DK201500313A1 - Second pass lactose crystallization - Google Patents

Abstract

A method for obtaining crystallized lactose from an aqueous solution comprising lactose in a batch process, comprising a first crystallization pass, a concentration pass, and a subsequent crystallization pass.

Description

TITLE

SECOND PASS LACTOSE CRYSTALLIZATION FIELD OF THE INVENTION

The application generally relates to a method of obtaining solid lactose from one or more aqueous solutions comprising lactose.

More specifically the invention relates to a method of obtaining solid lactose derived from whey or whey permeate .

The invention is described with the help of a method for obtaining a solid crystallized lactose product.

BACKGROUND OF THE INVENTION

Crystallization is an important processing step in the manufacture of alpha lactose monohydrate from liquid solutions, in particular whey solutions. The efficient recovery of alpha lactose monohydrate is an important issue for industry and in particular, for the dairy industry .

During crystallization lactose is typically lost in one or more waste streams, reducing the lactose yield.

In the art, it is known to recycle some of the lactose waste streams continuously. For example, the wash water from sieving is sometimes recycled, since it is very pure . WO2014141164 discloses a method of obtaining lactose from a lactose-containing liguid source comprising providing a lactose-containing liquid source, crystallizing the lactose in the lactose-containing liquid source to generate one or more lactose-containing liquid streams, obtaining a lactose-containing extract from the one or more lactose containing liquid streams by subjecting the one or more lactose-containing liquid streams to filtration to remove cells, proteins, polypeptides, polysaccharides, lipid, ions or salts. The method also includes processing the lactose-containing liquid streams using at least nanofiltration, ultrafiltration and/or centrifugal separation and continuously recycling the lactose-containing extract into the lactose-containing liquid source.

However, when a high fraction of the lactose is recycled continuously, it increases level of impurities to an undesirable level. Therefore, typically only a minor part of the lactose is recycled. The rest is discarded as waste .

The present inventors have now realized that the overall lactose yield can be significantly increased with the same product quality if mother liquor and/or wash water is recycled in a batch process.

SUMMARY OF THE INVENTION

In one embodiment the invention relates to a method for obtaining crystallized lactose (14), comprising: a first crystallization pass (II) comprising subjecting an aqueous solution comprising lactose to a lactose crystallization process (9-12) to obtain crystallized lactose (14) and a mother liquor (15), and, optionally, washing said crystallized lactose (11, 12) thereby generating one or more batches of wash water comprising lactose (16,17), collecting said mother liquor (15) or a mixture of said mother liquor (15) and said one or more batches of said wash water (16, 17) as a first pass lactose solution; a concentration pass (IV) comprising demineralizing (20) in a batch process (15-21) said first pass lactose solution to obtain a demineralized first pass lactose solution, concentrating (21) said demineralized first pass lactose solution to obtain a concentrated demineralized first pass lactose solution; and a subsequent crystallization pass (II) comprising subjecting said concentrated demineralized first pass lactose solution to a lactose crystallization process (9-12) to obtain a second pass crystallized lactose (14) and a second pass mother liquor (15), and, optionally, washing said second pass crystallized lactose (11, 12) thereby generating one or more batches of second pass wash water comprising lactose (16,17), and, optionally, collecting said second pass mother liquor (15) or a mixture of second pass mother liquor (15) and one or more batches of said second pass wash water (16, 17) as a second pass lactose solution.

In another embodiment the invention relates to a method, wherein said second pass lactose solution is further subjected to said concentration pass (IV) and said subsequent crystallization pass (II) at least once.

In another embodiment the invention relates to a method, wherein said first pass lactose solution or any of the second pass lactose solutions obtained during said one or more repeated concentration passes (IV) is accumulated in a tank for mother liquor and wash water (18) prior to each crystallization pass (II).

In another embodiment the invention relates to a method, wherein crystallization of lactose (8) is allowed to proceed until at least 50% of total lactose present in said aqueous solution comprising lactose or any of said first or second pass lactose solutions is crystallized.

