Beverage container

Abstract

A beverage container or package that includes an internal surface for promoting nitrogen bubble nucleation and growth. The surface incorporates a plurality of nanoscale structures, e.g. between 6 and 100 nanometers in size. Most preferably the structures are pits, greater than 15 nm in depth/height. Upon opening the container filled with a Nitrogen (and carbon dioxide) supersaturated beverage, a foaming effect occurs which provides a desirable head of fine bubbles when transferred to a drinking glass.

Claims

1. A beverage container, containing a beverage product with supersaturated nitrogen or a gas mixture with nitrogen in solution, the container including a surface for promoting bubble nucleation and growth that includes a plurality of pits between 6 and 100 nanometers in width.

2. The beverage container of claim 1 wherein the pits only become wet during the action of opening and pouring the container.

3. The beverage container of claim 1 wherein the pits are arranged in a defined pattern.

4. The beverage container of claim 1 wherein the pits are between 20 to 30 nm in width.

5. The beverage container of claim 1 wherein the pits are greater than 15 nm in depth.

6. The beverage container of claim 1, the surface being hydrophilic or hydrophobic.

7. The beverage container of claim 6 wherein the surface has a contact angle of 50 to 80 degrees.

8. The beverage container of claim 1 wherein the approximate total number of pits is defined and confined within a known surface area with a specified location on the container.

9. The beverage container of claim 8 incorporating a closure/opening sized to enable regulation of the egress of liquid from the container to ensure a minimum residence time for said liquid in the container.

10. A method of manufacturing a container for promoting nitrogen bubble nucleation and growth including the steps of: applying a pattern of pits of 6 to 100 nm diameter, with greater than 15 nm depth, to at least a portion of a beverage contacting wall of the container; filling the container with a beverage containing supersaturated nitrogen, or a gas mixture containing nitrogen, in solution and sealing the container with a closure means.

11. The method of claim 10 wherein the approximate total number and location of pits is defined and confined within a known surface area or multiple areas within the container.

12. The beverage container of claim 1 wherein the pits are between 20 to 40 nm in width.

13. The beverage container of claim 1 wherein the pits are between 10 to 80 nm in width.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1 to 19 illustrate various experimental results and proposed structures that aid description of the invention. Some of the figures and related description outline experimental results that were assessed as support for the inventive concept, but do not fall within the scope of the invention itself.

DETAILED DESCRIPTION OF THE INVENTION

(2) According to the invention, the best results are achieved with surfaces having a cavity diameter in the range of 6-100 nm (0.006-0.1 m) and shallow cavity depth (see FIG. 1). Surfaces at the extreme ends of behaviour, either highly wetting or superhydrophobic were expected to provide the fastest bubble growth. A slight preference was expected towards superhydrophobic (see FIG. 2). Calculations suggest that the target nucleation rate for sufficient foam to form can be achieved with a nucleation site density inside the can of approximately 0.003%, with the assumption that the target bubble rate is 5.310.sup.4 bubbles/mL.Math.s; Inner surface area of can is 364 cm.sup.2 and volume of Beer=441 mL; each site is 100 nm diameter; bubble growth time is 4 s.

(3) FIG. 1 shows a two-dimensional plot describing how the detachment diameter (in m) for a bubble growing from a cavity depends on the cavity radius and the contact angle of the surface. To achieve 50 m bubbles in the head of stout beers, the cavity radius must be less than approximately 0.01 m for contact angles in the range of 10-170. It is generally accepted that, on solid surfaces, contact angles of less than 90 are hydrophilic, whereas a contact angle of greater than 90 indicates a hydrophobic surface.

(4) FIG. 2 shows a calculation of bubble growth time using the model described by Jones et al. The time axis describes the time for a bubble to grow and detach from a cavity, using a detachment diameter of 55 m and level of supersaturation ratio of 2.9. Knowledge of the bubble growth time per site, the total surface area, and the target nucleation rate allows an estimate of the nucleation site density.

(5) To test the inventive concept it was necessary to produce various structured surfaces for experimental purposes.

(6) In the production of microstructure test surfaces, patterns were created by photolithography/etching in Silicon. Patterns can be transferred to other substrates. Shapes: Pits, Lines, Concentric Circles Sizes: 10 m to 70 m Surfaces: Si, Cycloolefin Copolymer (hydrophobic), Polylactic Acid (hydrophilic), anodized aluminium oxide.

(7) In the production of nanostructure test surfaces, patterns were created by e-beam lithography in photomask (hydrophobic). Pits and pillars of 50 nm and 25 nm to be evaluated.

