Kimchi juice is a key ingredient in many Korean dishes, providing both flavor and a probiotic punch. While it can be difficult to find outside of Asia, there are a few substitutes that can be used in a pinch. The simplest replacement is to mix together equal parts gochujang (Korean chili paste) and rice vinegar. This combination will give you the acidity and spice of kimchi juice without the fermented flavor. If you're looking for something closer to the real thing, you can try substituting pickle juice or sauerkraut brine. Both of these options will provide the desired tang, but they may be too salty for some recipes. As always, use your best judgment when substituting ingredients in your cooking.