Hydrometer-v- Refractometer

[CaptMogul]

I have gotten lazy over the years. I have only been checking the OG with the refractometer and FG with the hydrometer. Last week to my surprise when I cross checked I found a .005 difference. Yes I did check the calibration and it was right on the money. I always thought the hydrometer was the gold standard. What are your thoughts?

 

[AlexKay]

I’ve never understood the hydrometer bias. Neither hydrometer nor refractometer measure what you’re actually interested in, which is something along the lines of alcohol %, along with separate fermentable and non-fermentable sugar concentrations. So why is density better than refractive index?

 

[bracconiere]

why not really do it up, measure with three things....weight/volume, density, AND refractive index? lol


005 is pretty big a difference though...was temperature a factor?

 

[AlexKay]

Not to belabor the point, but density is only a proxy for ABV when you’re converting a maltose solution to an ethanol one. If there are other sugars or other fermentation products, the reading changes. This is why a hydrometer doesn’t tell you so much for kombucha.

 

[RufusBrewer]

Refractometers require a small test sample. I do not expect my 10 year old el cheapo refractomer to be dead nuts accurate. I use it as a delta meter. I can take a quick sample and compare it to the last sample. If it is less than the previous sample I do not call the beer finished.

I trust my hydrometer is accurate enough in an absolute value reading. If it says my beer is 1.064, then it is 1.064. When it reads 1.010, I consider it as face value.

Then again, I do not get too distracted by OG, efficiency, ABV, etc values. I accept my beer is what it is. I brew beer to drink my beer, not read numbers. If it tastes good, then it is good. When friends drink my beer, I do not tell them, "Sorry, I was shooting for 6.5% ABV, it us only 5.0%. My beer sucks."

 

[downzero]

I don't own a refractometer and have only used it to take measurements along the way in a commercial brewery. I think a lot of brewers are doing more harm than good with them and should use a hydrometer instead.

 

[Oleson M.D.]

We are at the point where the refractometer is used exclusively. It works quite well. You need to do the conversion if alcohol is present.

 

[catalanotte]

Are you using the 4% correction factor for the refractometer reading? That could explain 2-4 points. The remaining couple points could just be small differences in how you’re reading the hydrometer. I did a side by side from 1.100 down to 1.010 and with the 4% correction factor learned to trust my refractoneter over my ability to accurately read a hydrometer to +/- .002.

 

[dallasd9]

We are at the point where the refractometer is used exclusively. It works quite well. You need to do the conversion if alcohol is present.

How do you do the conversation if alcohol is present (FG I'm assuming)?

 

[catalanotte]

How do you do the conversation if alcohol is present (FG I'm assuming)?

https://www.brewersfriend.com/refractometer-calculator/

 

[balrog]

How do you do the conversation if alcohol is present (FG I'm assuming)?

This is one example. Refractometer Calculator - Brewer's Friend

 

[RufusBrewer]

Are you using the 4% correction factor for the refractometer reading? That could explain 2-4 points. The remaining couple points could just be small differences in how you’re reading the hydrometer. I did a side by side from 1.100 down to 1.010 and with the 4% correction factor learned to trust my refractoneter over my ability to accurately read a hydrometer to +/- .002.

Where I cannot get my head around my refractometer is the line is pretty fuzzy. I do not know how to identify where the line landed on the scale.

Maybe there is operator error on my part? How do others deal with this?

 

[bobtheUKbrewer2]

both are inaccurate in opposite directions but by so little ignore it - worry about flu instead

 

[balrog]

Where I cannot get my head around my refractometer is the line is pretty fuzzy. I do not know how to identify where the line landed on the scale.

Maybe there is operator error on my part? How do others deal with this?

Make up some known sugar solutions and measure them. An example here.
And every refractometer is different. I've owned two, both were about $25USD. The first died an ignominious death when it leapt from my hand into the firey bubbling maw of the brew kettle. I valiantly tried to clean and resuscitate it, but it apparently had a DNR. (Dead. Nolonger Refractometer). The second one I have to adjust for zero every single time. Basement temps, one zero point. Outdoor 80°F, another zero point. Never trust anything that can be calibrated, unless you calibrate it, kids.

 

[kartracer2]

Where I cannot get my head around my refractometer is the line is pretty fuzzy.

This. I bought a cheap refrac thinking I would save on sample volume size but the view in mine too is a wide gradient until the beer is clear. I guess I expected too much out of it.
Cheers,
Joel B.

 

[BrewnWKopperKat]

[...] the line is pretty fuzzy [...]

How do others deal with this?

