Ceviche is a dish of fresh raw fish cured in citrus juices, most commonly lemon or lime. In Peru, it is considered a national heritage dish. The science behind ceviche is 'denaturation.' The citric acid in the lime juice causes the proteins in the fish to unfurl and recombine, effectively 'cooking' the fish without heat. This changes the texture from translucent and soft to opaque and firm. Historically, the Moche people of coastal Peru used fermented juice from local 'banana passionfruit' to cure fish nearly 2,000 years ago. After the arrival of the Spanish, limes and onions were introduced, creating the modern version we see today. The leftover marinade, a mix of fish juices and lime, is known as 'Leche de Tigre' (Tiger’s Milk) and is often served in a small glass as a potent tonic.