route. The modern two-step fermentation process, originally developed in China in the 1960s, uses additional fermentation to replace part of the later chemical stages. The Reichstein process and the modern two-step fermentation processes use sorbitol as the starting material and convert it to sorbose using fermentation. The modern two-step fermentation process then converts sorbose to 2-keto-l-gulonic acid (KGA) through another fermentation step, avoiding an extra intermediate. Both processes yield approximately 60% vitamin C from the glucose feed. In 2017, China produced about 95% of the world supply of ascorbic acid (vitamin C), which is China's most exported vitamin, having total revenue of US$880 million in 2017. Due to pressure on Chinese industry to discontinue burning coal normally used for vitamin C manufacturing, the price of vitamin C rose three-fold in 2016 alone to US$12 per kg. History Scurvy at sea In the 1497 expedition of Vasco da Gama, the curative effects of citrus fruit were known. Later, the Portuguese planted fruit trees and vegetables in Saint Helena, a stopping point for homebound voyages from Asia, which sustained passing ships. Authorities occasionally recommended plant food to prevent scurvy during long sea voyages. John Woodall, the first surgeon to the British East India Company, recommended the preventive and curative use of lemon juice in his 1617 book, The Surgeon's Mate. In 1734, the Dutch writer Johann Bachstrom gave the firm opinion, "scurvy is solely owing to a total abstinence from fresh vegetable food, and greens." Scurvy had long been a principal killer of sailors during the long sea voyages. According to Jonathan Lamb, "In 1499, Vasco da Gama lost 116 of his crew of 170; In 1520, Magellan lost 208 out of 230;...all mainly to scurvy." The first attempt to give scientific basis for the cause of this disease was by a ship's surgeon in the Royal Navy, James Lind. While at sea in May 1747, Lind provided some crew members with two oranges and one lemon per day, in addition to normal rations, while others continued on cider, vinegar, sulfuric acid or seawater, along with their normal rations, in one of the world's first controlled experiments. The results showed that citrus fruits prevented the disease. Lind published his work in 1753 in his Treatise on the Scurvy. Fresh fruit was expensive to keep on board, whereas boiling it down to juice allowed easy storage but destroyed the vitamin (especially if boiled