Mayonnaise is a thick, creamy emulsion, which means that it consists of two liquids that don't mix well under normal conditions. An emulsifier binds the liquids together. In the case of mayonnaise, the emulsifier is egg yolks.
Without the egg yolks to bind the vinegar and oil during blending, the oil would form beads atop the vinegar and never combine. Certain environments, such as freezing, may break these bonds.
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Whether they have a fish, pasta, egg or a poultry base, it's not a good idea to freeze salads that contain mayonnaise. The ingredients in the mayonnaise do not fare well as a bonding agent during freezing.
According to the United States Department of Agriculture, the ingredients in mayonnaise separate during the freezing process. The end result is a salad that doesn't have the same texture and consistency as it did before freezing. Instead, the salad becomes an oily mess upon thawing.
What Makes It Happen
When you place food in your freezer, they undergo a slow-freeze process, during which ice crystals form on and within the food.
According to the University of Kentucky Cooperative Extension Service, these ice crystals are what contribute to the separation of mayonnaise after freezing. As the ice crystals melt, they cause the ingredients in emulsified food such as mayonnaise to separate. This separation tends to give the mayonnaise a curdled look that may be unappealing.
There are times when ice crystals don't pose a problem during the freezing of foods that contain mayonnaise. For instance, some recipes call for the use of mayonnaise instead of shortening. After the baking process is complete, it changes the structure of the emulsifier.
Thus, the ice crystals formed during freezing have no effect on the baked item during thawing. The same holds true for cream cheese, whipped cream and meat salads that contain minute amounts of mayonnaise. When combined with cream cheese, whipped cream or small amounts of meat, mayonnaise remains unaffected during freezing.
If you use a mayonnaise substitute in your recipes, you may be in luck. Unlike real mayonnaise that separates during freezing, mayonnaise substitutes fare well.
Mayonnaise substitutes usually contain the same main ingredients as real mayonnaise — eggs and vinegar — but the oil content is much lower. Real mayonnaise has an oil content of at least 65 percent. Since the oil content in a mayonnaise substitute is significantly lower, less separation occurs during freezing.