He made a name for himself as a capable handyman and befriended his neighbors, a pair of brothers named Jules and Paul. Jules and Paul had a small vineyard in front of their house where they grew their own grapes and turned them into a fruity, sweet wine that they referred to as American-blood wine.

At that point the brothers were old men, so they asked Garnier to help them harvest the grapes. When the brothers died, Garnier started the process of buying the vineyard.

But he didn’t get very far. He soon discovered that the type of wine Jules and Paul had been making for decades was illegal, and had been since the 1930s, when the French government and European Union outlawed the use of hybrid grapes, like the Franco-American ones grown on the brothers’ vineyard.

But why? And how could Garnier get the law changed?

To answer that, he had to learn the history of these hybrid grapes—how they originated, how they got to France, and how they fell out of favor after once being deemed the “savior” of the French wine industry. (That history involves a murderous louse, claims of madness, and the subjectivity of “good-tasting” wine.)

Check out this episode of Proof, in which Paris-based reporter Rebecca Rosman talks to Garnier about his decades-long, David-and-Goliath fight to get the law reversed.

• Read Hervé's impassioned letter that he sent to the European Commission in 2003.