To provide an improved treating method leading to the effective utilization of Shochu lees and the reduction of a treating cost, and to provide a useful utilization method.

The treating method includes stirring/mixing the Shochu lees and subjecting the product to solid-liquid separation while distilling under reduced pressure. The distillation is carried out at low pressure at a low temperature by dividing the process to three steps. The extract rich in components containing organic acids such as acetic acid and propionic acid in high concentration and obtained at the second step is utilized as a proliferation promoter of Spirulina platensis of microalgae.