A Reflux Rinsing method for purifying crystals using solvent vapor through dynamic equilibrium recrystallization. Feed material having tetrahydrocannabinol (THC) is inserted into a reaction vessel having walls, and upper portion, and a lower portion with a bottom surface. The feed material is exposed to a hydrocarbon liquid in the reaction vessel in a quantity sufficient to keep liquid present in equilibrium with gas in the reaction vessel through the recrystallization process, forming a raw extract having THC. The walls and bottom surface of the reaction vessel are coated with raw extract. The reaction vessel is heated and then the heating is discontinued. Vapor/thin-film DER is promoted in the reaction vessel for a predetermined length of time with no solvent reflux, resulting in formation of purified crystals of THC acid under pressure. The hydrocarbon solvent is reclaimed from the reaction vessel, leaving the purified crystals and impurities. When the reaction vessel is opened, the purified crystals and impurities are removed.