Process of High-Temperature Short-Time (HTST) Pasteurization
Since listeria events, the ice cream factory pay more attention to food safety. Ice cream sterilization is a important step in the process of ice cream production.
The High-Temperature Short-Time (HTST) pasteurization stan-dard was designed to achieve a five-log reduction, killing 99.999% of the number of viable micro-organisms in milk. This is considered adequate for destroying almost all yeasts, molds, an-d common spoilage bacteria an-d also to ensure adequate destruction of common pathogenic, heat-resistant organisms (including Mycobacterium tuberculosis, which causes tuberculosis, but not Coxiella burnetii, which causes Q fever).
As a precaution, modern equipment tests an-d identifies bacteria in milk being processed. HTST pasteurization processes must be designed so the milk is heated evenly, an-d no part of the milk is subject to a shorter time or a lower temperature.
HTST milk is forced between metal plates or through pipes heated on the outside by hot water, an-d the milk is heated to 72 ºC (161 °F) for 15 seconds. Milk simply labeled "pasteurized" is usually treated with the HTST method.
Process of High-Temperature Short-Time (HTST) pasteurization:
Cold raw milk (39.2 ºF an-d 4 ºC) is fed into the pasteurization plant.
The milk passes into the regenerative heating section of the plate heat exchanger. The plate heat exchanger is basically a series of stainless steel plates stacked together with some space in between, forming chambers to hold the milk as it passes through. Let us call the odd-numbered chambers "A" chambers, an-d the even-numbered chambers, "B" chambers. In the regenerating section, cold milk is pumped through the A chambers, while milk that has already been heated an-d pasteurized is pumped through the B chambers. The heat from the hot milk passes to the cold milk through the steel plates. This warms the milk to 134.6 to 154.4 ºF (57 to 68 ºC).
Next, the milk passes into the heating section of the plate heat exchanger. Here, hot water in the B chambers heats the milk to at least 161.6 ºF (72 ºC). This is the goal temperature for HTST pasteurization.
The hot milk is then passed through a holding tube. It takes the milk about 15 seconds to pass through the tube, fulfilling the time requirement for this method of pasteurization. The milk has been officially pasteurized once it passes through the holding tube.
Now the pasteurized milk is sent back through the re-generative section, where it warms the incoming cold milk. This cools the pasteurized milk to about 89.6 ºF (32 ºC).
In the last part of the process, the cooling section of the plate heat exchanger uses coolant or cold water to bring the milk to 39.2 ºF (4 ºC).
The High-Temperature Short-Time (HTST) pasteurization stan-dard was designed to achieve a five-log reduction, killing 99.999% of the number of viable micro-organisms in milk. This is considered adequate for destroying almost all yeasts, molds, an-d common spoilage bacteria an-d also to ensure adequate destruction of common pathogenic, heat-resistant organisms (including Mycobacterium tuberculosis, which causes tuberculosis, but not Coxiella burnetii, which causes Q fever).
As a precaution, modern equipment tests an-d identifies bacteria in milk being processed. HTST pasteurization processes must be designed so the milk is heated evenly, an-d no part of the milk is subject to a shorter time or a lower temperature.
HTST milk is forced between metal plates or through pipes heated on the outside by hot water, an-d the milk is heated to 72 ºC (161 °F) for 15 seconds. Milk simply labeled "pasteurized" is usually treated with the HTST method.
Process of High-Temperature Short-Time (HTST) pasteurization:
Cold raw milk (39.2 ºF an-d 4 ºC) is fed into the pasteurization plant.
The milk passes into the regenerative heating section of the plate heat exchanger. The plate heat exchanger is basically a series of stainless steel plates stacked together with some space in between, forming chambers to hold the milk as it passes through. Let us call the odd-numbered chambers "A" chambers, an-d the even-numbered chambers, "B" chambers. In the regenerating section, cold milk is pumped through the A chambers, while milk that has already been heated an-d pasteurized is pumped through the B chambers. The heat from the hot milk passes to the cold milk through the steel plates. This warms the milk to 134.6 to 154.4 ºF (57 to 68 ºC).
Next, the milk passes into the heating section of the plate heat exchanger. Here, hot water in the B chambers heats the milk to at least 161.6 ºF (72 ºC). This is the goal temperature for HTST pasteurization.
The hot milk is then passed through a holding tube. It takes the milk about 15 seconds to pass through the tube, fulfilling the time requirement for this method of pasteurization. The milk has been officially pasteurized once it passes through the holding tube.
Now the pasteurized milk is sent back through the re-generative section, where it warms the incoming cold milk. This cools the pasteurized milk to about 89.6 ºF (32 ºC).
In the last part of the process, the cooling section of the plate heat exchanger uses coolant or cold water to bring the milk to 39.2 ºF (4 ºC).
