U.S. patent application number 12/072074 was filed with the patent office on 2009-08-27 for process and apparatus for pretreatment of fresh food products.
Invention is credited to James C. Meng.
Application Number | 20090211274 12/072074 |
Document ID | / |
Family ID | 40985800 |
Filed Date | 2009-08-27 |
United States Patent
Application |
20090211274 |
Kind Code |
A1 |
Meng; James C. |
August 27, 2009 |
Process and apparatus for pretreatment of fresh food products
Abstract
A method and apparatus for pretreating a fresh food product to
relieve the internal (turgor) pressure and adjust the product
temperature has an enclosure with an internal space, an air inlet
and an air outlet. An exhaust fan is in fluid communication with
the internal space. First and second spaced apart rows of product
containers are disposed on either side of the exhaust fan to form
an airflow aisle with an open end. A cover extends over the airflow
aisle and the open end to form an air plenum tunnel. The exhaust
fan is activated to lower the air pressure within the tunnel and
pull enclosure air through openings in and between the product
containers and over and around the food product. The exhaust fan
further circulates exhaust air over cooling coils and returns
exhaust air to the internal space of the enclosure. An air
conditioning mechanism is attached at a first end to the enclosure
outlet. The mechanism conditions a withdrawn portion of the
enclosure air by a) dehydrating a portion of the withdrawn air in
response to a predetermined relative humidity set point within the
internal space; b) heating or cooling the withdrawn portion of the
enclosure air in response to a predetermined temperature set point
for the fresh food products; and c) returning at a second end of
the conditioning mechanism the conditioned portion of the withdrawn
air to the internal space through the air inlet.
Inventors: |
Meng; James C.; (San
Antonio, TX) |
Correspondence
Address: |
JACKSON WALKER, L.L.P.
112 E. PECAN, SUITE 2400
SAN ANTONIO
TX
78205
US
|
Family ID: |
40985800 |
Appl. No.: |
12/072074 |
Filed: |
February 22, 2008 |
Current U.S.
Class: |
62/93 ;
62/271 |
Current CPC
Class: |
F26B 21/086 20130101;
F26B 9/066 20130101; F26B 21/04 20130101; A23B 7/0053 20130101;
A23B 7/148 20130101 |
Class at
Publication: |
62/93 ;
62/271 |
International
Class: |
F25D 17/08 20060101
F25D017/08; F25D 23/00 20060101 F25D023/00 |
Claims
1. An apparatus for pretreating a fresh food product comprising: an
enclosure having an internal space, an air inlet and an air outlet;
an exhaust fan in fluid communication with said internal space;
first and second spaced apart rows of product containers disposed
on either side of said exhaust fan to form an airflow aisle with an
open end; a cover extending over said airflow aisle and said open
end to form an air plenum tunnel; said exhaust fan adapted to lower
the air pressure within said tunnel and pull enclosure air across
said fresh food product, said exhaust fan further adapted to
circulate exhaust air over cooling coils to remove sensible heat
from said product and return said exhaust air to said internal
space; an air conditioning mechanism attached at a first end to
said enclosure outlet, said mechanism adapted to a) dehydrate a
withdrawn portion of said enclosure air in response to a
predetermined relative humidity set point within said internal
space; b) adjust the temperature of said withdrawn portion of said
enclosure air to achieve a predetermined temperature set point for
said fresh food products; and c) return at a second end of said
conditioning mechanism said conditioned portion of said withdrawn
air to said internal space through said air inlet.
2. The apparatus of claim 1, wherein said air conditioning
mechanism further comprises: a modulating bypass duct to bypass a
first selected portion of said withdrawn air around or through a
dehydrator to provide a dehydrated air portion; a recycle heater or
cooler for selectively heating or cooling said dehydrated air
portion; and a blower assembly for producing a lower air pressure
at said first end than at said second end and for directing said
heated or cooled, dehydrated air portion through said air inlet in
said enclosure into said internal space.
