Note: Descriptions are shown in the official language in which they were submitted.
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METHOD AND DEVICE FOR REDUCING THE GROWTH OF THERMOPHILIC BACTERIA IN HEAT
EXCHANGERS OF DAIRY PROCESSING PLANTS
TECHNICAL FIELD
The invention relates to a method and a device for reducing the growth of
thermophilic bacteria
in heat exchangers of dairy processing plants, in which untreated milk or the
fractions thereof,
cream and skimmed milk, that has/have not undergone heating to a high
temperature to
deactivate thermophilic bacteria, is/are subjected in this state to a thermal
treatment in a
further treatment process in a recuperative heat exchanger, at least in a
temperature range of
50 C to 70 C, wherein the optimum temperature for the optimal growth of the
thermophilic
bacteria lies in a temperature range of 63 C to 68 C. Indirect heat transfer
occurs in a
recuperative heat exchanger, between two substance flows separated by a
diathermic wall. The
skimmed milk may, for example, be milk produced in a processing room of a
dairy processing
plant downstream of a separator to separate untreated milk into cream and
skimmed milk, that
is subsequently passed to another processing step with or without heat
treatment, or that is
passed into an evaporator after being stored in a storage tank and cooled to
storage
temperature. The reduction of the growth of thermophilic bacteria and thereby
the reduction
of thermophilic bacteria per se in the original skimmed milk does affect the
bacterial content
significantly in the downstream skimmed milk products.
BACKGROUND OF THE INVENTION
In heat exchangers in dairy processing plants, irrespective of the design as
either plate or pipe
heat exchangers, thermophilic microorganisms or bacteria from the untreated
milk or fractions
thereof (skimmed milk and cream) that were not subjected to heat treatment and
therefore not
inactivated, or the metabolic products of these bacteria can adhere to the
surface and form
what is known as a biofilm. This biofilm is most prevalent in a heat
exchanger, particularly in a
regeneratively operated one, where the milk is generally thermally treated in
a temperature
range of approximately 50 C to 70 C. At temperatures over 50 C, while
pathogenic bacteria
can no longer grow, the pathogens mentioned above can, i.e. the thermophilic
microorganisms
and bacteria. Hereinafter the term "thermophilic bacteria" will largely be
used for thermophilic
microorganisms or bacteria. Thermophilic bacteria use a temperature range of
approximately
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40 C to 80 C, while the temperature range for optimum growth of thermophilic
bacteria is in a
range of approximately 63 C to 68 C (known as the optimum temperature, i.e.
the most
favourable growth temperature (optimum)) (see for example "mikrobiol.de/Teil A
(103-104)
HO"). As well as this optimum temperature, there must also be sufficient
nutrients and oxygen
for growth.
During operational lifetime of the heat exchanger, its so-called service life
between two
adjacent cleaning cycles (CIP cleaning), based on a bacterial count of 5x102
CFU/ml in the
advance line to the heat exchanger, there can be an increase in the heat
exchanger itself to
considerably more than 4x105 CFU/ml after 4 to 6 hours (note: CFU stands for
colony-forming
units). This increase can result from accretions in the low-flow areas of the
heat exchanger. It
can be assumed that this is the case in most heat exchangers of the kind
addressed here. The
content of thermophilic bacteria is relatively even in untreated milk in
Germany. Tests at two
dairies showed bacterial counts in each of approximately 200 to 600 CFU/ml.
If the skimmed milk is added to a concentration in evaporation plants, the
proportion of organic
acids that are formed by the metabolism of thermophilic bacteria and that form
the biofilm is
inevitably concentrated. When the pH in the concentrate is reduced to 6.20,
the end of the
service life is reached and the evaporation units have to be cleaned. Plants
that process the milk
further, such as cheese dairies or milk drying plants otherwise will run into
technological
difficulties as the concentrate is no longer marketable. In part, bacterial
levels of under 2x105
CFU/ml are required in the specifications for the skimmed milk concentrates.
This cannot be achieved with the current production conditions.
