# Refractometer

So I defintely want to invest in one of these little buggers. I was checking out things online and saw tons for sale on ebay. Are the ones selling on there worth it?

Here is an example: http://www.ebay.com/itm/0-32-Brix-Wort- … 3f091967a6

Just curious. You can’t beat the price.

Yup, it’s the same one HBS sell. Just know that the SG scale is inaccurate.

How inaccurate?

yeah, how? The picture show 15 Brix=1.060. Sounds about right to me.

[quote=“fightdman”]yeah, how? The picture show 15 Brix=1.060. Sounds about right to me.[/quote]15 Brix = 1.056

It depends on the gravity. 10°Bx = 1.040, 20°Bx = 1.083, 30°Bx = 1.129, etc. If you use a “multiply by four” rule, you’ll be 0.0005 or more off any time the gravity exceeds 1.051. So at that point it’s less precise than a consumer-grade hydrometer.

ETA: Though if we’re being honest, most home brewers aren’t getting near that level of precision. I doubt many people check the sample temperature, de-gas the sample, know which side of the meniscus to read, etc.

It depends on the gravity. 10°Bx = 1.040, 20°Bx = 1.083, 30°Bx = 1.129, etc. If you use a “multiply by four” rule, you’ll be 0.0005 or more off any time the gravity exceeds 1.051. So at that point it’s less precise than a consumer-grade hydrometer.[/quote]

Is the brix wrong too? or just the conversation?

Is this all of them out there? or just the ebay one he posted?

Compared to these. are they better or just as bad?

http://www.brewhardware.com/refractometer http://www.northernbrewer.com/shop/brix ... w-atc.html

I don’t get that from any place I look.

http://www.fermsoft.com/gravbrix.php

1.056 = 13.79

http://brew.stderr.net/refractometer.html

1.056 = 13.8

http://www.winning-homebrew.com/specifi ... -brix.html

1.056 = 13.79

AFAIK, the Brix scale is accurate. But as with any instrument, the first thing you should do is calibrate it.

Sweet find! I didn’t know anyone had a corrected model out. So the BH one should be fine, but the model NB carries (assuming the pictures are current) is inaccurate.

[quote=“muddywater_grant”]I don’t get that from any place I look.[/quote]That’s because they’re just using the Brix for sugar water and not using the 1.04 correction factor for wort, which contains other forms of sugar besides sucrose.

Something still doesn’t add up. 15/1.04 = 14.4°Bx, or 1.058.

Well, what do you know? The correction factor that I was using in BeerSmith was 1.02861 (default). Looks like I might need to change that when I get my replacement refractometer.

Ideally, you’d want to check it against a hydrometer and determine the correction factor for whatever you consider to be a “typical” wort. In higher-attenuating American ales, for example, I’ve found it to be closer to 1.02.

[quote=“a10t2”]Something still doesn’t add up. 15/1.04 = 14.4°Bx, or 1.058.[/quote]You take the corrected Brix and then calculate the gravity with this formula: OG=1.000019+0.003865613*(Bx)+0.00001296425*(Bx)+0.00000005701128*(Bx) I’m sure there are other ways to do it, but the results match my hydrometer readings.

Edit: I’ve been messing around with the various formulas and this isn’t correct for OG by itself (it was something I was trying as part of the FG calculation and it’s in an old version of the spreadsheet at work, not the “real” version at home) - my apologies.

I’m assuming that was supposed to be a cubic and that the exponentials didn’t copy-paste properly. When I apply that formula to 15°Bx with a correction factor of 1.04, I get an SG of 1.0586.

I use de Clerck’s formula, SG = 1 + [P/{258.6 - (227.1*P/258.2)}], but they give results that are basically identical: WolframAlpha link

.

[quote=“a10t2”]I’m assuming that was supposed to be a cubic and that the exponentials didn’t copy-paste properly. When I apply that formula to 15°Bx with a correction factor of 1.04, I get an SG of 1.0586.

I use de Clerck’s formula, SG = 1 + [P/{258.6 - (227.1*P/258.2)}], but they give results that are basically identical: WolframAlpha link

.[/quote]

Well, then I’ll sorta stand by my orginal statement: “The picture show 15 Brix=1.060. Sounds about right to me.”