A liaison is a mixture of egg yolks and cream that is used to finish some classical French sauces. Although a liaison will slightly thicken a sauce, it’s biggest contribution is richness and mouth feel.
When using a liaison it is important to understand that pure egg yolks will curdle around 140-150 F and about 60-70 C. When you mix the egg yolks with cream, it raises the curdling temperature to around 180-185 F and about 83 C.
Standard Ratio for Liaison
The standard ratio for a liaison is 16 x 1 x 2. So for every 16 ounces (or one pint) of sauce, you will need 1 egg yolk and 2 ounces of cream.
Incorporating a Liaison Into a Sauce
To incorporate a liaison into a sauce, first beat your egg yolks and heavy cream together in a separate bowl. Heat your sauce to about 180 degrees F or 80 degrees C, which is just below the simmering point. If you allow your sauce to simmer or boil, it will curdle your eggs.
Now slowly add some of your hot sauce to your cream and yolk mixture, whisking constantly. Once you have added about 1/3 of your total sauce to your liaison, add the entire mixture back into your original sauce.
Heat the sauce to about 180 F (80 C) and strain through a fine chinois before serving.