I made vinaigrette which is composed of red wine vinegar, olive oil, salt, and sugar. Does this need to be refrigerated, or is it safe to leave it out of the fridge?
None of the listed ingredients require refrigeration so you are safe to leave the vinaigrette at room temperature as long as it's not fluctuating much. Leave it in a cool, somewhat shaded area (out of direct sunlight if possible). If you wanted, you could absolutely leave your vinaigrette in the fridge.