DE 10 2005 015 713 Al describes a method to deaerate and maintain a continuous
volume flow
of a milk to be treated in an ultra-high-temperature (UHT) plant with indirect
heating
(recuperative heating in heat exchangers) and an integrated separator for the
milk fat
standardisation and an interim storage of a (standardised) milk leaving the
arrangement
comprising a separator. The method is characterised among other things by the
fact that the
volume flow is continuously treated as described in steps a) to d) below in an
arrangement with
a deaerating and storing unit downstream of the arrangement comprising a
separator, whereby
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a) the volume flow generates a point symmetric film flow which when viewed
from a
radial perspective flows from the inside to the outside, initially
horizontally and then
radiating downwards,
b) the film flow is generated at the level of one surface of a storage volume
in the
deaerating and storing unit and then layered on this surface,
C) a piston flow evenly distributed transversely across the storage volume is
generated in
the storage volume oriented against gas bubble buoyancy
d) the volume flow is obtained from the storage capacity centrally at the
lower end.
The known method deaerates milk standardised according to its fat content,
which is then
transferred to a UHT plant. Standardised milk is defined as milk with a
predefined fat content. It
has been demonstrated that an air content of less than 8 mg atmospheric
oxygen/dm3 milk has
a favourable effect on the service life for the heat exchangers in these UHT
plants with indirect
heating. Above a threshold value for this there is an increased risk of
burning, particularly in
heat exchangers of the heating zone and heat retention units, whereby the
service life of these
heat exchangers is significantly reduced.
The defined object of the method described in DE 10 2007 037 941 Al is the
avoidance of
burning, particularly in heat exchangers in the heating zone and heat
retention unit of UHT
plants, by reducing the air content to below 8 mg atmospheric oxygen/dm3 milk.
According to a preferred design, this is characterised by a liquid product,
particularly a liquid
food such as cheese milk, cream or UHT milk, namely in form of a total flow of
a gas-loaded
product is fed to an inlet of a distributor pipe. In the distributor pipe, the
gas-loaded product is
transformed or respectively branched into at least one forced partial flow;
the partial flow(s)
is(are) transported against gravity into a gas discharging collection chamber,
and after the flow
direction is changed is(are) transformed into film flows radiating with the
force of gravity with a
free surface in the direction of the collecting chamber. The partial flows
that are respectively
generated by the film flows of a product to be deaerated are deaerated by
separating the gas
bubbles in the gravity field of the earth, and subsequently collected and
supplied as a total flow
of the deaerated product to an outlet of the collecting chamber.
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WO 2006/011 801 Al describes a method for conditioning particularly the oxygen
content in
pasteurised milk or pasteurised milk products, wherein improved
microbiological quality,
improved physical and / or chemical stability of the respective product is
envisaged. This prior
art does not go beyond the prior art, which has been recognized above. The
inhibition of
thermophilic bacteria in skimmed milk with the object of inhibiting the growth
rate of the
biofilm formed by these bacteria in recuperative heat exchangers, particularly
in heat
exchangers operated regeneratively, is not disclosed or suggested.
The content of air or atmospheric oxygen and other gas admixtures in untreated
milk, cheese
milk (vat milk), cream or UHT milk and the need to reduce these gas admixtures
was and is
given special attention, because the reduction serves to optimise the quality
and the above-
mentioned negative effects are evident. The number of thermophilic bacteria in
dairy products
so far played a minor role and was therefore not considered from a technical
perspective. In
future, this bioburden will certainly be quantified between users and will
become a part of the
quality reports for the traded products. In this context, the level of
thermophilic bacteria in
skimmed milk is of particular importance. In this regard, the relationship
between the results
for the content of thermophilic bacteria from the untreated milk in skimmed
milk and the
negative impact of these bacteria on the formation of a biofilm in primarily
renewably powered
heat exchangers in the non-boiling zone of processing plants (reduction of
service life) has so
far not been recognized or at least not taken into account, and therefore
there have also been
no effective solutions to date.
The object of the present invention is to create a method of the generic type
and a device for its
implementation, so that the service life of recuperative heat exchangers that
come into contact
with untreated milk or fractions thereof (cream and skimmed milk),
particularly if they are
regeneratively powered, is increased.
SUMMARY OF THE INVENTION
This object is achieved by a method having the features of claim 1.
Advantageous embodiments
of the method are the subject of the dependent claims. Two preferred devices
for performing
the method according to the invention are characterised by the features of
independent claim 9
or 10.
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The fundamental solution concept of the invention assumes that up to now the
relationship
between the results of the content of thermophilic bacteria in skimmed milk
and the negative
impact of these bacteria on the formation of a biofilm (reduction of service
life) in primarily
renewably powered recuperative heat exchangers of the non-boiling zone of
dairy processing
plants (temperature range of approximately 50 C to 70 *C) has not been
recognized or at least
has not been taken into consideration. The growth and in turn the increase in
the content of
thermophilic bacteria are both only possible by virtue of the available oxygen
and the presence
of nutrients in the substrate at the applicable optimum temperature for
bacterial growth. As
the presence of nutrients and the temperature conditions are inevitable in a
dairy process, the
only parameter that can change the speed of growth and thus limit the
reproduction of
thermophilic bacteria is a reduction in the oxygen content.
