Kraut (or kapusta) 101. It has to be cold. If it rotted it was probably too warm. I make it ever year, sometimes just a #6 crock, sometimes a #6 and a #8. We are in west Michigan with an attached garage. I put it up in the garage on a table late October and in mid January it is done and I can most of it in quart wide mouths. In Chicago where I grew up, Dad did it in a separated garage. Not a big deal if it freezes, just not frozen solid for a month. My dad was the sauerkraut guru. He walked into a bar once and as soon as he smelled the air he said to the owner, “someone’s got kraut going bad in here.” Sure enough the owner took him in the basement where he had a barrel right near the furnace. Dad helped him dig out what was still good and they put it somewhere colder.
Seems like I remember my mother canning sauerkraut a time or two.