Refactometer Question?

[Brewmarc]

Iv just got myself a 0-32% refractometer , & without a current brew to take a few samples along the way Iv just been pumping a few figures into promash to see what comes up :wha: Q1, I have calibrated it with distilled water to 0 Brix, What is Brix corection factor? how can there be a difference in accuracy between (asuming both instruments are accurate)a hydrometer & a refractometer reading? it says a typical difference value is .002 to .008 SG. & do I really need to do this calibration after all Im not looking to get accuracy to customs & excise proportions. :wha: Q2,I understand that you have to compensate for the alcohol content in fermented wort when using a Brix refractometer, but assuming I have brewed a beer & say, not taken an OG reading , am I right in thinking that after taking a Brix refractometer reading & an FG hydrometer reading of fermented wort, & after entering these figures into the calculator in promash the % ABV & OG figure is correct? Im just curious how its worked this out?

 

[screamlead]

MIne was spot on when i got it - but did a test at 20c and it was perfect

 

[timbim]

If you can read a hydrometer to .01, I'd be very impressed. Mine you couldn't read to better than 0.5 on a good day. A refractometer is in principle much easier to read accurately. The thing to remember is that the refractometer measures the refractive index, a very different property. For a mixture of sugar and water, you can calculate the SG from refractive index and hence calibrate a scale for it. When you have alcohol present as well, things become much more complicated, so a specific calculator is required.

Tim

 

[Aleman]

Refractometer - Brix Correction Factor:


A Brix refractometer reading is based on the known values for percentage sucrose solutions. However, wort contains many substances other than sucrose, and many of them have different refractive indices than sucrose. For this reason, it is necessary to use a correction factor to convert from a Brix refractometer reading of raw wort to the actual gravity of the wort. The literature suggests this factor is between 1.02 and 1.06, with 1.04 often used as a default value.

To determine your own, brewery-specific Brix correction factor:

(1) Take a hydrometer sample of unfermented wort.

(2) Measure its gravity with the most accurate, calibrated hydrometer you have. Do not forget to do the temperature offset calculations. (Alternative: use a digital density meter or pycnometer -- the idea here is to get a very accurate measurement of the actual SG / Plato of the sample.)

(3) Convert this value to Plato if you measured in SG.

(4) Using a zeroed refractometer, take the refractometer reading of the same sample.

(5) Convert this value to Brix if measured in RI or Zeiss units.

(6) Brix correction factor = Refractometer reading (in Brix) / Measured Gravity (in Plato) E.g., Refractometer reading = 13.1 Brix Measured gravity = 12.7 Plato Brix Correction factor = 1.0315

(7) Do this with several different samples and average the results. The literature suggests that the value should be consistent within a particular brewhouse.

 

[Loetz]

(4) Using a zeroed refractometer, take the refractometer reading of the same sample.

So, I've been having problems with beersmith and my cheap-o ebay refractometer. When I do a distilled water test, it reads as 2brix. I can adjust that up, but I can't adjust it down. The screw just won't go any tighter. In beersmith, it gives an option to calibrate the refractometer. I typed in '2' in the blank where it says 'distilled water reading' and assumed that it was doing the correction for me. Out of curiosity, I recently changed that 2 to some other numbers to see what would happen and it didn't change anything when converting my specific gravity. What do I do? Can I just subtract 2 from my brix readings and assume that is accurate?

 

[sib67]

(4) Using a zeroed refractometer, take the refractometer reading of the same sample.

So, I've been having problems with beersmith and my cheap-o ebay refractometer. When I do a distilled water test, it reads as 2brix. I can adjust that up, but I can't adjust it down. The screw just won't go any tighter.

Are you sure there isn't a lock-nut that is preventing you from adjusting the screw downwards?

 

[Loetz]

I'm positive. So does anyone have any thoughts on this?

 

[Aleman]

I'm positive. So does anyone have any thoughts on this?

Yep, you have a knackered cheapo ebay refractometer.

As far as beersmith goes I don't use it so can comment on how it does things.

I'm not sure you can just subtract 2 from the brix readings either . . . especially for 'calculation' of fermenting wort gravity