It was the wine broker, Pierre Moreau, the man trusted by De la Trémoille, who formed a committee of purchasing shareholders of Margaux and who took control of the running of it. He named Marcellus Grangerou as cellar master ; his son Marcel and his grandson Jean later had the same responsibilities. The most important innovation introduced by Pierre Moreau was the compulsory bottling of the wine at the château. It was adopted in 1924 and became a true guarantee of authenticity for buyers. The economic crisis of the 1930s and the disastrous vintages of this decade destabilized the shareholders and momentarily put an end to the principle of compulsory château bottling, which only re-appeared after 1949. Fernand Ginestet and his son, Pierre, then came on to the scene. Fernand, who liked singing as much as trading (he had a beautiful baritone voice) had made his fortune as a wine merchant. It was his friend, Boylandry, the mayor of Saigon, and a wine importer, who sent him the necessary funds to buy the estate, and the Ginestet family only bought the totality in 1950. Fernand and Pierre re-organized the vineyard patiently. Pierre's son, Bernard, looked after their wine merchant business and made it into one of the most respected businesses in Bordeaux.

But the 1970s' recession and the disastrous, unsaleable vintages of 1972, 1973 and 1974 put Pierre and Bernard into a desperate situation. They nevertheless wished to honour their commitments. Their only negotiable asset was Château Margaux, which they resigned themselves to selling.