Method and system for processing cheese

A method and system for processing cheese. The method comprises the steps of blending ground cheese with additional ingredients to form a blended cheese material, and cooking and then cooling that cheese material. The method further comprises the steps of measuring a moisture content of the blended cheese material, generating a signal representing that moisture content, and adjusting the moisture content of the blended cheese material to a preset level in response to the generated signal. The moisture content of the cheese product may be measured at any appropriate stage of the processing line. Preferably, the moisture content of the cheese material is measured by transmitting microwave signals across the cheese material, and measuring the phase shift in the transmitted microwave signals. Also, preferably, the moisture content of the cheese material is measured, and any necessary adjustments made, after that material has been cooked and cooled.

BACKGROUND OF THE INVENTION 
This invention generally relates to methods and systems for processing 
cheese products, and more specifically, to controlling the moisture 
content of cheese products as those products are being processed. 
Processed cheese products typically are prepared by forming a blend of one 
or more comminuted natural cheeses, together with various additives such 
as whey or emulsifying salts. The processed cheese products are produced 
by heating, melting, and mixing the cheese blend to form a homogenous 
emulsified molten mass, followed by cooling and solidification of the 
molten mass. Such processing, for example, with emulsifying salts such as 
sodium phosphate and/or sodium citrate in amounts of 2-3 wt. % permits 
manufacture of soft-bodied, easily meltable processed cheeses and 
processed cheese foods. 
Because of their molten, easily handled form, processed cheese products may 
be readily packaged to provide convenient consumer products. Packaging may 
take any one of a number of forms such as hot packing in a plastic film 
tube that is cross-sealed and cut to provide individually wrapped slices. 
The molten process cheese product may also be formed into slices by 
distributing a thin layer of the product upon the surface of a cooled 
rotating chill roll, solidifying that layer into a sheet and removing the 
sheet from the roll. The sheet is then cut into strips and subsequently 
into slices, followed by packaging of the sliced processed cheese product. 
Various prior art methods and systems for processing cheese or cheese 
products are disclosed, for example, in U.S. Pat. Nos. 5,165,945, 
5,104,675, and 4,689,234. U.S. Pat. No. 5,165,945 discloses a process in 
which milk clotting enzymes are introduced into a feed stock containing 
cheese ingredients, and the enzyme-treated feed stock is heated to produce 
a desired body, texture, and solids level. U.S. Pat. No. 5,104,675 
discloses a process for preparing cheese products on a continuous in-line 
basis by providing a uniform blend of specific types of natural mozzarella 
and cheddar cheeses with limited amounts of sodium citrate. U.S. Pat. No. 
4,689,234 discloses a process for producing cheese, in which milk is 
initially concentrated by ultrafiltration and diafiltration to obtain a 
desired buffer capacity to lactose ratio in the retentate. A lactic acid 
producing starter culture is then inoculated into the retentate, and the 
retentate is then fermented to obtain a desired final pH. 
The moisture content of the final cheese product is a key parameter, having 
a significant effect on the quality and cost of the product. Controlling 
that moisture content is complicated by the fact that, conventionally, 
water is added to and removed from the cheese blend at various points in 
the manufacturing process, and the amounts of water that are added to and 
removed from the cheese blend at these points are not always precisely 
controlled. 
For instance, in a common process, water is added while the comminuted 
natural cheeses and the additives are blended. The blended mixture is 
cooked to a target temperature by the direct injection of steam either 
continuously into a pipework or batchwise into a vessel containing the 
mixture. After a product-specific holding time at the target temperature, 
the cooked cheese product is cooled by the direct flashing of steam from 
the cheese product. The amount of water that is added to the cheese 
product during the blending step can be controlled relatively precisely. 
However, similar precise controls cannot be exercised over the amounts of 
water that are absorbed by and subsequently drawn out from the cheese 
product during the above-mentioned cooking and cooling steps. 
With prior art processes, the moisture content of the final product can be 
controlled to within a range of plus or minus 2% of a target value, 
depending on the product type, the manufacturing equipment, the raw 
material, and other factors; and generally, these processes produce 
excellent products. Nevertheless, it is believed that the cost of the 
processes can be reduced and the uniformity of the product quality can be 
improved by narrowing the above-mentioned moisture range. 
