Opt for kimchi, which is at least 2 weeks old. As it matures, kimchi undergoes lactic acid fermentation, which converts the sugars in the cabbage into lactic acid. This not only makes it taste sour but also increases the amount of glutamic acids. This process makes it taste sour and add a depth of flavor to it. You will also get more juice from mature kimchi as opposed to newly made ones. If in case, you don't have enough kimchi liquid, then replace the shortfall with rice vinegar.