Caviar is one of the most expensive foods in the world. Selling for up to $35,000 per kilo, it's revered and relished by aristocrats across the globe. But it's an acquired taste. Turns out, caviar wasn't always so valuable. In the 19th century, sturgeon species in the US were so common that there are accounts of caviar being offered in saloons for free, like bar nuts. In Europe, fishermen were feeding the eggs to their pigs, or leaving it on the beach to spoil. What changed?