"I didn't know if I could successfully shoot the scenes when I took the job, as there was no reference point," says Zhu.

One difficulty for her was to make her scenes fit into the documentary. Her previous videos were simply pure observation through recording, but this time, the scenes had to help tell the story.

Before shooting, Zhu and her team would do a lot of research about the ingredients and hold discussions with the documentary directors about how to best shoot the scene.

"Previously, I just made sure the shots were clear enough, but this time we had to use the light and the movement of the lens to find a way to tell the story," says Zhu.

In the third episode of Once Upon A Bite, Zhu records the moment when brine is added to soybean milk and veins appear when the two liquids are mixed. The scene can't be seen with the naked eye, but can be seen under a microscope with proper lighting.

The micro photography scenes take up less than 3 percent of the whole documentary, but the failure rate when shooting them was so high that they took Zhu five months to finish.

For example, the growth of penicillium in the fourth episode only lasts for 10 seconds, but it took Zhu four months to capture that moment.