MXPA97003879A - Preparation of suspension of ice crystals in a sugar solution and its use to make concrete - Google Patents

Abstract

The present invention relates to a suspension containing a large number of very small ice crystals in a sugar solution which is obtained by mixing a concentrated sugar solution with a less concentrated sugar solution or water, both solutions being cooled to a temperature from just above the metastable limit temperature of the respective solution to just above the melting point of the respective solution, before mixing

Description

PREPARATION OF SUSPENSION OF ICE CRYSTALS IN A SUGAR SOLUTION AND ITS USE TO MAKE CONFECCIONES DESCRIPTION FIELD OF THE INVENTION: The preparation of a suspension of ice crystals is a usual step in the manufacture of ice confections, such as ice cubes, granites, ice cream and water-based ice. These confections are formed from an aqueous solution of sugars, which may include optional ingredients such as, for example, flavors, fats, milk proteins, emulsifiers, gas, colors and fruit pulp.

BACKGROUND OF THE INVENTION It is desirable to be able to provide a suspension of ice crystals having an average crystal size, which is as small as possible. Conventionally, the ice crystal suspension is manufactured in a scraped surface heat exchanger (SSHE). This procedure mixes and cools the aqueous solution of sugars, simultaneously. A disadvantage of this procedure is that there is a temperature gradient between the wall of the SSHE and the center, in this way the crystallization is located in the wall of the SSHE.

This results in a non-uniform crystal distribution. An additional disadvantage when using an SSHE to provide the suspension of ice crystals is that a SSHE is an expensive piece of equipment. Alternatively, the ice crystal suspension can be manufactured through a freezing procedure at rest, within, for example, a candy mold. Crystallization occurs in the walls of the mold with the growth of large dendrite crystals in the center of the product. It has now been possible to show a simple procedure for the production of the ice crystal suspension, by which ice crystals having the desirable small crystal size are produced. In addition, the process allows the formation of a large number of uniformly distributed crystal cores. This procedure initially involves cooling individually a first concentrated sugar solution and a second water solution or a less concentrated sugar solution before mixing the cooled solutions.

GENERAL DESCRIPTION OF THE INVENTION According to the invention, there is provided a method for preparing a suspension comprising ice crystals in a sugar solution, wherein a first concentrated sugar solution and a second less concentrated sugar solution or water, are individually cooled at a temperature just above the temperature of the metastable limit of the respective solution just above the melting point of the respective solution before mixing; provided that if one or both solutions is cooled to a temperature just above the temperature of the metastable limit of the solution below the melting point of the solution, the respective solution is supercooled. The present invention provides a convenient method for preparing a suspension containing a number of relatively small ice crystals. The size of the ice crystals can also be reduced, if at least one of the solutions is supercooled before mixing. The term "just above the melting point" means that the temperature is on the scale of up to about 5 ° C above the melting point for the ice in the solution.

The term "just above the metastable limit temperature" means that the temperature is approximately 0.5 ° C above the metastable limit temperature for the solution, or higher. The term "metastable limit temperature" is a term well known in the art. A suitable method for measuring is described in "Crystalization", J Mullin, Butterworth 1972, pl78 & 179 & Fig 6.4. The first solution is a concentrated sugar solution. This solution will preferably have a concentration above about 45% w / w, more preferably above about 45%. The second solution is a solution of either water or a less concentrated sugar solution. Preferably, the second solution is water, since this is the most efficient method for commercial use. The less concentrated sugar solution will preferably have a concentration below about 20% w / w, more preferably below about 10%. The sugar will usually be sucrose but other sugars can be used, for example glucose, dextrose and fructose. In some procedures, it may be beneficial to have different sugars in the two solutions. Any solution may contain small amounts of flavor, citric acid, sodium citrate, fats, milk proteins, emulsifiers, gas, fruit pulp, fruit juice or stabilizers. The use of more than two solutions having either different concentrations of sugar or identical concentrations, each solution being individually cooled to a temperature of just above the temperature of the metastable limit of the solution just above the melting point of the solution before mixing, it is clearly possible and falls within the present invention as claimed; provided that at least one solution is concentrated sugar and at least one solution is less concentrated sugar or water. Typically, the method of the invention will be to provide an ice suspension containing 0.5 to 10% by weight of ice crystals in a sugar solution. The ice suspension forms quickly. The level of ice formed is too low for commercial use for, for example, an ice cream or water ice cream. Therefore, a second freezing step is required to increase the phase volume of the ice in the suspension. This second freezing step is required to increase the volume of ice phase in the suspension. This second freezing step can occur simultaneously with the mixing step. Alternatively, the ice suspension according to the invention can be prepared first, and then introduced into a suitable freezing system. Advantageously, any convenient means for mixing the cooled solutions can be used. The use of different mixing procedures will modify the size and / or shape of the crystals produced. In this way, static mixers can be used, which pass liquid currents through a mechanical device without movement arranged to combine the currents and quickly mix them. An example is the Kenics mixer. This route provides a resulting stream containing the suspension of fine ice crystals. The method of the invention also extends to the introduction of the streams into a container, for example a mold, optionally containing a stirrer. This route allows the suspension to be formed in a container in a cooler, so that the suspension is then frozen at rest. An alternative route is to have performed the mixing step in a vessel capable of providing dynamic freezing, for example a scraped surface heat exchanger (SSHE) or a cavity transfer mixer. In this route, the ice crystal suspension is formed inside the apparatus providing the second freezing step.

