refractometer sensitive to amount of liquid?

[wactuary]

In the past, I've heard people ask about getting inconsistent results with their refractometers. Advice tended to be about calibration, temperature adjustment, sugar striation in the kettle, or even evaporation of the droplet of wort.

This weekend, I took a measurement and the result was implying over 100% efficiency. Knowing that was not the case, I started checking things. What I found was that the amount of liquid on the glass significantly altered the reading of the gauge. If there was a very thin film (from half a drop or less on the glass, I could see 11.5 brix. A heavy drop brought the level down to about 8.5 brix, which was the correct reading. Varying the quantity could predictably change the reading until enough liquid to fully cover the glass and get squeezed out by the plate converged to the right reading.

Note this was not from evaporation or striation in the sample, nor particulate in the sample. I could begin with half a drop and add wort to converge to the right result, or start with 3 drops to saturate the plate, then remove wort and see the measurement rise.

This only impacted wort samples. Pure water measured 0 no matter the quantity on the glass.

I have never seen anything mention this sensitivity to the amount of liquid, and a quick google didn't turn this up either. I thought others might find this useful. I'd be interested to know if others observed the same thing. My refractometer is one of the ATC type.

 

[Brandonovich]

My understanding is that once the sample is on the lens, you are supposed to put the cover down so that it is sandwiched between the two pieces and flattened out.

 

[wactuary]

And as long as there is enough liquid (about 2-3 full drops) that liquid is squeezed out, then the reading is accurate. But with only 1 drop, enough that the sample flattens, but doesn't "fill" the lens area, the sample thins too much on the plate, impacting the refraction.

It makes sense to me intuitively, but I'm surprised I never saw a warning about this or other people comment on this when discussing inconsistent refractometer readings in past threads.

 

[Brandonovich]

The instructions in mine also said to make sure there were no air bubbles or that could throw the reading off. I wonder if it makes a difference how tightly you squeeze the glass down.

 

[wildwest450]

Reason #35 that refractometers stink.

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[Bobby_M]

That's like saying that cars stink because you're able to press your foot down on the accelerator until the car crashes into a brick wall. Of course, disclaimer... I sell them so my opinion of refractometers may be biased. Then again, as a homebrewer, I use them.

 

[wildwest450]

Perfect analogy from the guy with one attached to his face.


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[Brandonovich]

They stink unless you want to take gravity readings from your first runnings, first wort, during the boil, and just before pitching without wasting a half gallon of beer. There's no better way to keep a running tally of what is going on with your beer and adjust your processes.

 

[Bobby_M]

I disclaimed bias but seriously, it's the tool of choice for any all grain brewer that wants to record several data points throughout the process or to know when to stop sparging. They can be finicky and require calibration from time to time, but until a supply of hydrometers that are calibrated to 170F become available, we're pretty much stuck with these.

 

[bigbeergeek]

They stink unless you want to take gravity readings from your first runnings, first wort, during the boil, and just before pitching without wasting a half gallon of beer. There's no better way to keep a running tally of what is going on with your beer and adjust your processes.

Four wort samples in my hydrometer column (the tube in which it was originally packaged) would work out to one cup of wort, not a half gallon -- plus I'd dump three out of the four samples back into the batch anyway. I'm OK with losing 1/4 cup of wort to be certain that my gravity readings are spot on throughout a brew day. To each their own.

 

[rack04]

I disclaimed bias but seriously, it's the tool of choice for any all grain brewer that wants to record several data points throughout the process or to know when to stop sparging. They can be finicky and require calibration from time to time, but until a supply of hydrometers that are calibrated to 170F become available, we're pretty much stuck with these.

Austin Homebrew has one that is calibrated to 155 degrees F with a +.005 correction for 170 degree F. Note, I haven't used it and can't verify it's accuracy but it's an option.

http://www.austinhomebrew.com/product_info.php?cPath=178_67_64&products_id=12972

The problem that I have had with my hydrometer is the how varied the results are. For example, I pull a 3 drop sample from a sample and get a reading of 12 and pull another 3 drop sample from the same sample and get a reading of 11. Which is a 0.004 difference.

 

[bigbeergeek]

I disclaimed bias but seriously, it's the tool of choice for any all grain brewer that wants to record several data points throughout the process or to know when to stop sparging. They can be finicky and require calibration from time to time, but until a supply of hydrometers that are calibrated to 170F become available, we're pretty much stuck with these.

