How penicillin is made
The best penicillin-making mold was found on a moldy cantaloupe in a market in Peoria, Illinois.
- stations
- 7
- things upstream
- 23
- raw sources
- 11
- steps from the ground
- 6
The short version
Penicillin is grown, not assembled. A mold, Penicillium chrysogenum, is fed sugars and corn steep liquor in large stirred, aerated tanks. After days of fermentation the drug is filtered from the broth and purified. For many drugs in the penicillin family, the natural molecule is then chemically modified, and the final powder is made sterile.
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Prepare the seed culture
A small sample of mold is grown in flasks and then in progressively larger vessels. This builds up enough healthy mold to start a full-size tank.
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Mix the nutrient broth
Corn steep liquor, a by-product of corn wet milling, is mixed with sugar and water and sterilized with steam. It is rich in the nutrients the mold needs.
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Ferment in deep tanks
Mold goes into enormous stainless steel tanks and stirred while sterile air is pumped in. The mold needs oxygen, so airflow and agitation are monitored continuously.
Goes in -
Filter out the mold
When the broth holds as much drug as it will, filters remove the mold. What remains is a liquid containing dilute penicillin.
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Extract and purify
The drug is moved from the broth into a solvent and back into water, then crystallized. These steps strip away the other products of fermentation.
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Modify the molecule
Many penicillins used today are semisynthetic. The natural core is chemically altered in a plant to make versions that work against more bacteria or survive stomach acid.
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Sterilize and pack
The purified drug is filtered through sterile membranes and dried. It is then filled into vials or made into tablets and capsules.
Goes in
Worth repeating
- Alexander Fleming discovered penicillin in 1928 as a crude extract of a mold.
- The moldy cantaloupe from Peoria held a strain that made six times as much penicillin as Fleming's mold.
- Research on corn steep liquor let the United States make 2.3 million doses in time for the invasion of Normandy in spring 1944.
Back to the ground
Follow every input upstream and penicillin starts as these 11 raw sources.
Everything it is made of See it on the map
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Sources
Cite this page: "How penicillin is made." Assembly Line, 2026-11-03. https://assemblyline.org/make/penicillin