Free Amino Nitrogen
Free Amino Nitrogen (FAN) is a significant nutrient for yeast. Too little can lead to stalled ferments, too much can lead to excess tails (Fusel alc/oils). FAN is a group of amino acids than yeast uses to build esters, sterols (used in cell walls) and other compounds. In whiskey it is created when the grain is in heated in the malting process or during a protein rest. Proteins and complex amino acids are broken down by proteolytic enzymes (peptidase and protease).