Aioli (Provençal Occitan alhòli, Catalan allioli) is a sauce made of garlic and olive oil. Normally egg is also added for ease of mixing. There are many variations, such as the addition of mustard. In France, aioli is traditionally served with seafood, fish soup, and croutons. It is usually served at room temperature. The name aioli (alhòli) comes from Provençal alh 'garlic' (< Latin allium) + òli 'oil' (< Latin oleum).
Aioli is, like mayonnaise, an emulsion or a suspension of small globules of oil and oil soluble compounds in water and water soluble compounds. Egg yolk is a commonly used emulsifier but mustard and garlic both have emulsion-producing properties. Classic aioli is made without egg, though many aioli recipes use it.
The garlic is often ground with salt in a mortar and pestle to lead to a smooth aioli. Egg yolks, garlic and Dijon mustard (if adding this as a common variation on the basic aioli), are combined first with a whisk, and the oil is added slowly with whisking and the lemon juice is added slowly with whisking to create the emulsion. The additions of the dissimilar ingredients must be slow to start and then can be faster once the initial emulsion has formed.
Similar sauces are found elsewhere in the region.
Note: Many restaurants refer to any flavored mayonnaise as an aioli. This is an incorrect definition unless the resulting sauce includes the addition of garlic.