Refractometer - Different readings from same sample

[roper4092]

Hey folks,

Started using a refractometer a while ago and am running into some weirdness. This weekend, I took a reading from the cooled sample from a batch I just got done brewing and came out at 1.052. I ended up a couple of points lower than my target, so a tad bummed, I took another reading with some fresh drops and read the same thing. The next morning the sample cup was still out on the counter, so I took another reading just to satisfy my curiosity. It was reading an unmistakable 1.055.

What could be the reason for the change of 3 points using the same sample? Temperature was the same, and I ensured there was adequate sample on the glass and that there were no bubbles.

 

[raysmithtx]

Maybe evaporation?


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[roper4092]

Hmmm....that could possibly be the culprit. Next time I'll seal the sample and take another reading the following day just to see.

 

[helibrewer]

Was the temp the same? Did you use the SG scale or calculate it from Brix?

 

[Orthobrewsky]

Hey folks,

Started using a refractometer a while ago and am running into some weirdness. This weekend, I took a reading from the cooled sample from a batch I just got done brewing and came out at 1.052. I ended up a couple of points lower than my target, so a tad bummed, I took another reading with some fresh drops and read the same thing. The next morning the sample cup was still out on the counter, so I took another reading just to satisfy my curiosity. It was reading an unmistakable 1.055.

What could be the reason for the change of 3 points using the same sample? Temperature was the same, and I ensured there was adequate sample on the glass and that there were no bubbles.

If it was cooler in the morning and you didn't recalibrate, that would do it. Otherwise, as already mentioned, if there was significant evaporation, it would happen.

 

[william_shakes_beer]

Perhaps the wort striated overnight, with the heavier sugars settling to the bottom? (that would assume you took a sample from the bottom half. If not, never mind)

 

[roper4092]

Temperature of sample was the same. I was looking at the SG scale, but also took note of the Brix. Refractometer has ATC. And the sample was just in a tinyl tupperware container...there was probably only a tablespoon in it and left uncovered overnight. Not sure how much evaporation could have occurred but that may be it. I gave the sample a swirl before sampling so it should have mixed it up well.

One other thought is that perhaps my pipette had a small amount of water left in it from when I rinsed it out last time and some of it diluted the initial sample. When I took the sample the next morning, I sucked up and squeezed out the pipette 2-3 times before drawing what I would use for the sample. With only using 2-3 drops for the refractometer, I can see that perhaps even a small amount of residual water in the pipette affected the reading.

 

[acidrain]

Refractometer has ATC.

ATC only means that it samples at room temperature. Room temperature is cooler in the morning, right?
That's why you have to calibrate it every time you use it... not because it changes, but because the ambient temperature changes.

 

[william_shakes_beer]

...And the sample was just in a tinyl tupperware container...there was probably only a tablespoon in it and left uncovered overnight.....

there's your answer. I was assuming you were samplihg from a 5 gallon batch. A small sample could experience significant evaporation even over night.