HUGE difference btwn refractometer and hydrometer

[OrthoBrewer]

Hello, I know there have been many other posts on this topic on these and other forums. I know that many people have explained the difference in measurement of specific gravity between the two tools. I could not find anything in a forum about such a big difference between measurements as I am seeing.

Recently brewed up Hop Scare from Midwest supplies, extract kit. I measured OG with both hydro and refracto when wort was at 75 deg F before pitching. Hydro read 1.061, refracto read 1.066 (unfortunately, I don't have the brix measurement from the OG). I have used a hydrometer since I started brewing, this was first time using refracto. Beer fermented at 72 deg F, but never had a great krausen or bubbling airlock. Got busy with work, and beer sat for 4 weeks. Took a refracto reading, and it read Brix 7.1, SG 1.033. Raised the temp to 75 deg F, stirred yeast cake gently with sterile spoon, let sit another week. Took refracto again, Brix 7.1, SG 1.033. At this point, I thought I had a stuck fermentation. So, I got another packet of yeast, made a yeast starter, and pitched it. No fermentation noticeable. Took refracto reading again a week later, Brix 7.1, SG 1.033. This got me nervous, so I took a hydro reading just now, and it reads as 1.010. Refracto reading at same time says Brix 7.1, SG 1.033. All instruments, fluids, beer were at 72 deg F. Before every measurement, I calibrated with distilled water. Hydro reads exactly 1.000, refracto always read 1.001, never adjusted it.

I never thought about doing a sucrose solution to have another point to calibrate the refractometer with. However, has anyone ever seen such a LARGE difference between the two instruments? I can understand my OG measurements of 1.061 and 1.066 being measurement error and what not. I can't understand my FG measurements being 1.010 and 1.033. I'm thinking of pitching the refractometer and relying on the hydrometer forever even though I break them about every 6 months.

Thanks, John

 

[QuercusMax]

You cannot use a refractometer to miss your final gravity, only original gravity. The presence of alcohol throws off the refraction . But there are some very good tools that will give a good estimate, like this one:

http://seanterrill.com/2012/01/06/refractometer-calculator/

It gives 1.010 for your FG based on your OG and final refractometer reading.

 

[pcollins]

You CAN use your refractometer for FG readings as long as you DO use the conversion tools to get the correct reading.

The refractometer is made to measure the refraction of light in a solution of sugar and water. Alcohol has a different refractive index which leads to "off" readings in the refractometer. The conversion tools correct for that difference.

IF you're genuinely concerned about super accurate readings I would use the hydrometer beginning to end. I use my refractometer for OG and my hydrometer for FG only because I'm going to sample the final product prior to carbing anyway and I'm not super concerned about accuracy. I'm not really going to taste the difference between 6.5% or 6.6%.

 

[dmcman73]

I've used my Refractometer for FG as well, but, as others have said you need to use different conversions. I use an app called Brewzor calculator on my Android phone. You can fine tune the calibration by taking a measurement with your refractometer and Hydrometer and enter those values into the calibration screen.

 

[OrthoBrewer]

Thanks for all of the help friends. Makes me feel a lot better about my refractometer. I do like the fact I just have to use a few drops, and hopefully it won't be as easy to break as the hydrometers.

Merry Christmas