Refractometers and Brix Conversion

[HansH]

[/quote]
We are measuring a spectrum of sugars of which sucrose is only a small percentage but the fact that we do not encounter much sucrose has but a minor effect. The apparent (20/20) specific gravities of 10 % w/w solutions (10 °P, 10 °Bx) of, respectively, sucrose, glucose, fructose and invert sugars are, respectively, 1.04838, 1.04785, 1.04886 and 1.04835.
quote]
Do you also know the refractive index at 10% w/w for the sugars as this actually determines the Brix readout. where I can download it ? If Brix*1.04 = Plato for maltose solution, then I would expect that at least the Brix reading differ more than the SG readings for different sugars at equal %w/w
HansH

[whatsontap]

Mylo taught me this (it may have been posted but there's a lot of reading here and math hurts my head).

Take the brix reading and multiply by 4 so say it's 6 brix

4x6=24

put a 1.0 in front of it, that means it's 1.024 SG or thereabouts. Usually when brewing I don't worry about more than N.NN resolution. Fermenting wort, forget it lol use beersmith.

[driver8rws]

It is WIDELY written that the "multiply by 4" thing is WRONG/inaccurate...

Use THIS table instead:
http://www.winning-homebrew.com/specifi ... -brix.html
Or this one:
https://docs.google.com/a/barleypopmake ... i&hl=en_US

What has just recently blown my mind after using a refractometer for about a year now, is this totally new (to me) concept of "brix conversion factor". Google it...
So now, not only is the S.G. scale on my refractometer totally WRONG and I have to use the Brix scale and convert to SG... but now I have also found out that the refractometer isn't even really meant to measure WORT/beer, so the Brix scale is really "wrong" too and you have to divide by a "conversion factor" (something like 1.04) to even get the BRIX to be right !!
GEEZZZZ !!
What a mess !

-Randy
Cincinnati, OH

[ajdelange]

It's actually a pretty good approximation for the typical range of beers we brew

1 °P ~ 1.00389 SG
2 °P ~ 1.00780
4 °P ~ 1.01569
6 °P ~ 1.02369
8 °P ~ 1.03180
10 °P ~ 1.04003
12 °P ~ 1.04837
14 °P ~ 1.05683
16 °P ~ 1.06542
20 °P ~ 1.08297
25 °P ~ 1.10567

As you can see it's better that 0.001 SG for 1 < °P < 15 and fine for mental calculation in the brewery. But it is very easy to calculate the correspondence exactly:

°P = -616.868 + 1111.14*SG - 630.272*SG*SG + 135.997*SG*SG*SG

Finding °P from SG is thus seen to be trivial in a spreadsheet. Going the other way is a little trickier. There is a closed form solution but it is much easier to just plug in values of SG until you get the °P number you want. Those familiar with the Solver can let it do this for them automatically.

All this is for 20 °C/20 °C apparent SG. For any other temperature(s) and for true SG the game is different.

I have never advocated the use of refractometers in brewing except to monitor the decline in extract during sparging at that is because, while they are accurate in many cases in some they aren't and the only way I know to tell is to check them against a hydrometer. Just the other day I had some folks over here for brewing and when we did that we found the refractometer off by 0.8 Bx