Hydrometer reading vs Refractometer reading

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Mpavlik22

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Whats up all?

I just got done brewing a Pale Ale (all grain). I just got a refractometer and decided to try it out. I still used my hydrometer to compare. I got completely different reading pre-boil & post-boil.

Before you ask, i did calibrate the refractometer with distilled water. Also it is a ATC (auto temp correction) unit. regardless since i take my hydro reading at 60 deg F, I cooled to 60 deg and took my hydro reading and refrac reading at the same time and temp.

Anyways my readings:
Pre Boil:
Target - 1.042
Hydrometer - 1.041
Refractometer - 1.033

Post Boil:
Target - 1.054
Hydrometer - 1.051
Refractometer - 1.043

So can anyone explain why my readings are so different between the hydrometer and refractometer?

Thanks
 

jd3

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Is your hydrometer calibrated?
 

jd3

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The only reading I take anymore is a OG and a FG. Why are you taking pre and post boil readings. I'd worry less about them and more about results.
 

Yooper

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The only reading I take anymore is a OG and a FG. Why are you taking pre and post boil readings. I'd worry less about them and more about results.
A preboil reading is very useful. If you are way over or under on your target OG, you can fix it right then. You can also get your post boil OG just from doing some simple math from the preboil reading (If you have a preboil gravity of 1.060 with 7 gallons, for example, you KNOW what your gravity will be with 5.25 gallons in the fermenter), and adjust any hopping rates accordingly. You can also figure your efficiency from the preboil reading. Once you have your system completely locked in, maybe a preboil reading is less useful, but I wouldn't dismiss it.
 

jd3

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While I know there is a simple formula to get the reading post boil, I think it makes more sense to just take the reading.

I suspect the refractometer is either poorly calibrated, or just general poor quality and giving a bad reading. I use them in fish tanks and if they are the cheaper variety I can get different readings back to back.

Obviously one of the items is wrong. While I'd hope that the hydrometer is right since it is closest to the predicted readings, you would be a better judge of how things went.

I'd try it on some other known samples and go from there....
 

Sithdad

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Get some distilled water and test both your hydrometer and your refractometer. Your refractometer may need adjusting. Also, some refractometers need to have their results adjusted based on a comparable hydrometer result. For example, after adjusting your refractometer you test a wort sample with your hydrometer and your refractometer. If, your temperature adjusted, hydrometer reads 1.040 and your refractometer reads 1.044 your refractometer has and adjusted wort value of 0.004. This would mean that all of your readings, from your refractometer, would require an additional 0.004 being added.
 
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Mpavlik22

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As already stated I have calibrated both with distiller water
 

iaefebs

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As already stated I have calibrated both with distiller water
I'm not sure what kind of an answer you are looking for. It seems people have trouble with refractometers. I don't know if it is because the newer cheaper ones have defects or if they are not getting the proper temp for a reading. I take a small sample of pre boil wort and place it in my ferment chamber for a few minutes then take a reading. I do the same post boil. When I sample during ferment I just insert a straw through the airlock hole to grab a sample. I hardly ever use a hydrometer untill it gives me an excuse to taste a sample. My refractometer is 5 years old.... maybe they made them better back then. I think you are experiencing temperature problems.
 

ajdelange

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So can anyone explain why my readings are so different between the hydrometer and refractometer?

Thanks
Refractometers are calibrated for sucrose solutions in water. Wort is not a sucrose solution. It contains a complex spectrum of sugars including some, but not very much, sucrose. A hydrometer is also calibrated against a sucrose solution. Thus neither instrument reads the true extract of the wort but density measurements track solution strength better than measurements based on refractive index i.e. a hydrometer reading will compare much more favorably to a true density reading made with an oscillating U-tube meter or pycnometer than a refractometer reading will. Refractometers really should not be relied on for anything other than monitoring the decline of extract as time progresses in sparging but home brewers insist on using them for a purpose to which they are not really suited. It must be said that the agreement between hydrometer and refractometer with wort is usually better than what you observed. In fact the agreement is often quite good but it is not unusual at all for them to disagree by a couple °P as in your case. The problem is you have no way of knowing whether the agreement is good or bad unless you make a comparative measurement in which case there is no point in taking the refractometer reading as you have to take a hydrometer reading to verify it. The exception to this is in commercial brewing where a calibration curve between refractometer and densitometer reading are made and used for a particular beer. When that same beer is brewed again a refractometer reading can be entered into the calibration curve and a good estimate of the extract taken out.

ATC may be partially responsible in your case. The ATC in a refractometer is based on the shift in refractive index of a pure sucrose solution relative to 20 °C (68 °F). Wort's refractive index does not shift at this same rate so all measurements with a refractometer should be taken with ATC turned off at a temperature of 20 °C. Not saying that this explains all your discrepancy but it might explain some of it. Another thought is turbidity. In the instruments where the light actually passes through the sample (the kind you look into) scattering may make the delineation between the dark and light parts of the field fuzzy. In the electronic instruments where the light never actually enters the sample you have better immunity to this effect.
 

