Homemade dressings often contain fresh ingredients like garlic, lemon juice, and herbs, which can spoil if not refrigerated properly. To prevent your dressings from going bad, it is important to store them in an airtight container in the fridge. To check if your homemade dressing is bad, look for signs like mold, separation, or an off smell or taste. If you see any of these signs, I recommend discarding the dressing immediately and making a fresh batch. Fortunately, this Parmesan Dressing is simple to make, and it only takes a few minutes to whip up a new batch.