Freeze-drier tray

Abstract

A freeze-drier tray 1 comprising a base 2 and one or more walls defining a receiving space 3 for holding a frozen product to be freeze-dried. The receiving space comprises an arrangement of columns 10, that may be free-standing columns and may each extend upwardly from the base, and are in thermal connection with the base. The columns may be in thermal connection with the base. The columns may be in a regular arrangement, an irregular arrangement, or have a polygonal cross-section. The columns may comprise rows that extend in a first direction, and be spaced apart in a second direction orthogonal to the first. The columns may be formed of a metal. A method of freeze-drying comprising at least partially filling the receiving space with frozen product such that the product is packed around the arrangement of columns and then subjecting the tray to a freeze-drying process is also claimed.

Description

Field of the disclosure The disclosure relates to a freeze-drier tray. Background Freeze-drying is a process for removing moisture from a product that involves lowering the temperature of the product to freeze water within the product into ice and then subjecting the frozen product to low pressure conditions to remove the ice by sublimation. Freeze-drying typically comprises a primary drying phase where the product is heated to sublimate the ice followed by a secondary drying phase where additional heat is supplied to remove unfrozen water molecules still present in the product. During freeze-drying it is important to avoid over-heating the product. For example, in the case of freeze-drying of coffee granules deleterious meltback of the granules can occur if the product is overheated above its glass transition temperature. When freeze-drying at an industrial scale is it typically to contain the frozen product in a freeze-drier tray. Freeze-drying trays are typically flat with raised sides to contain the frozen product. Freeze-drying requires significant energy inputs and can require substantial time (for example over two hours per batch). In addition, frozen product held in the freeze-dryer tray may experience inconsistent and / or incomplete drying. For example, inconsistencies in the drying process may lead to meltback of a portion of the product if the drying is continued for too long in an attempt to obtain sufficient dryness in all of the product. Conversely, a portion of the product may remain too moist if the drying is stopped prematurely in an attempt to prevent any meltback occurring within the product. Consequently, freeze-drying processes can be difficult to control accurately and consistently at the industrial scale. Summary of the disclosure In one aspect of this disclosure, there is provided a freeze-drier tray comprising a base and one or more walls defining a receiving space for holding a frozen product to be freeze-dried; the receiving space comprising an arrangement of columns. Advantageously, it has been found that the use of the columns can lead to a more accurate and consistent freeze-drying process. A more uniform treatment of the frozen product contained within the tray is enabled compared to prior art trays. The use of the columns can be used to reduce the maximum heat transfer distance between a surface of the tray and the product granules or particles contained within the receiving space. The time required to complete the drying process can be reduced leading to efficiency gains in terms of product throughput. Additionally or alternatively, the use of the columns may allow for a reduced temperature to be used in the freeze-drier leading to the potential for energy savings. Additionally or alternatively, the use of the columns may allow a greater quantity of frozen product to be freeze-dried, i.e. increasing the fill weight of the freeze-drier tray. In some examples the arrangement of columns is in thermal connection with the base and / or the one or more walls. Advantageously, ensuring a thermal connection between the columns and the base and / or the one or more side walls may enable better conduction of heat into the frozen product. The additional thermal mass of the base and / or the one or more side walls may allow for more efficient freeze-drying to take place. In some examples the arrangement of columns may be an arrangement of free-standing columns. By ‘free-standing’ is meant that the distal end of the column, typically its upper end, is not attached to or supported by another structure. This can be advantageous in maximising the ease of filling frozen product into, and emptying freeze-dried product out of, the receiving space since additional support structures at or near the distal ends of the columns may impede filling and emptying of the freeze-drier tray. However, in some alternative examples, additional support structures may be provided between the columns if required, for example in the form of thin support arms that extend between the distal ends of the columns to form a grid-like mesh. In some