Kimchi control

For those lacking the patience to wait for their kimchi to attain the tartness appropriate for kimchi stew or fried rice, it is (I'm told) OK to take it out of the refrigerator to speed the process. Three days at room temperature should be enough. Once it's sour enough, you can put it back in the refrigerator and it'll remain stable for "a long time."
Again, Japanese kimchi doesn't get sour. It just goes bad.
The hot pepper for which kimchi is famous is a relatively new addition; the original kimchi (still abundant today) is just pickled vegetables. As is well known, all hot peppers originated in Central America and stayed there until the Spanish Conquest. They were brough to Japan by the Portuguese in the 1500s, and from there spread to Korea, where they were called "Japanese mustard" (in modern Japanese it's called "Chinese mustard.") The first known mention of them in a Korean text reads, "The Japanese mustard is very poisonous; many have died from eating it."
But hot peppers quickly became widely used. Scholars have suggested it was intended to ward off ghosts. Korea had just been catastrophically invaded by the Japanese (bearing the hot peppers) and Chinese, and subsequently been swept by epidemic disease. The ghosts of such multitudes dying before their time might be kept at bay by eating food strongly tinted with the atropopaic color red. I think this explanation is based on broad generalizations about Sino-Korean beliefs rather than direct evidence, but it makes a good story.