Temperature sensing method and system for pasteurization

A method and system are provided for pasteurizing a fluid product. Heated fluid product flows through a passageway to a directional flow valve for directing the heated fluid product through either a primary flow path or a divert flow path. A temperature sensor senses temperature of the heated fluid product at a location in the passageway spaced from the valve so that change in temperature of a portion of the heated fluid product is sensed before that portion of the heated fluid product flows to the valve. The valve directs flow of the heated fluid product from the passageway to the divert flow path when the sensed temperature is below a predetermined temperature for pasteurization of the fluid product, and continues to direct the flow to the diverting flow path at least until the sensed temperature is at or above the predetermined temperature for a predetermined period of time. Optionally, a second temperature sensor is provided near the valve to monitor temperature of the fluid product before switching the valve for flow along the primary flow path.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method and system for pasteurizing a 
fluid product. More particularly, the present invention relates to a 
method and system for sensing temperature of a heated liquid product and 
controlling a directional flow valve based on the sensed temperature to 
ensure proper pasteurization. 
2. Description of Related Art 
Many different types of liquid products are pasteurized to reduce or to 
eliminate microorganisms. During a pasteurization process, liquid product 
is heated for a sufficient amount of time and at a sufficient temperature 
to kill all or substantially all of the microorganisms initially present 
in the liquid. As a result of numerous scientific studies, governments and 
industries have established standard operating parameters for 
pasteurization of particular products. For example, these standards 
include the recommended minimum temperature at which the product should be 
heated and the recommend minimum time during which the product should be 
at or above the minimum temperature. 
If a liquid product is not heated for a sufficient amount of time or at a 
sufficient temperature, serious consequences could result. When a liquid 
product is not adequately pasteurized, surviving microorganisms can grow 
and cause spoilage. The survival of microorganisms intended to be killed 
in the pasteurization process can cause health risk to the consumer and/or 
economic loss to the producer. 
Various attempts have been made to improve pasteurization processes, but 
some of these approaches have had limited success. In one approach, a 
temperature sensor for sensing temperature of heated liquid product is 
placed in a holding coil between a liquid heater and a valve, immediately 
adjacent to the valve. When the temperature sensor senses that the liquid 
product is below a predetermined required temperature, the valve directs 
flow of liquid product to a secondary flow path rather than a path for 
properly pasteurized liquid. However, the inventor has discovered that 
this configuration allows for flow of under-pasteurized product to the 
path for properly pasteurized liquid before reduced temperature liquid 
product is sensed by the sensor. Such an arrangement also may allow flow 
of under-pasteurized product to the path for properly pasteurized liquid 
when flowing liquid product includes cycles of low temperature product 
mixed with relatively higher temperature product. 
In another approach, liquid product is heated to a higher temperature and 
for a longer time than that which is required to perform adequate 
pasteurization. Although this approach is sometimes successful at ensuring 
adequate control of microorganisms, the increased temperature and 
increased duration for heating may destroy vitamins in a liquid product 
and/or alter flavor of a liquid product. This increased heating also 
requires more energy and is therefore less efficient. 
In light of the foregoing, there is a need in the art for an improved 
method and system for pasteurization. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention is directed to a pasteurization method 
and system that substantially obviate one or more of the limitations of 
the related art. 
To achieve these and other advantages and in accordance with the purpose of 
the invention, as embodied and broadly described herein, the invention 
includes a method of pasteurizing a fluid product, comprising passing the 
fluid product through a heat exchanger to increase temperature of the 
fluid product, flowing the heated fluid product through a passageway to a 
valve, the valve selectively placing the passageway in flow communication 
with either a diverting flow path or a primary flow path, sensing the 
temperature of the heated fluid product at a predetermined location in the 
passageway, the predetermined location being spaced from the valve so that 
a change in temperature of a portion of the heated fluid product is sensed 
before that portion of the heated fluid product flows to the valve, 
controlling the valve so that the valve directs flow of the heated fluid 
product from the passageway to the diverting flow path when the sensed 
temperature is below a predetermined temperature for pasteurization of the 
fluid product, and continues to direct the flow to the diverting flow path 
at least until the sensed temperature is at or above the predetermined 
temperature for a predetermined period of time, and operating the valve to 
direct flow of the heated fluid product from the passageway to the primary 
flow path. 
