does mayonnaise need to be refrigerated
Manufacturers universally tell you to refrigerate mayonnaise once opened, though, because it helps preserve the flavor. Warmth causes mayonnaise to break down after a while, and it gets to the point where it just tastes oily. Homemade mayonnaise, of course, is a different matter. With its use of raw eggs, it is highly perishable and should be consumed immediately or refrigerated and finished off very shortly.