Roughly grind the coriander seeds in a mortar and pestle, and roast for 2-3 minutes in a dry pan.
Wash the peppers and cut into thin rings. Peel the ginger and cut into fine strips.
Place the seeds, peppers, and ginger in a saucepan. Pour the oil over the contents and apply very low heat for approximately 30 minutes. Keep an eye on it – do not let the oil get even close to boiling or reaching its smoke point.
Prepare a pot of boiling water and fill the bottle/put it inside for about 10 minutes to sanitize, then empty it out and let it drain on a clean towel.
Season the oil with salt and pepper. Wash and dry the rosemary.
Place the rosemary sprigs into the bottle. Using a funnel, fill the bottle with the oil. Seal with a lid.