3. A process for pretreating a fresh food product comprising the
steps of: providing an enclosure having an internal space and an
air inlet and an air outlet; disposing at one end of said enclosure
an exhaust fan; placing first and second, spaced-apart rows of
product containers having fresh food product therein on either side
of said exhaust fan to form an air flow aisle with an open end;
extending a cover over said airflow aisle and said open end to form
an air plenum tunnel; activating said exhaust fan to lower the air
pressure within said tunnel to draw enclosure air toward a low
pressure zone in said tunnel thereby sweeping enclosed air over
said fresh food product; circulating said swept enclosure air over
cooling coiling to achieve a temperature controlled exhaust air
temperature; returning said exhaust air to said internal space;
withdrawing from said internal space a portion of said enclosure
air for conditioning; passing said withdrawn air through a
dehydration mechanism sufficiently to modify the relative humidity
of said withdrawn air in response to a predetermined relative
humidity set point within said internal space; adjusting the
temperature of said withdrawn air sufficiently to modify the
temperature of said withdrawn air to achieve a predetermined
temperature set point for said fresh food product; and returning
said conditioned air to said internal space to mix with said
enclosure air.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an improved process and
apparatus for pretreating fresh food products or produce prior to
packaging or further and final processing. Most fresh fruits and
vegetables are grown outside and exposed to considerable variances
in environmental factors of light, temperature, humidity, moisture,
and nutrient levels. When these factors combine resulting in
accelerated growth conditions, high internal (turgor) pressures
occur in the fruit or produce. High internal pressures also
commonly occur in fruits and vegetables that are grown in the
"forced" growth conditions employed in greenhouse environments.
[0002] Fresh fruit and vegetables, especially those grown under
accelerated conditions, develop internal pressures sufficiently
high to rupture cellular walls and epidural encasements resulting
in interstitial cracks. Once cracks occur they not only have
deteriorated cosmetic appearance, but also have released the
enzymatic mechanism (Phenoloxidase) that begins the breakdown of
the fruit. Additionally, a crack in the epidural layer and the
ruptured underlying cells exposes the inner sugars, providing a
fertile media for growth of molds, yeasts, and bacteria, which
further breakdown the fruit.
[0003] For some products genetic manipulation has been explored to
alter the nature of the produce, creating a product with a thicker
epidermal layer or skin and more hardy cellular structure. These
structural modifications to the plant can create fruit that can
better contain the internal pressures until they are reduced by the
natural moisture transpiration. This transpiration of moisture for
all fruits and vegetables begins upon picking and continues until
the fruit or vegetable has either been used, processed or
discarded. During the transportation and storage portions of the
post harvest process, the transpiration of the product may be
accelerated because of the lower humidity conditions resulting from
the direct expansion refrigeration units used in these areas. Often
the post harvest processing of fresh fruit and vegetables includes
the application of oil or wax to seal the surface to slow the rate
of moisture loss to extend the shelf life of the product.
[0004] Fruit and vegetables that are picked from the field during
normal growing seasons are picked at the temperatures in the
growing environment. Typically this is hot, on the order of 80, 90
or even 100+ degrees. This product is said to contain "field heat."
Currently there are numerous ways that this heat is dealt with
prior to inspection and packaging. These include: a) Let the
product "rest" in the packing shed, with or without forced air
ventilation, for a period of time generally ranging from several
hours to over a day to allow the some of the field heat to
dissipate; b) Wash the product in cool water; c) Place the product
in a forced air cooler; d) Place the product in a vacuum cooler; or
e) Forced air evaporative cooling.
[0005] a) "Resting" the Product. [0006] It has been shown that
prolonged exposure of the product to temperatures over 80.degree.
F. accelerates the breakdown of the product, causing it to loss
firmness and shorten the shelf life. Additionally, product with
high turgor pressures may spontaneously yield to the internal
pressures resulting in cracking. This process is often made worse
by micro damage occurring to the fruit as the result of the
handling and transportation prior to the "resting" phase. Also
temperatures in the packing sheds can often exceed the 80.degree.
F. thereby minimizing the cooling effect and effectiveness of this
method.
