It all started with a coffee. When a homeless man asked Dino Impagliazzo for an espresso, the Italian pensioner thought: "Why not help?" Soon he and his wife were making sandwiches for homeless people who hung around one of Rome's train stations. As word spread, the lines for food grew longer. Eventually Impagliazzo switched to hot meals, cooking them first at home and later using the kitchen of a nearby church.

"The nuns had a large pot that came in handy," he recalled. A decade on, the 86-year-old prepares hot meals for up to 250 migrants and needy people in Rome four days a week, using a tiny fraction of the 1.3 billion tons of food waste that the world generates each year.