Nisin is polypeptide produced by the food grade dairy starter bacterium, Lactococcus lactis subsp. lactis. It is an antimicrobial agent and is used as a natural food preservative with high efficiency. It has wide inhibition effect on gram + ve bacteria and widely accepted as safe biological preservative. Nisin is used as a food preservative in a number of thermal processed foods, particularly in dairy products, canned foods, plant protein foods and cured meat etc. The use of nisin as food preservative can reduce the temperature of the heat processing and shorten the time of the heat processing required, so that the use nisin can reduce the energy consumption of the process. It can enhance food product quality, and significantly extend the shelf life of food. This book focuses on the isolation, characterization and assay of nisin producing cultures from cheddar cheese samples. This book also covered the activity and quantification of extracted nisin form lactic acid bacteria.