When you’re in a
restaurant, considering the items on the
menu, you might want to think twice about ordering anything with
Hollandaise or
Béarnaise sauce. They need to be kept warm for service, but below 140°F (60°C) or they
curdle. Such sauces can be kept safely at these temperatures for an hour and a half, at the most.
Airborne bacteria grow best at temperatures between 40°F and 140°F (4°C and 60°C), known as “the danger zone” in the food preparation industry. Bacteria are also most happy fed a combination of moisture, air, and protein (i.e. eggs). The airborne bacterium that finds its way into the Hollandaise sauce sitting in a warming bath in the kitchen can double in number every 15 to 30 minutes. And given the chaotic nature of restaurant kitchens, it’s doubtful that anyone remembers exactly when that bowl of Hollandaise sauce was made.
While it is possible that the chef would stop what he or she is doing to make up a fresh batch of sauce just for your order…it’s highly unlikely.