Until what year did Mars contract with Hershey's for the supply of chocolate coating for the Milky Way?
Answer
1965, when Forrest Mars brought chocolate production in-house.
Early in the history of manufacturing the large Milky Way bars in Minneapolis, Mars did not possess the necessary capital or dedicated facilities required to produce their own chocolate coating. Consequently, the company entered into a contractual agreement to source this essential component from a competitor, Hershey's. This supply relationship lasted for many years until 1965. In that year, Forrest Mars reportedly surprised Hershey’s by abruptly terminating the agreement and moving the chocolate coating production internally, which represented a substantial financial blow to Hershey’s chocolate coating revenue stream.

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