Pasteurization is process where every particle of milk and milk products is heated to a minimum required temperature and held there for a minimum required time to kill all pathogenic bacteria and 99.99% of all non-pathogenic bacteria. There are two methods commonly used to pasteurize frozen dairy dessert mixes, vat or High Temperature Short Time (HTST). Product produced for commercial use on either of these systems requires them to be inspected and certified by regulatory officials.

The vat method requires that the mix be heated to a minimum of 1550F for a minimum of 30 minutes. The mix is then homogenized and cooled immediately to below 450F. The term “immediately” is not specifically defined, but most States consider that it must reach this temperature in less than four hours. Mix pasteurized in this method can have a “cooked” flavor note to it that can be more pronounced as the fat content of the mix increases. There is also some discussion that due to the extended heating time, there may be some nutrient loss in the dairy portion.

The HTST method is a higher temperature for a shorter time process than vat pasteurization. This method is usually done through a multi-section plate and frame heat exchanger. A series of stainless steel plates are compressed together with either a heating or cooling medium on one side and product on the other. There are at least three sections to a heat exchanger. A homogenizer is incorporated into the process of pasteurizing the mix. Raw mix enters a “regeneration” section where hot pasteurized mix exchanges heat with the cold raw mix. The heated raw mix is homogenized at this point. The homogenized heated raw mix then passes into the “heater” section where this mix is heated to the pasteurizer set temperature. This hot mix is then held for a preset time based on the pasteurizer set temperature, capacity of the pasteurizer and length of the holding tubes. After being held for the proper temperature and for the correct time, the hot pasteurized mix enters the “regeneration” section where it will transfer up to 90% of its heat to the cold raw mix. The cooled mix then enters the “cold” section of heat exchanger where is cooled to less than 450F. The time required to pass through all three sections of the heat exchanger is based on the number of plates, heating and cooling capacity, and speed of the pump used for timing the mix in the system. The minimum temperature and time for a frozen dairy dessert mix is 1750F and held at this temperature for 25 seconds. The time decreases as the temperature increases, at 1800F the minimum time is 15 seconds.

The Frozen Dessert Center vat pasteurizes small batches of 7 gallons of mix in a Stephans vat pasteurizer. The mix is heated to 1850F, the hot mix is then transferred to a homogenizer and then returned to the vat for cooling. This machine is used for research and development projects. It is not inspected by regulatory officials. All of the dairy components that we use have been pasteurized or heat treated in the case of powders. We are confident that this system produces safe product for evaluation in the laboratory. We do not recommend that product produced in this method be used for sales or distribution.

The Babcock Dairy Plant can pasteurize a minimum of 50 gallons of mix through a State inspected and sealed High Temperature Short Time pasteurizer. The mix is heated to a minimum of 1800F for 15 seconds, homogenized and cooled. Then cooled mix is pumped to a vat for either freezing or bagging into 2.5 gallon bags.