Classically, cream soups and veloutés are bound with a white roux (roux blanc) and a mixture of heavy cream and egg yolks (liaison) or cream alone, added at the end of the cooking process. Cream soups are always made with milk, since the soup will be finished with heavy cream. The classic preparation of a velouté is similar, except that stock is used as the liquid in place of milk, and a liaison of egg yolks and heavy cream is added just before serving; it cannot then be reheated or it will curdle. Both cream soups and veloutés should have a velvety-smooth consistency. The stock or liquid used to make the soup or its dominant ingredient determine its name. Unfortunately, the classic distinctions between these two soups are now less clear, as modern kitchen appliances such as the blender and food processor have replaced the traditional techniques of emulsification required to obtain a thick, creamy soup.