The longevity of kimchi brine in the fridge depends on several factors, including the ingredients used, the storage conditions, and personal preferences. Generally, kimchi brine can last for a few weeks to a few months in the refrigerator.
If the kimchi brine is from homemade kimchi and contains mainly salt, water, and the natural fermentation byproducts, it can last for several weeks to a few months when stored properly. Make sure to keep it in an airtight container to prevent contamination and to maintain its quality.
However, if you've used other ingredients like garlic, ginger, or other seasonings in the brine, it may not last as long, and the flavors could change over time. It's always best to use your senses to determine if the brine is still good to use. If it develops an off smell, strange appearance, or tastes sour or unpleasant, it's better to discard it.
Remember that the brine is the liquid that preserves the kimchi's vegetables, so it's crucial to maintain its quality to ensure that any kimchi made using the brine remains safe to eat. If you're unsure about the freshness of the brine, it's better to prepare a new batch or find alternative uses for it, such as using it as a flavoring agent in other dishes.