Wash the grapefruits thoroughly under cool running water to remove any dirt or residue. Dry them completely with a clean kitchen towel.
Using a vegetable peeler or zester, carefully remove the zest from the grapefruits, avoiding the white pith as much as possible. The zest should be in thin strips or fine pieces.
Place the grapefruit zest into the sterilized glass jar, ensuring the jar is clean and dry before use.
Pour 1 cup of olive oil over the zest in the jar, making sure the zest is fully submerged in the oil.
Seal the jar tightly with the lid and store it in a cool, dark place for 48 hours to allow the oil to infuse with the grapefruit flavor.
After 48 hours, strain the oil through a fine-mesh sieve or cheesecloth into a clean container to remove the zest. Discard the used zest.
Transfer the infused grapefruit essential oil into a clean, airtight bottle or jar. Store it in a cool, dark place for up to 2 weeks.