In this way, the method forms a large number of small crystals in the volume of the water and not on the surface of a containment vessel. After preparing the suspension as a stream, it can be conducted to an SSHE within which the freezing is completed. Aeration can be introduced in this stage. One or both of the solutions can be supercooled before mixing. Supercooling allows for particularly small ice crystals to form. By super cold it is meant that the solution has been cooled to a temperature lower than the melting temperature for the ice in solution without having formed the ice. In order to supercool a solution, the solution is cooled slowly. Supercooling can be achieved by any known technique or it can be done by cooling the solution in a system in which the cooling temperature is below the metastable limit of the solution. In order to provide the desired final ice making, for example, ice water, ice cream, granite, slush, the resulting suspension of ice crystals can be mixed with the components of the ice making. Alternatively, and preferably, the components of the icemaking can be added to one or both of the solutions used to prepare the initial ice suspension. Typically, the additional components of ice making will be included in the water or less concentrated sugar solution. A further alternative is that the components of the ice making can be added in the mixing stage.

SPECIFIC DESCRIPTION OF THE INVENTION Now examples will be presented to illustrate, but not to limit the method of the invention. Ice water mixtures were formed by mixing two solutions. A stream of concentrated sucrose A was cooled (30-62% w / w sucrose) at a temperature on the scale of 0-4 ° C higher than its equilibrium melting point. This was mixed with a stream of dilute sucrose B (0-15% w / w sucrose) which was cooled to a temperature of 0-4 ° C higher than its equilibrium melting point. Both streams may contain small amounts of flavorings, citric acid, sodium citrate, fruit juice or stabilizers, for example, guar and LBG. The two streams were mixed at a weight ratio of between 8: 1 and 1: 2 of the concentrate (A) to the dilute stream (B). The total flow was 300 Kghr-1.

This created a mixed stream with an initial temperature lower than the equilibrium melting point of the stream and some of the crystallized water. The current had a temperature on the scale of -18 ° C to -3.0 ° C. The mixer used was a Kenics static tube mixer (obtainable from Chemineer Ltd, Derby, England) comprising a tube of a length of 30 cm and a diameter of 2.5 cm. This tube contained 12 curved elements disposed along the tube parallel to the liquid flow with alternative elements being perpendicular to the adjacent elements. Each curved element rotates the flow of the liquid in a different direction. An alternative mixer is of the Sulzer type (obtainable from Sulzer-Chemtech, interhur, Switzerland). This mixing created a physical environment where the ice crystals formed spontaneously. A mixture of water ice was formed, which contained between 0.5% and 15% w / w ice. Four examples were made and their conditions are presented in Tables I and II. The resulting ice mixtures had mass fractions calculated from 1% to 5%. The final structure obtained after the second freezing stage had a smooth texture and was distinct from the dendrite structure provided by freezing at rest.

