The nitrogen in foods and other materials that exists in amino (NH₂) groups — a practical measure of protein-derived nitrogen, distinct from total Kjeldahl nitrogen, which counts everything. Alpha-amino nitrogen is used as an index of the amino acid nitrogen content of raw materials, intermediates and finished products; brewers know it as free amino nitrogen (FAN). In brewing it is a critical process parameter: yeast needs enough FAN to grow and ferment cleanly, and too little leads to sluggish or stuck fermentations and off-flavours. Maltsters and brewers therefore monitor amino nitrogen closely as a predictor of fermentation performance.