In a modern oven in Pasadena, Calif., this week, yeast that could be as old as ancient Egypt was used to bake an especially aromatic loaf of sourdough bread.

The baker, Seamus Blackley, was experimenting with yeast he had extracted from a 4,000-year-old Egyptian loaf. He was trying to make his own bread using the same ingredients, and some of the same methods, as the ancients.

It turned out well, and Mr. Blackley — who is also a creator of the Xbox, a physicist and a self-professed “bread nerd” — posted the results on Twitter. “The crumb is light and airy,” he wrote. “The aroma and flavor are incredible. I’m emotional.”

Thousands of people responded in a surge of interest that extended far beyond niche communities of bread nerds and yeast enthusiasts, whose interests traverse science, gastronomy and history.