SUMMARY OF THE INVENTION 
The present invention relates to a method and system for processing cheese. 
The method comprises the steps of blending ground cheese with additional 
ingredients to form a blended cheese material, and cooking and then 
cooling that cheese material. The method further comprises the steps of 
measuring a moisture content of the blended cheese material, generating a 
signal representing that moisture content, and adjusting the moisture 
content of the blended cheese material to a preset level in response to 
the generated signal. 
The present invention may be embodied with conventional cheeses and with 
conventional cooking and cooling means and steps. Preferably, the moisture 
content of the cheese material is measured by transmitting microwave 
signals across the cheese material, and measuring the phase shift in the 
microwave signals, which correlates to the amount of moisture in the 
cheese material. Also, preferably, the moisture content of the cheese 
material is measured, and any necessary adjustments made, after that 
material has been cooked and cooled.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, there is illustrated a schematic flow diagram of a 
continuous cooking system 10 for processing cheeses and embodying the 
present invention. A plurality of cheese components and additives are fed 
via conventional conveying/transport systems into blender 12, which is 
utilized to provide a homogeneous raw material mixture in proper condition 
for cooking. This mixture is then fed, via discharge pump 14, augure pump 
16, and line 20, to cooking subsystem 22. 
Any suitable cheese components and additives may be used in system 10, and 
the composition of the mixture in blender 12 depends on the formulation of 
the final processed cheese product. That mixture may include, for example, 
cheddar cheese, mozzarella cheese, enzyme-modified cheese flavor 
materials, sodium citrate, as well as other ingredients. Preferably, the 
cheese components of that mixture are comminuted in grinder 24 before 
being conveyed to blender 12. 
Also, any suitable mixer or blender may be used in system 10. In FIG. 1, a 
single blender 12 is shown for mixing the ingredients, but it is to be 
understood that additional blenders may be utilized to provide a raw 
material in proper condition for cooking. For example, in a preferred 
embodiment of the invention, at least two mixers are used alternately to 
feed the raw material mixture to the continuous cooking system 22. 
The continuous cooking system 22 may have any design suitable for direct 
injection of steam into the raw material mixture providing condensation of 
steam and thus a fast heating and melting of the cheese material. With the 
embodiment of system 10 shown in FIG. 1, the continuous cooking subsystem 
22 receives steam from a suitable source through a line and a control 
valve (not shown). A temperature sensing device (not shown) may be 
utilized with a conventional system to control the amount of steam 
conducted into cooking system 22 to maintain a target temperature of the 
cooked product, which may be in the range of 85.degree. C. to 140.degree. 
C. If the target temperature is high and cannot be achieved using only one 
continuous cooking stage, then a second cooking stage (not shown), 
arranged in series with the first stage, may be used for injection of 
steam in order to elevate the product temperature to the target. 
From cooking subsystem 22, the molten mass is delivered through a holding 
pipe 26 to a flash tank 30, which is maintained at a pressure lower than 
the pressure in the steam injector 22 and the holding pipe 26. When the 
molten mass is delivered into flashtank 30, the rapid reduction in 
pressure causes a portion of the water contained in that mass to be 
vaporized, thereby reducing the temperature of the molten mass. A further 
effect in flash tank 30 is deaeration of that molten mass. 
Flash tank 30 is kept at a low pressure, generally referred to as a vacuum, 
depending on the target cooling temperature; and the flash tank is 
connected by a conduit to a condenser, which functions to provide the 
vacuum for the deaerator. The vacuum may be maintained at the desired 
level by means of a vacuum control circuit (not shown), which may be of a 
conventional design, including a sensor and a vacuum controller that 
controls a valve in a vacuum line. 
From flash tank 30, the molten mass is pumped, via discharge pump 32, 
through conduit 34, which carries the mass through moisture measuring and 
control subsystem 36 and to balance tank 40. From tank 40, the molten mass 
is conducted to filling station 42 and thence to palletizer 44. 