In another aspect of the invention, temperature of the fluid product is 
sensed adjacent to the valve to determine whether the temperature of the 
fluid product is at or above the predetermined temperature before 
switching the valve from divert flow to primary flow. 
In another aspect, the invention includes a system for pasteurizing a fluid 
product. The system comprises a heat exchanger for heating the fluid 
product, a passageway fluidly coupled to the heat exchanger so that the 
heated fluid product flows from the heat exchanger and through the 
passageway, a valve fluidly coupled to the passageway, a primary flow 
path, and a diverting flow path, the valve selectively placing the 
passageway in flow communication with either the diverting flow path or 
the primary flow path, a first temperature sensor for sensing the 
temperature of the heated fluid product in the passageway, the first 
temperature sensor being spaced from the valve so that the first 
temperature sensor senses a change in temperature of a portion of the 
heated fluid product before that portion of the heated fluid product flows 
to the valve, and a controller for controlling the valve to direct flow of 
the heated fluid product selectively to the primary flow path or to the 
diverting flow path, the controller controlling the valve so that the 
valve directs flow of the heated fluid product from the passageway to the 
diverting flow path when the sensed temperature is below a predetermined 
temperature for pasteurization of the fluid product, and continues to 
direct the flow to the diverting flow path at least until the sensed 
temperature is at or above the predetermined temperature for a 
predetermined period of time. 
In a further aspect, a second temperature sensor is provided for sensing 
whether temperature of fluid product adjacent to the valve is at or above 
the predetermined temperature before switching the valve from divert flow 
to primary flow. 
It is to be understood that both the foregoing general description and the 
following detailed description are exemplary, and are intended to provide 
further explanation of the invention as claimed.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference will now be made in detail to the present preferred embodiment of 
the invention, an example of which is illustrated in the accompanying 
drawing. 
In accordance with the invention, there is provided a fluid product 
pasteurization system. As shown in the drawing, the system includes a 
liquid product source 10, a heat exchanger 20, a passageway 30 fluidly 
coupled to the heat exchanger 20, and a directional flow valve 40. As 
explained below, the directional flow valve 40 directs flow of liquid 
product heated in the heat exchanger 20 either along a primary flow path 
42 or along a diverting flow path 44 depending on the temperature of the 
heated liquid product. 
The system of the present invention can be practiced to pasteurize many 
different types of fluid products such as pure liquid products or liquid 
products carrying particles. For example, the system is capable of 
pasteurizing beverages containing fruit juice, fruit flavor, vegetable 
juice, or tea. The system is also capable of pasteurizing dairy products, 
such as milk, ice cream, or cheese. In a preferred embodiment of the 
invention, the present system is capable of pasteurizing a beverage 
containing grape juice. 
The primary flow path 42 is preferably in fluid communication with a 
container filling device 50, such as an apparatus capable of filling 
bottles or cans with the liquid product. The container filling device 50 
may optionally include a bowl shaped reservoir for temporarily storing the 
liquid product. Alternatively, the liquid product flowing through the 
primary flow path 42 could be processed further and/ or stored in a large 
container or tank (not shown). In some instances, such as when the liquid 
product is a dairy product, it may be desirable to cool the liquid product 
as it flows through the primary flow path 42. An optional cooler 48 may 
also be provided in the primary flow path 42 to cool the liquid product as 
it flows from the directional flow valve 40. 
As shown in the drawing, the divert flow path 44 is preferably in fluid 
communication with the liquid product source 10 to return 
under-pasteurized liquid product back to the source 10. Optionally, a 
cooler 46 is positioned in the divert flow path 44 between the diverting 
valve 40 and the source 10 to cool the liquid product before it returns to 
the source 10. The cooler 46 is used when the liquid product in the source 
could be damaged by prolonged heating, such as when the liquid product is 
a dairy product. 
The liquid product source 10 is any type of storage container or tank 
capable of storing the liquid product. When the system is used to 
pasteurize liquid products, such as dairy products, requiring 
refrigeration during storage, the liquid product source 10 preferably 
includes refrigeration equipment. 