In another embodiment the invention relates to a method, wherein any of said first pass or second pass lactose solutions is pasteurized (19) before demineralization (20) in said concentration pass (IV).

In another embodiment the invention relates to a method, wherein said demineralized first pass or second pass lactose solution, is collected in a collection tank (22) prior to undergoing concentration (21) and crystallization in said subsequent crystallization pass (II) to obtain crystallized lactose.

In an embodiment the invention relates to a method wherein at least two batches of said first pass or said second pass lactose solutions are combined in said collection tank (22) prior to undergoing concentration (21) and crystallization in said subsequent crystallization pass (II) to obtain crystallized lactose.

In another embodiment the invention relates to a method, wherein aqueous solution comprising lactose is whey or whey permeate (1).

In another embodiment the invention relates to a method, wherein said demineralization (20) is performed by nanofiltration.

In another embodiment the invention relates to a method, wherein crystallized lactose is further dried in a post treatment step (III).

In another embodiment the invention relates to a method, wherein whey or whey permeate is subjected to a pretreatment step (I) thereby obtaining an aqueous solution comprising lactose.

In another embodiment the invention relates to a method, wherein said pretreatment step (I) comprises a) purifying whey or whey permeate to remove one or more of protein, polypeptides, polysaccharides or lipids, and b) concentrating said whey or whey permeate.

In another embodiment the invention relates to a method, wherein said purification of whey or whey permeate (a) is performed by ultrafiltration.

In another embodiment the invention relates to a method, wherein said concentration (b) is performed by evaporation .

To those skilled in the art to which the invention relates, many changes in construction and differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the present invention is illustrated by way of example in the accompanying drawings in which like reference numbers indicate the same or similar elements.

Figure 1: Flow diagram of lactose crystallization starting from whey or whey permeate according to one of the embodiments of the invention, wherein the concentrated demineralized first pass lactose solution and/or second pass lactose solution re-enters the concentration step (IV) in a batch process.

Figure 2: Flow diagram of lactose crystallization starting from whey or whey permeate according to one of the embodiments of the invention, wherein the concentrated demineralized first pass lactose solution and/or second pass lactose solutions re-enters the concentration step (IV) in a batch process, wherein the first pass lactose solution and/or the second pass lactose solution is gathered in a collection tank prior to concentrating.

DETAILED DESCRIPTION OF THE INVENTION

The process for obtaining a solid crystallized lactose product from an aqueous solution comprising lactose is described below with reference to the drawings, Figures 1 and 2. The processes described in the flow-diagrams are meant as an illustration of the inventive concept, and the skilled person will be able to make modifications thereof, following the content of the present disclosure, without departing from the disclosed inventive concept.

The present invention relates to a method for obtaining crystallized lactose (14) , comprising: a first crystallization pass (II) comprising subjecting an aqueous solution comprising lactose to a lactose crystallization process (9-12) to obtain crystallized lactose (14) and a mother liquor (15) , and, optionally, washing said crystallized lactose (11, 12) thereby generating one or more batches of wash water comprising lactose (16,17), collecting said mother liquor (15) or a mixture of said mother liquor (15) and said one or more batches of said wash water (16, 17) as a first pass lactose solution; a concentration pass (IV) comprising demineralizing (20) in a batch process (15-21) said first pass lactose solution to obtain a demineralized first pass lactose solution, concentrating (21) said demineralized first pass lactose solution to obtain a concentrated demineralized first pass lactose solution; and a subsequent crystallization pass (II) comprising subjecting said concentrated demineralized first pass lactose solution to a lactose crystallization process (9-12) to obtain a second pass crystallized lactose (14) and a second pass mother liquor (15), and, optionally, washing said second pass crystallized lactose (11, 12) thereby generating one or more batches of second pass wash water comprising lactose (16,17), and, optionally, collecting said second pass mother liquor (15) or a mixture of second pass mother liquor (15) and one or more batches of said second pass wash water (16, 17) as a second pass lactose solution.

