Refractometer reading is way off compared to hydrometer. What am I missing?

[Byaka]

So I just received my new refractometer. The reason I decided to purchase one was to eliminate the need to waste my precious brew just so I can measure SG - I like the idea of only using a couple of drops.

Today was the day I was transferring my cider into the secondary and it was a perfect opportunity to play with the new toy. First, I calibrated it with distilled water and made sure it reads SG of 1.000 (0% Brix). Then I measured SG with both the hydrometer and the new refractometer. The cider was at room temperature (~70F). The hydrometer read a little lower than 1.000 (that's what I expected to see) but the refractometer showed SG to be around 1.015. A difference of 0.015!!!

Next I decided to try it on my IPA that has been sitting in the secondary for about a week. The hydrometer showed a believable 1.012, whereas the refractometer's SG was around 1.035. A difference of 0.023!!!

Any insight, please... Am I doing something wrong? Is it possible that it is the beverage temperature that affects the readings this much? The refractometer does have the ATC (automatic temperature compensation)... Or is it that the refractometer is not working right?

 

[waldoar15]

Once there is alcohol you have to run it through a conversion.

Like this one.
https://www.northernbrewer.com/learn/resources/refractometer-calculator/

 

[Silver_Is_Money]

Refractometers are calibrated to read the refractive index of sugar in water (which is then correlated via a scale to specific gravity). They are not scaled to properly read the refractive index of alcohol in water. They are fine for OG readings but not for FG readings.

There are calculators which have worked hard to overcome this deficiency, and to give decently accurate readings for FG. The best one is found at: http://seanterrill.com/2012/01/06/refractometer-calculator/

I have found that the output of this calculator comes reliably close to my hydrometer for FG.

 

[ancientmariner52]

I use my refractometer to check for fermentation completion, knowing full well that the reading is off. I do this because the sample size is very small. Once the indication stops changing, I take a hydrometer sample to measure the actual FG.

 

[PADave]

I quit using my refractometer shortly after I got it, due to no repeat-ability. I'd take a reading, then take another reading of the same wort within minutes and get totally different readings.

After fermentation, the alcohol requires a conversion like posted above.

 

[ancientmariner52]

Odd. It should repeat, even if the number is not correct. Conversion chart won't mean much if the reading doesn't repeat.

In the plant where I still get called in from time to time, we use a brix refractometer to check concentration of water-mixed coolant. The coolant rep provided the refractometer. We all know it is calibrated for sugar, but we also know what readings give good coolant performance. The units don't matter as long as we get results. I suppose if we needed to know actual concentration we'd use a hydrometer. That's why I measure my beer the way I do.

 

[Byaka]

Thank you! It all makes sense now.

 

[RM-MN]

I quit using my refractometer shortly after I got it, due to no repeat-ability. I'd take a reading, then take another reading of the same wort within minutes and get totally different readings.

After fermentation, the alcohol requires a conversion like posted above.

I use my refractometer only before fermentation. When the wort is cooled and ready to pitch yeast the refractometer matches the hydrometer reading nearly exactly. You should not be getting different readings with two samples. The procedure I use is to take a sample and read it immediately, then rinse and dry the refractometer stage before taking another sample so there is no partially evaporated wort on the stage to skew readings. If you are following these procedures and still getting different readings your refractometer may be defective.

 

[Roland_deschain]

I don’t trust my refractometer. I have calibrated it with distilled water and it holds its zeroed setting well, but my measurement on a stout the other day was 1.074 versus my 60degree calibrated hydrometer reading of 1.092. I don’t consider my hydrometer samples to be unacceptable losses from the batch.

 

[Miraculix]

Refractometers are calibrated to read the refractive index of sugar in water (which is then correlated via a scale to specific gravity). They are not scaled to properly read the refractive index of alcohol in water. They are fine for OG readings but not for FG readings.

There are calculators which have worked hard to overcome this deficiency, and to give decently accurate readings for FG. The best one is found at: http://seanterrill.com/2012/01/06/refractometer-calculator/

I have found that the output of this calculator comes reliably close to my hydrometer for FG.

Thx, just what I needed!

 

[PADave]

I don’t trust my refractometer. I have calibrated it with distilled water and it holds its zeroed setting well, but my measurement on a stout the other day was 1.074 versus my 60degree calibrated hydrometer reading of 1.092. I don’t consider my hydrometer samples to be unacceptable losses from the batch.

Same here, I just don't trust the thing. IMO, hydrometer is much more accurate.

 

[Mothman]

I've had a refractometer for my last few brews, and I still find myself confirming it's readings with my hydrometer. Usually they are close, but some readings are off, and I've not yet figured out why...

I've wondered if the small sample of hot wort, for the refractometer, is undergoing rapid evaporation, changing the reading?

Or is there stratification in hot wort at all, where a small sample is not getting the same uniform result that a larger hydrometer sample would get?

 

[ancientmariner52]

Stratification is an issue, for sure. I always like to stir before taking a sample. The tiny volume of a refrac sample would greatly magnify the effect, I think. You may have found the answer, because I don't have problems with accuracy or repeatability.

 

[ancientmariner52]

Then again, the boil should keep things well stirred. Hmmm.

 

[portguy]

Bought a cheap ATC refractometer from China. It is spot on on every reading i make. And using a calculator it's still very accurate when reading FG. I love that thing

 

[Mothman]

Then again, the boil should keep things well stirred. Hmmm.

In my last brewday (past Sunday) it was my pre-boil gravity where I seemed to have inconsistent refractometer readings.

Can there be stratification in the mash, or would convection during the mash adequately distribute the sugars?

 

[ancientmariner52]

Sure can. Convection only happens with a temp gradient. Dense (cold) fluid falls, less dense (hot) fluid rises, and there she sits. Stratified, until something stirs the system up.

I just put a BoilCoil in my bk. Imagine my suprise when, with a vigorous boil going on, the bottom of the pot was cool to the touch. Doesn't make sense to have to stir during a boil, but there it is.

So, yeah. Run cooler wort in under warmer wort, and stratification happens. Gotta stir to even out temps and concentrations.

 

[kh54s10]

My refractometer is indispensable. I find it very accurate, I take a sample, watch it for a minute and it settles. I only use it to check for stable readings after fermentation. On the rare case that I want an accurate FG, I use my hydrometer.

My problem today was thermometers. I have a Thermapen which is acting up. Two cheap turkey fryer dial probes. 2 other digital, and one glass lab thermometer. The really puzzling one was the lab thermometer which read 62 degrees ambient air. It was in the mid to high seventies today. All six read different... Between 62 for the low and 85 for the high....

 

[Mothman]

When you say you "watch it for a minute", do you mean you place the sample , close the glass, and then let it sit a minute before taking a reading?

 

[ancientmariner52]

I read the Beersmith Blog's writeup on refractometers a few minutes ago. They stressed natural light, repeatedly. Also, they point out that wort is not simply sugar solution, so brix scale is off even before fermentation. Another conversion chart! I think I'm gonna just stick my finger in the wort and give it a lick. Whoopee, middle ages here I come.

 

[PKnotlost]

Hey ancientmariner I don’t think enough brewers do that. It’s the part where the art comes in not just a science brewer. Learn what it should taste like! Keep it fun.

 

[ancientmariner52]

I agree. I taste all along the way. When I bought my first malt, my lhbs owner had me chew at bit of each. I've never stopped. I draw the line at StarSan though.

Seriously though, I like to imagine how it all worked with no thermometers, hydrometers, thisometers, thatometers. When Godisgood was the word for yeast. I wouldn't want to live then, of course. I like electricity, reliable food and drink, medicine that often works. I just like to think about.