(8) Random nanostructured surfaces can be created by embedding nanoparticles into thin layers of polymer cast on Si. Particles: Nanoparticles and Nanoraspberries Surfaces: Cycloolefin copolymer Surface Treatment: PDMS (Polydimethylsiloxane) or Perfluoroalkane (attachment via free epoxy or amine groups)

(9) In the production of microstructures and nanostructures, random nanostructured surfaces can be created by embedding nanoparticles into micropatterned surfaces Shapes: Lines Surfaces: Cycloolefin copolymer Surface Treatment: PDMS or Perfluoroalkane (attachment via free epoxy or amine groups)

(10) Qualitative screening of experimental test surfaces was performed to assist identifying the most effective embodiment of the invention. All surfaces were pre-screened by placing a droplet of un-nucleated beer on the surface and observing results through a microscope. An example of the experimental procedure of this method is illustrated by FIG. 3.

(11) In most cases, the structured surfaces were significantly more active than the unstructured surfaces. However, structure-property relationships (e.g. structure size, shape and surface energy) could not readily be determined from the qualitative screening method

(12) Accordingly a quantitative method was developed in accordance with FIGS. 4 to 6.

(13) Referring to FIG. 4, a 20 mm10 mm quartz cuvette was prepared and a sample inserted. By virtue of an incline, bubbles rise to cuvette surface and are captured on video (FIG. 5) to record bubble evolution (adjustable framerate).

(14) Referring to FIG. 6, these image samples are converted to grayscale, then to a threshold (binary) image to enable identification of bubble boundaries. Finally, a Hough transformation is performed to identify locations (center and perimeter, assumes circular shape).

(15) It was necessary to identify a target rate for bubble formation over time for the screening test. To determine the rate, the number of bubbles in a head was calculated. Initially, the number of bubbles in the head was calculated by using an estimate of 55 m for the average bubble diameter. Combining this with the required head volume yielded a target rate of approximately 600 bubbles/mm.sup.2.Math.s.

(16) However, further testing and some open literature suggested that the average diameter may be closer to 100 m. In which case: Bubble diameter=0.1 mm/Bubble volume=9.0510.sup.4 mm.sup.3 Head height=20 mm/Head volume=9.610.sup.4 mm.sup.3 Packing density=0.64 Bubbles in head=6.810.sup.7

(17) It follows that for 441 mL with a surge time of 30 seconds, bubbles need to nucleate and detach at rate of=5.110.sup.3 bubbles/mL.Math.sec.

(18) For evaluation of surfaces, the rates must be expressed in units of available inner surface area.

(19) FIG. 7 illustrates target rates based on which part of the can has a structured surface and for how long the exposure to this surface is. However, it does not take into account the effects of pouring the beverage which will have a further influence (via agitation) on head formation.

(20) Experiments for surface structural features on a microscale range, such as 15 m bars (5-10 m depth) in Silicon, generally show that bubble growth rates are two orders of magnitude lower than needed to achieve the required head formation. However, this experimentation did confirm that it is important to test samples that have been pre-wetted.

(21) Initial experiments were conducted on surfaces with structural features in the nanoscale range, e.g. embedded nanoparticles (40 nm) and nanoraspberries (micron-sized particles functionalized with nanoparticles) into cycloolefin copolymer (COC), functionalized with perfluoroalkane. These results were inconsistent due to challenges with achieving homogenenous coatings, particularly for patterned COC; nonetheless, the suggestion is that when coverage is moderately good, rates are improved compared to microstructures.

(22) Analysis of over 45 surfaces showed that patterned surfaces are more active (i.e. create more bubbles) than unpatterned surfaces. Higher activity due to the inherent increase in surface area cannot be distinguished from an increase due to Type 4 nucleation.

(23) Although bubble growth is enhanced by patterned surfaces, as mentioned, bubble growth rates for microstructured surfaces are two orders of magnitude lower than the existing estimate of bubble release rate to achieve the required head and bubble sizes are twice as large as is desired. While bubble growth rates for nanostructured surfaces could not initially be adequately characterized due to poor surface coverage of the nanoscale features, early results confirm that these surfaces produce smaller bubbles.

(24) A next series of experimental surfaces were produced. FIGS. 8 to 16 illustrate graphical results for these various test surfaces. The nature of the surface is indicated in the Figures, including notes on the observations.

(25) As a consequence of the test surfaces the following conclusions have been made: Nanostructures create surfaces that promote sustained nitrogen (and mixed gases containing nitrogen) bubble nucleation and growth, not just burst observed with high surface area powders and microstructures. Hydrophilic structures appear to be more effective than superhydrophobic Superhydrophobic surfaces may not interact as well with beer Bubble detachment diameter for superhydrophobics is higher than for hydrophobic and much higher than hydrophilic (whereas a smaller detachment diameter is favourable) Pits appear to be more effective than pillars Sharp edges may be more effective than rounded

(26) In further development of the invention it is proposed to establish the difference between screening rates and actual head formation in a standard pint glass by scaling-up the promising candidates: e.g. AAO (anodized aluminium oxide), etched cellulose; and performing head height testing from a pressurized container (holding pint) and pouring into glass.