This is the approach the inventive solution takes, wherein the air oxygen
content is reduced by
sufficient deaeration of the skimmed milk. The solution is that the non-
deaerated skimmed milk
that is provided during the treatment process is subject to deaeration and
thus transformed
into deaerated skimmed milk before its thermal treatment, the thermal
treatment taking place
either in the optimum temperature range or when passing through the optimum
temperature
range in one or the other direction. The optimum temperature range should be
defined as the
initially mentioned temperature range of between approximately 63 C and 68 C
(63 C < top <
68 C).
As the thermophilic bacteria have a very short generation time with a high
metabolic rate, they
are also equally sensitive in terms of their speed of growth if oxygen is no
longer available. The
deaeration according to the invention allows sufficient deaerated skimmed milk
into the heat
exchanger and the thermophilic microorganisms or bacteria thus have
insufficient oxygen as a
necessary nutrient for their reproduction. This slows down the growth speed of
the
thermophilic microorganisms. As oxygen is or may be already encapsulated in
the existing cells
of the microorganisms and the process does not guarantee complete deaeration,
one to two
generations of growth are expected. The production of organic acids associated
with the
reproduction of the microorganisms only has a minor effect on the skimmed
milk. Thus, the
processing plant can be operated for longer while maintaining the necessary
quality
parameters, and the service life can be extended. The thermophilic bacterial
count is
maintained at a correspondingly low level and the development of a biofilm is
inhibited.
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An advantageous embodiment of the method provides that the deaeration is
performed at a
deaeration temperature below the optimum temperature. This measure ensures
that on the
one hand the deaeration is supported by raising the deaeration temperature,
and on the other
hand the growth of the thermophilic bacteria remains inhibited during the
deaeration process.
The deaeration temperature is generally below 63 C, while preferably a range
between 53 C
and 58 C is provided, with a preferred deaeration temperature of 55 C.
The method further provides that the deaerated skimmed milk is added in its
state after
deaeration immediately after a treatment process subsequent to the deaeration.
This process
can be advantageous if during the course of the process the skimmed milk is at
an optimum
deaerating temperature and this temperature is used for deaerating, and this
course of process
does not provide for the skimmed milk to be cooled down to storage temperature
with
subsequent stacking at this storage temperature.
In all other cases it is expedient, as the method further suggests, to use an
optimum deaerating
temperature for the deaerating which is first given in the course of the
process or can be easily
realised, and then to cool the deaerated skimmed milk down to a suitable
storage temperature
after deaerating, and to store it at this temperature. It has been shown to be
appropriate if this
temperature is between 8 C and 15 C.
Another advantageous embodiment of the method provides that deaerating is
carried out for a
period that can be freely adjusted to the needs of the deaerating process.
This measure means
virtually all separable gas components of the skimmed milk in the designated
deaerating facility
have the chance to separate within what is known as the mean dwell time (a
parameter
determined by the time) of the skimmed milk to be deaerated.
The invention further suggests two preferred devices to implement the method
according to
the invention, that are relatively simple in their design, and in which the
mean dwell time of the
skimmed milk to be deaerated is freely adjustable within limits.
The first device is designed as a container having a central discharge pipe
for the deaerated
skimmed milk at its bottom end, which is penetrated concentrically by an
intake pipe for the
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skimmed milk to be deaerated engaging concentrically into the container from
beneath. The
intake pipe connects to a peripheral ring gap which is formed between a
distributor screen and
a baffle plate that is smaller than the distributor screen in terms of its
flat dimensions and
arranged concentrically and with a space above the distributor screen. The
distributor screen
extends horizontally transverse to the longitudinal axis of the container and
subsequently
extends radially downward sloping with gravitational force and ends outside at
the same level
as a level of the milk to be deaerated in a storage volume in the container.
