Ernst Chain suggested freeze drying to turn penicillin solution into a dry powder.
Penicillin was fragile, and ordinary evaporation or boiling could damage it. After the Oxford team extracted the drug into solution, Chain proposed removing the water by freeze drying, also called lyophilisation. The process froze the material and removed water under reduced pressure, avoiding the heat that could destroy the antibiotic.
The result was a dry, brown penicillin powder that was easier to preserve, handle and transport than a dilute liquid extract. This mattered because the team needed to store samples, conduct animal experiments and begin clinical testing with a preparation that retained its antibacterial activity.
Freeze drying was only one part of a larger technical achievement. Norman Heatley helped develop extraction and assay methods, while Edward Abraham contributed to purification and chemical investigations. Florey coordinated the project and led the biological and medical programme.
A common mix-up is spray drying, which also produces powders but uses a heated stream to evaporate liquid. For early penicillin, heat avoidance was the decisive advantage of Chain’s freeze-drying suggestion. The technique helped convert a delicate laboratory solution into a usable form.