How cold is too cold?

[Glass_A_Day]

I have outgrown my two mini cellars as everyone told me I would and have come up with an idea for cheap additional storage. My home has a workshop off of the cellar. The way it was build is it is under the front porch which is a cement slab. Therefore all sides, top, and bottom are all cement. Ceiling walls and floor. There is a window in it so I could use that for a vent if I wanted to add active cooling, but I don't think that is necessary. I am actually worried that opposite is the case. Right now it is 50 degrees outside and the ground hasn't even frozen, yet the temp in that room is only 52. I am afraid that it will get colder in there as winter comes into full swing although I just started monitoring the temp and am not really sure. So, what is too cold for wine storage?