[0007] b) Hydrocooling or Washing the Product in Cool Water. [0008]
This is an effective method of dropping the temperature inside the
product. Unfortunately when dealing with a product with high turgor
pressure, the cooling effect is too rapid to allow the necessary
slow conduction of heat to lower the core temperature. The effect
of this rapid drop in temperature is that the exterior of the
product cools more quickly and, as it cools, it shrinks. The
shrinking of the exterior surface increases the internal pressure
in the product, resulting in substantially increased incidence of
cracking.
[0009] c) Forced Air Cooler or Conditioning Room. [0010] The
ultimate effect of this treatment, while potentially slower in
effect than the washing the product in water, also results in
increased incidence of cracking. The existing technology typically
produces a cooling effect by passing air across a direct expansion,
cooling coil. The surface temperature of the coiling coil, which is
determined by the expansion characteristics of the refrigerant, is
well below the dew point of the air stream. This results in air
with a very low dew point. This cold dry air both cools and
dehydrates the product. The high temperature and vapor pressure
differentials between the air and the product combine to rapidly
shrink the outside layers first, and increase the core pressure
within the fruit, resulting in cracking.
[0011] d) Vacuum Cooling. [0012] This is used on certain fruits and
vegetables with a high surface to mass ratio, things like lettuce,
corn, celery, peppers, etc. For this process the product is put
into a chamber and the pressure in the chamber is reduced thereby
cooling the product by evaporation. The evaporation loss, which is
primarily water, results in about 1% loss in weight for every
10.degree. F. temperature loss. This method can also be combined
with the use of refrigeration coils in the chamber. This method is
ill advised for product with high internal pressures. As pressure
in the chamber is reduced the differential pressure within the
cells and the atmospheric (external) pressure becomes greater,
splitting the fruit that is already at risk.
[0013] e) Forced Air Evaporative Cooling. [0014] An alternative
method for cooling products is the use of forced air through a
cascade of falling water droplets or a mist spray. This method of
cooling the product is often used because the equipment is much
less expensive. The air is cooled by the releasing its heat to the
latent heat of vaporization of the moisture droplets. The air exits
the cooler unit with a high relative humidity. Depending upon the
humidity of the air stream, the product may be slightly cooled (on
the order of about 10.degree. F.) but at best little has been done
to relieve the internal pressure. In most cases, the internal
pressure is increased, which results in increased cracking.
[0015] The present invention seeks to safely and slowly relieve the
internal cell pressure, while also adjusting the product to the
desired processing temperature. This preprocessing of the produce
is most effective when employed as quickly as possible after the
harvest and before the cracks have formed. This effectively
salvages fruit or vegetables that would otherwise be separated and
discarded as waste. The producer is able to retain a greater
portion of the product as saleable, than currently is possible.
[0016] A principle underlying this present inventive process and
apparatus is controlling the temperature and humidity of the air
media and then circulating that media to insure intimate contact
with the surface of all the fruit or vegetables. The system is
designed to separate the latent and sensible heat loads of the
product so that the differential driving force can be controlled to
remove the excess moisture and still be able to deliver the final
desired product temperature. The current state of the art does not
allow the separation of these functions. Failure to separate the
two heat loads results in imbalance between the humidity and
temperature resulting in an overly aggressive environmental
conditions which will either dehydrate the product too far and/or
too quickly, or not allow the desired final product temperature to
be attained.
[0017] Adjusting the differential between the partial pressure of
the moisture within the produce and the relative humidity in the
air media surrounding the product controls the rate of moisture
transference between the product and environment. This relieves the
turgor pressure without rupturing the cellular structure. The rate
of transference is controlled to allow diffusion through the
semi-permeable membranes of the cells from the core to the epidural
layers of the fruit or vegetable.
[0018] The airflow must insure intimate contact with the surface of
the fruit or vegetable. This is accomplished using a high volume of
forced air movement around the produce, effectively washing away
the surface boundary layer of heat and moisture. Failure to provide
a sufficiently high velocity across the fruit or vegetable allows
the development of a saturated boundary atmosphere at the food's
surface and a retarded migration rate.