A pump 12 pumps the liquid product from the source 10 to the heat exchanger 
20. In the heat exchanger 20, steam or hot water flowing to the heat 
exchanger 20 via a line 22 transfers heat to the liquid product to 
increase the temperature of the liquid product and thereby kill 
microorganisms in the liquid product. The heat exchanger 20 is designed so 
that steam/hot water and liquid product flowing into the heat exchanger 20 
do not mix with one another. For example, the heat exchanger 20 may 
include a heat conductive plate separating respective passages for the 
liquid product and for the steam/hot water. Alternatively, the heat 
exchanger 20 may be a shell and tube heat exchanger or any other known 
heat exchange design. 
To maximize heat transfer, the heat exchanger 20 is preferably a 
counter-flow heat exchanger wherein relatively warmer steam/hot water 
entering the heat exchanger 20 heats relatively warmer liquid product just 
before it exits the heat exchanger 20. In addition, the heated liquid 
product could be used for regeneration by configuring the heat exchanger 
20 so that heated liquid product exiting the heat exchanger 20 heats 
relatively cooler liquid product flowing to the heat exchanger 20. A 
controller 60 including one or more microprocessors controls operation of 
a valve 24 in the line 22 to regulate flow of the steam/hot water supplied 
to the heat exchanger 20 and thereby regulate temperature of the liquid 
product heated in the heat exchanger 20. As explained in more detail 
below, the controller 60 also preferably controls a significant number of 
other components of the system. 
The pump 12 pumps the heated liquid product from the heat exchanger 20 and 
through the passageway 30 to the directional flow valve 40. In response to 
signals from the controller 60, the directional flow valve 40 is movable 
between a primary flow position, in which the directional flow valve 40 
permits flow from the passageway 30 to the primary flow path 42 while 
preventing flow along the divert flow path 44, and a divert flow position 
in which the diverting valve permits flow from the passageway 30 to the 
divert flow path 44 while preventing flow along the primary flow path 42. 
Many different types of valve designs could be used for the directional 
flow valve 40. In an embodiment of the invention, the directional flow 
valve 40 is a pneumatic plunger valve. 
The passageway 30 is preferably insulated so that the liquid product does 
not lose a significant amount of heat as it flows from the heat exchanger 
20 to the directional flow valve 40. If the liquid product is heated 
sufficiently in the heat exchanger 20, the heated liquid product remains 
at or above the predetermined pasteurization temperature for the liquid 
product while it flows in the passageway 30 to the directional flow valve 
40. Preferably, the length and flow capacity of the passageway 30 are 
sufficient enough to allow the flowing liquid product to reside in the 
passageway 30 for at least the minimum amount of time required for 
pasteurization of the liquid product at this predetermined temperature. 
Although the passageway 30 shown in the drawing is straight, the passageway 
30 may be a curved or coiled to reduce the space required for installation 
while providing a sufficiently long flow passage. Optionally, the 
passageway 30 may include an adjustable length portion for changing the 
length of the passageway 30 during pasteurization of different types of 
liquid products. 
A first temperature sensor 70 and a second temperature sensor 72 are 
positioned at opposite end portions of the passageway 30. The first 
temperature sensor 70 is immediately adjacent or adjacent to the heat 
exchanger 20 to sense temperature of heated liquid product entering the 
passageway 30. The second temperature sensor 72 is immediately adjacent or 
adjacent to the directional flow valve 40 to sense temperature of the 
liquid product flowing from the passageway 30 to the directional flow 
valve 40. The first and second temperature sensors 70 and 72 send signals 
to the controller 60 corresponding to the sensed temperatures of the 
liquid product. The controller 60 controls switching of the directional 
flow valve 40 between the primary flow position and the divert flow 
position based on the temperatures sensed by the first and second 
temperature sensors 70 and 72 to ensure that unpasteurized or 
under-pasteurized liquid product flows through the divert path 44 rather 
than through the primary flow path 42. 
The first and second temperature sensors 70 and 72 may be any type of 
temperature sensor capable of being used for liquid pasteurization 
systems. For example, the temperature sensors 70 and 72 are preferably 
resistance thermocouple devices or even liquid capillary temperature 
sensing devices. Each of the sensors 70 and 72 preferably includes 
multiple sensing elements in a single probe to allow for detection of 
faulty operation of one or more of the sensing elements in the probe. 
