Jyotirmayi : A devotee name Pritaputra was the director of a chain of vegetarian stores that were in the main cities of France. At that time vegetarianism was very rare, so in a sense he was an extraordinary personality, because he was the only one in all of France who had vegetarian stores. This director gladly came to see Prabhupada and they discussed pure life and pure eating. The director explained his idea of a healthful vegetarian diet and how organic food is pure. But he agreed that it's very difficult to have absolutely pure food, because even though one may grow food organically, there is still acid rain and other toxic things that come on the field. Honeybees may take pollen from some flowers that have pesticides, and even paper plates have some animal fat in them. Prabhupada said, "Because it's impossible to have food that's completely pure, we chant Hare Krishna. The chanting makes the food completely pure." After you have tried everything else, the holy name of the Lord is the only thing that will make food completely pure. This discussion was another learning experience on how to talk to people.
Reference:Memories Anecdotes of a Modern Day Saint - Volume 2 by Siddhanta Dasa