A Study of the chemical changes involved in the ripening of Cheddar cheese becomes largely a study of protein degradation. The result of the breakdown of the casein through the combined effect of rennin, milk enzymes and proteolytic bacteria is to furnish water-soluble decomposition products which increase in amount as the ripening progresses. In consequence a method used by many workers in the past to follow the course of ripening was to determine at intervals the percentage of soluble nitrogen present in the cheese. It must be remembered, however, that the decomposition products which make up this soluble nitrogen factor comprise different compounds such as caseoses, peptones, polypeptides, amino acids and ammonia, which are of decreasing molecular complexity in the order named. All these compounds are soluble in water to varying extents and, therefore, a determination of the soluble nitrogen merely gives an estimate of the sum total of the nitrogen which they represent, and gives no information as to the way in which it is distributed amongst the different types.