As kimchi started gaining its superfood status, my friends started asking me all sorts of kimchi related questions. And two of the most common questions among them were 1. Does kimchi ever go bad if you keep it too long? 2. What do you do with a few weeks or months old sour tasting kimchi?
To answer the first question, as long as it is refrigerated properly in an air-tight container, it won't go bad. My family back home has 1,2 and 3 year-old homemade kimchi in our kimchi fridge (yes, Koreans have special fridge just for the kimchi), and they are extremely delicious. And more importantly they serve different purpose from fresh new kimchi. There are certain dishes that we must use old, sour and more fermented kimchi instead of fresh one. But for the store bought kimchi that is kept in a normal fridge, it'd be best to be consumed before its use-by date, and the longer it gets the tartness of kimchi gets sharper.
So for the next question, "what do you do with old kimchi that is just a little too sour to eat as it is?" There are multiple ways we use old kimchi in Korean food, but the most simple one is to stir-fry it with a little bit of oil. And if you happen to have some cold leftover rice from a takeout, throw that in too. It becomes kimchi fried rice! And this is a kind of dish that we don't use the fresh kimchi to make. Fresh kimchi lacks the depth of flavor needed for proper kimchi fried rice.
And of course, you can eat it with freshly made rice instead, it would be even healthier. You can stir-fry kimchi with vegetables or meat (pork goes extremely well with kimchi), but it is still great without anything else. I would insist on adding a couple of sunny side up to serve with though, because the flavor of rich egg yolk mixed with fried kimchi is way too heavenly to miss out.
I like using regular olive oil (extra virgin is too good and expensive for stir-frying). I know some people are skeptical about the flavor combination of olive oil and kimchi, but based on my experience and reactions from people who tasted it, olive oil fried kimchi is awesome. Kimchi has such a strong flavor, it does not get over shadowed by a bit of olive oil. I actually think slightly pungent and peppery olive oil flavor is beneficial to the end product, not the other way around. If you simply dislike the flavor of olive oil, go with neutral flavored oil like grapeseed or sunflower.