If you brew an herbal remedy on a stovetop, the remedy gets put in the sim's inventory. If you brew an herbal remedy on a grill, the remedy gets put on the grill (which is admittedly an improvement over having it get dropped on the ground when the brewing sim resets). However, if the grill is one with a closable cover such as GrillWise by GrillMania, the grill is rendered unusable because the remedy is now under the cover and unreachable to remove it from the grill. I strongly recommend that the remedy be placed in the brewing sim's inventory as with brewing on a stovetop.
Attached is a screenshot of the pie menu of the grill at the Lakeside Retreat lodge in Granite Falls after brewing an herbal remedy on it.