Crystallized lactose in the context of the present invention preferably means alpha-lactose monohydrate. Aqueous solution comprising lactose can be whey or whey permeate as detailed further below.

In the art it is known to crystallize lactose from aqueous solutions in a various manners. For example, lactose can be crystallized at room temperature by evaporation of water or by heating and subsequent cooling of the crystallized lactose. Any suitable method for lactose crystallization can be used without departing from the scope of the invention.

In industry there is a constant demand for high yield lactose crystallization processes. In the improved process of the invention lactose is recycled in a batch process and not continuously. It is advantageous to recycle all mother liquor and wash water obtained in crystallization pass (II) as first and/or second pass lactose solution back to the subsequent crystallization process (11) .

Traditionally a yield of up to 69-70% can be obtained by single pass lactose process without recirculation of mother liquor or wash water.

In a prior art, this amount has been increased by circulating wash water from the sieve back into the process, however, to avoid build-up of impurities only a relatively small part of the lactose in the mother liquor and wash water can be circulated continuously back into the process. The rest has been discarded as waste.

According to the present invention preferably all mother liquor and optionally wash water is collected as a first pass and/or second pass lactose solution, purified and returned to the process, e.g. running on the same process equipment as the first crystallization pass (II) . When a concentration pass (IV) and a subsequent crystallization pass (II) is used, it is possible to increase the yield significantly with the same product quality.

As detailed according to the present invention second pass lactose solution is further subjected to a concentration pass (IV) and a subsequent crystallization pass (II) at least once.

Once the first pass lactose solution is demineralized and concentrated it is suitable for re-entering said crystallization pass (IV). According to the invention more than 70%, preferably more than 75%, more preferably more than 80%, more preferably more than 85%, more preferably more than 90%, most preferably more than 95%, of the lactose present in the aqueous solution comprising lactose prior to said first pass crystallization (II) can be recovered following the method of the invention. By performing the method of the invention little or no lactose is lost as waste, in particular since it is possible according to the principle of the invention to collect further pass lactose solutions after repeating the concentration pass (IV) and the crystallization pass (II) to additionally increase the amount of lactose recovered without sacrificing product quality.

As detailed a method, wherein said first pass lactose solution or any of the second pass lactose solutions obtained during said one or more repeated concentration passes (IV) is accumulated in a tank for mother liquor and wash water (18) prior to each said crystallization pass (II) is described.

As further detailed a method, wherein crystallization of lactose (8) is allowed to proceed until at least 50% of total lactose present in said aqueous solution comprising lactose or any of said first or second lactose solution is crystallized. Preferably, crystallization is permitted to proceed until at least 55%, at least 60%, at least 65% or at least 70% of total lactose present in said aqueous solution comprising lactose or any of said first or second lactose solution is crystallized. Further preferably, said crystallization is terminated before at least 90%, preferably at least 85%, or most preferably at least 80% of total lactose present in said aqueous solution comprising lactose or any of said first or second lactose solution is crystallized.

Crystallization of aqueous solutions comprising lactose in crystallization tanks as detailed in the prior art is a slow process, typically based on cooling de-colored and concentrated whey permeate by an initial rapid cooling followed by subsequent slow cooling at about 1°C per hour.

In the prior art in order to maximize the yield of lactose from crystallization, a maximal time is allocated to the crystallization step, typically in excess of 20 hours. A problem of the prior art crystallization methods is that that part of the lactose initially present which after crystallization is still in solution (solvated) or present as very small crystals (suspended) will not be recovered in the subsequent isolation of lactose crystals under industrial conditions, and will therefore go to waste with mother liquor and wash water.

The present invention is highly efficient in regaining and obtaining by further crystallization a large part of this lactose, because said first pass and/or second pass lactose solution is recycled into the crystallization in the batch process after concentration to sufficiently high lactose concentrations for efficient crystal growth.

