful for seeing the correction factor.

That is weird you have the different BCF for my numbers. You are using an actual "mathematical formula" - right? I'm trusing BeerSmith - plugging in the Brix and SG, it gives the BCF and when you use ther refractometer tool, it uses that adjustment until you change it. I wonder if BS has an error in that calculation, and what impact it has.

End of mash instead of pre-boil makes a lot of sense. I should have read more carefully.

Yes, I wrote a small program to do the calculations based on information provided by the writer of Promash. I verified the accuracy of the program by entering my BCF into Promash, and using the Promash refractometer tool. It always gives the same SG for a given Brix value.

I don't know what algorithm Beersmith uses to convert Brix to SG, but I do know it is slightly different than that used by Promash.

In the case of the 15.9 Brix reading, if you use my BCF instead of that generated by Beersmith, you get a SG of 1.06745 instead of 1.067. i.e. less than 1/2 point difference. I don't think it is an error in Beersmith, Promash, or my calculator. I think it is just a different algorithm that gives very slightly different results. However, if you try putting a BCF < 1.000 into Promash, it won't accept it because it is theoretically impossible.

-a.

 

[luke2080]

However, if you try putting a BCF < 1.000 into Promash, it won't accept it because it is theoretically impossible.

-a.

My getting readings < 1.0 when yours were > 1.0 I thought was odd, but also thought it could have been the refrac setting from China.

Thanks for all the input through this thread. After my next 4 or 5 batches of better recordings, I'll post some results to see what correlations I get with my refrac.

 

[ajf]

I checked my refractometer to ensure it was giving accurate Brix readings.
I dissolved 90g table sugar in 210 grams water and measured the Brix and gravity. Then I diluted the solution by adding 60g, 90g, 150g, 300, and 900g water taking a Brix and gravity reading after each dilution. This should give Brix readings of 30, 25, 20, 15, 10, and 5 Brix respectively.
The results were:

Sucrose Water   Brix    Gravity BCF
  90g    210g   30.00   1.1268  1.0198
  90g    270g   25.25   1.1055  1.0134
  90g    360g   20.00   1.0825  1.0055
  90g    510g   15.00   1.0609  1.0032
  90g    810g   10.00   1.0402  0.9960
  90g   1710g    5.00   1.0196  1.0044

In each case, the BCF should be 1.0000 as I was working with a pure sucrose solution.

The first 2 gravity readings were taken with a cheap triple scale hydrometer, the next 2 were taken with a 1.0500 - 1.1000 hydrometer, and the last 2 were taken with a 1.0000 - 1.0500 hydrometer.
The triple scale hydrometer had a resolution of 0.002, and the other 2 had a resolution of 0.0005

With the accurate hydrometers the largest error in the BCF was 0.55%, whereas with the triple scale, the errors were greater (up to 1.98%). However, this translates to an error of 2 gravity points in the calculation (which is the resolution of the hydrometer).

I don't think I mixed the sample for the second reading well enough (hence the Brix reading being a little high), however the BCF was still within the range dictated by the accuracy of the instruments.

If your refractometer has a Brix scale that is different than mine, it would make a difference if you don't use a BCF to correct the reading, but I don't think it would make any difference if you divide the observed Brix reading by the BCF before converting to SG. However, the above experiment does confirm that the refractometer does provide accurate readings over the full range of the instrument. It doesn't matter if the BCF is greater than or less than 1.000 providing it doesn't deviate from the average by more than 1 or 2%.
If you get a BCF that increases or decreases as the Brix reduces, then you have a problem that may need to be addressed, depending on the magnitude of the change.

-a.

 

[ajf]

Sorry for the delay.
I have done a small experimental batch, mashing 200g Maris Otter at 1 quart per lb at 154F for 60 minutes. The results are on the left, and as per the 5g batches, the pre-boil BCF is slightly greater than the post-boil. However the pre-boil BCF is considerably lower than for the 5g batches. This could be because of a sample of one, mashing at 154 vs 148 - 150, or the inclusion of some crystal malt.
The difference in the BCFs accounts for less than 0.5 gravity points.

The reading on the right are the result of stepping some 60L crystal grains for 30 minutes. I find it interesting that the pre-boil BCF is < 1.0000, but the post boil BCF is > 1.0000. I shall have to repeat this later to rule out measurement error. In this case, the difference in the BCF causes a difference of 6 points in the conversion from Brix to Gravity.
[edit] I typed something wrong into the calculator when calculating the difference of 6 points. I just repeated the calculation, and the difference is just 1 point. [/edit]

Next experimental batch will be a 50/50 mixture of Maris Otter and Crystal 60.
I don't know when I will be able to do this, as SWMBO is ill and needs a lot of looking after.

