When did Louis Pasteur begin his swan-neck flask experiments?

Pasteur began the swan-neck flask experiments in 1859 and continued refining them into the early 1860s. By boiling nutrient broth in flasks with curved necks, he showed that air could enter but dust-borne microorganisms could not, so the broth stayed sterile unless the neck was broken or tilted. These results became a landmark in microbiology because they undermined the long-held idea of spontaneous generation. The work helped establish the modern germ theory framework that later transformed medicine, food safety, and sanitation.