I brewed a batch of Imperial Red Ale in my garage yesterday. It was 7F outside. I'm not really sure what I was thinking, but I was off work and I had the itch to brew. My water hose froze within about 15 minutes, but I got through it somehow.
However - I had a weird issue with my refractometer. I have a fairly new ATC refractometer. It's not super high-end, but it's not a cheapie either.
My pre-boil gravity reading was 15 Brix (~1.060). I boiled for 60 minutes and added 1 lb of corn sugar to the recipe at flame-out. I boiled off about 1.5 gallons of liquid. My post-boil reading was 19 Brix (1.078). I was fairly happy because my predicted target was just slightly higher.
Once I cooled my wort to about 65F, I re-took a reading. I was surprised because I got 15 Brix. I took another sample and got 15 Brix again.
It didn't make any sense, so I'm assuming equipment problems. I re-tested my refractometer with water. It checked out, but I did this after it was brought inside and it had warmed up a bit.
Anyone have an idea of what happened here? Is it a temperature thing? Even with the ATC, is there a set temperature range (min-max) to use a refractometer? Is 7F a little too cold for an accurate reading?