-a.

Pre-boil
Brix         7.25        3.00
SG           1.02801     1.01190
BCF          1.0261      0.9865
Post-boil
Brix        12.6         4.60
SG           1.05029     1.01715
BCF          1.0115      1.0540

 

[latium]

I'll admit that I haven't read through all the responses yet, so I may be repeating what's already been said, but some of the dual-scale refractometers (particularly the cheaper ones) use the rule of thumb where you multiply the degrees Brix by 4 to get a rough estimate of the fractional part of the SG. For example, 15 degrees Brix is approximately 1.060 SG. This estimate gets less and less accurate the higher you go and is of decreasing utility as you get much past 1.060.

 

[brewkinger]

Yes, just to be sure I wasn't blowing smoke, I checked one and the scale puts 23 brix at 1.096.

Good to know as I purchased mine from you.

 

[brewkinger]

I have recently been struggling to fine tune the tweaks on my refractometer (that I purchased from BobbyM)

I too have struggled to get what I would consider to be trustworthy and consistent measurements with my refractometer until I recently took the ATC concept to the literal translation.

I always calibrate before use with distilled water. I allow the water and the tool to come to ambient air temp. (a couple of winter brews done inside at temp of 65 degrees and 3 more outside brews calibrated to temps in the 40's and 50's).
I tested my runnings using a pipette and sample that I assume was pretty close to mash temps. I would assume as BobbyM once told me in a post that the small sample that we place on the glass will cool and most likely some of the water will evaporate before we can get the cover closed. I always verified the OG after transferring to fermenter by taking both a refraction and hydrometer reading.
My values were never really consistent and I always seemed to be lower than expected on OG, but I always ended up with drinkable beer. It was while drinking these beers that I pondered ways to fine tune this process.
I have my own grain mill and get consistent crush (removed from checklist)
Process dialed in and repeatable every brew day. (considered constant now)

What I did three brew days ago was calibrate refractometer and distilled water to 64 degrees (nice day in northern VT finally)
Then I took WELL STIRRED pipette and hydro sized samples of 1st runnings, 2nd runnings and preboil and sealed the open tips of the pipette as well as covered the other samples with saran wrap (to prevent any evaporation from occurring) and then allowed them all to cool to 64 degrees.
Each and every sample matched readings on both instruments (refract and hydro) with only slight variances due to operator error when reading the scales.
I conclude that all other variances mentioned in this thread might be pertinent, but that temperature plays a huge role in the correct readings on both hydros (we knew this) as well as refractometers.
The ATC on these refractometers allows us a +/- 20 degree range of testing, but given that most of us paid under $50 and the upper models can cost significantly more in some cases, we cannot expect them to be super accurate unless we use them like were designed to be used.

If the instrument and calibration sample are allowed to reach ambient and equivalent temperatures to be considered accurately calibrated then it only seems logical that we need to allow the wort samples to reach the same ambient temperatures for them to be scientifically as accurate as they could be.
One of the basic scientific principles that I used to teach my students when it came to accuracy and precision of measurements was that you can only be as accurate (and therefore precise) as the methods of measurement allow you to be. (ie you cannot expect a yardstick to give you measurements to the thousandths of an inch.)

So in conclusion:
You cannot take a $40 refractometer (which is a cheapened version of a much more pricey and accurate instrument, many of which are made in China), calibrate it "accurately" according to instructions and expect it to give consistent results in any repeatable way if you do not bring your sample to the calibrated temperature.
In addition to this, many of the posts in this thread address conversion factors and a large number of discrepancies between Brix and SG scales which I think are just one more inconsistency that is present in these affordable instruments.

Just my .02, but I promise you that the scientific theory is sound. My expected readings on my last 2 batches using this method were spot on according to BeerSmith.
I am using 75% brewhouse efficiency which I base on my last couple of batches using this new technique, but the readings that I have gotten are exactly the same as BS says that I should be getting. To me that represents that my thinking is pretty much spot on.

Hope this helps.

 

[TAK]

I just got my refractometer in the mail today. There's a lot of info to take in here; great stuff.

 

[ddavis7426]

Ny head hurts from reading all 11 pages!

So, are the $20-70 ATC refractometers ok or not, for measuring the FG or am I better off using the ole hydrometer?

All tis knowledge is difficult to decipher.