(27) The best candidate structure (25 nm pits in ZEP) is to be reproduced using a scalable process. ZEP (zinc ethyl phenyl dithiocarbamate) is a polymer material suitable for marking with electron beam lithography so can be used to create nanostructured surfaces for experimentation, but not likely suitable for commercial application.

(28) In connection with scaling experimentation, AAO samples (a magnified image of which is illustrated by FIG. 17) have been prepared on aluminum: 10 cm10 cm (100 cm.sup.2) Small scale screening showed that these generated bubbles at a rate of 1 bubble/mm.sup.2s. Large scale tested by: placing sample into standard can dimensions (12 oz), waiting 30 seconds, and then pouring into pint glass.

(29) Results are given in FIG. 18 which suggests the target rate may be less than first calculated. This further supports the preferred utilisation of pits, 20 nm deep.

(30) The best mode presently known for implementing the invention involves the following process:

(31) The surface of a can or bottle (or any suitable package) is marked with a defined pattern of 25 nm diameter pits separated by unmodified can or bottle wall. Preferably the pit will be >20 nm deep. The total number and location of pits is preferably defined and confined within a known surface area within the package. This area may be below the liquid level of a full resting container and may be enhanced by structures which only become wet during the action of opening and pouring the container.

(32) On filling the container with a supersaturated N.sub.2 solution in the known way, the pits will remain dry because of surface tension effects in the liquid but the existing gas in them will gradually be replaced by N.sub.2 from the liquid. That is to say, when the package is sealed the system will reach equilibrium where the amount of gas in the pits is stablethere is no gas transfer between the pits and the liquid. In practice a mixed gas (N.sub.2 and CO.sub.2) may be in equilibrium in the pits/cavities; however, the invention is hypothesised to be mainly reliant on N.sub.2.

(33) Once the container is opened, the equilibrium is moved so there is excess N.sub.2 dissolved in the liquid which comes out of solution into the gas space in each pit. Gas is supplied to the pit by diffusion from the surrounding liquid to a remnant of gas in the pit left by the departure of a preceding bubble. I.e. after release of a first bubble, more gas migrates into the pit and the process of bubble generation continues. A critical radius of the gas bubble is needed for detachment from a site (pit); that occurs when buoyancy overcomes the surface tension force. It is believed that the primary reason for bubble growth as it rises to the stout head is through infusion of gas from the liquid (mainly CO.sub.2).

(34) It has been demonstrated that a single pit can continue to generate multiple bubbles, e.g. say 20 per minute. A desirable foamy head requires a very large number of bubbles (which are very small) but, to achieve this, the nanostructure surface provides a very large number of nucleation sites in a small surface area.

(35) Overall, the engineered surface of the invention creates the spontaneous bubble generation phenomenon required upon opening a container which further results in the appearance of liquid draining down between a large mass of slowly rising N.sub.2 gas bubbles, leading to the formation of a stable white head on the beer of approximately 18 mm in depth.

(36) FIG. 19 illustrates the above described process where a pre-existing nuclei is present in a nanoscale pit, followed by migration of N.sub.2 and CO.sub.2 thereinto which grows a gas bubble and, finally, detachment when the bubble overcomes the surface tension. Nucleation surfaces can work for N.sub.2, CO.sub.2 and a mixture of both depending on the size of the pits. In the case of stout beer it is likely a mixed gas is present so pit sizes are calculated accordingly.

(37) There may also be an effect from bubbles in the body of the liquid growing from nitrogen migrating into them and then splitting into two and so on. This increases the total number of bubbles generated and is the result of the initial bubble formation.

(38) Generating sufficient foam for a desirable head is partly dependent on how long the liquid is in contact with the engineered surface/wall after opening of a beverage container. For this reason it is foreseen that consumers may be given explicit pouring instructions (e.g. on the side of the package) so the desired result is achieved. Alternatively or additionally, the size of the container opening can be calculated to restrict flow such that a minimum contact time is guaranteed when pouring under gravity, e.g. after opening the container it will take a predetermined time to be completely emptied (possibly up to 30 seconds) by virtue of the opening.

(39) The invention is embodied by the insight to investigate nanostructures, to be incorporated into a package surface, for promoting nitrogen (and mixed gases containing nitrogen) bubble nucleation and growth.

INDUSTRIAL APPLICABILITY

(40) The nanostructures of the invention can be incorporated into adhesive labels or other carriers in order to apply the structured surface to the inside wall of a beverage container or, as is preferred, formed directly onto a surface coating which covers the metal or glass etc.

(41) It is also proposed to use an inverse image AAO (anodized aluminium oxide) material to imprint pillars and pits into hydrophilic polymers. Furthermore, porous material is a good candidate for realizing the invention because surface area can be increased by coating thickness.