examples the arrangement of free-standing columns may each extend upwardly from the base and may be in thermal connection with the base. Advantageously, such an arrangement may be straightforward to manufacture and in particular may allow the base and some or all of the free-standing columns to be formed in an integral manner, e.g. by casting or moulding. In some other examples the arrangement of columns, in particular where they are freestanding columns, may each extend upwardly from a support that is in thermal connection with the one or more walls. Optionally the support may be spaced from the base. For example, the support may take the form of a layer or plurality of support arms that interconnect the free-standing columns to one another and to the one or more side walls at or near the proximal ends of the free-standing columns. For example, the support may comprise a grid-like mesh of support arms. In some examples the arrangement of columns may be an irregular arrangement of columns. In other examples the arrangement of columns may be a regular arrangement of columns. In some examples a regular arrangement of columns may be preferred since this can provide a more uniform maximum heat transfer distance between a surface of the tray and the frozen product. The arrangement of columns may comprise rows that extend in a first direction, with the rows being spaced apart in a second direction that is orthogonal to the first direction. In some examples the columns in adjacent rows may be aligned with each other with respect to the first direction. Using aligned rows of columns may be preferred in some circumstances as it may result in easier manufacture of the tray. In other examples the columns in adjacent rows may be out of alignment with each other with respect to the first direction. Using out of alignment rows may be preferred in some circumstances as potentially offering a means to further reduce the maximum heat transfer distance between a surface of the tray and the particles or granules of product. In some examples the arrangement may have an inter-row spacing between the rows of 1 to 50 mm. In this specification the term “inter-row spacing” refers to the spacing between adjacent columns within the same row. Additionally or alternatively, in some examples the arrangement may have an intra-row spacing between the columns of 1 to 80 mm. In this specification the term “intra-row spacing” refers to the spacing between adjacent rows of columns. In some examples the inter-row spacing may equal the intra-row spacing within the arrangement. This may be preferred in some examples since this can provide a more uniform maximum heat transfer distance between a surface of the tray and the product. In some examples the columns may be distributed on a regular square-based two-dimensional grid. The columns may have a cross-sectional shape selected from the group of circle, triangle, square, pentagon, hexagon, heptagon or octagon. The cross-sectional shape may be a regular polygon or an irregular polygon. Differing shapes for the columns may be chosen to vary the surface area of the tray available for contacting the product. In some examples a square cross-sectional shape may be preferred to reduce the manufacturing complexity of the tray. In some examples all of the columns in the arrangement may have the same cross-sectional shape. In other examples the columns in the arrangement may have a mixture of cross-sectional shapes. In some examples the columns may have a constant cross-sectional area from a proximal end to a distal end of the columns. In such cases the columns may have a cross-sectional area of 1 to 900 mm2, optionally 4 to 100 mm2, optionally 5 to 16 mm2. In some examples the columns may have a square cross-section with a side length of 1 to 30 mm, optionally 2 to 10 mm, optionally 2.5 mm. Beneficially, the cross-sectional area of the column should be large enough to ensure the mechanical strength of the column and also to allow efficient heat transfer along the column. At the same time, the cross-sectional area should not be made too large otherwise the volume of the receiving space able to receive frozen product would be adversely affected. The present applicant has discovered, using square shaped columns purely as an example, that a side length of 1 to 30 mm is appropriate, while a side length of 2 to 10 mm may be preferred and a side length of 2.5 mm may give a particularly preferred optimisation of the mechanical and thermal characteristics of the column while minimising the adverse effects on the packing density of the frozen product within the receiving space. In some other examples the columns may be tapered such that a cross-sectional area of the columns decreases from a proximal end to a distal end of the columns. In such cases the columns may have a cross-sectional area of 4 to 900 mm2, optionally 4 to 100 mm2, at the proximal end and a cross-sectional area of 1 to 785 mm2, optionally 2 to 64 mm2, at the distal end. In some examples the columns