Hydrometer and Refractometer disagree...sometimes.

[xoltri]

Got a refractometer from ebay today. I calibrated it with RO water. I tested it against my hydrometer with RO water and they matched. Also with apple juice and they matched. I made a 15 brix solution with 60 grams of sugar and 340 grams of RO water and they matched.

However I tested it with some red wine that is actively fermenting using the morebeer spreadsheet. The wine started at 1.089 according to the hydrometer (I didn't have the refractometer when it started). Now it is showing at 11 brix, and according to the spreadsheet it should be 1.017. But my hydrometer is showing 1.034.

I'm wondering what is throwing off the reading so much if the spreadsheet is supposed to compensate for the alcohol. Does the spreadsheet only work for beer? Does the carbonation in the wine affect the hydrometer reading that much?

I want to figure this out because I bought it so I could stop taking such large samples from my beer and wine to measure SG.

 

[rawlus]

are you adjusting the hydrometer reading for temp?
is your refractomer ATC (auto temp correcting?)
morebeer does have a wine-version of the spreadsheet, but i believe the formulas are the same for both.

i use the spreadsheet from valley vintner, they have a very good explanation of the process and measurement against a hydrometer. but bascially, alot can affect a hydrometer reading during fermentation, including CO2 bubbles.
check here: http://valleyvintner.com/Refrac_Hydro/Refract_Hydro.htm
in their testing they found less than a 1% deviation between hydrometer and refractometer over the entire course of fermentation.
with wine, however, the most important readings are initial gravity and confirming fermentation has ended below 0.996 somewhere.

 

[xoltri]

Yes it's an ATC model.

Thanks for the information about the valley vintner experiment, I wasn't aware of that one. It's good to have confirmation that they should agree (with the spreadsheet correction). I have 4 different things fermenting (mist wine, red wine, cream ale, and a skeeter pee) so I'll compare them against my hydrometer and see if I can figure out what's going on.

 

[Chemkrafty]

Also check out a recent podcast from Basic Brewing Radio. They actually discuss refractometers and hydrometers. There are many reasons it could be off and the guest is well versed in the science behind it all.

 

[prosper]

I've found that mine, when correctly calibrated and corrected for beer, will usually agree with my hydrometer within .001, sometimes .002 points for both OG and FG - accurate enough for my needs.

But it's critically important that you use a correction formula to get a decent reading, especially for FG's

 

[jfkriege]

The index of refraction is changed by the presence of alcohol. You need to use a calculation to take the OG reading and FG reading of the refractometer and output an actual FG.

 

[xoltri]

Also check out a recent podcast from Basic Brewing Radio. They actually discuss refractometers and hydrometers. There are many reasons it could be off and the guest is well versed in the science behind it all.

Thanks for this tip, I learned a couple of things, particularly about turbidity with the refractometer bluring the line. I actually noticed this with the red wine compared to the sugar solution which made a solid line. I discovered on my own that turning it upside down sharpens the line...a later google search revealed that it's because the solids 'sink' away from the prism and onto the diffuser. They didn't mention this on the pocast even though it is a good tip.

I'll keep making readings with both the hydrometer and refractometer for a few batches and see how the numbers line up. Even if it's not deadly accurate if it's consistent that's all I'm hoping for. It's so much more convenient to make a measurement with the refractometer compared to the hydrometer.