Weird thing, I had a batch of wort which I started fermenting in 2 different vessels (in the same fridge - so conditions where effectively the same). After a few days, one of them gave me a refractometer reading of 5.5 Brix, and the other was 6.1 (took several readings of both - these numbers remained consistent throughout the readings). However, When I took a hydrometer reading, both presented a gravity of 1.013. So, the gravity is the same, but the Brix reading is different. The only explanation I could think of for this is different ABV or something, but why would that be the case, if they fermented in similar conditions? (one of the containers was open, but it was at 18C, so I don't think there was a lot of alcohol evaporation going on) Any thoughts?