Greater capacity is secured by adding more plates. Raised sections (corrugations) on the plates in the form of knobs, diamonds and channels, help provide the turbulent action. They are tightened into place, and designed to provide a uniform, but somewhat turbulent flow for rapid heat transfer. The plates are numbered and must be properly assembled. A space of approximately 3 mm is maintained between the plates by a non-absorbent rubber gasket or seal which can be vulcanized to them. The heat moves from a hot to a cold medium through stainless steel plates. These plates are supported in a press between a terminal block in each heating and cooling sections.
Its plates may be used for heating, cooling and regeneration. The PHE is a compact, easily cleaned unit. The Plate Heat Exchanger (PHE) (also called Paraflow) is commonly used in the HTST system. Maintains a constant head of the milk for feeding the raw milk pump also receives milk diverted by FDV (if at all diverted).Įither a rotary positive pump between the regeneration and heating sections (USA), or a centrifugal pump with a flow control device to ensure constant output, after FCBT (UK and Europe) is used. There is some variation in the use or order of these steps in different milk processing plants.Ģ8.7.4.1 Float-controlled balance tank (FCBT) The HTST pasteurizer gives a continuous flow of milk which is heated to 72☌ for 15s and then promptly cooled to 5☌ or below.Īn arrangement for incorporation of the filter/clarifier, homogenizer, etc., in the circuit is also made possible. It is the modern method of pasteurizing milk and is invariably used where large volumes of milk are handled. The turning coil agitates the product (but additional agitation may be necessary).ĭisadvantage: Coils are difficult to clean.Ģ8.7 High-Temperature Short-Time (HTST) Pasteurization The heating/cooling medium is pumped through a coil placed in either a horizontal or vertical position, while the coil is turned through the product. A rapidly moving continuous film of water provides rapid heat transfer.
During the holding period, an air space/foam heater (steam or electrically heated) prevents surface cooling of milk.Īdvantage: Flexibility in usage - multipurpose vat.Ī film of water is sprayed from a perforated pipe over the surface of the tank holding the product which is continuously agitated. When heating, the vat cover is left open for escape of off-flavors and when holding, the cover is closed. The milk is agitated by slowly revolving paddles/propellers. The difference between temperature of the hot water and the milk is kept to a minimum. The heat-exchange takes place through the wall of the inner lining. The outer wall (lining) is usually insulated to reduce heat loss. This is double-walled around the sides and bottom of the vat in which hot water or steam under partial vacuum circulates for heating, and cold water for cooling. The LTLT pasteurizer may be of three types After pasteurization, the milk is immediately cooled to 5☌ or below.įig. In general, the term pasteurization as applied to market milk refers to the process of heating every particle of milk to at least 63☌ for 30 min or 72☌ for 15s or to any temperature-time combination which is equally efficient, in a properly operated equipment. In order to retain as many sensory and nutritive properties of the raw materials as possible, different heating methods have been developed to destroy pathogenic organisms (pasteurization) or destroy all microorganisms and inactivate enzymes (sterilization).Īccording to International Dairy Federation (IDF), pasteurization can be defined as ‘a process applied to a product with the object of minimizing possible health hazards arising from pathogenic microorganisms associated with milk by heat treatment, which is consistent with minimal chemical, physical and sensory changes in the product’. Further, a more or less complete inactivation of enzymes occurs, depending on temperature and treatment time.
Heat treatment destroys microorganisms present in milk. This process is widely employed in all branches of dairy industry. Pasteurization came into use on a commercial scale in the dairy industry shortly after 1880 in Germany and Denmark. The word pasteurization is derived from the name of an eminent French scientist Louis Pasteur (1860), who found that heating certain liquids specially wines to a high temperature improved their keeping quality.