Explanation of the climax scene in “Trading Places”

WiseBread makes me feel much better that I never really understood the ending of Trading Places by linking to a Wikipedia entry which goes into detail about that damn orange crop report.

With the authentic orange crop report indicating a good harvest of fresh oranges, frozen concentrated orange juice (FCOJ) would be less important to food producers and so would be likely to drop in price once traders heard the news. However, by way of a fraudulent report, the Duke brothers are led to believe that the orange harvest would be less successful, necessitating greater demand for stockpiled FCOJ in orange products in the coming year, thereby driving the price up. By capitalizing on this knowledge (and the Duke brothers’ missteps), the protagonists are able to profit by manipulating the futures market as follows: