The antibiotic penicillin is produced commercially by fermentation of the penicillum mold in special submerged-fermentation tanks through which oxygen is pumped. Although the antibacterial action of penicillin was first discovered in the late 1920s, the penicillum mold required large amounts of oxygen and proved to be difficult to work with. It was not until the 1940s that the sub-surface liquid-culture method was devised, in which the proper deep-tank fermentation conditions were created that could produce a high yield of the antibiotic.
The search for a means of mass-producing penicillin was spurred on by the outbreak of World War II and the impending June 6, 1944, D-Day Allied invasion landing at Normandy. United States and British scientists working on the penicillin mass-production process knew that thousands of lives hung in the balance because a wounded soldier could die from an infected wound even if the wound itself was not fatal.
By 1944, production of penicillin increased dramatically due to the newly developed fermentation process. American production of the antibiotic in 1944 was more than 1,600 billion units compared to 21 billion units produced during the previous year. By 1945, the new manufacturing techniques were capable of producing 10,000-gallon tanks at 80 to 90 percent yield.
Restrictions that were initially placed on penicillin to prioritize its use in the war effort were eventually lifted and the drug became available through U.S. consumer pharmacies on March 15, 1945. The U.S. annual production of penicillin reached more than 133,000 billion units in 1949.