The method suggested by the present invention allows for the possibility of differentiating the crystallization of each subsequent crystallization pass (II) . Since most of the lactose from the first pass lactose solution is recovered in a subsequent crystallization pass (II), it is no longer so important to maximize the yield of the first crystallization pass (II) . This means that it is possible to shorten the crystallization time for the first crystallization pass (II). It can for example allow for using the remaining time for the subsequent crystallization pass (II) so that no extra capacity on crystallization tanks is required even when capacity for second pass is used while still resulting in a higher overall yield. If extra capacity for crystallization is reserved for the second pass, then this will increase the overall yield even further.

The subsequent crystallization pass (II) is usually performed on the same equipment. The mixture obtained during the concentration pass (IV) enters the subsequent crystallization pass independently from the mixture obtained during the first crystallization pass (II). The entering point has a connection (8); connection can be for example a valve, but it should be understood that any suitable connection is possible and the type of connection is not in any way limiting for the invention.

According to suitable methods of the prior art of lactose crystallization and repeated here by way of example, permeate concentrated in an evaporator in step (9) can be cooled to at least 55°C, more preferably 60°C, in a flash cooler built together with the evaporator and kept at this temperature during filling of the crystallization tank(s). When a tank is full, the temperature is lowered by approximately 3°C per hour, until a temperature of approximately 30°C is reached. The cooling speed is then regulated to approximately 1.5°C per hour, until the temperature reaches 15°C. If filling a tank through the bottom, the tank temperature is adjusted to approximately the temperature of the liquid exiting the flash. When cooling starts, cooling e.g. by tower water is used to bring the temperature down as far as possible. Other cooling techniques are equally suitable. As is known in the art, this will result in precipitation of alpha-lactose monohydrate at a good product quality.

The cooling temperature as well as the cooling time can be changed if needed, as it is known to the skilled person .

Mother liquor (15), as known, is that part of a solution which is left over after crystallization. Typically, mother liquor comprises solvated lactose and a number of impurities. Therefore, continuously re-circulating the mother liquor into the process typically results in an ever increasing amount of impurities. Also, wash water used to wash crystallized lactose will comprise both lactose and impurities, presenting the same recycling problem vis-a-vis recycling of the mother liquor.

To overcome the above limitations it is suggested by the present inventors that in a concentration pass (IV) said first pass and/or second pass lactose solution can be collected and demineralized (20) in a batch process (15— 21) to obtain a demineralized first and/or second pass lactose solution, followed by concentration (21) of said demineralized first and/or second pass lactose solution to obtain a concentrated demineralized first and/or second pass lactose solution comprising lactose.

It is exemplified in the drawings (Fig. 1 and 2) that concentration (21) of the demineralized aqueous solution is carried out on dedicated process equipment during the concentration pass (IV); but it should be understood that it can be carried out on equipment for concentration of aqueous solution comprising lactose during pre-treatment step (I), or any other suitable equipment. A batch process in the context of the application means that the mother liquor and optionally the wash water do not enter the lactose crystallization process continuously but rather is collected and subjected to the steps of extra demineralization (20) and crystallization (21) prior to re-entering lactose crystallization process (II) .

Crystallized lactose after crystallization (9) can e.g. in one embodiment, initially be separated in a decanter (10), wherein the separated mother liquor (15) contains most of the minerals. The mother liquor (15) will typically be collected in a tank (18) prior to mixing of the mother liquor and the wash water (16, 17).

As exemplified, it is possible to wash the crystals obtained from the crystallization step (9) in a decanter. Optionally, further washing (12) may be done in a tank connected to a decanter. In this manner wash water (16) may also be collected in the mother liquor + wash water collecting tank (18), thereby directly mixing these liquids .

In the method, the crystals from the tank and decanter (11) are separated in a separation stage (12), typically by sieve centrifugation optionally further comprising a tank in front, and the wash water (17) formed during this process can then be collected in a mother liquor + wash water collection tank (18).

Concentration of the demineralized first pass and/or second pass lactose solution can be performed by several techniques, for example by evaporating aqueous component as it is known in the art.