I just stir my tiny, 1/4 cup of hot wort with a frozen water bottle for a minute or less. Drops it to 70 degrees just fine. I own a refrac and never use it anymore -- couldn't depend on it when I needed to.

 

[samc]

I had trouble coming up with 35 reasons why I don't like mine, so I will add your findings to my list.

Hydro sample prior to any point prior to final boil gets cooled, tested, tossed back in or sampled.

I use both but still prefer the Hydro for it's consistent reads. Now if someone was to buy me a digital model I might be convinced of refractometer goodness.

 

[reezle]

I had trouble coming up with 35 reasons why I don't like mine, so I will add your findings to my list.

Hydro sample prior to any point prior to final boil gets cooled, tested, tossed back in or sampled.

I use both but still prefer the Hydro for it's consistent reads. Now if someone was to buy me a digital model I might be convinced of refractometer goodness.

I picked up a digital model from Hanna Instruments (about $120?).
Works very well for me. Only issue like stated above to to make sure to not have air bubbles in the samples. I do get a few strange readings here and there (usually from bubbles or temp), but when it's only a couple of drops to get a sample, I take 3 or 4 samples, and ignore the odd one out.
It's very nice to know pre-boil that I've hit my target, or that I should sparge a bit more and then boil a bit longer. Also kind of fun to graph out the gravity over weeks/months on a long project to see that the yeast is still happy, or perhaps needs some help.
Sorry I don't have a spare one to send your way, but I could send you my old hydrometer that gathers dust in the garage...

 

[iaefebs]

I just checked my refractometer on a sample that has achieved FG. I tried to use less than a drop and took a reading. I made several more checks at 2 drops, 3, 4, 5 drops. I didn't see much of a change at all. I usually take a quick sample from the BK after I've finished my sparge to make sure I'm in the ball park. I can take such a small sample and have it cooled down quickly. I also fill my hydrometer at the same time and allow it to cool down. The hydrometer sample is usually cooled down enough by the time I'm done with the boil.... which is too late to make any adjustments but it verifys what my refractometer reading was. I also can remove the airlock while fermenting and stick my pipette in the hole and draw a sample to check readings. If I wanted to check with my hydrometer I need to remove the lid and draw a sample. I don't understand what 35 reasons to not like a refractometer are. I highly recommend one.

 

[wildwest450]

How about the simple fact their not accurate? Mine calibrated perfectly at 68f with distilled water and never came within 2 points anytime after that. Add alcohol to the mix and it get's worse, plus you need a silly chart. I used mine once then sold it.

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[iaefebs]

How about the simple fact their not accurate? Mine calibrated perfectly at 68f with distilled water and never came within 2 points anytime after that. Add alcohol to the mix and it get's worse, plus you need a silly chart. I used mine once then sold it.

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Simple fact? I guess you gave it your one best shot then. When you say 2 points do you mean .2 or 2 ? I've used mine for 6 years now and have done many side by side comparisons. I find them very accurate. Need a chart? I guess the first time you used one a chart would help... then you see the pattern.... multiply by 4 to convert to gravity or you just go by experience and keep things in Brix.

 

[emjay]

Digital refractometers take the cake, if you don't mind the price.

 

[Catt22]

Simple fact? I guess you gave it your one best shot then. When you say 2 points do you mean .2 or 2 ? I've used mine for 6 years now and have done many side by side comparisons. I find them very accurate. Need a chart? I guess the first time you used one a chart would help... then you see the pattern.... multiply by 4 to convert to gravity or you just go by experience and keep things in Brix.

+1 Exactly! I find the refractometer to be an essential tool, accurate and reliable. I've never had to calibrate mine and it always checks out OK. I take a hydrometer sample at the end of the boil to confirm and I always have very close agreement. I think that many of the reported problems are due to operator error and not a problem with the instrument itself.

 

[shortyjacobs]

There's no way thickness of sample changes the reading. The reason for the glass plate is to thin out the sample enough that enough light can get through so that you can easily discern the line between the light and dark regions, (which are really bright regions and regions in shadow). Refractometers, at least the handheld version, work on the principle of TIR, or Total Internal Reflection. This is ONLY a function of the refractive indices of the two materials at the interface, in this case the RI of the wort and the RI of the prism plate, (the glass, or is it quartz?, part). All that matters is the interface between prism and wort, not how much prism or wort is on either side of that interface.

And yeah, I love my refractometer too. But love em or hate em, that's how they work.

