Author Topic: weird disparity readings between refractometer and hydrometer?  (Read 10030 times)

Offline Mercs own

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weird disparity readings between refractometer and hydrometer?
« on: January 01, 2012, 06:01:40 PM »
Story so far: Kolsch - mashed at 68.5 - 70 degrees C for about an hour - recirc 40 minutes temp of grain bed went up to about 75 then one hour sparge - sparge water 78 or so. Boil one hour. Final runnings on the sparge 1013.

My gravity reading prior to ferment was 1051 (the aim was for 1053) Fermenter went in the fridge at around 18 - 19 degrees

after 7 days I racked the beer and got a hydrometer reading of 1020, my refractometer reading was 7.1 brix (1027ish) when this is corrected in beersmith 2 it says the reading corrected is 1014

My fg aim is 1014

Beer went back in the feerment fridge at around18 degrees for another 5 days. I took a reading today and got 1021 on my hydrometer and 7.1 brix on the refractometer so there has been no change since I racked the beer.

I have always used my hydrometer so I am perplexed as to why the beer is still sitting on 1020 unless the mash was too high etc btw I used two packs of liquid kolsch yeast.

I am also perplexed as to why there is a .006 diference in the readings between the corrected refrac and the hydro?? I have calibrated both - the hydro is calibrated for 20 degrees c

Any help would be appreciated

Offline justggw

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Re: weird disparity readings between refractometer and hydrometer?
« Reply #1 on: January 05, 2012, 06:50:50 PM »
I have the same problem. OG looks good but the FG seems to be way off.
My taste tells me that the refractometer is way off.

Offline rdewsbury

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Re: weird disparity readings between refractometer and hydrometer?
« Reply #2 on: January 05, 2012, 08:07:39 PM »
Let's look at the figures here.  The Refractometer(Brix) to specific gravity calculation is a standard that is published all over the place.  I just googled around to find one of the many calculators on the web and came upon this one. http://onebeer.net/refractometer.shtml

First, if you want to use a Refractometer as your standard tool, vs. A hydrometer, get used to taking the OG with it to.  Without that, you are introducing the error from your hydrometer calibration in 20C distiller water to the error from your reading on the optics of the Refractometer.

Your OG of 1.051 is probably around 12.4 Brix. 12.5 works too, but is farther over than 12.4 is under.  You need this original value to get the final gravity. Given the original 12.4 Brix and a final 7.1 Brix yields the 1.014 FG that you calculated.

I may be going off on the wrong tangent here, but the beer smith Value is spot on too, this being a simple calculation.  So the problem is calibration.

- did you calibrate with distilled water or tap water?  Both for hyrdo and Refractometer.

- did you read the devices at the right way ?  Look at the hydro instructions to see where on the meniscus you were looking. 

- did you temperature compensate for the hydro ? The Refractometer may be temperature compensating, but your need to put the wort sample on there and wait a while before taking the reading to let it compensate.

- lastly, given that the hydro is quoted at 1 part per thousand roughly, and the Refractometer is onle read at 1 per hundred, you can see that 0.006 is really trivial given all the other areas where error can be induced.

Don't get me wrong, a Refractometer is a great tool to have in the brew kit, but it is not the most accurate if you are aiming for a target gravity and want to be spot on.  Your need to get used to reading between the lines (literally on the graticule) to get that kind of accuracy.

It is a great device for checking to see whether the gravity is changing and fermentation is over, but you may want to get a bottling hydrometer with it's expanded scale (Williams brewing has one, but calibrate it and be careful of it's fragility) to get the FG, and don't forget to compensate for the temperature.


Offline Wingeezer

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Re: weird disparity readings between refractometer and hydrometer?
« Reply #3 on: January 12, 2012, 12:02:31 PM »

It is a great device for checking to see whether the gravity is changing and fermentation is over,


I don't haver a refractometer yet, but have one on order.

I was wondering if the refractometer was a good tool to take multiple samples over a few days to conform no change and thus completion of fermentation.

But then I got to wondering if this would work.    What I mean is that if the wort is still fermenting and converting sugar to alcohol,  is it possible that the combination of decreasing sugar together with increasing alcohol might result in the net effect of no change in
refractometer reading from day to day giving the impression thet fermentaion is complete - but it is not?

Just wondering!   Any thoughts on that?


Brian







Offline rdewsbury

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Re: weird disparity readings between refractometer and hydrometer?
« Reply #4 on: January 12, 2012, 08:56:36 PM »
The main advantage that I find is the amount of wort needed per sample.  To fill a test jar with enoung liquid ton float a hydrometer in, means you may lose a bottle or two in the final run - depending upon how patient you are.  A Refractometer only uses a small amount of sample 1/2 teaspoon will do the job.

The disadvantage is accuracy.  Most refractometers are temperature compensated, but at some point they all need to be calibrated well.  The visual line is not open to interpretation, so much as fuzzy enough to be plus/minus a secgment or two.

That said, you can still look for the same thing on a once-per-day Basis and see if anything changes.  In that case, the absolute accuracy is not as important as whether there is a change from last time.

For those that ferment in a bucket rather than a Carboy, the solon is even simpler - just drop in the hydro and you waste next to nothing, just theg film on the hydrometer as it dries off.

Whichever you use, keep and use a spray bottle of iodophors solution in you fridge to make sure you are not messing up the wort when you take a smaple.

For the less accuracy obsessed, you can actually leave the hydrometer I  lace and watch it.  Austin home brew sells a set of "brew balls" which make your fermented look like a da Vinci thermometer with 5 balls floating or sinking with the gravity.

Bottom line is that you get a better reading with a hydr9, but spoil less worry per sample with a Refractometer.

When I got the Refractometer, it was more to be able to chech my efficiency with cooling wort than it was to check fermentation.


R

Offline Myk

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Re: weird disparity readings between refractometer and hydrometer?
« Reply #5 on: January 13, 2012, 11:37:50 AM »
A refractometer would work to check for completion of fermentation if you actually do such a thing. You would have to correct it for the presence of alcohol, which means you would need an original gravity.

For those having a problem with fuzzy lines because of suspended particulates turn the refractometer over. The particulates settle on the cap and your line gets clearer.
This is a not so accurate way to test for starch conversion in fruits and vegetables (not so accurate because as I found seeing if it would work for beer it's not just starch that makes the line fuzzy).

IMO a refractometer is a needed luxury for all grain. It's not the loss of sample size that makes it so, it's the small amount of wort doesn't need to be chilled to 60° to get an accurate reading. Even for a non-ATC model the 3 drops you need will be cooled in seconds.

 

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