Data from Sean Terrill does not match what Kai posted (Brix to wort Plato & OG)

[p_p]

Hi all,
need some help here

I am comparing the table posted by Kai: Refractometer Brix reading to wort Plato and SG conversion table
http://braukaiser.com/documents/Kaiser_Brix_Plato_SG_table.pdf

With the data posted by Sean and his implementation: fg_calculator_v3.0.xls
http://seanterrill.com/2011/04/07/refractometer-fg-results/

They both use correlation factor of 1.04, yet the result are not the same.
Sean use the factor as reciprocal while Kai doesn't.

For example, for a Brix reading of 16.4
SG (Kai) 1.070
SG (Sean) 1.064

What is wrong here? I am confused :/

Thanks,
p_p

 

[ajdelange]

Refractometry is not a reliable way of determining wort SG. Different people have used different data sets to find the conversion factors and it is not surprising that they came up with different results.

 

[trentm]

Hi all,
need some help here

I am comparing the table posted by Kai: Refractometer Brix reading to wort Plato and SG conversion table
http://braukaiser.com/documents/Kaiser_Brix_Plato_SG_table.pdf

With the data posted by Sean and his implementation: fg_calculator_v3.0.xls
http://seanterrill.com/2011/04/07/refractometer-fg-results/

They both use correlation factor of 1.04, yet the result are not the same.
Sean use the factor as reciprocal while Kai doesn't.

For example, for a Brix reading of 16.4
SG (Kai) 1.070
SG (Sean) 1.064

What is wrong here? I am confused :/

Thanks,
p_p

I think Kia's table is simply converting Brix to Plato and SG while Sean's calculator is attempting to correct for alcohol in a FG refractometer reading. But I can't find where Kai has any detailed explanation of the table and I don't understand Sean's calculator (I've never used a refractometer). It is a bit confusing because Kai's table is titled "Refractometer Brix reading to wort Plato and SG conversion table". I use a Brix hydrometer and an app to convert to SG. It's interesting that Kia's table is a little different from my app's conversion. To use your example, my app converts 16.4 Brix to 1.067 SG.

 

[p_p]

Refractometry is not a reliable way of determining wort SG. Different people have used different data sets to find the conversion factors and it is not surprising that they came up with different results.

Ok, I agree AJ, but in this case both came up with a factor of 1.04 (which seems the default factor to use if you haven't generated data yourself), but:

Kai: °P = Brix * 1.04
Sean: °P = Brix * (1/1.04)

Is it just a coincidence that the two factors they individually came up with are reciprocal of each other? (in their publications they claim the factor is 1.04 and not 0.9615)

Thanks

 

[p_p]

I think Kia's table is simply converting Brix to Plato and SG while Sean's calculator is attempting to correct for alcohol in a FG refractometer reading. But I can't find where Kai has any detailed explanation of the table and I don't understand Sean's calculator (I've never used a refractometer). It is a bit confusing because Kai's table is titled "Refractometer Brix reading to wort Plato and SG conversion table". I use a Brix hydrometer and an app to convert to SG. It's interesting that Kia's table is a little different from my app's conversion. To use your example, my app converts 16.4 Brix to 1.067 SG.

Thanks for that ...

Like you said, Kai's table converts Brix to Plato and SG.
Sean's calculator does that as well, as an intermediate step to correct for alcohol in a reading.

So, if you ignore the alcohol correction part in Sean's calculator and just fill in Orig °Brix (cell C7), you get the conversion to OG in cell E7.
These are the values I am using to compare Kai vs. Sean.

If you type 16.4 in cell C7, you get 1.064 as OG.
While 16.4 Brix in Kai's table is 1.070 OG.

both using correction factor 1.04 ...

 

[ajdelange]

I do rather think that one guy got 1.04 and the other 0.96 but I really don't know. Now 1° P = 1 Bx (to 5 decimal places) but a change of 1 °P means a change of 0.040 only at about 10 °P and changes with the concentration. This has nothing to do with refractometry.

 

[p_p]

Thank you for all your posts.
Sean kindly answered an email I sent and confirmed what AJ said above.

"I know that Kai defines the wort correction factor as being the inverse of most sources. So a WCF of 1.04 in someone else's calculator/spreadsheet would correspond to about 0.96 in Kai's, for example"

 

[broadbill]

Refractometry is not a reliable way of determining wort SG. Different people have used different data sets to find the conversion factors and it is not surprising that they came up with different results.

Are you referring to them being inaccurate with post-fermentation samples, or beer wort in general (which is how I am reading your post).

Thanks.

 

[ajdelange]

Yes, you read it correctly.

 

[broadbill]

Yes, you read it correctly.

Then source? I'd like to understand why measuring sugar content by light refraction is different/inferior to doing so by density.

 

[ajdelange]

Source?

Pure water has a refractive index that is a function of temperature. If you dissolve something in the water it will change the refractive index. If you make solutions of sucrose of known strength (% w/w) then you can make a table of RI vs Bx that works for sucrose or, better yet, put the table in a digital instrument or engrave Bx on the reticle of an analogue one. Great if what you are measuring are pure sucrose solutions. But wort contains very little sucrose and a lot of other sugars. Their RI's don't vary in the same way that sucrose's does. Sort of the same way, though, so you can get a rough answer with refractometry but not a terribly accurate one. "Isn't the Plato scale also based on sucrose solutions?" you ask. Yes it is but sugars' specific gravity vs w/w variations are amazingly close over the various sugars and even soluble starches and concentration based on SG estimates are very good.

The fact that one investigator got 1.04 and another got 0.96 attests to this situation as I said in my first post.

In my own experiments I compared the Bx readings with the Plato readings for several mash samples and worts. In general the reading were close but in some cases they differed by half a degree Plato and in other cases by as much as 2 °P. I tell people you can use a refractometer to measure OG and most of the time you will be very close to the correct answer. The question is as to how to tell when you have one of those situations where your error will be 1 - 2 °P.

 

[broadbill]

Source?

Pure water has a refractive index that is a function of temperature. If you dissolve something in the water it will change the refractive index. If you make solutions of sucrose of known strength (% w/w) then you can make a table of RI vs Bx that works for sucrose or, better yet, put the table in a digital instrument or engrave Bx on the reticle of an analogue one. Great if what you are measuring are pure sucrose solutions. But wort contains very little sucrose and a lot of other sugars. Their RI's don't vary in the same way that sucrose's does. Sort of the same way, though, so you can get a rough answer with refractometry but not a terribly accurate one. "Isn't the Plato scale also based on sucrose solutions?" you ask. Yes it is but sugars' specific gravity vs w/w variations are amazingly close over the various sugars and even soluble starches and concentration based on SG estimates are very good.

The fact that one investigator got 1.04 and another got 0.96 attests to this situation as I said in my first post.

In my own experiments I compared the Bx readings with the Plato readings for several mash samples and worts. In general the reading were close but in some cases they differed by half a degree Plato and in other cases by as much as 2 °P. I tell people you can use a refractometer to measure OG and most of the time you will be very close to the correct answer. The question is as to how to tell when you have one of those situations where your error will be 1 - 2 °P.

thanks for the explanation.