[0019] The present invention reduces the specific volume of the
moisture within the cells to lower the internal cellular pressure
and is capable of removing the field heat of the product. The
combined effect of these two desirable outcomes effectively
stabilizes the fruit, allowing normal handling with minimized
probabilities of further deterioration or cracking.
[0020] The beneficial effects of the present inventive process on
the produce treated are increased firmness, increased retention of
firmness, increased shelf life, reduced damage in transit, and
reduced damage during post picking inspection, sorting and
packaging. Products that are picked with vine or stem and processed
using this invention also have improved attachment retention.
[0021] Internal pressures when present make the produce (fruit or
vegetable) more susceptible to damage from micro abrasions and
point concentrated impact, which are typical during processing.
When excessive internal pressures are present within the fruits or
vegetables, these incidental conditions can sufficiently compromise
the structural integrity of the containing encasement. When the
internal pressures exceed the containment strength of the
compromised skin, the produce will pop open (crack).
[0022] Use of the present inventive process and apparatus has no
deleterious effect on color, texture, taste, pectins, nutritional
values, and volatile flavor components. Because this process is a
low temperature process, it may also be used to concentrate the
nutritional elements, flavor components, vitamins, and sugars to
higher levels than as picked. Since the process is a tightly
controlled process for moisture removal, it could be used to
dehydrate or dry the product without loss of cell structure or
definition.
[0023] The process is well suited for use with fruit and vegetables
that are greenhouse, hydroponically, or otherwise grown under
environmentally controlled conditions.
[0024] It is also envisioned that the present invention may be
applied to field grown produce/vegetables that have been subjected
to environmental conditions which resulted in growth spurts. If the
internal pressure peaks, the portions of the crops that would be
most prone to cracking could be picked. The process could be used
to decompress the fruit and allow subsequent ripening to salvage
portions of the crop that would otherwise be lost.
SUMMARY OF THE INVENTION
[0025] A primary function of the present invention is to control
the partial pressure differential between the moisture in the
product and the vapor pressure of the humidity in the surrounding
air. This is done through the controlled removal of the excess
moisture present in the air volume surrounding the produce at the
starting environmental conditions and the moisture released from
the produce by the transpiration loss induced by the process.
[0026] Another function of the present invention is to control the
effect of the temperature on the internal pressure of the produce.
If the temperature of the produce is reduced too rapidly, it will
result in shrinking of the outer layers faster than the inner
layers. The rate of temperature reduction must be sufficiently slow
to allow thermal conduction of the heat within the fruit so that
the temperature differential between the inner and outer layers of
the fruit or vegetable are minimized. The effect of reducing the
temperature too quickly is similar to taking a piece of fruit in
hand and squeezing it until the internal pressure is increased and
the fruit ruptures.
[0027] The inventive process is intended to control the environment
and final temperature of the product so that is it above the dew
point of subsequent inspection and packaging operations. If the
temperature of the produce, when it is presented to subsequent
packaging and processing operations, is below the dew point,
moisture will condense on the product and could cause the
re-absorption of moisture into the product. Moisture that has
condensed on the surface of the fruit picks up dirt and juices from
the handling equipment. These contaminants foster mold, yeast, and
bacterial activity. Processing at temperatures below the dew point
effectively slows or kills the migration of moisture from within
the fruit, and may result in absorption of additional moisture.
[0028] The present process utilizes heating (captured waste heat
from the process) to increase the temperature of the produce to
above the dew point if required. This is important for products
that are winter grown (as in greenhouses) or where temperature
conditions vary significantly during the course of a picking and
packaging day.
[0029] The present inventive system is a closed loop system. Air is
forced past the product. This air is contained and run through an
axial vane fan, which provides the force to blow the air across the
coiling coils to remove the field heat from the product. A separate
side air stream is sent to a separate unit to remove the excess
moisture from the air stream. The separation of the two
sub-processes allows the separation of the latent heat load
(removing the moisture) from the sensible heat load (removing the
field heat).