may have a square cross-section with a side length of 2 to 30 mm, optionally 2 to 10 mm, optionally 2.5 mm at the proximal end and 1 to 28 mm, optionally 1 to 8 mm, optionally 2.0 mm at the distal end. Beneficially, the tapered form of the columns may aid in the emptying of the freeze-dried product from the receiving space since the tapering helps to prevent the granules or particles of the product becoming wedged between adjacent columns. The tapered form may also help to optimise the mechanical strength of the columns, by having a wider base at the proximal end at the joint / interface with the base of the tray, while not overly reducing the available volume of the receiving space for the frozen product. The arrangement of columns may be present throughout the receiving space. For example, the rows of the columns may extend into proximity with each of the walls of the tray. The columns may be evenly spaced throughout the receiving space. A proximal end of the columns may be connected to, or formed integrally with, the base of the freeze-drier tray or the support. Where there is a connection, this may be any suitable connection that ensures the necessary mechanical strength of the connection and allows for thermal transfer between the base and / or the one or more side walls and the column. One example is a welded connection. As an alternative, the columns may be integrally formed with the base or support by, for example, casting or moulding the columns and the base or support as one part or by machining the columns and the base or support from a single piece. The base of the freeze-drier tray may be formed from one part or multiple parts that are connected together. The one or more walls of the freeze-drier tray may be formed integrally with the base or may be connected thereto. In some examples a height of the columns (measured from an upper surface of the base) may be the same as or up to 10% less than an internal height of the one or more walls. The columns may be formed from a metal, for example stainless steel or an aluminium alloy. The base and / or the one or more walls may be formed from a metal, for example stainless steel or an aluminium alloy. The one or more walls of the freeze-drier tray may comprise, for example, a front wall, a back wall and two side walls. The freeze-drier tray may, for example have a rectangular or square shape in plan view. In another aspect of this disclosure, there is provided a method of freeze drying a frozen product using the freeze-drying tray of the aspect described above, comprising the steps of: at least partially filling the receiving space with the frozen product such that the frozen product is packed around the arrangement of columns; subjecting the freeze-drier tray and frozen product to a freeze-drying process; and removing the now freeze-dried product from the freeze-drying tray. In some examples the frozen product may be selected from the group comprising frozen coffee granules, frozen coffee containing microgrind particles, frozen dairy milk powder, frozen plant-based beverage powder, frozen fruit, frozen vegetables, frozen meats, frozen grains, frozen legumes, frozen meals, frozen tea, frozen fruit juice powder, frozen spices. Brief description of the drawings Aspects and embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a freeze-drier tray according to the present disclosure; Figure 2 is a plan view of the freeze-drier tray of Figure 1; Figure 3 is a side cross-sectional view of the freeze-drier tray of Figure 1; Figure 4 is a front cross-sectional view of the freeze-drier tray of Figure 1; Figure 5 is a schematic view of a first arrangement of columns for the freeze-drier tray of Figure 1; Figures 6 is a schematic view of a second arrangement of columns for the freezedrier tray of Figure 1; Figure 7 shows alternative cross-sectional shapes for the of the columns; Figure 8 is a cross-sectional view of columns having a tapered form; Figure 9 is a cross-sectional view of columns of another freeze-drier tray according to the present disclosure; and Figure 10 is a plan view of a portion of the freeze-drier tray of Figure 9. Detailed description The skilled reader will recognise that one or more features of one aspect or embodiment of the present disclosure may be combined with one or more features of any other aspect or embodiment of the present disclosure unless the immediate context teaches otherwise. Figures 1 to 4 show a freeze-drier tray 1 according to the present disclosure. The freezedrier tray 1 comprises a base 2 and one or more walls defining a receiving space 3 for holding a frozen product to be freeze-dried. The one or more walls of the freeze-drier tray may comprise, for example, a front wall 4, a back wall 5, a first side wall 6 and a second side wall 7. A first flange (not shown) may optionally extend outwardly from an upper edge of the first side wall 6. Likewise a second flange (not shown) may optionally extend outwardly from an upper edge of the second side wall 7. The first flange and