Method of increasing the durability of milk
This is a continuation, of application Ser. No. 793,251, filed May 3, 1977, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method of increasing the durability of fresh milk. Heretofore, two alternative methods were used to obtain a greater durability of packaged fresh milk, namely post-sterilization of milk in glass bottles in sterilization towers; or pre-sterilization of milk by ultra-high heating and subsequent cold filling under substantially aspetic conditions. 
     All known methods of filling milk while cold were subject to considerable disadvantages. An increase in the durability of the milk did impair especially the taste and nutrition-physiological qualities of the milk. In particular when preceded by ultra-high heating, a considerable re-infection risk existed which could only be reduced and held within bounds by high operational cost. 
     BRIEF SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide a method of increasing the durability of milk, and especially of fresh milk. 
     Another object of the invention consists in packaging fresh milk in a form substantially sterilized and disinfected and free of the risk of re-infection. 
     Still furthermore, it is an object of the invention to make fresh milk durable for storage of from 2 to 6 weeks depending on the quality of the milk. 
     It is still another object of the invention to package fresh milk in substantially sterilized form free of the risk of re-infection while avoiding any noticeable impairment of taste and/or reduction in the nutrition-physiological quality of the milk. 
     In addition, it is an object of the invention to keep operational costs relatively low when filling or packaging fresh milk in a sterilized and re-infection free manner. 
    
    
     The above mentioned objects have been realized in accordance with the present invention by recognizing that the disadvantages of heretofore known methods are caused primarily by cold filling or packaging of the milk and that the risk of re-infection can be eliminated, for all practical purposes, by including the filling and packaging process into the time period in which milk is kept hot, hereinafter referred to as the &#34;hot holding period&#34;. 
     Accordingly, the present invention proposes subjecting the fresh milk to pasteurization including a short-term preheating to approximately 100° to 120° C., preferably to 105° C., for reliably killing all pathogenic germs and to subsequent further processing at approximately 70° to 80° C., preferably at approximately 72° C. Thereafter, at a temperature of from 70° to 80° C. within an aseptic protective gas atmosphere, the milk is filled into heat-resistant, substantially gas-tight synthetic compound or laminated foil packages and immediately upon closing of the packages is cooled in several stages, first to approximately 50° to 60° C., preferably about 50° to 55° C., and thereafter to the planned storage temperature. 
     It was found that the raw milk germ content in practice varies widely (differences in the raw milk germ content differing by a factor of 100 are not unusual). If the germ content is low it is possible to achieve the increase in the durability of filled and packaged fresh milk, in accordance with the present invention, also without the short preheating step to 100° to 120° C., when retaining the other above-mentioned method steps. 
     Impairment of the taste of the milk can be avoided especially by limiting and shortening as far as possible the hot holding period, in which the milk is held at a temperature of, or above, approximately 55° C. With hot holding periods of from 40 to 50 seconds reached in practice and distributed over the hot treatment in the pasteurizer and the hot holding period in the package until reaching the first re-cooling stage of approximately 50° to 60° C., the taste of the thus treated milk was not noticeably affected. After filling at 70° to 80° C., preferably at 72° C., the milk should be subjected to shock cooling to a temperature of 50° to 55° C. in order to shorten the hot holding period. Thereafter, the pasteurized and hot packaged milk is cooled to the storage temperature. This last mentioned cooling to the storage temperature is not critical as to time. 
     Hot filling in an aseptic protective gas atmosphere eliminates the re-infection risk existing in known filling methods and prevents at the same time ingress of air into the packages which could otherwise cause oxidation processes and foster the formation of new bacteria or germs. 
     Preheating of the fresh milk, which is necessary particularly with raw milk of high bacteria or germ content, preferably should amount to approximately 3 to 5 seconds with a hot holding period (milk temperature at or above 55° C.) of approximately 40 to 50 seconds. 
     Several modifications are possible without deviating from the basic idea of the present invention. Thus, for instance, as mentioned above the preheating of raw milk having a low germ content can be eliminated, or instead of the short-term preheating to approximately 100° to 120° C., also ultra-high heating of the milk to temperatures up to 145° C. may precede the hot filling according to the present invention at a temperature of from 70° to 80° C. With the just-mentioned ultra-heating, however, there exists the danger that the taste of the milk will be somewhat affected.