The inventor has discovered that temperature sensors used in pasteurization 
systems, such as the temperature sensors 70 and 72, have a time lag from 
when the sensors actually encounter a temperature change to when the 
sensors sense this temperature change. For example, testing has shown that 
the time lag can be as long as 30 seconds to detect a 2.degree. Fahrenheit 
temperature change. This time lag can be attributed at least in part to 
the time required for heat transfer to take place between the liquid 
product and the temperature sensors. In other words, relatively cooler 
liquid product cools temperature sensors, such as temperature sensors 70 
and 72, over a period of time before the temperature sensors actually 
sense the decreased temperature. 
In the present invention, the sensor time lag is taken into account during 
design of the system and control of the directional flow valve 40 to 
ensure that potentially under-pasteurized or unpasteurized product flows 
through the divert flow path 44 rather than through the primary flow path 
42. The first temperature sensor 70 is preferably located a sufficient 
distance away from the directional flow valve 40 so that the first 
temperature sensor 70 senses temperature of a portion of the liquid 
product before that portion of the liquid product flows to the directional 
flow valve 40 assuming a maximum flow rate for the pump 12. 
In other words, the time required for liquid product to flow from the 
sensor 70 to the directional flow valve 40 at the maximum flow rate of the 
pump 12 is greater than the time lag of the first temperature sensor 70. 
To achieve this relationship, the flow capacity of the passageway 30 
between the first temperature sensor 70 and the directional flow valve 40 
is sufficient to accommodate all of the liquid product pumped from the 
heat exchanger 20 during maximum flow rate of the pump 12. For example, 
when the temperature sensor 70 has a 15 second time lag and the pump 12 
has a maximum pasteurization flow rate of 100 gallons per minute, the 
portion of the passageway 30 between the first temperature sensor 70 and 
directional flow valve 40 preferably has a flow capacity of at least 25 
gallons. 
The controller 60 monitors output from the first temperature sensor 70 to 
determine when to switch the directional flow valve 40 from the primary 
flow position to the divert flow position. When the first temperature 
sensor 70 senses a temperature less than the required pasteurization 
temperature for the liquid product, the controller 60 acts in response to 
the signal from the first temperature sensor 70 to switch the directional 
flow valve 40 to the divert flow position. The spacing of the first 
temperature sensor 70 from the directional flow valve 40 ensures that the 
directional flow valve 40 diverts essentially all of the relatively low 
temperature liquid product to the diverting flow path 44 before this 
liquid product has an opportunity to enter the primary flow path 42. 
The controller 60 also controls switching of the directional flow valve 40 
from the divert flow position to the primary flow position. After the 
directional flow valve 40 switches to the divert flow position, the 
controller 60 monitors output from the first temperature sensor 70. When 
the first temperature sensor 70 initially senses the liquid product is at 
or above the minimum pasteurization temperature, the controller 60 
continues to monitor output from the first temperature sensor 70 for a 
period of time sufficient to allow substantially all of the liquid product 
between the first temperature sensor 70 and directional flow valve 40 to 
flow into the diverting path 44. If the first temperature sensor 70 does 
not sense a temperature below the minimum required pasteurization 
temperature during this time period, the controller 60 then determines 
whether the temperature sensed by the second temperature sensor 72 is at 
or above the minimum pasteurization temperature. When the temperatures 
sensed by the temperature sensors 70 and 72 are both at or above the 
required pasteurization temperature at the end of the time period, the 
controller 60 switches the directional flow valve 40 from the divert flow 
position to the primary flow position. 
The pasteurization system has a delay from when the first temperature 
sensor 70 senses a sufficient temperature to when the controller 60 
verifies a sufficient temperature sensed by the second temperature sensor 
72 and switches the directional flow valve 40 to the primary flow 
position. The magnitude of the delay is sufficient to purge liquid product 
between the first temperature sensor 70 and directional flow valve 40 
through the divert flow path 44 after the first temperature sensor 70 
senses a sufficient temperature. Switching the directional flow valve 40 
to the primary flow position after the delay ensures that any relatively 
lower temperature liquid product positioned between the first and second 
temperature sensors 70 and 72 flows along the diverting flow path 44. This 
is particularly useful when cyclical flow of relatively warmer and 
relatively cooler liquid product fills the passageway 30 and causes both 
of the temperature sensors 70 and 72 to sense a sufficient temperature 
while the cooler liquid product is positioned between the temperature 
sensors 70 and 72. 
