The five flavors are from a metaphor preached in the Nirvāṇa Sūtra: “As fresh milk comes from a cow, cream from the fresh milk, butter curds from cream, fresh butter from butter curds, and clarified butter from fresh butter, so is the teaching of the Buddha.” The sūtra uses this metaphor to explain the development of the teaching of the Buddha through the twelve-fold scriptures, the Agama sūtras, the Expanded sūtras, the Wisdom sūtras, and the Mahāparinirvāṇa Sūtra. Zhiyi further utilized this five-flavor theory to explain the five periods by applying that classification — Flower Garland, Deer Park, Expanded, Wisdom, and Lotus/ Nirvāṇa. — to reflect the sequence of the teaching and growing maturity of the capacities of the listeners.