Carambola, also known as star fruit, is the fruit of Averrhoa carambola, a species of tree native to tropical Southeast Asia. The edible fruit has distinctive ridges running down its sides. When cut in cross-section, it resembles a star, giving it the name of star fruit. The entire fruit is edible, usually raw, and may be cooked or made into relishes, preserves, garnish, and juices. It is commonly consumed in Southeast Asia, South Asia, the South Pacific, Micronesia, parts of East Asia, the United States, parts of Latin America, and the Caribbean. The tree is cultivated throughout tropical areas of the world.

Oxalic acid is an organic acid with the systematic name ethanedioic acid and chemical formula HO−C(=O)−C(=O)−OH, also written as (COOH)2 or (CO2H)2 or H2C2O4. It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name comes from the fact that early investigators isolated oxalic acid from flowering plants of the genus Oxalis, commonly known as wood-sorrels. It occurs naturally in many foods. Excessive ingestion of oxalic acid or prolonged skin contact can be dangerous.