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Home Brew Forums > Home Brewing Beer > General Beer Discussion > Dang! which gravity is right?
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Old 11-29-2012, 10:35 PM   #1
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Default Dang! which gravity is right?

I have been chasing my efficiency issues with Beersmith. I had checked both my hydrometer and refractometer with distilled and tap water and they are within .002 as accurately as I can read them.

I have been using my refractometer before pitching and the hydrometer before bottling. I have been consistently low by .004 - .005 over the last 5 or so batches using the refractometer and the predicted OG in Beersmith. But the beers have tasted good and to my taste have had close to the right alcohol pct.

Tonight I have brewed a Wee Heavy and the predicted pre boil was 1.089 and my refractometer said 1.063 I boiled for 1/2 hour then drew off a sample and continued boiling before starting my 60 minutes with the hops.

The sample reads 1.080 with the hydrometer and 1.066 with the refractometer.

Dang! How do I check the accuracy at pre boil levels? Again they are close in distilled or tap water and way off after the mash.

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Old 11-30-2012, 12:22 AM   #2
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Now I have no idea where I am in my fine tuning.

I was really low looking at the SG side of my refractometer and it does not seem to be correct to the brix side.

I was not so low using the hydrometer.

I boiled for 1/2 hour before taking the hydrometer sample then boiled another 1/2 hour - then started my 60 minute schedule.

My predicted OG was 1.098 and I ended up with 1.096 which is great but I did have to boil an extra hour. I took some extra runnings and boiled it inside on the stove to concentrate it. (I figured the smaller volume would reduce faster than if I just added it to the boil kettle) I then added it to the boil pot so that diluted the preboil gravity some unknown amount. I ended up with just under 5 gallons.

I guess I am ending up with just a bit too much volume into the boil kettle or leaving a bit in the mash tun.

I am so confused. I will have to look into this tomorrow to see what I can learn.

Overall I am pleased with the final result, but what a PITA.

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Old 11-30-2012, 12:23 AM   #3
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I've heard that refractometers can be less accurate with darker beers and higher gravity beers. I would trust the hydrometer personally

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Old 11-30-2012, 03:00 PM   #4
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I'd go with the hydrometer. I've been fooled most by unmixed samples. The sample size is so small for the refractometer that I've assumed that it is even more subject to incomplete mixing. I also think that little noogies can really throw off the refractometer.

I love to check my gravities before and during the boil with the refractometer but I rely on the hydrometer after a well mixed sample has cooled. That and I don't worry about my efficiency much. Consistency is nice but it all comes out beer in the end!

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Old 11-30-2012, 03:30 PM   #5
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If you feel like doing some experimentation to get things very accuate, check out Stan's Beer and Wine Page for some ideas on calibration of your hydrometer. He has some good basic information about the process. If all checks out then calibrate the refractometer to your hydrometer.

I believe that the brix scale on a refractometer is defined for sucrose solutions, but has some inherent errors with more complex sugars as they don't have the same refractive index. I don't have any idea of the magnitude of the error though.

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Old 11-30-2012, 03:34 PM   #6
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I think you shouldn't worry about it. If it tastes good, pat yourself on the back and drink another.

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Old 11-30-2012, 03:36 PM   #7
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Personally I am a fan of hydrometers only. I read too many posts like this about refractometers to really feel they are worth their costs when making beer, especially post fermentation.

It is highly possible your samples are stratified and you are getting poor reads. For example, your hydrometer is reading from a vessel with more wort in it and the refractometer is a like a dot of wort. If that dot was on the light side of the sample it's off. Just be sure to calibrate the hydrometer at it's prescribed temperature in distilled water. It should read 1.000. The temperature your hydrometer was calibrated at should be on the small paper at the bottom, most are 60F, some are not.

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Old 11-30-2012, 03:46 PM   #8
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the conversion from SG to Plato/brix is only roughly linear to 1.040, and above that Grav it can be skewed. BUT you can calibrate a higher gravity with a correction adjustment in Beersmith. I do this and it has been very accurate for me. Just go into the options and you need to take a higher gravity sample reading with an accurate hydrometer and with your refractometer. The entry fields ask for all the numbers and it calculates your correction coefficient and saves it for you future use!

Do this and you will eliminate a lot of headaches!

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Old 11-30-2012, 05:43 PM   #9
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Ive used refractometers for measurings salinity in my aquarium and its not accurate unless you calibrate close to the range you are measuring..meaning i dont calibrate to zero because i want to measure around 1.024 - 1.026. If i calibrate to zero it throws off the accuracy. I guess something to think about dont know if you can get a calibration solution for the beer/wine refractometers or not. Sorry if this isnt relevant to beer but i thought i would share since I have seen no mention of calibration other than distilled water.

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