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?