Preferably, the viscous molten cheese mass is delivered to filling station 
42 at a temperature of 65.degree.-76.degree. C., and the cheese mass may 
be packaged at that station in any suitable form. For example, the product 
may be filled into conventional single slice inner wrap and over wrap 
packaging systems or in tub forms. 
Moisture control subsystem 36 is provided to measure and monitor the 
moisture content of the blended cheese material and preferably, if 
desired, to adjust the moisture content of that material to a preset 
level. The moisture measurement and the adjustment of the moisture content 
of the blended cheese material, may be done at any appropriate stage or 
stages of the cheese processing line. Preferably, though, as represented 
in FIG. 1, subsystem 36 is used to measure and to adjust the moisture 
content of the blended cheese product after cooling and prior to filling 
station 42. In addition, subsystem 36 may be used to divert product that 
is outside a given or determined moisture range, so that such product is 
not filled and packaged. 
The preferred embodiment of subsystem 36 includes measuring means 46, 
control means 48, liquid dosing means 50, and mixing device 52; and 
control means 48 includes signal processing means 54, control signal 
generating means 56, and dosing control means 58. Generally, measuring 
means 46 provides an output signal representing the moisture content of 
the cheese product in conduit 34, and in particular in a measuring cell 60 
that is disposed in that conduit. This signal is conducted to signal 
processing means 54 that produces an adjusted output signal, depending on 
the temperature and pressure of the material in line 34. This adjusted 
output signal is conducted to control signal generating means, which then 
generates an output signal representing the difference between the desired 
and actual moisture contents of the cheese product. This latter signal is 
applied to means 58, which then generates a signal that operates liquid 
dosing means to adjust the moisture content of the cheese product. 
Processing line or system 10 illustrated in FIG. 1 and described above 
operates on a continuous basis, so that cheese products are continuously 
moving through all subsystems for cooking 22, holding 26, cooling 30, 
moisture control 36, and filling 42. 
The present invention may also be embodied in a batch processing system, 
and FIG. 2 illustrates one example of such a batch processing system 70. 
Systems 10 and 70 have many identical components, and identical components 
are given the same reference numbers in FIGS. 1 and 2. Thus, in system 70, 
a plurality of cheese components and additives are fed to blender 12, 
which discharges a homogenous raw material mixture in condition for 
cooking, and that discharge is conducted to cooking subsystem 72. From 
subsystem 72, the cooked, cheese mass is conducted through line 34, which 
carries the cheese mass through control subsystem 36 and to balance tank 
40. From that tank 40, the cheese is conducted to filling station 42 and 
thence to palletizer 44. 
The principal difference between systems 10 and 70 is that in the former 
system, the cheese mass continuously moves through cooking subsystem 22, 
while in the latter system, a batch of cheese mass is collected and cooked 
in one or more vessels 74. Preferably, as illustrated in FIG. 2, a set of 
at least two parallel batch vessels 74 operate alternately to feed the 
molten cheese continuously through the on-line moisture measuring and 
control system 36 and to the filling station 42. 
FIG. 3 illustrates in greater detail a preferred embodiment of control 
subsystem 36. With reference to FIG. 3, measuring means 46 includes 
measuring cell 60, microwave transmitter 80, microwave receiver 82, and 
processor 84; signal processing means 54 includes comparator 86, set-point 
generator 90, processor 92, and sensor or probe 94. Control signal 
generating means 56 includes comparator 96 and variable strength signal 
generator 100; and dosing control means 58 includes processor 102, 
comparator 104, flowmeter 106, and flowmeter 110. 
Transmitter 80 and receiver 82 are positioned on opposite sides of flow 
through measuring cell 60; and, in use, transmitter 80 generates microwave 
signals and transmits those signals across flow through cell 60, to 
receiver 82. The microwave signals have a periodic, sinusoidal wave form 
or pattern, and the phase of the wave form is shifted as it passes through 
measuring cell 60 and the cheese product therein. In fact, with reference 
to FIG. 4, the extent to which the cheese product causes the phase of the 
microwave to shift is linearly related to the moisture content of the 
cheese product, and thus this phase shift provides a direct indication of 
that moisture content. 