the second flange may serve as supports for slidably mounting the freeze-drier tray 1 within a freezedrier. The freeze-drier tray 1 may, for example, have a rectangular or square shape in plan view as viewed in Figure 2. The receiving space 3 comprises an arrangement of columns 10. In the following description the columns 10 will be illustrated and exemplified as free-standing columns 10 wherein the distal ends of the columns 10 are not attached to or supported by another structure. However, it will be appreciated that the present disclosure extends to the use of columns more generally in a freeze-drier tray. In the example of Figures 1 to 4, each free-standing column 10 extends upwardly from the base 2 and is in thermal connection with the base 2. The arrangement of free-standing columns 10 shown in Figures 1 to 4 is a regular arrangement. However, an irregular arrangement of the free-standing columns 10 may also be used in this and other examples. In the illustrated example, the arrangement of free-standing columns 10 comprise rows 11 that extend in a first direction A, with the rows 11 being spaced apart in a second direction B that is orthogonal to the first direction A. In Figure 5, four rows 11 are shown numbered 11a, 11b, 11c, 11d. In practice the freeze-drier tray 1 may have many rows 11 as shown by way of example in Figure 2. As shown in Figures 1 to 4, and as also shown schematically in Figure 5, the free-standing columns 10 in adjacent rows 11 may be aligned with each other with respect to the first direction A. In other words the free-standing columns 10 may also form secondary rows 12 running in the second direction B, in which each secondary row 12 contains a free-standing column 10 from each row 11. In Figure 5, six secondary rows 12 are shown numbered 12a, 12b, 12c, 12d, 12e, 12f. In practice the freeze-drier tray 1 may have many secondary rows 12 as shown by way of example in Figure 2. However, as an alternative illustrated schematically in Figure 6, the free-standing columns 10 in adjacent rows 11 may be out of alignment with each other with respect to the first direction A. In this case the free-standing columns 10 may form secondary rows 12’ in the second direction B but these will only contain free-standing columns 10 from some of the rows 11. In Figure 6 three rows 11 a, 11 b, 11 c and three secondary rows 12a’, 12b’, 12c’ are shown by way of example. In the case of the example of Figure 6 the secondary rows 12’ contain free-standing columns 10 from every other row 11, i.e. secondary rows 12a’ and 12c’ contain free-standing columns 10 from rows 11 a and 11c while secondary row 12b’ contains free-standing columns 10 from row 11b. The arrangement may have an inter-row spacing 13 between the rows 11 of 1 to 50 mm. The arrangement may have an intra-row spacing 14 between the free-standing columns 10 of 1 to 50 mm. In the illustrated example of Figures 1 to 4 inter-row spacing 13 equals the intra-row spacing 14 within the arrangement such that the free-standing columns 10 are distributed on a regular square-based two-dimensional grid. The free-standing columns 10 may have a variety of cross-sectional shapes. As illustrated in Figure 7, the cross-sectional shape may be square 10a or a circle 10b or a hexagon 10c. Other possibilities (not illustrated in Figure 7) include triangle, pentagon, heptagon or octagon or a higher-order polygon. The cross-sectional shape may be a regular polygon or an irregular polygon. All of the free-standing columns 10 in the arrangement may have the same cross-sectional shape, for example all being square or all being circular. However, the free-standing columns 10 in the arrangement may have a mixture of cross-sectional shapes, for example with a mixture of square and circular columns. In some examples the free-standing columns 10 may have a constant cross-sectional area from a proximal end 16 to a distal end 17 of the free-standing columns 10 as most clearly seen in Figure 3. In such cases the free-standing columns 10 may, for example, have a cross-sectional area of 1 to 100 mm2, optionally 4 to 25 mm2, optionally 5 to 16 mm2. In some examples the free-standing columns may have a square cross-section with a side length of 1 to 10 mm, optionally 2 to 5 mm, optionally 2.5 mm. The arrangement of free-standing columns 10 may be present throughout the receiving space 3. For example, the arrangement may extend into proximity with the front wall 4, back wall 5, first side wall 6 and the second side wall 7. The spacing from an edge-most free-standing column 10 and its nearest wall may be, for example, 1 to 50 mm. The proximal end 16 of the free-standing columns 10 may be connected to, or formed integrally with, the base 2 of the freeze-drier tray 1. In some examples a height hi of the free-standing columns 10 (measured from an upper surface of the base 2) may be the same as or up to 10% less than an internal height h2 of the one or more walls. The free-standing columns 10 may be formed from a metal, for example stainless