Refractometer Question

[stever1000]

I have an ATC refractometer, but I usually wait a few minutes to drop the sample on the face so its about room temperature. I have noticed if I check the sample right away its, for example, 11.8 brix, and if I don't remove the sample from the face, I will check back 10-15mins later before I do my next sample and the brix has increased to 12/12.1.

The door on the refract is closed on the face so the sample isn't exposed and evaporating...which would be the most accurate reading? I've noticed this a few times.

 

[ba-brewer]

I have seen the increase in gravity for sample left on the refract too, I go with the first measurement. In general I believe lower numbers more then higher.

What you can do is save a little extra wort and allow to cool or sit and remeasure the sample 10-15min later and see if you get the same results.

When I first got a refractometer I did some testing with various wort strengths comparing the results against a hydrometer reading. I found I got closer correlation when I flooded the sample area vs just a few drops. More liquid normally lowers the reading for me.

 

[dmtaylor]

I've noticed this phenomenon myself and tested it a bit. I discovered in comparing results with a hydrometer that the refractometer readings from the first few seconds are always more accurate than the later readings. You won't get accurate results if you leave the droplets on the glass for a while. Regardless of what you might think, evaporation IS in fact happening over time. So you have to read it right away. Otherwise it's wrong.

 

[stever1000]

Glad I'm not going crazy. I will take the immediate reading as the true reading, as suggested.

Thanks!

 

[Smellyglove]

If I do a reading by just hosing the glass of the refractometer while mashing with the return from my herms hose, I have to wait because the refractometer is equally warm and the reading will go up by 3 points when it cools. Cooled hydrometer samples shows that this is correct when I do it like that. My refractometer has ATC.

 

[RM-MN]

I have an ATC refractometer, but I usually wait a few minutes to drop the sample on the face so its about room temperature. I have noticed if I check the sample right away its, for example, 11.8 brix, and if I don't remove the sample from the face, I will check back 10-15mins later before I do my next sample and the brix has increased to 12/12.1.

The door on the refract is closed on the face so the sample isn't exposed and evaporating...which would be the most accurate reading? I've noticed this a few times.

I thing you are taking a sample before conversion is complete and the wort on your refractometer still has active enzymes that are completing conversion on the plate of your refractometer.

 

[stever1000]

I thing you are taking a sample before conversion is complete and the wort on your refractometer still has active enzymes that are completing conversion on the plate of your refractometer.

But would it be changing that much? This is well into a 90min mash so I hope this isn't the case

 

[kh54s10]

I have always thought that the hot sample is outside the calibration of the refractometer so I wait a minute or so and use that number. (I really just let is stabilize) But the biggest change I have seen is .002

 

[pepindavid]

I think this is a case of evaporation. A few drops of a boiling liquid on a the refractometer will evaporate quickly (less water = higher density). I guess the idea would be to take a small sample, let it cool somewhat, and then take the measurement?

 

[stever1000]

I think this is a case of evaporation. A few drops of a boiling liquid on a the refractometer will evaporate quickly (less water = higher density). I guess the idea would be to take a small sample, let it cool somewhat, and then take the measurement?

I use a 5ml pipette to remove 3 samples from my kettle, then I drop that in a shot glass to get 15ml total, stir and wait. Then after a few minutes I use a clean pipette to drop a sample onto my refract and wait min. 30seconds to see the result (according to my instructions it says to wait a min. 30 seconds)

I could see evaporation occurring from the shot glass. But if the sample is between the face and the cover, I can't see evaporation occurring so quickly within a few mins to change the brix value

 

[kh54s10]

IMO, the small amount on the refractometer cools to the proper temperature quite quickly. I just watch for a while - maybe a minute. I see it changing a little, when it stops, that is what I take as the right number. As I said the largest change I see is usually .002. I sometimes take several readings to see that I am getting the same thing a couple of times.

If you are getting a big change in the numbers I think there is a different problem. Or you are waiting way too long and are getting the change from evaporation.

Even the few drops on the refractometer would take quite a while to evaporate. I would say 10 minutes or more to see a change from evaporation. YMMV.

 

[Conan]

Less water, specifically a thin sheet of water as on a refractometer, has a a lower thermal inertia and in this case higher ratio of surface area to volume, so evaporation has a more dramatic effect than a larger volume. I use a syringe, minus the needle, to capture and store my samples prior to reading on the refractometer. Works great, no evaporation, cools quickly.

Even with the door closed on the refractor eternal you're getting evaporation. It'd be great to test on a precise balance. Kyle