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The first time I used my refractometer, I used the difference between hydrometer reading and refractometer reading to calculate a correction factor. After applying this correction factor the two have agreed for every other reading I've done pre fermentation.

Obviously for mid or post ferment you will have to use some of the calculators or spreadsheets which are around that let you correct for the alcohol content, which affects the index of refraction.
 

jmf143

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Get some distilled water and test both your hydrometer and your refractometer. Your refractometer may need adjusting. Also, some refractometers need to have their results adjusted based on a comparable hydrometer result. For example, after adjusting your refractometer you test a wort sample with your hydrometer and your refractometer. If, your temperature adjusted, hydrometer reads 1.040 and your refractometer reads 1.044 your refractometer has and adjusted wort value of 0.004. This would mean that all of your readings, from your refractometer, would require an additional 0.004 being added.
Shouldn't he be subtracting .004 since the refractometer is reading "high" by that amount compared to the hydro?
 

ArcaneXor

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Readings can be thrown off a lot because the sample size is so small. You need to make sure the wort is well-mixed (stir it just before drawing the sample), that there is no break material or hop matter on the refractometer slide, and that there are no air bubbles. I always take three samples and average the readings, and usually end up within 2 or so SG points of my hydro reading.

At one point I thought my refractometer was a waste of money. Now that I know how to sample and use Sean Terril's correction formulas for FG calculations (vs. the rather terrible ones from BeerSmith, MoreBeer, etc) , I am very happy with it.
 

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You may need to adjust the conversion for that particular refractometer. I use a phone app called brewzor, usually, and you can tweak the correction factor.
 

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I recently bought a refractometer and noticed similar discrepancies when checking samples during fermentation. From what I've found so far it seems that the alcohol present after fermentation begins changes the refractive index and skews the reading. There are correction calculations that take into account OG I assume to infer the alcohol content and correct for it.

I'm getting ready to go all grain, and so I think I will keep the refractometer to monitor gravity when mashing but I'm not sure its worth the hassle of the conversions for monitoring the gravity during fermentation.
 

ajdelange

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From what I've found so far it seems that the alcohol present after fermentation begins changes the refractive index and skews the reading. There are correction calculations that take into account OG I assume to infer the alcohol content and correct for it.
Ethanol has a higher refractive index, 1.361, than water 1.330, (589.3nm) so adding alcohol to pure water increases its refractive index. Adding sugar to water also increases its refractive index. So as beer ferments the reduction in extract (sugar) lowers the refractive index but the increase in ethanol raises it thus partially offsetting the decrease.

There are formulas that try to correct for this and they tend to work well for families of beers but not very well when taken over the universe of beer types.
 
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Mpavlik22

Mpavlik22

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spook said:
I recently bought a refractometer and noticed similar discrepancies when checking samples during fermentation. From what I've found so far it seems that the alcohol present after fermentation begins changes the refractive index and skews the reading. There are correction calculations that take into account OG I assume to infer the alcohol content and correct for it.

I'm getting ready to go all grain, and so I think I will keep the refractometer to monitor gravity when mashing but I'm not sure its worth the hassle of the conversions for monitoring the gravity during fermentation.
The discrepancies I experienced are pre boil & post boil as explained in my first post. They are not from during fermentation as already stated alcohol throws the refractometers reading off.
 

ajf

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Download a copy of Promash
Run the program, and click on Options/System Settings/Instrument Calibration
Then read the description of the Brix Correction Factor, and click on help.
The help screen gives you an excellent description of what the correction factor is, and how to calculate it.

For pre-fermentation readings, I have found that my refractometer (using the correction factor) is very accurate for my pale ales, but it may need a different correction factor for other types of beers. I'm just too lazy to find out.

-a.
 

jordinio

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Whats up all?

I just got done brewing a Pale Ale (all grain). I just got a refractometer and decided to try it out. I still used my hydrometer to compare. I got completely different reading pre-boil & post-boil.

Before you ask, i did calibrate the refractometer with distilled water. Also it is a ATC (auto temp correction) unit. regardless since i take my hydro reading at 60 deg F, I cooled to 60 deg and took my hydro reading and refrac reading at the same time and temp.

Anyways my readings:
Pre Boil:
Target - 1.042
Hydrometer - 1.041
Refractometer - 1.033

Post Boil:
Target - 1.054
Hydrometer - 1.051
Refractometer - 1.043

So can anyone explain why my readings are so different between the hydrometer and refractometer?

Thanks

a refractometer reads pre fermented wort accurately. The refraction of light on the fermented wort is distorted once there is alcohol involved. northern brewers refractometer calculator works awesome for converting it.
 

jhurt

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Your readings could also be lower if there is any sort of water or sanitizer in your pipette when drawing a sample. This would cause the sample to be diluted and read lower than it should be.
 

RoadKing

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Does your refractometer have both Brix and SG ? I remember reading that the SG scale is not accurate. Try just the Brix and use a spread sheet of some
sort for conversion. I use the spread sheet from moorebeer and it always agrees with my Hydrometer when I check it.
 

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