Method and plant for treating milk

Details Method and plant for treating milk Method and plant for treating milk

2002-03-01

2003-10-21

Weier, Anthony J. (Department: 1761)

Food or edible material: processes, compositions, and products

Processes

Treatment of liquid with nongaseous material other than...

C426S583000

Reexamination Certificate

active

06635296

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an improved method and an improved plant for treating milk so as to obtain milk with a reduced content of spores and bacteria, wherein low-fat milk, such as skim milk, is subjected to microfiltration causing a separation into a spore- and bacteria-containing retentate and a permeate in form of a milk fraction, the content of milk proteins being substantially maintained and the content of spores and bacteria being considerably reduced. The treated low-fat milk may be used in this form or may be mixed with a fatty milk fraction, such as cream, which has been subjected to a bacteria-controlling treatment, eg a heat treatment, so as to produce standardized milk. The treated milk and the standardized milk are both suitable for direct consumption and as raw material for processed dairy products, eg for making cheese. The improvement in the method and the plant is in a special arrangement of the equipment for the membrane filtration which renders a more efficient removal of bacteria and spores and which is more safe in case of a membrane breakdown.
BACKGROUND ART
Danish printed accepted application No. 164.722 and the corresponding EP patent No. 0 194 286 (Holm et al.) disclose a plant for treating milk in such a manner that the milk has a low bacterial content. Fatty milk is divided by centrifugation into a cream fraction and a skim milk fraction. The skim milk fraction is caused to pass through a microfilter, in which the fat globules and the bacteria are separated off. The microfiltration results in a permeate consisting of skim milk with a low bacterial content and a retentate (concentrate) having a higher content of fat and bacteria than the permeate. The retentate is combined with the cream fraction resulting from the centrifugation, and the obtained mixture is sterilised. The sterilised material or a portion thereof is combined with the permeate to obtain milk with the desired fat content. The advantage of this known method is that only a minor fraction of the milk need be sterilised in order nevertheless to obtain standardised milk with a low bacterial content. The combination of a centrifuigal separation and microfiltration provides a significantly increased capacity of the microfilter.
DK 169 510 and the corresponding EP 0 697 816 (Krabsen et al.) disclose a similar plant, in which, however the retentate resulting from the microfiltration is recirculated to centrifugal separator, ie mixed with the added milk and centrifuged therewith, instead of being combined with the cream fraction. Bacteria and spores thus being recirculated to the centrifugal separator, are, however, not accumulated in the plant, as they are continuously or discontinuously removed with a sludge fraction. This possibility of removing sludge is known from many conventional centrifugal separators.
Microfiltration processes using the cross-flow principle, eg the processes used in the above plants, may be carried out by employing conventional microfiltration units of differing structural shapes. As a basic model a microfiltration unit (MF unit) with cross flow may be formed of a container divided by a microfiltration membrane into two chambers, a feed/rententate chamber and a permeate chamber. The retentate chamber is provided with a feed conduit for feeding the material to be filtered, and a retentate outlet. The permeate chamber is provided with a permeate outlet. Between the retentate chamber and the permeate chamber a pressure difference is etablished forcing the fluid and small particles through the membrane. The feed material is fed through the retentate chamber from one side along the membrane. On the other side of the retentate chamber the retentate is removed, said retentate consisting of the fluid and the particles, which have not passed through the membrane to the permeate chamber during the passage along the membrane. In order to prevent the membrane surface from being fouled too quickly, which causes clogging of the membrane pores, the flow rate (cross-flow rate) over the surface of the membrane should not be too low. This is often ensured by recirculating a portion of the retentate flow to the feed conduit. It is also well-known to recirculate a portion of the permeate to ensure a uniform pressure drop, the permeate chamber in addition to the permeate outlet also being provided with an inlet for receiving recirculated permeate. This principle is described in U.S. Pat. No. 4,105,547 (Sandblom). Such recirculation conduits for retentate or permeate leading to the same respective retentate chamber or permeate chamber from which said material has flown, are considered as components forming part of a basic model of the microfiltration unit.
For large scale plants a larger membrane area may be needed and often this is obtained by interconnecting a large or small number of the above basic models. Accordingly, a large filtration area may be obtained by parallel coupling several basic models. This principle is for instance described in connection with ultrafiltration of whey by Rud Frik Madsen in “Hyperfiltration and Ultrafiltration in Plate-and-Frame Systems”, Elsevier, 1977, page 134, FIG. 4.23. It is also known to interconnect several filtration units in series such that the portion of the retentate resulting from the first unit, which is not recirculated, is added as feed material to the subsequent filtration unit, etc. This principle is for instance shown in Perry's Chemical Engineers' Handbook, 6th edition 1984, page 17-32, FIG. 17-29.
U.S. Pat. No. 5,685,990 (Saugmann et al.) discloses how to membrane filtrate an aqueous dispersion by employing several primary membrane units interconnected in such a manner that the retentate or a portion of the retentate resulting from a membrane filtration step is used as feed material for one or more subsequent steps, while the permeate from said primary filtration steps is concentrated by evaporation or in a secondary membrane filtration step, in which the concentrate or the secondary retentate is recirculated to the aqueous feed dispersion in one or more of the primary filtration steps. As an essential feature the membranes in the secondary membrane filtration step should have a smaller pore size or molecular cut-off value in relation to the membranes in the primary filtration steps. Examples of the primary filters are ultrafiltration filters (UF filters), while the secondary filters may be hyperfiltration filters (HF filters), which are also known as RO filter, RO denoting reversed osmosis.
WO 94/13148 (Bounous et al.) discloses a process for producing an undenatured whey protein concentrate from skim milk, microfiltration being carried out in a first step with a microfilter retaining bacteria, but allowing the skim milk containing both whey proteins and other milk proteins, such as casein, to pass through the filter, and in a subsequent step microfiltration being carried out with another type of microfilter retaining casein, but allowing the whey proteins to pass. The known method thus cannot be used for producing a milk fraction in which the content of all types of milk proteins, ie both casein and whey proteins, are substantially maintained, while the content of spores and bacteria is considerably reduced.
The use of microfiltration for removing bacteria from a low-fat milk fraction as described in DK 164.722 and DK 169.510 is advantageous in that the bacteria may be removed without heat treatment which is substantially more gentle to the milk components. As a result the good taste is preserved and a denaturation of proteins and other changes of the properties of the milk can be avoided. In addition it is prevented that the milk fraction contains heat-treated and thus dead bacteria. Even when the skim milk fraction subsequently is to obtain a desired fat content by being mixed with heat-treated cream, the result is still an improved product as regards taste and the preservation of proteins. Products treated in this manner are suitable both for direct consumption and as raw material for processed

Affiliated with

Also associated with

Rating

Method and plant for treating milk does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method and plant for treating milk, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and plant for treating milk will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3131447