Both are made from a sabayon base. The Bearnaise involves a reduction* (of shallot, tarragon, peppercorns in white wine and/or vinegar).
Emulsified sauces are fairly delicate, as they will break or curdle easily.
In case of a break or separation of your preparation, you may give a try to restabilize your preparation with these tips.
- if too hot, adds a few drops of cold water and keep whisking
- if the sauce looks like it is about to break, cool the bottom of the bowl by dipping it into an ice bath
- if kept to cold, add a few drops of hot water and whisk again.
These two sauces are called sauces meres (mother sauce) as they are the base of many derivated sauces (sauce derivee).
Examples for Bearnaise, Foyot (add meat glaze), also known as Valoise, Colbert (addition of reduced white wine), Choron (tomato purée), Paloise (substitute mint for tarragon), Tyrolienne (oil instead of clarified butter)...
*Reduction is the process of Thickening or intensifying the flavor of a liquid mixture by evaporation.