The larger proportion of bacteria in cream as it is found in the creamery belong to the acid-producing class, but in the process of ripening, these forms seem to thrive still better, so that when it is ready for churning the germ content of the cream is practically made up of this type. ~Effect on churning.~ In fresh cream the fat globules which are suspended in the milk serum are surrounded by a film of albuminous material which prevents them from coalescing readily. During the ripening changes, this enveloping substance is modified, probably by partial solution, so that the globules cohere when agitated, as in churning. The result is that ripened cream churns more easily, and as it is possible to cause a larger number of the smaller fat-globules to cohere to the butter granules, the yield is slightly larger--a point of considerable economic importance where large quantities of butter are made. ~Development of acid.~ The result of this enormous bacterial multiplication is that acid is produced in cream, lactic being the principal acid so formed. Other organic acids are undoubtedly formed as well as certain aromatic products. While the production of acid as a result of fermentative activity is usually accompanied with a development of flavor, the flavor is not directly produced by the formation of acid. If cream is treated in proper proportions with a commercial acid, as hydrochloric,[154] it assumes the same churning properties as found in normally ripened cream, but is devoid of the desired aromatic qualities. Lactic acid[155] has also been used in a similar way but with no better results. The amount of acidity that should be developed under natural conditions so as to secure the optimum quality as to flavor and aroma is the most important question in cream ripening. Concerning this there have been two somewhat divergent views as to what is best in practice, some holding that better results were obtained with cream ripened to a high degree of acidity than where a less amount was developed.[156] The present tendency seems to be to develop somewhat more than formerly, as it is thought that this secures more of the "high, quick" flavor wanted in the market. On the average, cream is ripened to about 0.5 to 0.65 per cent. acidity, a higher percentage than this giving a strong-flavored butter. In the determination of acidity, the most convenient method is to employ the Farrington alkaline tablet, which permits of an accurate and rapid estimation of the acidity in the ripening cream. The amount of acidity to be produced must of necessity be governed by the amount of butter-fat present, for the formation of acid is confined to the serum of the cream; consequently, a rich cream would show less acid by titration than a thinner cream, and still contain really as much acid as the other. The importance of this factor is evident in gathered-cream factories.