As detailed, a method, wherein said first pass or second pass lactose solution is pasteurized (19) before demineralization (20) in said concentration pass (IV) is disclosed.

Pasteurization methods known from the state of the art are suitable for use in the method according to the invention. According to one of the embodiments of the present invention, said first pass or second pass lactose solution can be heat treated and cooled before it is demineralized (20).

The pasteurization (19) can for example take place in a regenerative plate heat exchanger by indirect heating with product and with hot water heated by steam. The mix of the mother liquor and the wash water is then kept at approximately between 70°C and 80°C, more preferably for 71°C and 69°C, more preferably 72°C and 68°C, more preferably 73°C and 76°C, more preferably 75°C in a holding cell, for the time sufficient to effectuate the pasteurization. During the pasteurization any remaining small lactose crystals will be dissolved.

After pasteurization (19) said first pass or second pass lactose solution is cooled, for example, in the heat exchanger.

As detailed a method, wherein said demineralized first pass or second pass lactose solution, is collected in a collection tank (22) prior to undergoing concentration (21) and crystallization in said subsequent crystallization pass (II) to obtain crystallized lactose is described.

Collecting the demineralized first pass and/or second pass lactose solution in the collection tank allows for operating both the first crystallization pass and (II) and the subsequent crystallization passed (II) on the same production line.

Since with each batch pass of the crystallization pass (IV) the amount of water is reduced by concentration; it will often be advantageous to combine third and higher pass lactose solutions from several process lines or process runs in a dedicated, separate, collection tank (22) until a sufficient volume of third or higher pass lactose solutions has been collected; which sufficient volume allows for efficient use of the crystallization tanks at hand in the production facilities where the method of the invention has been implemented.

Accordingly, in an embodiment the present invention comprises combining at least two batches of said first pass or said second pass lactose solutions in said collection tank (22) prior to undergoing concentration (21) and crystallization in said subseguent crystallization pass (II) to obtain crystallized lactose.

As detailed, a method wherein agueous solution comprising lactose is whey or whey permeate (1) is described.

Egually suitable is whey from diary processes, for example mozzarella whey, hard cheese whey and semi hard cheese whey. Incoming whey from e.g. cheese fabrication can initially be processed by separate methods as is known in the art and thus not described in this application. Once whey is pre-treated by the techniques known in the art to generate semi-purified whey suitable for filtration, it is suitable for use in the method of present invention.

As detailed a method, wherein said demineralization (20) is performed by nanofiltration is described.

Demineralization is performed in order to remove as much mineral impurities as possible. Numerous techniques are known in the art for removing mineral impurities from aqueous solutions. It is exemplified in the present application but not limiting the use of a nanofiltration membrane for demineralization.

As detailed, a method wherein crystallized lactose is further dried in a post-treatment step (III).

Different techniques known in the art can be used for lactose drying without departing from the scope of the invention. In one embodiment, as an example only, in a post treatment step (III) of lactose obtaining process, the product obtained after washing (10) or optional additional washing (12) is subsequently fed directly into fluid bed dryer (13), wherein the lactose (14) is finally dried and cooled in a fluid bed system (13).

In the examples, the product is fed from a separation (10) and optional washing (11, 12) section to a drying section (13) in the post treatment step (III).

As detailed, a method wherein whey or whey permeate is subjected to a pre-treatment step (I) thereby obtaining an aqueous solution comprising lactose is described.

The pre-treatment step (I) can be performed by using any of the several techniques known in the art. According to one of the embodiments said pre-treatment step (I) comprises a) purifying whey or whey permeate to remove one or more of cells, polypeptides, polysaccharides or lipids and/or b) concentrating said whey or whey permeate to obtain purified whey permeate.

Optionally, whey permeate can be purified, riboflavin can be removed from said concentrated whey permeate, or permeate can be de-calcinated prior to concentration.

Purification of whey or whey permeate in the pretreatment step (I)(a) is typically performed by ultrafiltration. The aim of ultrafiltration is to produce purified whey permeate for further processing according to the present invention.

