Refractometer reading drifting up
 

I took a Refractometer reading from the boil kettle - it reads 10.9 Brix. I put down the refractometer, record the reading and let it sit on my table. 5 Minutes later I pick it up and it reads 11.2 - another 5 minutes and it's now at 11.5 - slowly drifting up.

Does this have to do with the heat of the wort? Should I cool it down before reading or what else is going on?

It's definitely temp related. I use a pipette to grab the sample, then run a little cold water over the bulb for a 20 seconds before dispensing on the lens.

I've seen the same thing. It is due to the temp of the wort.

The automatic temp correction (ATC) of refractometers does not correct for hot wort. This ATC corrects for changes to the body of the refractometer.

The wort must be the same temp as the body of the refractometer. I always add 2 hot drops and set it down, then check in 5-10 minutes.