The low productivity of algal cultures in the production of high-value compounds is the most significant bottleneck for commercialization of this technology. Cultures in which cell mass is reused for continuous production are proposed as a solution to overcome this problem. Recently, a method was developed in which beta-carotene was harvested from the microalga Dunaliella salina grown in a two-phase bioreactor. This raises the question of whether this technique could also be used in the mass production of secondary metabolites. Understanding the mechanism of the milking process and its relationship to the product formation pathway should reveal whether other products can be milked from various species of microalgae.