When this happens for me, I take a second sample and include a couple of extra drops of wort. If that doesn't work ...

There's a tip I picked up a while back here at HomebrewTalk: turn the refractometer upside down & press on the tab.

 

[balrog]

Tiny bubbles in the wine may make you feel fine, but they fuzz the crap out of a refractometer line.
So does the powdery hop debris or anything that isn't clear water.

Cool about the pressing the tab @BrewnWKopperKat

 

[Golddiggie]

Not being able to easily read the needed color break in the manual refractometer was one of the reasons I picked up the digital one. Now it's crazy easy to get the OG numbers and be confident it's accurate. The Tilt Pro units I have don't always give the same OG number. I do let the OG sample settle for a while (during cleanup or however long needed) to make sure I can get a particle free sample. Using the two means I get solid OG numbers and 'close enough' FG numbers. IF I'm concerned about the FG number from the Tilt (within it's .002 +/- factor) I take a sample, degas it, and put it on the digital refractometer. So far, the FG numbers have been 'close enough' but I did check the early batches when I started using the Tilt Pro.

I do like how I can get a better reading for temperature and if the batch is reaching FG with the Tilt. I think I tossed the manual hydrometer years back. Honestly haven't looked for it since I don't use it. Haven't in ages.

 

[CaptMogul]

Wow, I really didnt mean stir things up like this. I always make a mess trying to collect a sample out of the BK, so I have been using refractometer. I think I am going to cross check both and if constant ill just assume the .005. Thanks for all the info, some of it is beyond me though. Ha " B " Cool, will try that

 

[Golddiggie]

I don't pull a 'hot' sample to test the OG with. Even if I pull a sample from the MT, I let it cool at least some before testing. Pretty easy since I also let it settle so I don't have floaters in it.

 

[Jeremy W]

Anyone found that their refractometer (talking about the $25 plastic variety) is less accurate with high OG wort? I did an imperial stout on the weekend and when I measured the OG after the boil I was about 12 SG points off what I was expecting (1.082 vs. 1.094). I measured with my hydrometer and sure enough I was right around 1.093. Also had a real heard time getting a defined line on the refractometer, will definitely use the tab pressing method mentioned above.

 

[Golddiggie]

Anyone found that their refractometer (talking about the $25 plastic variety) is less accurate with high OG wort? I did an imperial stout on the weekend and when I measured the OG after the boil I was about 12 SG points off what I was expecting (1.082 vs. 1.094). I measured with my hydrometer and sure enough I was right around 1.093. Also had a real heard time getting a defined line on the refractometer, will definitely use the tab pressing method mentioned above.

IMO, going cheap is a poor decision when you're looking at precision test instruments. I tested my manual and digital refractometers against each other and they were both identical on the OG readings.

IME, cheap tools (a refractometer IS a tool) are cheap for good reason.

 

[Brooothru]

The "fuzzy line" phenomena of reading a refractometer is due to a cloudy sample. Clear wort before yeast pitch, no problem. Clear beer after fermentation and settling, no problem. Murky beer during fermentation with lots of solids, problem.

Solution? Use a settled, degassed sample. That's the only accurate way to get a valid reading. Which, coincidentally, is the only way to get a valid reading from a hydrometer. Also with both devices, accuracy is dependent on calibration of the device and temperature correction of the sample. During the brew session I take a shot glass sample of wort, agitate it with a pipette and chill it in the freezer to bring down the temperature to 16C/61F and precipitate solids. Takes about 10 minutes. During fermentation I take the sample and stir vigorously for 20~30 seconds to degas the sample and raise the temperature to 16C/61F.

Clarity makes it much easier to get rid of the fuzzy reading of refractive index. And remember, you are reading refractive index of the sample, measured as brix (glucose), not specific gravity and not the primary sugar found in wort (maltose). That's why you have to factor in a wort correction factor which is commonly 1.04 (4%). From there you merely consult a chart to obtain an equivalent specific gravity value, many of which already include the common wort correction factor of 1.04.

In addition, if alcohol is present you must also account for its influence on refractive index. There are many online calculators that do the math for you, but be aware that there are two different popular algorithms used in these calculators. One gives more accurate values for lower gravity worts (<1.060) and the other for O.G. >1.060, though at the end of the day the differences aren't significant for home brew level accuracy. If that's what you need, go buy a gas spectrometry device for a couple hundred thousand $$$. Trust me. The process may sound daunting and cumbersome and requires using "numbery" stuff. But hey, I'm a guy who barely made it through calculus (more than one attempt!) and if I can do it, it ain't that hard.