H.—34,

(b) Milk-quality Control. —The following tests were made daily on all milk supplied to the dairy factory : (1) Direct miscroscopic count; (2) standard agar plate count; (3) methylene-blue reductase test; (4) B. coli test; (5) curd test. As has been observed in previous seasons, the grading of milk by the direct count, the reductase and curd tests, has shown good agreement between the three tests. Daily determination of the bacterial-content of pasteurized milk by the standard agar plate method enabled a check to be kept on the efficiency of pasteurization throughout the season. (c) Vitality of Starter Cultures used in Cheese-manufacture. —Records have been kept of the activity of starter cultures used in all cheesemaking experiments by means of the vitality-test in pasteurized whole milk and in reconstituted skim-milk as control. The latter test has provided a means of checking variations in the vitality of the starter distinct from influences caused by the milk. (d) Cream-quality Control. —The quality of cream-supplies has been determined by means of the standard agar plate count and the B. coli test on both raw and pasteurized creams. It is seldom that the count of pasteurized cream exceeds a few hundred per cubic centimetre, and frequently the count is less than one hundred with no coli present in 1 cc. (e) Control of Yeasts and Moulds in Butter. —Some time was devoted to this matter. Yeasts were found to predominate in all counts carried out, and investigations showed that the main source of these was the churn. An appreciable reduction in the yeast-count was obtained by filling the churn about three-quarters with boiling water and maintaining at boiling-point for a period of one hour. Such treatment, while effectively reducing the yeast-count, was considered to be too drastic and liable to injure the structure of the churn if practised too frequently. Thorough steaming and rinsing with boiling water regularly before and after use was found to restrict the yeast-count within reasonable limits. It is proposed to continue the work on this subject during the forthcoming season. Dissemination of Results. The fourth annual factory-managers' week was held during the first week in May, when fifty-seven managers and first assistants were present at the Institute. A monthly bulletin was supplied to the Dairy Exporter. Addresses were given at various meetings convened by the New Zealand Dairy Factory Managers' Association, dairy companies, and the National Dairy Conference. The following technical publications were issued during the year : —

The following are in the press : —

22

Institute Publication Title. Author. Journal. No. 49 Observations on Sudden Changes in the Kate of Acid H. R. Whitehead and J. Dairy Research. Formation in Milk by Cultures of Lactic Steptococci G. A. Cox 53 Dairy Factory By-products and Drainage Wastes .. F. H. McDowail . . J. R. San. Ins., N.Z. Branch. 55 The Influence of Lactic Streptococci on the Ripening I. R. Sherwood and J. Dairy Research. of Cheddar Cheese H. R. Whitehead 57 A Simple Method for Detecting " Non-acid" Milk .. G. A. Cox .. .. N.Z. Jour. Agri. 59 The Spreadability of Butter .. . . G. M. Valentine and N.Z. Jour. Sci. & Tech. J. D. Sargent 60 Selection of Starter Culture for Cheese-manufacture.. H. R. Whitehead and N.Z. Jour. Agri. G. A. Cox 63 The Occurrence of Bacteriophage in Cultures of Lactic H. R. Whitehead and N.Z. Jour. Sci. & Tech. Streptococci G. A. Cox 66 Payment for Milk for Cheesemaking .. F. H. McDowail . . Exporter.

Institute Publication Title. Author. Journal. No. Studies in Cheddar-cheese Making— 51 Part 1 .. .. . • ■ • P. H. McDowall and R. M. Dolby 52 Part 2 .. .. .. .. .. F. H. McDowall and R. M. Dolby 56 The Role of Rennet in the Ripening of Cheddar Cheese I. R. Sherwood 61 The Estimation of Diacetyl and Acetyl Methyl Carbinol C. R. Barnicoat 62 The Function of Pepsin and Rennet in the Ripening of I. R. Sherwood Cheddar Cheese 64 The Estimation of Salt in Butter .. .. F. H. McDowall and C. L. McDonald 65 Diacetyl in Cold-stored Butters .. .. C. R. Barnicoat 67 Rate of Temperature Change in Butter packed in Boxes F. H. McDowall of Different Types 68 The Walker Test for Casein in Milk .. .. „ 69 Bacteriophage Phenomena in Cultures of Lactic H. R. Whitehead and Streptococci G. A. Cox 70 Estimation of Casein by Formol Titration after F. H. McDowall and Precipitation with Acid A. K. R. McDowell