steel or an aluminium alloy. In addition, the base 2 and / or the one or more walls may be formed from a metal, for example stainless steel or an aluminium alloy. Figure 8 illustrates a portion of a freeze-drier tray 1 showing an alternative form for the freestanding columns 10. As illustrated, the free-standing columns 10 may be tapered such that a cross-sectional area of the free-standing columns 10 decreases from the proximal end 16 to the distal end 17 of the free-standing columns 10. In such cases the freestanding columns 10 may, for example, have a cross-sectional area of 4 to 100 mm2, optionally 4 to 25 mm2, at the proximal end 16 and a cross-sectional area of 1 to 64 mm2, optionally 2 to 16 mm2, at the distal end 17. In some examples the free-standing columns 10 may have a square cross-section with a side length of 2 to 10 mm, optionally 2 to 5 mm, optionally 2.5 mm at the proximal end 16 and 1 to 8 mm, optionally 1 to 4 mm, optionally 2.0 mm at the distal end 17. In use a method of freeze drying a frozen product may use the freeze-drying tray 1 as described above. The method may comprise the steps of: at least partially filling the receiving space 3 with the frozen product such that the frozen product is packed around the arrangement of free-standing columns 10; subjecting the freeze-drier tray 1 and product to a freeze-drying process; and removing the now freeze-dried product from the freeze-drying tray 1. The frozen product may, for example, be selected from the group comprising frozen coffee granules, frozen coffee containing microgrind particles, frozen dairy milk powder, frozen plant-based beverage powder, frozen fruit, frozen vegetables, frozen meats, frozen grains, frozen legumes, frozen meals, frozen tea, frozen fruit juice powder, frozen spices. Using the freeze-drier tray 1 of the present disclosure has been beneficially found to enable faster freeze-drying of the frozen product. For example, drying times for an example freezedrier tray 1 according to the present disclosure and a comparative tray were tested. The comparative tray comprised uniaxially extending fins that extend sideways through the receiving space from one side to the other with a spacing between the fins of 12.5 mm. The h2 of the one or more walls surrounding the receiving space was 47 mm. The example freeze-drier tray 1 comprised free-standing columns 10 having a square cross-sectional shape and a constant cross-sectional area from the proximal end 16 to the distal end 17. The side length was 2.5mm and thus the cross-sectional area was 6.25 mm2. The inter-row spacing 13 and the intra-row spacing 14 were equal at 5 mm. The freestanding columns 10 were present throughout the receiving space 3. The height hi of the free-standing columns 10 equalled the internal height h2 of the one or more walls surrounding the receiving space 3 at a height of 47 mm. Both the example freeze-drier tray 1 and the comparative tray were filled with a frozen product in the form of frozen coffee granules. For the frozen product in the comparative tray a total drying time of 2 hrs 24 was required to achieve a suitably dried end product. With the example freeze-drier tray 1 a suitably dried end product was achieved with a drying time of only 2hrs. Consequently, use of the example freeze-drier tray 1 resulted in an approximately 17% reduction in the drying time of the frozen product for this example. Figures 9 and 10 show another freeze-drier tray 1 according to the present disclosure. Other than for the differences discussed below, the freeze-drier tray 1 of this example may be as described in the above examples. In particular, the columns 10 may be free-standing or may have additional supports interconnecting their distal ends 17. In addition the columns 10 may have a constant cross-sectional area along their lengths or may be tapered as discussed above. In this example the arrangement of columns 10 is in thermal connection with the one or more walls (connections to the walls 5 and 7 are shown by way of example in the enlarged portion shown in Figure 10 and to wall 6 in Figure 9) as opposed to being in direct thermal connection with the base 2. In particular, the arrangement of free-standing columns 10 each extend upwardly from a support 20 that is in thermal connection with the one or more walls. The support 20 is spaced from the base 2. Consequently, there may be in some examples no direct physical connection between the base 2 and the columns 10. As such, a gap 21 as shown in Figure 9 may be present between the support 20 and the base 2. The support may be a sheet or layer, but in the illustrated example comprises a plurality of support arms 20 that interconnect the free-standing columns 20 to one another and to the one or more side walls 5-7 at or near the proximal ends 16 of the free-standing columns 10. For example, the support may comprise a grid-like mesh of the support arms 20. In all other respects the freeze-drier tray 1 and its use is as described above with reference to Figures 1 to 8.

