Refractometer Reading Differs

[greggo]

Hi. Had a brew day yesterday and tried out my new 30 brix refractometer. Took a reading at flame out and it gives me 1.047. To compare with my hydrometer i cooled a sample to 20 deg C and it gave a reading of 1.050. Temp corrected would be 1.051. Did another reading of same sample with refracto and still read 1.047 My hydrometer reads 1.000 with tap water at 16 deg and i zeroed my refractometer with same water. I know the instructions say to use RO water but i didn't have any. I don't think this should make any difference. Is there something i have done wrong here. Help appreciated.

Cheers greg

 

[bcp]

Hi. Had a brew day yesterday and tried out my new 30 brix refractometer. Took a reading at flame out and it gives me 1.047. To compare with my hydrometer i cooled a sample to 20 deg C and it gave a reading of 1.050. Temp corrected would be 1.051. Did another reading of same sample with refracto and still read 1.047 My hydrometer reads 1.000 with tap water at 16 deg and i zeroed my refractometer with same water. I know the instructions say to use RO water but i didn't have any. I don't think this should make any difference. Is there something i have done wrong here. Help appreciated.

Cheers greg

Try your refractometer with water and see what you get. Might need calibrating.

 

[srcossens]

I had the same thing happen to me the other week. The refractometer was set to 0 on water, but when I checked it with a wort and the hydrometer it was 0.03 out. I have a properly calibrated hydrometer, so I checked it with that on a 1.060 wort. The small hydrometer was correct and so I adjusted my refractometer to 1.060. I'm not using the refractometer as the true measurement, so I am happy to know that between 1.030 to 1.090 that it is going to be atleast +/-0.02. I use the refractometer during the mash and boil to check sugar points and then the hydrometer afterwards to check the gravity... If I can be bothered. The refractometer is also now accurate, compared to the hydrometer, when measuring fermented wort with the adjustment calculator in beersmith.

So I know everyone says to adjust it using water, but how often do you measure gravity of a 1.001 wort?

 

[Nick JD]

Are you reading the bottom of the meniscus?

 

[ashley_leask]

I've found the same thing, both hydro and refractometer calibrate correctly with water. I've tried distilled as well as tap water and found no difference there. There's just always a difference between the two readings which gets bigger as the gravity increases.

Don't know if it's just a quality issue (ebay refractometer) but I just use the calibration feature in Beersmith to correct the refractometer readings and I've found that to be accurate when I tested side by side.

Edit: this is using the SG reading on the refractometer, I ignore that now and calibrate in BS from the Brix reading.

 

[greggo]

Thanks guys. Have checked it with water and pretty sure i an reading it correct. I could do as you did scott and callibrate my refracto to read the same as my hydrometer but it really is not the answer to my problem. which one is correct?. 1 liter of water and 100 gramms of DME is surposed to give 1.040 but is this completely accurate. Plan B would be to compare with other refracto/hydro's
cheers greg

 

[greggo]

Thanks ash. It is an ebay purchase. Really don't know about quality

 

[NicksExa_N13]

i think what ash was saying is to fine calibrate your refractometer using water as your control find the % + or minus possibly then apply the same % to your mash reading then that should give you the correct reading. That would be my simple fix. I am still a newbie to brewing hower having been reading these forums for years and now trying to become more active on the forum so forgive me if i use the wrong terms

 

[glenwal]

As long as its consistant, does it really matter?

 

[NicksExa_N13]

Yeah Glen if if was a constant error it wouldn't matter but as per Another Ash suggests above "There's just always a difference between the two readings which gets bigger as the gravity increases." It sounds like the error is more so a exponential error meaning the higher the sg the greater the amount of error which wouldnt cancel itself out the same way as a constant error by taking a starting and final sg as the magnitude of the error would differ in both these cases. In saying this i have never checked the accuracy of my refractometer which i shall do in the near future (I have a cheapo ebay one too)

 

[tipsy]

I've found the same thing, both hydro and refractometer calibrate correctly with water. I've tried distilled as well as tap water and found no difference there. There's just always a difference between the two readings which gets bigger as the gravity increases.

This is why my refractometer sits on the shelf and I have gone back to the old hydrometer.

 

[Fourstar]

Are the samples you're reading from homogeneous wort? E.g. you haven't used wort at flameout with a lid on it dropping 0 brix condensed evaporation onto the wort post whirlpool and taking a pipette reading from the distillate?

I always take my flame out reading just before I knock-out the flame. Any other reading i take (before drain to cube or empty kettle/trub) always gives me a different number.

From experience, the number at knock-out is always the same as my cube reading once cool birx v/s brix or brix/sg hydro sample. Identical (well at least within 1.sg point.)

 

[tipsy]

My readings were all o.g. after I'd had dumped the cube into the feremter

 

[Fourstar]

My readings were all o.g. after I'd had dumped the cube into the feremter

Now that, is strange. They are always identical for me, I take my OG reading from fermenter and as a sanity check and also check the refrac reading from the hydro vial at the same time and they are the same (within 1 sg point.). mind you i have a standard 30 brix refrac and i convert the reading in brix to SG with beersmith to compare the results. hits the nail on the head every time.

I usually find the refrac to be the culprit for inaccurate readings. e.g. when 1/2 way through fermentation and CO2 disrupting the reading. Final gravity's always match up as well (taking into account the correction calculation).

Interested to find out how the OP'er took their 'flame out' reading.

 

[stux]

Often the SG scale on a refractometer is not correct. They use a very basic conversion, when the actual conversion is much trickier.

If you use the brix reading and beersmith's (or similar's) refractometer tool, do you get a good reading then?

One of the reasons I ordered a refractometer without the SG scale

 

[Fourstar]

One of the reasons I ordered a refractometer without the SG scale

Same boat. I got a Refrac to read Brix/Plato, not SG.

 

[SJW]

all this is normal. Mark MHB explained it to be once.
A refractometer measures sugar in water, but our wort has high amounts of maltose in it that "refracts" light at a slightly different angle. There is a correction calculation somewhere for this.
To fix this I either add 3 points to the water only reading or do a hyrdo reading of a 1050 wort and set the refractometer to the same. Then double check with water and it always reads about 3 points higher.

Steve

 

[seamad]

Learn something every day. Thought my refract was crook, i found it was 3 pts out so adjusted it and it matches the hydro. Have used it like this for over a year, good to know why it was out.
Cheers
Sean

 

[sim]

all this is normal. Mark MHB explained it to be once.
A refractometer measures sugar in water, but our wort has high amounts of maltose in it that "refracts" light at a slightly different angle. There is a correction calculation somewhere for this.
To fix this I either add 3 points to the water only reading or do a hyrdo reading of a 1050 wort and set the refractometer to the same. Then double check with water and it always reads about 3 points higher.

Steve

This slight (sometimes 3 points now i think about it) inacuracy of my refract vs hydro readings has been doing my head in since i started using one (always calibrated with distilled water and still encountered discrepancies). Seemed to get worse at higher gravities too, which makes sense now. This really should be standard knowledge. Thankyou!

 

[greggo]

Thanks guys. Steve, thats exactly the answer i was after. Thanks heaps.
cheers greg