 

[Jsbeckton]

I'd say that are useful but to use with caution and double check against a hydrometer to get an idea of a correction factor. I find mine is usually within 3-4 points (usually measures low) so I use it to see if I need to make on the fly additions/dilutions. If I'm within a few points I don't bother to make changes due to the correction. You will get a feel for it. Plus take 2-3 readings to get an average as I have found I can easily get 5 point swing even when mixing well prior.


Sent from my iPhone using Home Brew

 

[TAK]

I've found it's useful for preboil gravity. After fermentation, it's a good way to see if gravity is stable over a few days without taking huge samples. For actual FG, I don't rely in it. However, you can also use it in conjunction with a hydrometer to get ABV without knowing OG, which is useful. I'd post the link, but I'm on my phone. It's in on if these threads on HBT.

 

[augiedoggy]

They are no good for FG once alchohol is present in the wort the readings will be off....

Just to clear things up a bit regardless of where you buy it most of these seem to be the same chinese refractometer with different scales...
there seems to be two versions (one being shorter than the other) and also blue vs black rubber handles...
Mine was $25 from amazon but the different amazon sellers charged a range of $24-$65 for the same product it seems.
I noticed my local LHBS had the exact same one as I do for $57... The only thing I'm not sure of is if the black rubber vs the blue rubber handle also means the scales are different? maybe one is for beer and the other wine?

I know my black handled RSG100ATC is for wort since it displays such at the bottom of the scale readout....

 

[ddavis7426]

Got my refractometer today.
My hydrometer readings the last few days (after fermentation) have stayed about 1.012 but two readings with the refractometer showed 1.020.
I checked it with tap water (not distilled) and the readings was ZERO- should it be this far off?

 

[ajf]

After fermentation has started the specific gravity scale on a refractometer is USELESS.
There are calculators that will give an approximation of the FG, if you have a record of the OG, but you need to enter the post fermentation reading in Brix.
See http://www.brewersfriend.com/refractometer-calculator/ for one example of such a calculator, there are many others.
In my experience, if you want a reliable FG reading, use a hydrometer, but you may have better luck than I do.
See posts 106, and 107 for gut feelings about this. (There are probably many others as well.)

-a.

 

[brewkinger]

A refractometer is very useful for brewday testing (if well calibrated)

Hydrometer is useful for FG, especially when I just drop a sanitized hydro in my bucket with no need for a sample.

Once ferment starts and alcohol is present, refractometers are pretty useless as the correction factors just make it more complicated.

In my 11 batches after my last post, I have been within a point or 2 of every expected brewday calculation.
When BeerSmith gives me a number and the tool that i am using gives me the same accuracy, I feel pretty confident in my refractometer and therefore it is a valuable tool.
If properly calibrated.


Sent from my iPhone using Home Brew

 

[TAK]

After fermentation has started the specific gravity scale on a refractometer is USELESS.

I don't feel this is 100% accurate. I would restate that a refractometer is "USELESS for FG."

I have found my refractometer very useful after fermentation has started. Even though it doesn't give you dimp for FG, you can use it to take small samples over consecutive days to confirm if fermentation is done or not. If gravity is still moving, the refractometer readings, though not to be used as FG, will also change.

 

[MalFet]

I don't feel this is 100% accurate. I would restate that a refractometer is "USELESS for FG."

Refractometers can be very useful in measuring FG if you've got a baseline established. In other words, if a certain recipe gave you a certain reading for your final gravity, in theory and in my experience you should get that same correlation again when you brew that beer a second time.

(And, for what it's worth, I always found Sean Terrill's conversion polynomial to be reasonably accurate, at least since I calibrated my refractometer for wort.)

 

[ajf]

I don't feel this is 100% accurate. I would restate that a refractometer is "USELESS for FG."

I don't feel this is 100% accurate. If you have a Brix scale, you can enter the post fermentation Brix value into various calculators together with the OG, or original Brix, and get an approximation of the final gravity. While it doesn't work for me, there are plenty of people who say these calculators are accurate, and have checked them against a hydrometer.

My point was that the specific gravity scale gives a wildly inaccurate reading under these conditions.

-a.

 

[TAK]

Ok, maybe I shouldn't have emphasized "useless", but I carried it through from the quote. I don't use them for FG, I've gathered data from several batches to get a mean wort correction factor, and the standard deviation from my sample was ridiculous. For others, it may adjust fine. Also, MalFet makes a good point.

I mostly just wanted to make the point that refractometers are NOT useless after fermentation begins.

Also, and I think I've posted on this thread a while back, they can be used in conjunction with a hydrometer to calculate ABV without knowing OG, which is very useful, and cool.