When it comes to how long your roasted cauliflower will keep, the answer is not as simple as you may think. The cauliflower will lose its quality, if you leave it out in the refrigerator. If you plan on eating it within a day or two, then you should keep it in the fridge. Check the cauliflower for blemishes or mold if you notice them. You can cut off the bad area or discard the whole head, if it's too small.