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a schematic illustration of the present inventive
apparatus.
[0031] FIG. 2 is a more detailed drawing of an embodiment of the
present invention showing the tarpaulin cover over the product
containers, the dehydrator, recycle heater/cooler, and the return,
conditioned air blower.
[0032] FIG. 3 is a schematic drawing showing various sensors used
in an alternative embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0033] The present invention is a process and an apparatus which
utilizes controlled atmospheric conditions of an air medium to
effect a controlled decompression of the turgor pressure within
fruit and vegetables, while simultaneously adjusting (either
increasing or decreasing) the temperature of the produce to the
optimal conditions required for further inspection, processing or
packaging.
[0034] Turning to FIG. 1, the major components of the system are
illustrated. An enclosure 10, having an internal space 11, is
provided with a product holding station 60, an exhaust fan 14,
sensible heat removing cooling coils 16, an air outlet 18, an air
inlet 20, and a recycle duct 21. The moisture removal
(dehumidification) subsystem includes a dehydrator 22 with a
modulating bypass duct 24 with control dampers or valves 26. The
inventive process and apparatus may either add heat with a heating
unit 28 or cool the dehydrated air with a cooler 30. The
conditioned air is then directed by a blower 31 from a second end
32 of the recycle duct 21 to the air inlet 20 in the enclosure. The
system is a closed loop air circulation system.
[0035] A first sub-system includes the closed loop air circulation
system within the enclosure 10. Conditioned air is forced past the
product 12 (usually retained in bins 12a) to ensure intimate
contact with the surface of the fruit or vegetable to effectively
"wash" away the surface boundary layer of concentrated moisture and
heat that have been released from the product. This circulation
system must also address the air distribution requirements to
ensure reasonably uniform delivery of air to and around all the
pieces of product 12.
[0036] Cooling coils 16 are intended to remove only the field heat
(sensible heat) from the product. This sub-system is designed to
remove the field heat from the product without also removing the
latent heat of vaporization for the moisture released from the
fruit. The surface temperature of the cooling coils are controlled
to prevent the attainment of temperatures at or below the dew point
of the circulated air.
[0037] The moisture level of the air stream sweeping over the
product as measured by the relative humidity or grains of moisture
per pound of air must be controlled. This is done using a
slipstream of air withdrawn from the enclosure that is dehumidified
and reintroduced into the main circulation air stream.
[0038] The control of the migration of moisture from within the
fruit is based upon a "water activity" ratio between the partial
pressure of the water vapor in the air surrounding the produce to
the vapor pressure of the free water within the fruit. There is a
differentiation between the free moisture and what is otherwise
bound to the fruit constituents.
[0039] The mass transfer is dependent upon:
[0040] 1. The surface area of the fruit;
[0041] 2. Removal of the boundary layer of the water vapor from the
surface;
[0042] 3. Sustained driving force between the inner to the outer
subsequent layers of the fruit or vegetable; and
[0043] 4. Sustained driving force between the outer boundary layer
of the fruit or vegetable and the surrounding air stream.
[0044] The present inventive process also includes a dehydration
sub-system which reduces the moisture levels in the main
circulating air stream. The moisture in the main circulating air
stream comes for the atmospheric environment in the internal space
11, and the moisture released from the product 12. This sub-system
involves a slipstream of air removed from the environment and after
conditioning is reintroduced into the enclosure and the main
circulation air stream.
[0045] The regulation of the humidity of the slipstream may be
accomplished a number of ways. These include, but are not
necessarily limited to:
[0046] a. Desiccant drying--Modulation control of the humidity of
the slipstream is achieved by a modulated splitting of this stream
so that all or part of it flows through the desiccant and the
remaining portion of the flow is routed around the desiccant unit.
These two portions are then recombined and mixed to produce the
desired moisture level in the slipstream air. This slipstream
subsystem may be either a low-pressure system (operated at
pressures on the order of 2'' to 6'' of water column) to a
high-pressure system (operating at several pounds per square
inch).
