Final answer:
The statement is false; culinary techniques, including those for making purees and bisques, have evolved since Escoffier's time due to advancements in technology and ingredients.
Step-by-step explanation:
The statement that the techniques for making purees and bisques have not changed since Escoffier wrote "Le Guide Culinaire" is false. While many of the fundamental techniques and principles established by Auguste Escoffier remain important, the culinary field is constantly evolving.
Innovations in technology, equipment, and ingredients have led to the development of new methods and variations in the preparation of purees and bisques.
Modern appliances such as immersion blenders and ingredients like hydrocolloids have introduced new possibilities that chefs of Escoffier's time did not have.