Jacques Margnat was the youngest of the three brothers. Born with the sound of guns standard (cannon) at the very beginning (1915) of the world war I. Jacques Margnat was bachelor of law at 19 years old and at the same time succeeded at the examination for the military academy of artillery. Jacques Margnat passed 10 months in London as employee of the English subsidiary of the domestic group before his integration in Poitiers. Four pounds a week of salary to sell grape must produced by the Company Barbier in Tarragone, Spain.

Since the age of 12 or 13 years, Jacques Margnat did the grape harvests in the one or other Algerian vineyards. During the years passed at the university, every day around midday Jacques Margnat went to the laboratory to practice wine tasting with his father Edouard. Afternoons were reserved to some accounting. Law studies in this time did not require 10 working hours a day.