[0047] b. Compression, refrigerated drying, and decompression--A
portion of the air stream removed is compressed, the moisture is
removed using a refrigerated dryer to remove the amount of moisture
being generated by the process. The air is then decompressed and
reintroduced into the main circulation air stream. Flow to this
unit is modulated through the air intake modulated bypass valves
and/or starting and stopping of the units.
[0048] c. Cooling, moisture condensation, and reheating--A portion
of the air stream removed and blown across a cooling coil that
effective lowers the temperature of the air to a temperature at or
below the dew point of the air stream. The temperature of the coil
controls the moisture removal. Further modulation can be effected
by modulation of the airflow across the coil.
[0049] If a desiccant wheel is used as the means of dehydration, it
has the additional benefit of sterilization of the air slipstream.
During the regeneration cycle, the temperature of the wheel is
heated to between 250 and 350.degree. F. This sterilizes the
surface of the wheel. Additionally, the air stream that passes over
the regenerated wheel is heated up also. This waste heat may be
used to warm the product.
[0050] Whenever the temperature of the produce is low, raising the
temperature assists in the reduction of the internal pressure
because of the thermal coefficient of expansion. The volume of the
fruit gets larger, thereby reducing the pressure within the fruit
or vegetable.
[0051] Depending upon the temperature of the produce in the product
station 60, the inventive process either adds heat, if necessary,
from external sources such as a heating coil or from utilization of
waste heat generated in the latent heat removal system or the
dehumidification system, to increase the temperature of the product
above the ambient dew point in the production area.
[0052] Various system monitors and controls are provided to measure
and adjust the system humidity and temperatures to meet the
requirements of the fruit or vegetables being pretreated.
[0053] While the present description illustrates an enclosure 10,
there may be various other environmental containment options. These
may include an enclosure or a tunnel(s) with various zones to
isolate the process from external conditions which would alter the
differential driving forces (temperature and humidity) established
between the produce and the process.
[0054] The scope of this invention is such that it may be employed
as a 1) batch process; 2) as a continuous transportation process
with various chambers of progressively different temperature and
humidity environments; or 3) as a mobile trailer mounted process
that could be transported to the field or farm to increase the
yield of good of the produce being picked.
[0055] FIGS. 2 and 3 illustrate an embodiment of the apparatus and
process of the present invention. The process includes providing an
enclosure 10 or containment environment having an internal space 11
wherein the temperature and relative humidity may be controlled.
The enclosure is provided with an air inlet 20 and an air outlet 18
and a product station 12 where bins or containers 12a of fresh
fruit or vegetables 12 may be placed in spaced apart rows on either
side of an exhaust fan 14 at one end of the enclosure. The rows
form an airflow aisle 15 with one open end 17. A tarp or cover 19
(FIG. 2) is extended over the product station, across the tops of
the produce bins 12a, along the sides of the product bins 12a, and
over the open end 17 to form an air plenum tunnel 23. The cover 19
has side curtains 51 that may be designed to have varying
percentages of open area to allow similar volumes of air to pass,
across the product 12 in bins 12a, and into the plenum tunnel 23
from all bin 12a positions along the rows, when the exhaust fan 14
is activated. The cover is intended to prevent air short-circuiting
either into the tops of the bins or at the ends of the rows. In
FIG. 3, the top portion of the cover 19 is not shown for clarity
purposes.
[0056] Sensors and controllers (FIG. 3) measure the following:
[0057] a. Product temperature T--This determines whether the
product needs to be heated or cooled during this process to attain
the predetermined exit temperature set point. It also serves as an
indication of the water activity within the product. Samples are
pulled and weighed at various intervals through the pretreatment
process to determine the total percentage moisture loss during the
process and also to determine rate of moisture loss. Methods to
determine this temperature include destructive insertion of a
temperature probe into several randomly selected samples of the
produce or non-destructively using a handheld infrared thermometer.
In one embodiment of the invention, the product temperature is
approximated, when the system is running, by air stream temperature
sensor DB2. Additional embodiments utilize a series of infrared
sensors to even more accurately determine the product
temperatures.