The second device comprises a collection chamber oriented in the direction of
gravity that is
delimited circumferentially by a container casing, on the base by a container
base and at the
headspace by a container lid. At least one riser pipe is provided that
penetrates the container
base, extends into the container casing and terminates open. Furthermore,
there are provided
a collection pipe opening from the collection space in the region of the
container base that is
connected with an outlet for the entire flow of the deaerated milk, a
distributor pipe that
branches below the container base into at least one riser pipe and a gas pipe
into which the
collection chamber in the region of the container lid opens. The riser pipe is
formed at its open
end as an overflow edge, wherein a partial flow of the skimmed milk to be
deaerated fed into
the riser pipe generates a film flow that spreads with gravitational force
onto the exterior
surface of the riser pipe and that has a free surface in the direction of the
collecting chamber.
The riser pipe is designed in the shape of a pipe and the overflow edge of the
riser pipe
generates a complete film flow on the exterior surface of the riser pipe. A
single riser pipe or
more than one riser pipe are provided in a circular or matrix shape in the
first container casing,
and the distributor pipe is connected with an inlet for the entire flow of the
skimmed milk to be
deaerated.
The deaeration of the skimmed milk can be accelerated in both of the devices
defined above, if
a vacuum source is connected to the headspace of the device, which acts on the
skimmed milk
to be deaerated.
BRIEF DESCRIPTION OF THE DRAWINGS
A more detailed presentation of the results which can be achieved with the
invention with a
view to reducing the growth of thermophilic bacteria in a recuperative heat
exchanger of a
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dairy processing plant is shown in the following description and the appended
figures of the
drawing and from the claims. The drawings show in:
Figure 1 is a schematic representation of a plant part of a dairy processing
plant in which the
effectiveness of deaerating according to the invention was investigated in
skimmed milk and
Figure 2 is a diagram showing a selection of measurement results obtained in
the part of the
plant according to Figure 1, representing a dependence of the logarithmically
presented
thermophilic bacteria count in CFU/ml on the linear time shown in hours.
DESCRIPTION OF THE TEST ARRANGEMENT AND COMMENTING ON THE TEST RESULTS
Test arrangement
A plant part of an existing and real producing process plant 100 (Figure 1) is
fed through an
advance line 3 from a source SR for non-deaerated skimmed milk M or deaerated
skimmed milk
M*. This source SR may be a storage tank or a stacking container, the outlet
from a heat
exchanger or another process aggregate (e.g. a separator) of the processing
plant or the outlet
of a deaeration device. Correspondingly, the skimmed milk M, M* is fed into
the advance line 3
at a storage temperature TS if it originates from the storage tank, at a
processing temperature
TP if it originates from a heat exchanger or process aggregate, or at a
deaeration temperature
TD if it originates from a deaeration device. From here the skimmed milk M, M*
passes through
a first pump 11 to a junction where the advance line 3 branches into a first
and a second
advance line section 4, 5. The first advance line section 4 leads to a
regeneratively operated first
heat exchanger 1 and the second advance line section 5 leads to a
regeneratively operated
second heat exchanger 2. The outlet of the first heat exchanger 1 on the
product side is
connected to a first return line section 6, and the outlet of the second heat
exchanger 2 on the
product side is connected to a second return line section 7. The first and
second return line
sections 6 and 7 open at a connection point in a return line 8, which leads
into an area
designated as target TR, which operates the process plant for further
processing of the
skimmed milk M, M*.
The first heat exchanger 1 is pressurized via a first heating circuit line 9
and a second pump 12
in counterflow to the first heat transfer medium, for instance with vapours
VP, and the second
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heat exchanger 2 is pressurized via a second heating circuit line 10 and a
third pump 13 in
counterflow with a second heat transfer medium, for instance skimmed milk
concentrate SMC.
As the heat exchangers 1 and 2 are generally operated at different temperature
levels, a
desired mixed temperature can be set in the return line 8 by means of a
control valve 16
arranged in the second return line section 7.
In the advance line 3 seen in the direction of flow, an initial sampling point
14 is provided
upstream of the first pump 11, where a first sample P1 can be collected at a
first sample
temperature Ti. A second sample collection point 15 is arranged in the first
return line section
6, where a second sample P2 can be taken at a second sample temperature 12.
Test results
The test results shown below were collected in an existing processing plant
under the local
severe operating environment and not in a laboratory. Measuring deviations or
any measuring
errors and scatter of the measuring results are unavoidable and should
therefore be accepted.
No measuring values collected in the context of the tests presented below were
suppressed.
The test results from tests 1.1 and 4.2 discussed below document the state of
the art in terms
of the growth of thermophilic bacteria in non-deaerated skimmed milk M by
thermal treatment
in a regenerative first heat exchanger 1. The content of thermophilic bacteria
before and after
the thermal treatment are recorded and documented as a result of sample
collection P1, P2 at
the first and second sample collection points 14, 15. Test 4.1 shows how the
application of the
method according to the invention affects the growth of thermophilic bacteria
in deaerated
skimmed milk M*.