As for multiple readings - if you are taking HOT readings, that bimetallic strip that gives the refractometer ATC powers can only compensate so much, and can only compensate if it's at the same temp as the prism. If you keep taking samples with 212 wort in rapid succession, you can heat up the body, (or if you rinse it in very hot water, then take another reading), bumping the body temperature outside of the range the ATC can correct for. Or you can heat up the prism without getting enough thermal conductivity to the strip, so it won't be able to correct. We only get consistent readings with hot wort because the hot wort cools very quickly, not heating the prism up much. If we keep dumping hot wort on the prism, it will heat up the prism, and you'll get a funky reading....we want both the prism and the wort to be at the same temp as the bimetallic strip controlling the reticule, and we want that temperature to be within the correction range of that strip, or else yes, it won't read right. Best bet for this is rinsing the prism with room temp water after taking a reading to "reset" it to where the bimetallic strip has adjusted for.

It's a tool people. Like any other tool, if you use it wrong, or don't understand WHY it's giving you a funky response, you can't trust it.

 

[RoadKing]

How about the simple fact their not accurate? Mine calibrated perfectly at 68f with distilled water and never came within 2 points anytime after that. Add alcohol to the mix and it get's worse, plus you need a silly chart. I used mine once then sold it.

_

Mine allways checks out right on the money, Maybe you hydrometer was off?
(Just a thought)

 

[wildwest450]

Mine allways checks out right on the money, Maybe you hydrometer was off?
(Just a thought)

We'll for $54, it needs to be right on, it calibrated fine. I believe most people will admit theirs is off a point or two.

+ I take a hydrometer sample at the end of the boil to confirm and I always have very close agreement.

That say's it all. If you have a refractometer you still need a hydrometer.


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[emjay]

One thing I've never heard mentioned, but seems like an interesting concept is the possibility of using both a refractometer and hydrometer and using the two figures to mathematically determine what the OG of a beer was. If you think about the fact that to figure out the FG using a refractometer, the presence of alcohol requires you to know the OG in order to calculate it, I would imagine if you instead have the FG variable, with the OG being unknown, the equation can probably be manipulated to figure it out.

I realize it's of very limited value, but I've actually seen a few instances where it could have helped. Plus, even just the concept alone I find interesting.

 

[rcrabb22]

A common theme among the refractometer detractors is the assumption their hydrometers are 100% accurate.

I wouldn't bet my next paycheck on either my hydrometer or refractometer accuracy.

If there is 1 clock in the room you know what time it is, If there are 2 clocks you don't. Pick a clock.........

 

[emjay]

True, I've compared multiple hydrometers and they're never equal. It's a piece of paper in a tube for cryin' out loud, and I even had it somehow slip quite a bit in one of mine.

 

[mcflyfisher]

One thing I've never heard mentioned, but seems like an interesting concept is the possibility of using both a refractometer and hydrometer and using the two figures to mathematically determine what the OG of a beer was. If you think about the fact that to figure out the FG using a refractometer, the presence of alcohol requires you to know the OG in order to calculate it, I would imagine if you instead have the FG variable, with the OG being unknown, the equation can probably be manipulated to figure it out.

I realize it's of very limited value, but I've actually seen a few instances where it could have helped. Plus, even just the concept alone I find interesting.

I actually do this quite often. Promash, and a few other software packages allow you to input the refractometer and hydrometer readings in a finished beer. It will then give you the OG, ABV, and such. It is very dependent upon the numbers you input, so an accurate reading on both instruments is essential.
As for one vs. the other. The hydrometer is hard to beat for certain applications and the refractometer is the beast for other applications. They are a lot more useful when used together.

 

[Catt22]

You can successfully brew beer without a refractometer, a hygrometer or even a thermometer. I prefer to use all three and some other paraphernalia as well. I like tools...turtles too, of course. I once heard about a sloppy carpenter who would always blame his tools for any mistakes.

 

[emjay]

Yeah, I don't know anybody who uses a hygrometer to brew.

 

[shortyjacobs]

Yeah, I don't know anybody who uses a hygrometer to brew.

I'm pretty sure he meant hydrometer, but I also use hygrometers in my fridge and fermentation chamber...

 

[Starderup]

I have compared both my hydrometer and refractometer, and they are consistently giving me the same readings. The refractometer is so much easier, I hardly use the hydrometer anymore.

 

[emjay]

I'm pretty sure he meant hydrometer, but I also use hygrometers in my fridge and fermentation chamber...

I know what he meant...