I did a test with a mason jar with a 1 1/2" of water and a temp sensor in it. It took 3 days but here it is. So I need to be on 3 1/2 or 4? I guess 1 and 2 are too warm, but don't they dryout and cure sausages at 50°?
1 - 45°
2 - 43°
3 - 41°
4 - 39°
5 - 37°
6 -34°
I would go with about 4 1/2--4 3/4,--5 which if accurate should be about 37° to 38°.
But if you can't leave the jar in, I would check it now & then, because even if your Fridge setting doesn't move, the Temp can move. Hard to believe, but I've seen mine do it. I've seen it wander up to 39°, and I had to tap it to get it back to between 37° and 38°. 39° would be fine, but I figure if it can stray to 39° it can go higher.
That curing above 40° "50°" is a different thing altogether---Using Cure #2 for longer drying & curing. Don't confuse that with what you're doing here.
Bear