Claims

1. A freeze-drier tray comprising a base and one or more walls defining a receiving space for holding a frozen product to be freeze-dried;the receiving space comprising an arrangement of columns.

2. The freeze-drier tray of claim 1, wherein the arrangement of columns is in thermal connection with the base and / or the one or more walls.

3. The freeze-drier tray of claim 1 or claim 2, wherein the arrangement of columns is an arrangement of free-standing columns.

4. The freeze-drier tray of claim 3, wherein the arrangement of free-standing columns each extend upwardly from the base and are in thermal connection with the base.

5. The freeze-drier tray of claim 3, wherein the arrangement of free-standing columns each extend upwardly from a support that is in thermal connection with the one or more walls; and optionally wherein the support is spaced from the base.

6. The freeze-drier tray of any preceding claim, wherein the arrangement of columns is an irregular arrangement or a regular arrangement of columns.

7. The freeze-drier tray of any preceding claim, wherein the columns comprises rows that extend in a first direction, with the rows being spaced apart in a second direction that is orthogonal to the first direction.

8. The freeze-drier tray of claim 7, wherein the columns in adjacent rows are aligned with each other with respect to the first direction.

9. The freeze-drier tray of claim 7, wherein the columns in adjacent rows are out of alignment with each other with respect to the first direction.

10. The freeze-drier tray of any one of claims 7 to 9, wherein the arrangement has an inter-row spacing between the rows of 1 to 80 mm.

11. The freeze-drier tray of any one of claims 7 to 10, wherein the arrangement has an intra-row spacing between the free-standing columns of 1 to 80 mm.

12. The freeze-drier tray of any preceding claim, wherein the columns have a cross-sectional shape selected from the group of circle, triangle, square, pentagon, hexagon, heptagon or octagon.

13. The freeze-drier tray of claim 11, wherein the cross-sectional shape is a regular polygon or an irregular polygon.

14. The freeze-drier tray of any preceding claim, wherein all of the columns have the same cross-sectional shape or the columns have a mixture of cross-sectional shapes.

15. The freeze-drier tray of any preceding claim, wherein the columns have a constant cross-sectional area from a proximal end to a distal end of the columns.

16. The freeze-drier tray of claim 15, wherein the columns have a cross-sectional area of 1 to 900 mm2, optionally 4 to 100 mm2, optionally 5 to 16 mm2.

17. The freeze-drier tray of claim 15 or claim 16, wherein the columns have a square cross-section with a side length of 1 to 30 mm, optionally 2 to 10 mm, optionally 2.5 mm.

18. The freeze-drier tray of any one of claims 1 to 14, wherein the columns are tapered such that a cross-sectional area of the columns decreases from a proximal end to a distal end of the columns.

19. The freeze-drier tray of claim 18, wherein the columns have a cross-sectional area of 4 to 900 mm2, optionally 4 to 100 mm2, at the proximal end and a cross-sectional area of 1 to 784 mm2, optionally 2 to 64 mm2, at the distal end.

20. The freeze-drier tray of claim 18 or claim 19, wherein the columns have a square cross-section with a side length of 2 to 30 mm, optionally 2 to 10 mm, optionally 2.5 mm at the proximal end and 1 to 28 mm, optionally 1 to 8 mm, optionally 2.0 mm at the distal end.

21. The freeze-drier tray of any preceding claim, wherein the arrangement of columns is present throughout the receiving space.

22. The freeze-drier tray of any preceding claim, wherein a height of the columns may be the same as or up to 10% less than an internal height of the one or more walls.

23. The freeze-drier tray of any preceding claim, wherein the 3 columns are formed from a metal, for example stainless steel or an aluminium alloy.

24. A method of freeze drying a frozen product using the freeze-drying tray of any preceding claim, comprising the steps of:at least partially filling the receiving space with the frozen product such that the frozen product is packed around the arrangement of columns;subjecting the freeze-drier tray and frozen product to a freeze-drying process; and removing the now freeze-dried product from the freeze-drying tray.

25. The method of claim 24, wherein the frozen product is selected from the group comprising frozen coffee granules, frozen coffee containing microgrind particles, frozen dairy milk powder, frozen plant-based beverage powder, frozen fruit, frozen vegetables, frozen meats, frozen grains, frozen legumes, frozen meals, frozen tea, frozen fruit juice powder, frozen spices.15

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