Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~05(~438
The present in~ention relates to a filtering
method for separating skim milk from milk products, espe-
cially from whole milk or cream.
Centrifuging has been used for many years for
separating liquid milk products. Thus, milk has been cen-
trifuged to recover cream having a varying degree of fat
percentage, and cream having a low fat percentage has been
centrifuged to concentrate it for the production of butter.
The present invention aims at providing an inex-
pensive alternati~e to centrifugal separation of milk or
crea~. In order for filtering to be practical as an alter-
native, it is necessary that the throughput capacity of the
filter he satisfactorily high. It is known through Swedish
patent specification 17,335 to separate milk by filtering,
but the throughput capacity of the device there disclosed
is limited by the capability of the cream to rise to the
outlet for the cream under the influence of gravity. ~his
means that the velocity of the milk flow past the filter
suriace is so low that the filter surface becomes clogged
20 by cream, and the device rapidly becomes incapable of func- -
tioning~ ObYiously this device is not practical for com-
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mercial use.
The present invention has for its principal object
to provide a separation method based on the filtering prin-
ciple and which is practical for commercial use. Themethod is characterized in that the separation of skim milk
from milk or cream is carried out by means of a filter in
which the main quantity of the filter pores each has a di-
ameter of 0.2 - lO ~ m (micrometers), that the milk or
cream i5 caused to flow along the filter surface with a
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velocity of at least 0.5 m/sec. from an inlet to an outlet,
while skim milk passes through the filter under a pressure drop
of at least 19.6 kilopascals, and that the greater part of -the
product, enriched with cream, is returned to the ~ilter inlet.
In this way, the fat globules in milk or cream are retained by
the filter so that they do not pass through it, and they are
torn away from the filter surface by the liquid flow sweeping
past the latter with sufficient velocity, so that the filter will
not be closged and thereby become incapable of functioning owing
to a cream layer adhering to the filter.
Since the fat droplets and the bacteria of the milk
are of the same size magnitude, the skim milk obtained by this
method will be substantially free of bacteria, this action being
more effective with finer pore size of the filter. When the
filtration of the fat droplets is satisfactory, the skim milk
will be completely free from bacteria so that it is not neces-
sary to sterilize the skim milk by heating. The latter is an
~ important advantage because heating of the skim milk injures
; the proteins present in ît and also impairs the taste of the
skim milk. The present invention also makes it possible to
separate off the fat droplets of a milk product more completely
;, than by centrifuging. Thus it is possible to obtain a skim
; milk which is even more fat-free than heretofore, such as a
skim milk with a fat percentage below 0.05%, if the separation
is carried out by means of a filter in which the main quantity
~ of the filter pores has a maximum diameter of 1.0 ~m.
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The higher the flow velocity ~f the milk or
cream past the filter surface, the better the latter is
kept free from cream deposits. However, the high flow
velocity leads to a correspondingly low cream concentra-
tion in the product, which has merely swept past thefilter surface. In order to avoid excessive recirculation
of this product to the filter inlet, this flow velocity
preferably should not exceed 20 m/sec.
If it is desired to carry out a separation with
a high khroughput rate, the milk product can first be sep-
arated by means of a filter in which the main quantity of
the filter pores has a diameter of at most 10 ~ m. A
cream is thus obtained which, owing to its great droplet
size, is suitable for butter production. Furthermore, a
skim mil~ with a relati~ely high fat percentage is ob-
tained. This skim milk is then separated by means of a
filter having a smaller pore size, thereby obtaining cream
separately from a skim milk with a desirably low fat per-
centage. For the latter separation, a filter may be used
in which the main quantity of the filter pores has a di.
; ameter of at least 0.2~1 m.
Cream obtained when separating according to the
invention and having a fat percentage of 15%, for example,
can be concentrated further, by means of repeated separ-
ation according to the present method, to a fat percentagesuch as 50%. The cream thus obtained is suitable for
butter production.
The invention is described more in detail below
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`~ with reference to the accompanying drawing which shows an
example of a device for carrying out the present method.
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~050438
In the drawing, Fig. 1 is a vertical sectional view of the
filter device, and Fig. 2 is a flow diagram in which the
filter device is included.
In Fig, 1, two hollowed plates 1 and 2 are kept
together by releasable fastening means, such as bolts la,
rect~ n~u /Q r
and form a hollow space 3 which is preferably of rctangular
shape. A diaphragm 4, serving as a filter, is clamped be- ~ `
tween the plates. This filter, which to advantage can be
a diaphragm of porous plastic, is compressed aLong an an-
nular surface where two annulax rubber gaskets 5 and 6
seal the space 3 against leakage along the opposing sides
of the plates. The filter 4 is supported against the fil-
tering pressure by a plate 7 of porous material, such as
sintered stainless steel. An inlet 8 is provided for -~
supplying a milk product at a temperature of 50 to 55 C,
for example, by means of a pump (not shown) generating the
necessary filtering pressure. The device is also provided
with an outlet 9a for the cream-enriched concentrate and
an outlet 9b for the skim milk which has passed through
the diaphragm 4,
The system shown in Fig. 2 allows the filtering
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operation to be continued for a long time. The inlet 8 of
the deYice is fed by a pump 10, and the necessary filtering
' pressure is adjusted by means of a throttle valve 11 in-
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serted in the outlet 9a for the concentrate. In order to
~ attain a desired concentration of the concentrate, a rela-
:$ tively great part of the latter may be returned through a
pipeline 12 to the inlet of the pump 10.
In the operation of the device, the milk product
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~, 30 to be filtered enters through the inlet 8 and sweeps over
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the surface of the filter 4 on its way to the outlet 9a. Due
to the throttling of the outlet 9a and the pressure thereby gen-
erated in the upper part of the space 3, skim milk penetrates
through the filter 4 and its support 7 and discharges through
the outlet 9b. The pressure drop through the filter can amount
to 19.6 to 294 kilopascals and the velocity of the flow along
the filter surface can be 0.5 to 20 m/sec.
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