Although the preferred embodiment of the invention includes both 
temperature sensors 70 and 72 to monitor whether the liquid product is 
sufficiently pasteurized, the present invention could also be practiced 
without the second temperature sensor 72. In such an arrangement, the 
controller 60 switches the directional flow valve 40 from the divert flow 
position to the primary flow position after the delay without sensing 
temperature of the liquid product immediately adjacent to the directional 
flow valve 40. 
A method of pasteurizing a fluid product with the structure shown in the 
drawing is discussed below. Although the invention is described in 
association with this structure, the method of the invention in its 
broadest sense could be practiced with other structures. 
At the beginning of a pasteurization procedure, the controller 60 opens the 
valve 24 to initiate steam flow through the heat exchanger 20 via the 
steam line 22, while the pump 12 pumps liquid product from the source 10 
and through the heat exchanger 20. The steam flowing through the heat 
exchanger 20 heats the liquid product to eliminate microorganisms present 
in the liquid product. 
The liquid product flows from the heat exchanger 20 to the passageway 30, 
and the temperature sensor 70 senses temperature of the liquid product as 
it enters the passageway 30. As the heated liquid product flows through 
the passageway 30, the liquid product is not cooled significantly. 
Maintaining the increased temperature of the liquid product in the 
passageway 30 eliminates additional microorganisms as the liquid product 
flows to the directional flow valve 40. 
At the beginning of the pasteurization process, the directional flow valve 
40 is in the divert flow position so that the liquid product flows 
initially through the divert flow path 44. Optionally, the cooler 46 cools 
the liquid product, and the diverted liquid product returns to the source 
10. 
The controller 60 monitors the temperature sensed by the first temperature 
sensor 70. When this sensed temperature is at or above the minimum 
temperature required for adequate pasteurization of the liquid product, 
the controller 60 continues to monitor the temperature sensed by the first 
temperature sensor 70 for a period of time long enough to allow all of the 
liquid product between the first temperature sensor 70 and directional 
flow valve 40 to flow along the diverting flow path 44. When the second 
temperature sensor 72 is not present, the controller 60 switches the 
directional flow valve 40 to the primary flow position if the temperature 
sensed by the first temperature sensor 70 is at or above the minimum 
pasteurization temperature during this time period. 
The system operates similarly when the second temperature sensor 72 is 
included. If the temperature sensed by the first temperature sensor 70 is 
at or above the minimum pasteurization temperature during the time period, 
the controller 60 determines the temperature sensed by the second 
temperature sensor 72 at the end of the time period. If the temperatures 
sensed by the first and second temperature sensors 70 and 72 are at or 
above the required minimum pasteurization temperature, the controller 60 
switches the directional flow valve 40 to the primary flow position. 
In the primary flow position of the directional flow valve 40, the liquid 
product flows along the primary flow path 42 for further processing or 
storage. During processing of certain liquid products, such as milk, the 
cooler 48 cools the liquid products. In a preferred practice of the 
invention, the container filling device 50 fills containers with the 
liquid product flowing in the primary flow passage 42. 
The controller 60 preferably monitors the first and second temperature 
sensors 70 and 72 throughout the pasteurization process. If one or both of 
the temperature sensors 70 and 72 senses a temperature below the minimum 
pasteurization temperature at any time during the pasteurization process, 
the controller 60 controls the directional flow valve 40 to continue flow 
to the divert path 44 or to switch flow to the divert path 44. This limits 
the amount of under-pasteurized liquid product flowing to the primary flow 
path 42. 
It will be apparent to those skilled in the art that various modifications 
and variations can be made to the structure and methodology of the present 
invention without departing from the scope or spirit of the invention. The 
system and method of the present invention can be practiced to pasteurize 
many different types of fluid products such as pure liquid products or 
liquid products carrying particles. In view of the foregoing, it is 
intended that the present invention cover modifications and variations of 
this invention provided they fall within the scope of the following claims 
and their equivalents.