Concentration of the purified permeate in the pretreatment step (I) can be performed by for example, reverse osmosis or any other method known in the art.

In accordance with one suggested process of the invention as detailed in the exemplary flow-diagram Figure 1, whey or whey permeate (1) is purified (2) and salts are removed by nanofiltration which will also concentrate the lactose (3) . If not already concentrated in (2), then it is concentrated to remove surplus water in a permeate concentration step (4). It is generally preferred that concentration is by reverse osmosis, but other methods of concentrating whey permeate are equally useful.

Whey permeate suitable for use in the present invention is typically concentrated to between 10 to 40% dry solids (DS) , between 15 to 35% DS, between 17 to 30% DS, preferably between 18 to 25% DS, and most preferably 20% DS. Concentrated solutions comprising lactose are highly viscous and inefficient processes will typically result if concentrated beyond about 40% dry solids.

The plants used in for concentration of permeate are in general intended for continuous operation. The product is pumped to the plant only once and leaves when concentrated to the required solids content. The choice of membrane is based on the pre-treatment history of the incoming UF-permeates and on the capacity composition and quality of the raw materials, as well as the mass balance, as is known in the art.

The permeate obtained in step (4) is usually treated to a riboflavin removal step (5) for the removal of riboflavin present in the whey permeate, typically by passing the concentrated whey permeate through a column comprising active carbon, thereby removing riboflavin by adsorption (de-colouring process). Other methods of removing of riboflavin are equally useful and the present invention is not limited by the manner in which riboflavin is removed.

In a method for obtaining crystallized lactose (14), optional de-calcinating of said protein free whey in a pre-treatment step (I) can be performed by heating and cooling of said concentrated protein free whey permeate. It can also be beneficial to adjust the pH of the concentrated solutions. The above techniques are known in the art and not limiting for the invention. During this time most of the calcium is precipitated as calcium phosphate and can be removed from the solution e.g. by clarification.

EXAMPLES

Example 1 0.075% NaOH was added to the initial pre-treatment step (I) wherein it has been heated to 75°C for 1 hour, clarified and 0.04% HC1 was added. Product was evaporated (6) to 60% DM and crystalized (9), separated (10), washed (II) and dried (13).

All wash water (15, 16) and mother liquor (14) was collected for the concentration pass (IV). From this step (IV) the monovalent salts was removed in NF plant (20). The retentate was then heated to 75°C for 1 hour (5), clarified (6), and 0.04% HC1 was added. The obtained product was then concentrated to 64% DM (7), crystallized (9), separated (10), washed (11), and dried (13). The total crystallization time was about 23 hours. a. Results of product was 0.13% sulfated ash in the first crystallization pass (II) product and 0.11% sulfated ash in a subsequent crystallization pass (II) product. b. Yield of the first crystallization pass (II) was 69% measured on anhydrous lactose and yield of the subsequent crystallization pass (II) was 15% measured on anhydrous lactose, giving a total yield of 84% measured on anhydrous lactose. This yield includes all losses in process.

Example 2 0.065% NaOH was added to the initial pre-treatment step (I) followed by heating to 76°C for 1 hour (4), clarified (6), and 0.04% HC1 was added. Product was evaporated to 60% DM (7) and crystalized (9), separated (10), washed (II) and dried (13) . All wash water (16, 17) and mother liquor (15) was collected for the concentration pass (IV) . From this concentration pass (IV) the monovalent salts was removed in NF plant (20). The obtained product then entered the subsequent crystallization pass (II). The retentate was then heated to 75°C for 1 hour (5) , clarified (6), and 0.03% HC1 was added. Subsequent crystallization pass product (II) was then concentrated to 64% DM (7), crystallized (8), separated (10), washed (11), and dried (13). The total crystallization time was about 23 hours. a. Results of product was 0.11% sulfated ash in the first crystallization pass (II) product and 0.12% sulfated ash in the subsequent crystallization pass (II) product. b. Yield of the first crystallization pass (II) was 68% measured on anhydrous lactose and yield of the subsequent crystallization pass (II) was 14% measured on anhydrous lactose, giving a total yield of 82% measured on anhydrous lactose. This yield includes all losses in process.

