Cooking & Baking

If it were stored in a cool pantry--perhaps in a basement, it would likely remain optimal. Vinegar doesn't go bad.

So, what's left? Well, dried herbs would probably not be a major issue for bacterial contamination, nor fresh herbs that you wash well. If sugar is added to the dressing, it would potentially have some bacterial-inhibiting (bacteriocidal) effects. There are some reasonably rare issues that could come up, but are mostly an issue if very young children (infants) were to eat your dressing (e.g., botulinum spores in honey or potentially on dried herbs from questionable sources). But, I wouldn't think the risk would be at all likely for your dressing--I just feel the need to mention.

So, leaving it out in hot temps. Bad idea. Storing it out of the refrigerator in cool pantry-type temps (e.g, 60 degrees or cooler)--probably pretty optimal. Mustard should not be an issue. Any product with egg or mayo WOULD BE and must be refrigerated.