Debating on a refractometer....

[NWesterner47]

Hey Im not sure if anyone has mentioned this yet but I bought a refractometer as a present for my self last year. I thought it was super awesome! invaluable for all-grain taking multiple readings at different points in the brewing process.

BUT,(and its a big but) I either did not read directions or something because while using it for post fermentation readings I could never get the measurement to go below 1.030 FG. so after a year of messing with everything but my refrac, and dumping too many batches that could have turned out well juts because I thought they were not done fermenting, I finally started to suspect my refractometer.:smack:

basiclly because of the alcohol in the beer you cant use the refrac (or have to make inaccurate conversions). So dont toss your hydrometer and use it for post ferm, also not a bad idea to check your refractometer with your hydrometer ever once and a while.

know your tools. Cheers

 

[snccoulter]

I got mine fro Bobby M at Brew Hardware. Nice guy good service. It sure is nice to be able to check the gravity without having to mess with a hydrometer.

 

[Brewdiction]

Thanks for the info. It totally makes sense a refractometer will have an error factor that is different for wort vs must vs sugar, etc. But that same factor would apply to plato, brix, and sg. I e 20 brix would always equal 1.083. When you apply the CF, both values change. The correction factor is needed since your refractometer displays something outside of 20 and 1.083.

In other words, the statement above is like saying 1" = 2.54cm when you measure steel but when you measure wood 1" =2.50cm which is not true. They may expand at different rates with temperature but that CF applies to both scales.

 

[ajf]

A refractometer does not actually measure Brix. It measures the refractive index of a solution, and expresses the result as a value equivalent to that of a pure sucrose solution in water at 20C.
The composition of the wort most certainly has an affect on the algorithm used to calculate this equivalence.

-a.

 

[Brewdiction]

Thanks ajf. I understand what you are saying. Different sugar solutions will refract the light differently, hence the correction factor described in the linked article. Your comment that a reading of 20 brix will mean different SG depending on the solution just isnt true. Both brix and SG will change together based on your CF adjusted measurement.

Is anyone else following my thought process?

 

[alestateyall]

Thanks ajf. I understand what you are saying. Different sugar solutions will refract the light differently, hence the correction factor described in the linked article. Your comment that a reading of 20 brix will mean different SG depending on the solution just isnt true. Both brix and SG will change together based on your CF adjusted measurement. Is anyone else following my thought process?

You are assuming a linear relationship between brix and specific gravity. The relationship as described by the polynomials used to convert from brix to SG is not linear. As such the correction factor is also different for the two scales. It is true there is a correction factor for both but the correction factors are different.

 

[alestateyall]

You are assuming a linear relationship between brix and specific gravity. The relationship as described by the polynomials used to convert from brix to SG is not linear. As such the correction factor is also different for the two scales. It is true there is a correction factor for both but the correction factors are different.

This article has a cubic equation to covert from brix to SG. Even that equation is an approximation.

http://byo.com/stories/item/1313-refractometers

 

[ajf]

Thanks ajf. I understand what you are saying. Different sugar solutions will refract the light differently, hence the correction factor described in the linked article. Your comment that a reading of 20 brix will mean different SG depending on the solution just isnt true. Both brix and SG will change together based on your CF adjusted measurement.

Is anyone else following my thought process?

I do understand your thought process, and it would be correct if you were measuring a solution of sucrose in water, but you aren't. You are measuring a solution of wort. This causes the Brix reading to be reported incorrectly.
I ran a simple experiment in October 2012 to verify this,
see https://www.homebrewtalk.com/f36/refractometer-question-362437/index3.html post number 25.

-a.

Don't take my word for it. Try it yourself

 

[tschafer]

Love my refactormeter! It's the most important tool in my opinion. I use with my starter and throughout my brew day. It's a must have tool in my opinion.

 

[Brewdiction]

For a typical beer wort, 20 brix would translate to about 1.080. If you were measuring wine must, then 20 brix would translate to about 1.083

-a.

Guys, appreciate the replies but think we are all saying the same thing. Let's go back to the original quote that raised my question. I think ajf is saying the 'reading of 20' on the refractometer will have different SG for different solutions...which is true since a specific correction factor has yet to be applied which differs across solution types and temperature.

If you think about it, the number you read on the refractometer (or hydrometer) is useless until it is corrected for these errors. Then, it is a measurement.

I interpreted the word 'measurement' in the statement as a 'post corrected measurement' of 20 brix could have several corresponding SG values. I think we will all agree that cannot be true. The equation can have only one positive real number solution.

Brix -> SG Equation:
SG = (Brix / (258.6-((Brix / 258.2)*227.1))) + 1
(Source: Brew Your Own Magazine)

Right? If you measured 20 brix (after applying correction factors) you should calculate approx. 1.083 SG regardless of the solution because the variances in solution from sucrose is exactly why you have the CF!