A thick, creamy dressing that's an emulsion of vegetable oil, egg yolks, lemon juice or vinegar and seasonings. If egg yolks aren't used, the product is called salad dressing, which is also sweeter than mayonnaise. Commercial mayonnaise (which must contain at least 65 percent oil by weight) sometimes contains other additions including emulsifiers and sweeteners. There are many reduced-fat mayonnaises — ranging from about 25 percent to 50 percent less fat than regular margarine — as well as fat-free mayonnaise. Besides less oil (or none, as the case with fat-free spreads), these mayonnaises contain ingredients like modified food starch, cellulose gel and other thickeners and emulsifiers, all of which help contribute to the proper consistency. Electric mixers, blenders and food processors make homemade mayonnaise a cinch. All mayonnaise should be refrigerated once made or opened. Unfortunately, the homemade style — which is far superior in taste and texture — lasts only 3 to 4 days. The commercial product can be stored up to 6 months. Mayonnaise is widely used as a spread, a dressing and a sauce. It's also used as the base for a plethora of other mixtures including tartar sauce, thousand island dressing, Aïoli and Rémoulade.