Test 1.1 (temperatures TP = 15 C and TS = 8 C in advance line 3)
Test 1.1 (figure 2; label: curve with 1.1-V; listed in the legend as 1.1
advance ¨ not deaerated)
ran for a total of 13 hours and was operated over the entire test time with
non-deaerated
skimmed milk M. Up to the time t = 6 h, the non-deaerated skimmed milk M
passes from a
plate heat exchanger into the advance line 3 at a processing temperature TP of
approximately
15 C. After the time t = 6 h the non-deaerated skimmed milk M passes into the
advance line 3
at a storage temperature 15 of approximately 8 C.
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The curve 1.1-V shows the initial bacterial contamination (bacterial count
CFU/ml) of the non-
deaerated skimmed milk M fed into advance line 3 under the above conditions.
The measuring
results are from the first sample P1 of the first sample collection point 14
in the advance line 3.
The measured values stagnate approximately in a range oft = 0 to 4 hours at
230 (minimum) to
420 CFU/ml (maximum) and then increase until t = 6 h to approximately 19,000
CFU/ml (first
test section). At 19,000 (minimum) and 1,100,000 CFU/ml (maximum), the non-
deaerated
skimmed milk M added from the tank storage from the time t = 6 h tot = 13 h at
IS = 8 C
(second test section) has a much higher bacterial count than the non-deaerated
skimmed milk
M in the first section of the test.
The non-deaerated skimmed milk M is heated in the first heat exchanger 1
according to the
above curve 1.1-V to an output temperature of approximately 62 C. A second
sample P2 is
taken of this non-deaerated skimmed milk M at the second sample collection
site 15. The
assigned measuring values are shown in the curve 1.1-62 C in Figure 2 (label:
listed in the
legend as 1.1-62 C ¨ non-deaerated).
Until the time t = 6 h according to the curve 1.1-62 C, a significant
increase in the thermophilic
bacterial count can be seen, namely of 330 (minimum) to 2.300.000 CFU/ml
(maximum fort =
5 h). This increase correlates with the start of the biofilm in the first heat
exchanger 1.
From the time t = 6 h according to the curve 1.1-62 C, the high initial
bacterial count in the
advance line 3 leads to a significantly higher proportion of thermophilic
bacteria also in the first
heat exchanger 1. Throughout the period from t = 6 h to t = 13 h these were
1,700,000 CFU/ml
(minimum) and 4,300,000 CFU/ml (maximum), therefore consistently above the
proportion in
the advance line 3 (curve 1.1-V; maximum: 1,100,000 CFU).
Test 4.2 (temperature TP = 15 C in advance line 3)
Test 4.2 (figure 2; label: the curve at 4.2-V; listed in the legend as 4.2-
advance line ¨ non-
deaerated) ran for a total of 9 hours and was operated over the entire test
time with non-
deaerated skimmed milk M. Over the entire test period the non-deaerated
skimmed milk M
passed from a plate heat exchanger to advance line 3 at a process temperature
TP of
approximately 15 C.
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The curve 4.2-V shows the initial bacterial contamination (bacterial count
CFU/ml) of the non-
deaerated milk M passing into advance line 3 under the aforementioned
conditions. The
measuring results are from the first sample P1 of the first sample collection
point 14 in advance
line 3. The measured values stagnate at 100 (minimum) to 240 CFU/ml (maximum)
with the
exception of an outlier at t = 7 h at 1,700 CFU/ml.
The non-deaerated skimmed milk M in accordance with the aforementioned curve
4.2-V is
heated in the first heat exchanger 1 to an outlet temperature of approximately
62 C. A second
sample P2 of this non-deaerated skimmed milk M is taken at the second sample
collection point
15. The assigned measuring results are shown in the curve 4.2-62 C in figure
2 (label: listed in
the legend as 4.2-62 C¨ non-deaerated).
With the exception of an outlier at t = 2 h at 3500 CFU/ml, until the time t =
6 h there is a
significant increase in the thermophilic bacterial count in the curve 4.2-62
C, namely from
17,000 (minimum) to 280,000 CFU/ml (maximum). This increase, in turn,
correlates with the
start of the biofilm in the first heat exchanger 1. From time t = 6 h the
portion of thermophilic
bacteria remains at a high level, i.e. between 110,000 CFU/ml (minimum) and
950,000 CFU/ml
(maximum) and is thereby always two to three to the power of ten higher than
the portion in
advance line 3 (curve 4.2-V; maximum: 240 CFU).
