Coffee, but not just any old coffee: it's the Agatha Heterodyne goes into Spark hyperfocus (with an emphasis on "hyper," Agatha never having experienced a caffeine jag before) and rebuilds Vanamonde von Mekkhan's coffee engine in her own, . The effect that this miraculous brew has on young von Mekkhan is ... well ... . However, equally important is the effect that preparing the stuff has on the townfolk of Mechanicsburg (for example Herr Mitrant, whose tools she appropriates to start working on the coffee engine, and Rinja, the irascible innkeeper whose coffee beans she co-opts for the project), who rapidly get the idea that Agatha may just be a real Heterodyne. That's important.stuff that emerges when
It seems that Agatha later adjusted the coffeemaker slightly so that it would be merely "", rather than perfect. It's also possible the machine requires constant monitoring and fine-tuning to maintain perfect coffee output (which Agatha is no longer performing), or someone else tampered with its perfect settings.