[0058] b. Temperature, relative humidity, and dew point within the
enclosure are recorded as the starting point and monitored
throughout the process via sensor/recorder 52.
[0059] c. Temperature, relative humidity, and dew point in the
production area (not shown) are measured. The production area is
where the product will be further processed or packaged. These
factors determine the desired final temperature of the product.
Normally this will be at the controlled temperature of the
production environment, or 5 to 10 degrees above the dew point of
the production area.
[0060] d. Humidity sensor 50 located in the air duct 21 is used to
sense the humidity of the air slipstream and adjust the modulation
of the dehumidifier controls to maintain a desired humidity set
point or profile.
[0061] e. Temperature (dry bulb) DB 1 of the volume of air in the
enclosure is used to set the minimum temperature differential to be
allowed for cooling the product.
[0062] f. Temperature (dry bulb) DB 2 of the air that has passed
over the product. This may be used as the set point of the desired
final product temperature.
[0063] g. Temperature (dry bulb) DB 3 of the air slipstream that
has passed through the dehumidification process and the cooling 30
or heating 28 coils. This is used to control the operation of these
coils to either provide a neutral temperature effect from the
dehumidification process, or to adjust the rate of further removal
or addition of heat to the process.
[0064] The operator sets the desired relative humidity to be
maintained or the relative humidity removal profile to be
established, and the final temperature set point or temperature
profile to be followed during processing to control the rate and
extent of moisture loss from the produce. He then sets the control
from sensor DB2 at the desired final temperature of the product and
sensor DB1 at the slightly (approximately 5 degrees) below the
desired final temperature if the product is to be cooled or
slightly above the desired final temperature if the product is to
be heated. The exhaust fan 14 is started, which also initiates the
refrigeration condensing unit if product cooling is required.
[0065] The temperature of the sensible heat removal cooling coil 16
is adjusted to maintained a coil temperature above the dew
point.
[0066] The dehydration unit is set for the desired relative
humidity within the enclosure. The temperature and relative
humidity sensor 50 for this unit may either be located within the
enclosure (as noted in broken lines in FIG. 3) or in the air duct
21 from the enclosure 11.
[0067] The dehydrator 22 and its recirculation fan are started
(FIG. 2). The level of dehydration is controlled by modulating the
air slipstream to either direct it through the dehydration unit, or
to bypass 24 a portion of it around the dehydration unit.
[0068] The process continues until the pre-weighed samples have
achieved the desired level of moisture loss required to prevent or
reduce product cracking to an acceptable level and the final
product temperature is achieved. At this point the exhaust fan 14
and its condensing unit 16 are turned off. The dehydrator 22 and
its recirculation fan are turned off or switched to a standby
mode.
[0069] Finally, the pretreated product is removed from the
enclosure and moved to the production area.
[0070] It should be understood that in the current process, if the
initial temperature of the product while in the enclosure is below
the dew point of the production area, waste heat and/or a heater 28
are used to adjust the temperature of the air in the enclosure to
achieve the desired product temperature. If the product needs heat,
the enclosure room temperature (DB1) will determine the cutoff
point of the heater coil 28. If the product does not require heat
or if the product requires cooling, then the discharge temperature
(DB3) is controlled to adjust the cooling coil 30 to match the
temperature in the enclosure 11. If the product requires the
removal of field heat, the cooling coils 16 are used to adjust the
exhaust temperature of the air reintroduced into the enclosure.
[0071] While the system and method of this invention have been
described in terms of preferred embodiments, it will be apparent to
those of skill in the art that variations may be applied to the
systems, methods, and in the steps or in the sequence of steps of
the method described herein without departing from the concept,
spirit and scope of the invention. More specifically, it will be
apparent that certain materials that are both functionally and
mechanically related might be substituted for the materials
described herein while the same or similar results would be
achieved. All such similar substitutes and modifications to those
skilled in the art are deemed to be within the spirit, scope and
concept of the invention as defined by the appended claims.
* * * * *