430 ENGINEERING ASPECTS OF PASTEURIZATION 



ing the foam, or to keep the foam up to the pasteurizing temperature by heating the 

 air in the holder. The worst offenders as foam creators are the separator, the old- 

 type clarifier, and the centrifugal- type heater. The barrel-type heater will also cause 

 foam under certain operating conditions. Pumps which suck air will incorporate it 

 in the milk, causing foam. Dropping milk into a storage vat or pasteurizer holder 

 with considerable force and turbulence also creates foam. 



Intelligent study and experimenting with the various units will usually be re- 

 warded by complete elimination or marked reduction of foam present during pas- 

 teurization. The new type, "non-froth" clarifier when operated properly creates very 

 little, if any foam. Schier' reports that foam can be practically, if not entirely, elim- 

 inated while using a centrifugal-type heater, by passing the milk through a specially 

 elevated float tank, before discharging it into a holder. Pumps can be repaired or re- 

 placed to eliminate foam creation at this point. Inlet pipes extending to the side or 

 bottom of a pasteurizer holder will usually accompHsh the smooth, non-turbulent 

 discharge of milk into a holder without foam if none is already present in the milk. 



In some instances it does not prove feasible to eliminate foam from the milk 

 during pasteurization. In these cases the foam should be kept up to the pasteurizing 

 temperature by heating the air above the milk in the pasteurizer holder with steam. 

 Steam valves operated automatically by a thermostat and solenoid, or by a sensitive 

 bulb containing a medium of gas or vapor, can be attached to the top of a pasteurizer 

 holder to admit just sufficient steam to keep the atmosphere and foam above the 

 milk at the pasteurizing temperature at all times. 



Milk splash which is thrown out of the main body of the milk on the cover ami 

 sides of a pasteurizer holder will cool and often drop into the milk again. This de- 

 fect occurs principally in coil vats owing to too rapid rotation of the coils, and can 

 usually be corrected by reducing the speed of the coil to thirty revolutions per minute 

 or less. 



Defective continuous-flow units. — Continuous-flow holders are defective if they fail 

 to hold every particle of the milk at the pasteurizing temperature for thirty minutes. 

 The type consisting of a vertical cylindrical copper tank with nested baffles in which 

 the milk is discharged in at the top and flows down through the holder by gravity has 

 been found to be very unreliable as to holding period. Huelings, Grim, and Horn,' 

 Chilson and Wisler,^ and others report instances where part of the milk was held 

 varying intervals as small as three, ten, and twelve minutes in regular installations 

 of this holder in milk plants. Following an extensive study of this holder North and 

 Phelps'' outlined certain conditions under which it could be relied upon to give sat- 

 isfactory results. These appear to be so exacting as to be practically impossible to 

 attain in the average milk plant. This type of equipment, although still on the 

 market, is being rapidly replaced by new holders of improved design. 



' Schier, O. B.: Proc. Internal. Assoc. Milk Dealers, Plant Sec, p. 69. 1Q26. 



^Huelings, S. M., Grim, G. W., and Horn, D. W.: 13th Ann. Rep., Intcrnat. Assoc. Dairy b° 

 Milk Inspectors, p. 197. 1924. 



3 Chilson, C. H., and Wisler, C. O.: ibid. p. 243. 



"North, C. E., Park, W. H., Moore, V. A., Rosenau, M. J., Armstrong, C, Wadsworth, A. B. 

 and Phelps, E. B.: loc. cil., p. 86. 