Processor 84 is provided to generate microwave signals that are to be 
transmitted through the cheese product, to evaluate the measured microwave 
signals, and to process all data to a final continuous output signal 
representing the moisture content of the cheese product. This evaluation 
and electronic processing is based on a product specific calibration curve 
completed using flow-through cell 60. The following simplified equation 
for electronic processing in processor 84 applies for a constant geometry 
of the flow-through cell and for a constant product density (in practice 
constant density may mean constant temperature and constant pressure): 
EQU MC(%)=A.multidot.O+B (1) 
where 
MC: Moisture Content in %, 
A: Calibration factor, 
O: Measuring signal =phase shift, and 
B: Calibration constant (depending on salt content). 
The calibration constant B can be expressed in terms of the salt content of 
the cheese product according to the following equation: 
EQU B=B.sub.1 .multidot.SC+Bo (2) 
where SC is the salt content of the cheese product. Substituting the right 
hand side of equation (2) for B in equation (1) yields: 
EQU MC(%)=A.multidot.O+B.sub.1 .multidot.SC+Bo (3) 
Generally, signal processing means 54 corrects the output signal provided 
by processor 84 according to actual values of the temperature and/or 
pressure measured in the conduit 34 by means of relevant probe(s) 94. This 
compensation may become necessary, if the density of the product effected 
by any of these process parameters varies outside of a specified range. 
More specifically, comparator 86 is provided to compare the actual 
signal(s) delivered by probe(s) 94 with pre-set signal(s) generated by a 
set-point generator 90 for temperature and/or pressure, and to generate 
output signal(s) representing the difference between the actual values and 
the set values. Processor 92 is provided to correct the signal produced by 
measuring means 46 for moisture content, considering the output signal 
from comparator 86 according to a pre-calibrated and pre-stored 
compensation curve, in order to deliver a corrected output signal to 
control signal generating means 56. 
The corrected moisture content signal is determined by processor 92 
according to the following equations: 
EQU MC(%)=A.multidot.O+B(po,To)+.DELTA.MC(p)+.DELTA.MC(T), (4) 
EQU MC(%)=A.multidot.O+B(po,To)+CP.multidot.(p.multidot.po)+Dp+CT.multidot.(T-T 
o)+DT (5) 
where 
MC(%): Moisture content in %, 
A: Calibration factor, 
O: Phase shift, 
B: Calibration constant (depending on salt content, see equation (3)) at a 
pre-set pressure po and/or at a pre-set temperature To, 
.DELTA.MC(p): Deviation, correction of moisture content due to p.noteq.po, 
.DELTA.MC(T): Deviation, correction of moisture content due to T.noteq.To, 
Cp, CT: Compensation factor for pressure and/or temperature compensation, 
Dp, DT: Compensation constants for pressure and/or temperature compensation 
p: Pressure, measured by pressure gauge 94, 
T: Temperature, measured by temperature gauge 94, 
po: Pre-set pressure, and 
To: Pre-set temperature. 
Comparator 96 is provided to generate an output signal indicating whether, 
and the extent to which, the moisture content of the cheese product is 
above or below a desired value. More specifically, the output of processor 
92 is transmitted to a first input of comparator 96, and a second input of 
the comparator 96 is connected to and receives a signal from a variable 
strength signal generator 100, which is used to generate a signal 
representing the desired moisture content of the cheese product. 
Comparator 96 compares the two signals transmitted to its inputs, and 
generates an output signal representing the difference between those two 
input signals. The output signal from comparator 96 is then used to adjust 
the moisture content of the cheese product to the preferred level. 
As a practical matter, it is normally easier to add moisture to than to 
remove moisture from the cheese product. Thus, preferably, systems 10 and 
70 are designed and operated so that the moisture content of the cheese 
product is slightly below the desired level when the cheese product passes 
through conduit 34, and moisture is added to that product at or downstream 
of that point to increase that moisture content to the desired level. The 
measuring and control of the moisture content of the cheese product can be 
performed at any point in systems 10 and 70 depending, for example, on 
specific technical and local needs or conditions. In general, there are 
two possibilities for measuring and controlling the moisture content: (i) 
upstream measurement combined with downstream correction of moisture 
content, by, for instance, water injection, and (ii) upstream correction 
combined with downstream measurement. 
