What is this white spot on air-dried beef? Moldy? Or precipitated salt? It's very hot recently ...

This is grease. Don't worry, it doesn't matter if the white foreign body is granular. It is butter, and the fat in beef is formed after high temperature. If it is heated in a microwave oven, it will be gone, and beef jerky heated to 30-50 is more delicious.

Dried beef will go bad if it is kept for a long time, but most of the deteriorated dried beef has a taste. You can tell it by its color and smell.