To control the clarity and tannic/smoothness:
"In one demonstration, the researchers used a genetic network to precisely control a process in yeast that is crucial for brewing beer, called flocculation. The timing and strength of flocculation determines whether a beer is cloudy and tannic or clear and smooth, and initiating the process often relies on chemical additives. To genetically engineer flocculation control into yeast, the researchers constructed a toggle switch, a type of synthetic network that makes use of two mutually opposing promoters that can toggle between one state and another. If one promoter is weak and the other is strong, the stronger one will eventually overwhelm the weak one, flipping the switch. The length of time that it takes to flip the switch can be tweaked by changing the relative strengths of the two promoters, essentially creating a genetic timer. The researchers engineered this network into yeast so that when the toggle switches on, the yeast is made to flocculate."
Better brewing through chemistry.