As a general matter, the former arrangement, upstreammeasurement/downstream 
correction, is preferred; and with this arrangement, the signal from 
comparator 96 indicates that the moisture content of the cheese product is 
below the preferred level. This signal combined with the output signal of 
flowmeter 110 indicating the actual flowrate, preferably the mass-flowrate 
in conduit 34, is processed in processor 102 to a signal which indicates 
the amount of moisture that needs to be added to the cheese product to 
raise the moisture content thereof to that preferred level. 
Processor 102 may generate this signal according to the following equation: 
EQU mw=(MC.sub.o -MC).multidot.mpc (6) 
where 
mw: Mass flow rate of water to be added, 
mpc: Mass flow rate of processed cheese measured by sensor 110, 
MC: Moisture content calculated by equations (1), (3), and (5), and 
MC.sub.o : Pre-set moisture content, target value for product. 
Comparator 104 is provided to compare the signal from processor 102 and a 
flowrate signal delivered by flowmeter 106 and representing the actual 
amount of liquid added to the product in conduit 34, and to generate an 
output signal which may be used in any suitable manner to add liquid to 
the cheese product. For example, the output signal may be conducted to a 
pump controller integrated in liquid dosing system 50 that, in turn, 
operates a pump to add liquid to the cheese product. Alternatively, the 
output signal may be conducted to a valve controller integrated in the 
liquid dosing system 50 that adjusts the position of a valve in a fluid 
input line to increase or decrease the amount of fluid added to the cheese 
product. 
The signals for the pump controller or the valve controller may be 
generated in accordance with the following equations: 
EQU f. pump controller: n=En.multidot.(m.sub.W -m.sub.WM)+F.sub.W(7) 
EQU f. valve controller: x=Ex.multidot.(m.sub.W -m.sub.WM).multidot.F.sub.X(8) 
where 
mw: Mass flow rate of water calculated by equation (6), 
mwM: Mass flow rate of water measured by the flow meter 106, 
n: Rotational speed of pump, 
X: Controller output for valve 
En/Ex: Control factors for pump/valve controller, and 
Fn/Fx: Control constants for pump/valve controller. 
Preferably, sterile water or whey is mixed into the product in conduit 36 
to increase the moisture content thereof, and then the cheese product is 
passed through a dynamic or static mixer 52. As will be understood by 
those or ordinary skill in the art, any suitable mixer 52 may be used to 
mix the added water or whey with the cheese products. 
An advantage of the preferred upstream measurement/downstream correction 
arrangement is the potential of achieving the highest accuracy available 
for moisture control. The alternative approach, upstream 
correction/downstream measurement, simplifies the control set-up, however 
the achievable accuracy for moisture control is lower than that provided 
by the upstream measurement/downstream correction arrangement described 
above. In the alternative upstream correction/downstream measurement 
system, the water is injected and mixed into the cheese product prior to 
moisture measurement. This can be at any appropriate point of the 
processing line such as after flash cooling or directly into the flash 
tank. This set-up makes any measurement of flowrates redundant and thus 
unnecessary. 
FIGS. 5 and 6 illustrate in greater detail flow-through measuring cell 60 
as it is combined with microwave transmitter 80 and receiver 82. 
Generally, cell 60 includes windows 60a, internal casing 60b, end 
connectors 60c, outside housing 60d, end closures 60e, and seals 60g. 
Preferably, flow-through cell 60 is a pressure stable construction, with 
parts 60b, 60c, 60d, and 60e made of metal, preferably stainless steel or 
Teflon coated stainless steel, and with parts 60a and 60g made of 
non-metal. This construction allows fluids, in this specific case, 
processed cheeses, to be pumped through the cell along a flow-axis A, 
which is preferably arranged vertically as shown in FIG. 5 in order to 
remove air from the cell and achieve filling of the cell by 100%. In the 
product flow direction A, the cell is connected into conduit 36 on both 
ends 60c. These connections may be maintained by means of welding or any 
suitable commercially available pipe fitting system. 
