Yes, mixing green chili paste with oil before storage helps to preserve its color, flavor, and prevent spoilage by creating a barrier against air and moisture.
Green chili paste, when exposed to air, can oxidize and darken in color, losing its vibrant green hue. The oil acts as a protective layer, preventing oxidation and maintaining the paste's bright color. Furthermore, oil helps to prevent the growth of mold and bacteria by creating an anaerobic environment. This extends the shelf life of the chili paste and preserves its fresh, spicy flavor. To properly store it, mix a thin layer of oil (such as vegetable oil, olive oil, or even mustard oil, depending on your preference) into the paste after you've made it. Ensure the oil covers the entire surface of the paste. Store the mixture in an airtight container in the refrigerator.
Use a clean spoon each time you scoop out the chili paste to avoid introducing contaminants that could lead to spoilage, even with the oil barrier.