Table I "calculated Table II The melting points of the solutions used were: Sucrose (% w / w) C none 0 or 15 -1 ° C 50 -7.5 ° C 55 -9.3 ° C 62 -13.8 ° C This mixture, which comprised a mass of very small ice crystals, was then frozen in a second additional stage in a blast freezer or similar apparatus to give a water ice with an unusual structure, which retained a large number of small crystals. The resulting ice mixture was subjected to downstream freezing to generate commercially usable water ice. This downstream freezing step, that is to say, after mixing can be at rest, for example, in molds which are passed through freezing zones, or with movement, for example, in a scraped surface heat exchanger. Examples of freezing zones for freezing at rest are brine baths where the molds and freezing tunnels are placed using very cold gases. The precise freezing regime used will depend on the structure and the desired shape in the final product. A procedure identical to the previous one was used to prepare aerated water ice. Any of the two streams, either concentrated or diluted with air, was aerated (or any suitable gas) before the mixing stage. Small air bubbles were distributed through the suspension and were trapped in the frozen product. The method is particularly applicable to the formation of water ice, but it can also be used in the preparation of other foods where ice is a component. In this way, the method can be used in the preparation of ice cream.

Example V A mixture of water ice was formed by mixing two solutions. A stream of concentrated sucrose A (62% by weight) was cooled to -10.9 ° C. This was mixed with water having also 1.4% by weight of citric acid, 0.7% by weight of sodium citrate, 0.3% by weight of lemon flavor, which was cooled to 0.3 ° C. The two streams were mixed at a weight ratio of 1: 1. The total flow was 3.3 kg / min. The mixer used was a mixer of 12 kenics elements. Ice crystals were observed in the output stream, which had a temperature of -2.1 ° C.

Example VI A water ice solution was formed by mixing two solutions. At -7.5 ° C, 0.45 kg of 55% by weight of a sucrose solution was melted (melting point -9.2 ° C). This was mixed with 0.5 kg of water which had been supercooled to -1.7 ° C. The mixing was achieved using a Rushton turbine rotating at 200 rpm. Ice crystals were observed to form almost immediately in the mixture.

Example VII A solution of sucrose (60% by weight) at -12.8 ° C was mixed with water at 0.1 ° C in a weight ratio of 3: 2 in a Rushton turbine mixer at 240 rpm to form stream A containing a mixture of ice crystals. Stream B was a composition that contains, by weight: water 53.8% skim milk powder 25.0% butter fat 20.0% locust bean gum 0.4% emulsifier 0.8% which was pasteurized and homogenized. Currents A and B (at -2.6 ° C) were mixed at a weight ratio of 1: 1 and the resulting stream was aerated simultaneously with added nitrogen and brought to shear to give a sticky product. This product was then hardened at -16 ° C to give an ice cream confection.

Claims (10)

1. A method for preparing a suspension comprising ice crystals in a sugar solution, wherein a first concentrated sugar solution and a second less concentrated sugar solution or water, are individually cooled to a temperature just above the limit temperature metastable from the respective solution to just above the melting point of the respective solution before mixing; provided that one or both of the solutions is cooled to a temperature of just above the metastable limit temperature of the respective solution to below the melting point of the respective solution, the respective solution is supercooled.

2. A method according to claim 1, characterized in that the first solution is a concentrated sugar solution having a sugar concentration above about 45% w / w, preferably above about 55% w / w.

3. A method according to claim 1 or 2, characterized in that the second solution is water or a less concentrated sugar solution having a sugar concentration below about 20% w / w, preferably below about 10% p / p.

4. A method according to any of the preceding claims, characterized in that the second solution is water.

5. A method according to any of the preceding claims, characterized in that at least one solution has a temperature of just above the metastable limit temperature of the solution a below the melting point of the solution.

6. A method according to any of the preceding claims, characterized in that both the first and second solutions have a temperature of just above the metastable limit temperature of the respective solution to below the melting point of the respective solution.

7. A method according to any of claims 1 to 4, characterized in that at least one solution has a temperature at or just above its melting point.

8. A method according to any of claims 1 to 4, characterized in that both the first and second solutions have a temperature at or just above their respective melting points.

9. A method for preparing a product containing an ice suspension, wherein the suspension of any of the preceding claims is subjected to a simultaneous freezing step to the mixing step.

10. A method for preparing a product containing an ice suspension, wherein the suspension of any one of claims 1 to 8 is subjected to a freezing step after mixing.