A word about the food safety of hollandaise sauce. There is always a risk of food-borne illnesses when using undercooked eggs. If you are concerned about salmonella, use pasteurized eggs or cook the eggs to at least 165F to kill any bacteria; however, this can potentially cause the eggs to scramble. Egg yolks start to coagulate around 149F (65C) and will start to curdle around 160-170F (yolks completely curdle at 185F (85C). If a gastride is used to make the sabayon, the acid will provide a bit of leeway and minimizes the risk of the yolks coagulating if they are slightly overheated.
Hollandaise should be held between 120F to 145F (49 to 63C) so it does not split or curdle. If the sauce is heated above 150F, the eggs can overcook, become grainy and the sauce can potentially split. Because hollandaise is kept warm (and not hot), holding hollandaise at this temperature causes bacteria to rapidly grow, which will contaminate the sauce and make it unsafe to consume, especially if it is held for too long. Hollandaise should not be held for more than 1.5 hours; therefore, make only what you intend to serve and never mix and old batch of sauce with a new one.
