how does refractometer work?

how does a refractometer figure out the gravity of wort based on only a few drops sample?

does the temperature of the wort matter like with a hydrometer?

would you get a different reading if you drew wort from different parts of your mash runnings, BK, or carboy?

are the ones sold by home brew stores or e-stores accurate (like the northern brewer or morebeer ones) or are they like bimetal probe dial thermometers from harbor freight?

i'm trying to decide whether to get one or not. my hydrometer works fine but it takes large sample sizes and monkeying with the temp. might be nice to have a magic wort divining rod instead. if its worth the money.

Refractometers work by measuring the difference in refractive index between the lens and the stuff you put on it and comparing that to some calibration fluid (typically 60ºF distilled water) to give you a Brix reading. Temperature matters if you don't have a refractometer with "ATC" (and I think that means Automatic Temperature Calibration, or something like that).

You would get a different reading if the sugar concentration were not homogeneous throughout.

The ones sold by your fridnly LHBS probably is as good as the ones you find at the major online stores, but you can check that out.

It's a luxury, but a nice one. I just bought one tonight.


TL

thanks TexLaw.

i guess gentle stirring of the mash runnings before boil would be ok if careful not to oxygenate. shouldn't be an issue for the carboy.

did you get one with ATC? in any case i'd like to know what your impression of it is after you try it on your next brew.

Keep in mind that after fermentation starts, the readings need to be recalibrated since ethanol (and other alcohols) are present.

Morebeer.com has a nice spreadsheet to do just that: http://morebeer.com/learn_vids/vids_refract

mrkristofo said:

Keep in mind that after fermentation starts, the readings need to be recalibrated since ethanol (and other alcohols) are present.

Morebeer.com has a nice spreadsheet to do just that: http://morebeer.com/learn_vids/vids_refract

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Even using those calculators, your readings may be horribly inaccurate after fermentation starts. That's been my experience all the times I've tested it side-by-side with a hydrometer, and so far I've never heard from a single person who actually got accurate results. YMMV.

They do a decent enough job on unfermented wort, though, making them useful for checking mash/sparge runoff, pre-boil gravity, and OG - especially since you don't have to cool a sample of wort down to test it.

I did get one with ATC, and I only intend to rely on it for pre-fermentation gravity readings.

Just because I have it, I imagine I also will take readings during and after fermentation, but the sample will come from my hydrometer flask. I know that Louis Bonham came up with a formula that accounted for alcohol. I'll check that, along with with ProMash's and MoreBeer's adjustments, just to satisfy academic curiosity. I'll rely on the hydrometer, though.


TL

TexLaw said:

Just because I have it, I imagine I also will take readings during and after fermentation, but the sample will come from my hydrometer flask. I know that Louis Bonham came up with a formula that accounted for alcohol. I'll check that, along with with ProMash's and MoreBeer's adjustments, just to satisfy academic curiosity. I'll rely on the hydrometer, though.

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I'd love to hear your results. I've tried it on several batches, and tried to be careful about taking measurements properly at each step, but never got good results with either beersmith's calculator, or some of the other ones available online.

On my next batch I am planning to do as careful a test as I can, making sure to calibrate both instruments at each step, record temperature measurements, document the whole thing on paper and in pictures, and run the calculations using all the different calculators I can lay my hands on.

I'd sure LIKE it to work, as refractometers are nice and convenient, so I'll be crossing my fingers but not getting my hopes up after my previous experiences.

ok, thanks all. i've decided a refractometer would be a waste of money, so i won't buy one.

the reason is that it's easy to take readings of pre-boil mash runnings cuz the wort is readily accessible since you don't have to steal it out of a carboy and don't have to be quite as careful of sanitation. you just have to cool it. it's the readings during fermentation that are the most bother with a hydrometer since you have to be super sanitary and its harder to get a sample, and the refractometer doesn't help much there since it isn't accurate.

Even using those calculators, your readings may be horribly inaccurate after fermentation starts. That's been my experience all the times I've tested it side-by-side with a hydrometer, and so far I've never heard from a single person who actually got accurate results. YMMV.-Quote

My results where exactly the same using my hydrometer - refractometer and more beers spread sheet. I have only used it once though.