Test 4.1
(Deaeration at TD = 55 C; temperature approximately 8 to 15 C in the advance
line 3)
Test 4.1 (figure 2; label: the curve with 4.1-V; listed in the legend as 4.1-
advance ¨ deaerated)
ran for a total of 13 hours with deaerated skimmed milk M* over the entire
test period. This
deaerated skimmed milk M* was very effectively deaerated at approximately 55
C and then
cooled down to approximately 8 C to 15 C. Until approximately the time t = 5
h (first test
section) the deaerated skimmed milk M* passed from a plate heat exchanger to
the advance
line 3. From approximately the time t = 5 h (second test section) the
deaerated skimmed milk
M* passed from a tank storage to the advance line 3.
The curve 4.1-V shows the initial bacterial contamination (bacterial count
CFU/ml) of the
deaerated skimmedmilk M* passing into the advance line 3 under the
aforementioned
conditions. The measuring results are from the first sample P1 taken at the
first sample
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collection point 14 in the advance line 3. The measured values approximately
stagnate at very
low levels of 100 (minimum) to 350 CFU/ml (maximum) in the time range t = 0 to
5 h.
The deaerated skimmed milk M* from the tank storage added from approximately
the time t =
h to t = 13 h has much higher levels of contamination according to the curve
4.1-V in the time
t = 5 tot = 11 h at 6,800 (maximum) and 1,200 CFU/ml (minimum) than the
deaerated skimmed
milk M* added in the first test section of the test 4.1.
The deaerated skimmed milk M* is heated in the first heat exchanger 1 to an
outlet
temperature of approximately 62 C, according to the aforementioned curve 4.1-
V. A second
sample P2 is taken of this deaerated skimmed milk M* at the second sample
collection point
15. The assigned measuring values are shown in curve 4.1-62 C in figure 2
(label: listed in the
legend as 4.1-62 C ¨ deaerated).
Until the time t = 5 h there is no visible increase in the thermophilic
bacterial count in the curve
4.1-62 C with levels at 100 (minimum) to 360 CFU/ml (maximum), assuming a
value of 4,200
CFU/ml is an outlier at the time t = 4 h. The deaerated skimmed milk M* does
not cause a
measurable biofilm in the first heat exchanger 1.
From approximately the time t = 5 h the bacterial count increases in the
deaerated skimmed
milk M* to 3600 (minimum) to 7000 CFU/ml (maximum), whereby at the time t = 6
h and t = 9 h
the measurements 86,000 or 500,000 CFU/ml were probably outliers. However, the
portion of
thermophilic bacteria in the sufficiently deaerated skimmed milk M* is
approximately two to
the power of ten lower than test 4.2 (non-deaerated skimmed milk M) and
approximately three
to the power of ten lower than in test 1.1 (also non-deaerated skimmed milk
M).
This demonstrates that a sufficient deaeration of the skimmed milk
significantly lowers the
thermophilic bacterial count in recuperative heat exchangers operating in a
temperature range
of approximately 50 C to 70 C, and therefore leads to a reduced growth of a
biofilm on the
surfaces of the heat exchanger in contact with the product. This in turn means
that the service
life of the heat exchanger is extended and therefore the interval between
necessary adjacent
cleaning cycles is extended.
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REFERENCE LIST OF ABBREVIATIONS USED
100 Unit of a processing plant
1 First heat exchanger
2 Second heat exchanger
3 Advance line
4 First advance line section
Second advance line section
6 First return line section
7 Second return line section
8 Return line
9 First heating circuit line
Second heating circuit line
11 First pump
12 Second pump
13 Third pump
14 First sample collection point
Second sample collection point
16 Control valve
VP First heat transfer medium (e.g. vapours)
Skimmed milk (non-deaerated)
M* Skimmed milk (deaerated)
SMC Second heat transfer medium (e.g. skimmed milk concentrate SMC)
SR Source (skimmed milk M, M*)
Si First sample (advance line, Ti)
S2 Second sample (T2 = 62 C)
Ti First sample temperature (advance line)
T2 Second sample temperature (T2 = 62 C)
TD Deaeration temperature
TS Storage temperature
TP Process temperature
Top Optimum temperature (optimum bacterial growth)
TR