Microwave transmission axis B is arranged perpendicular to the product flow 
direction A. Along axis B, microwave transmitter 80 and microwave receiver 
82 are disposed within a non-metal microwave-conductive window 60a. This 
material may be any microwave-conductive material which is also suitable 
in connection with the product and cleaning and disinfection solutions to 
be pumped through the cell, such as polycarbonates (Macrolon), polyamides, 
polacetates, (Erthalon) or Teflon. Preferably microwave antennae 80 and 82 
are integrated into measuring windows 60a using means such as screws of 
suitable size, in order to have a compact and stable arrangement, to avoid 
water condensation between antennae and the windows, and to minimize the 
attenuation of microwaves by the window material. 
The windows 60a have a convex form, or lens shape, on the product side, 
which is symmetrical around axis B. In this way, the windows minimally 
interfere with the flow of the product through the measuring cell by means 
of a large hydraulic diameter and a minimum pressure drop along the cell. 
In addition, the lens shape avoids edges in the flow-path of the product, 
facilitating the in place cleaning of the cell by a solution of cleaning 
agents or rinsing water after the production. Furthermore, the lens shape 
provides a focusing effect of the microwaves, improving the performance of 
the measuring system. The sealings 60g prevent product from flowing out of 
the cell through the gap between windows 60a and metal housing 60d. This 
arrangement ensures, as a whole, that there is no direct contact between 
the product and the measuring system. 
Each of the units of cell 60 includes one measuring window 60a, and one of 
the integrated antenna 80 or 82 is attached to each of the metal housings 
60d, on each side of the flow through cell by means of screw-on closing 
parts 60e. The screw on closing parts 60e protect the antennae 80 and 82 
from splashing water or any liquids. Moreover, cell 60 is formed so that 
the microwave cables 80a, 82a, including the connection parts, are 
stabilized against vibrations and any other mechanical stressing. Thus, 
the whole flow-through cell 60, including the antennae 80 and 82, forms a 
single compact unit that maintains a tight flow-through path for the 
product with a consistent and defined geometry. 
FIG. 6 shows flow through cell 60 assembled. The preferred distance C 
between the windows 60a is an important design parameter, determined, in 
part, by the salt and moisture content of the cheese product. For example, 
in an embodiment of the invention that has been actually reduced to 
practice, a distance of 2.5 cm between the windows has been found to 
produce effective results. 
As discussed above, FIG. 4 illustrates the correlation between moisture 
content of the cheese product and the phase-shift of microwaves 
transmitted through this product using flow through cell 60. This 
correction is valid for a constant density of the product. Density changes 
due to temperature and pressure can be compensated for by means of the 
preferred control method and system described above and illustrated on 
FIG. 3. 
In some cases, such as when an inhomogeneous product is conducted through 
line 34, it may be preferred to use a direct on-line density measuring 
system to measure the density of the product flowing through line 34. FIG. 
7 illustrates a radiometric system 120 that may be used for this purpose. 
In this arrangement, the flow-through measuring cell 60 is combined with a 
radiometric source 122 and a scintillation detector 124 which transmit 
.gamma.-rays through the product in a direction perpendicular to the axis 
of the microwave transmission. 
More specifically, instrument 120 may be used to generate an output signal 
representing the density of the cheese product, and this output signal is 
combined with the output signal of the microwave system and may be 
converted to a final corrected signal representing or indicating the 
moisture content of that cheese product. This conversion is carried out 
according to the following equation: 
##EQU1## 
where 
ln: natural logarithm, 
MC: Moisture content in %, 
A: Calibration factor, 
O: Measuring signal=phase shift, 
B: Calibration constant, 
lo: Intensity on the unattenuated radiation, and 
l: Intensity of radiation. 
This final signal, in turn, may be used to control the operation of a 
subsystem employed to add enough moisture to the cheese product to adjust 
the moisture content thereof to the desired level. 
It should be noted that the present invention may be used with a variety of 
types of cheese products in addition to the specific examples described 
above. For example, this invention may also be used with cream cheese and 
with processed cheese. 
While it is apparent that the invention herein disclosed is well calculated 
to fulfill the objects previously stated, it will be appreciated that 
numerous modifications and embodiments may be devised by those skilled in 
the art, and it is intended that the appended claims cover all such 
modifications and embodiments as fall within the true spirit and scope of 
the present invention.