It was felt that it would be wholly unsatisfactory to make this investigation by means of laboratory brewings on a small scale, as the results thus obtained would not show the true conditions, because it is not possible in the laboratory to duplicate exactly the mashing or fermenting processes actually used in a commercial way. It was decided, therefore, to attempt, with the cooperation of several breweries, to make this study under the exact conditions prevailing in commercial plants. Access was secured to several breweries making different types of products from various kinds of raw materials, under such conditions that it was possible to obtain a complete history of the beer through its various stages to the finished product. One of the writers (Riley) watched the method of manufacture during its whole process and obtained samples of the product at the various stages of manufacture. Thus, it was possible to procure finished samples with practically the same degree of certainty, as regards knowledge of composition and history, as would have been the case had they been prepared in the laboratory. In three different breweries manufacturing a wide range of products samples of the wort and beer were obtained in this manner, the entire process of manufacture being studied in detail. A record showing the kind and amount of raw materials placed in the mash and in the cooker was made of the samples collected from these three breweries. A record also was kept of the time and temperature of each operation until the mash was ready to run into the kettle. The filtering and sparging[1] of the mash, the time of boiling in the kettle, the amount of hops added and the point at which they were added, and the break[2] of the wort were all noted. After the wort had been pumped from the kettle its course was followed through the hop jack[3] over the coolers to the settling tank. The specific gravity or Balling[4] of the original wort, the temperature at which the product was pitched,[5] the aeration of the wort, the kind and amount of yeast added, as well as the time and maximum temperature of the primary fermentation, also were noted. The course of the beer through the storage vats, chip casks, and filters to the racks was watched, and samples of the wort and of the beer in its various stages of production were collected and examined. [Footnote 1: Washing the grains with hot water to remove the extract or valuable constituents as completely as possible.] [Footnote 2: Precipitation and uniting, in the form of flakes, of the coagulable albuminoids, leaving the liquid clear.] [Footnote 3: A filtering tank.] [Footnote 4: Percentage of solids in the liquor according to the Balling hydrometer.] [Footnote 5: Pitching is the operation of adding the yeast to the wort.] METHODS OF ANALYSIS.