Using the known methods of the prior art and permitting the lactose comprising solution to crystallize for the same period as in the above examples (everything else constant) will yield below 75% lactose measured on anhydrous lactose.

CLOSING COMMENTS

The term "comprising" as used in the claims does not exclude other elements or steps. The term "a" or "an" as a used in the claims does not exclude a plurality. And although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the invention.

Claims (14)

1. A method for obtaining crystallized lactose (14), comprising: a first crystallization pass (II) comprising subjecting an agueous solution comprising lactose to a lactose crystallization process (9-12) to obtain crystallized lactose (14) and a mother liquor (15), and, optionally, washing said crystallized lactose (11, 12) thereby generating one or more batches of wash water comprising lactose (16,17), collecting said mother liquor (15) or a mixture of said mother liquor (15) and said one or more batches of said wash water (16, 17) as a first pass lactose solution; a concentration pass (IV) comprising demineralizing (20) in a batch process (15-21) said first pass lactose solution to obtain a demineralized first pass lactose solution, concentrating (21) said demineralized first pass lactose solution to obtain a concentrated demineralized first pass lactose solution; and a subsequent crystallization pass (II) comprising subjecting said concentrated demineralized first pass lactose solution to a lactose crystallization process (9-12) to obtain a second pass crystallized lactose (14) and a second pass mother liquor (15), and, optionally, washing said second pass crystallized lactose (11, 12) thereby generating one or more batches of second pass wash water comprising lactose (16,17), and, optionally, collecting said second pass mother liguor (15) or a mixture of second pass mother liguor (15) and one or more batches of said second pass wash water (16, 17) as a second pass lactose solution.

2. A method according to claim 1, wherein said second pass lactose solution is further subjected to said concentration pass (IV) and said subseguent crystallization pass (II) at least once.

3. A method according to either claim 1 or 2, wherein said first pass lactose solution or any of the second pass lactose solutions obtained during said one or more repeated concentration passes (IV) is accumulated in a tank for mother liguor and wash water (18) prior to each crystallization pass (II).

4. A method according to either claim 1 to 3, wherein crystallization of lactose (8) is allowed to proceed until at least 50% of total lactose present in said aqueous solution comprising lactose or any of said first or second pass lactose solutions is crystallized.

5. A method according to any of claims 1 to 4, wherein any of said first pass or second pass lactose solutions is pasteurized (19) before demineralization (20) in said concentration pass (IV).

6. A method according to any of claims 1 to 5, wherein said demineralized first pass or second pass lactose solution, is collected in a collection tank (22) prior to undergoing concentration (21) and crystallization in said subsequent crystallization pass (II) to obtain crystallized lactose.

7. A method according to any of the claims 1 to 6, wherein at least two batches of said first pass or said second pass lactose solutions are combined in said collection tank (22) prior to undergoing concentration (21) and crystallization in said subsequent crystallization pass (II) to obtain crystallized lactose.

8. A method according to any of claims 1 to 7, wherein aqueous solution comprising lactose is whey or whey permeate (1).

9. A method according to any of claims 1 to 8, wherein said demineralization (20) is performed by nanofiltration .

10. A method according to any of claims 1 to 9, wherein crystallized lactose is further dried in a post treatment step (III) .

11. A method according to any of claims 1 to 10, wherein whey or whey permeate is subjected to a pretreatment step (I) thereby obtaining an aqueous solution comprising lactose .

12. A method according to claim 11, wherein said pretreatment step (I) comprises: a) purifying whey or whey permeate to remove one or more of protein, polypeptides, polysaccharides or lipids, and b) concentrating said purified whey or whey permeate.

13. A method according to claims 11 or 12, wherein said purification of whey or whey permeate (a) is performed by ultrafiltration.

14. A method according to any of claims 11 to 13, wherein said concentration (b) is performed by evaporation .