NL1007219C2 - Ultra quick freezing process for fresh liquid foodstuffs, e.g. milk and dairy products - Google Patents

Abstract

A liquid foodstuff is atomized and contacted with a freezing gas to form droplets which are collected and later thawed to reconstitute the liquid. A method for freezing liquid foodstuffs comprises the following steps: (i) the foodstuff is atomized using a two-phase pneumatic atomizing nozzle (2), forming droplets with a size of 30-200 microns ; (ii) the droplets are brought into contact with a preferably flowing freezing gas, such that they are frozen in less than 10 (1) seconds; and (iii) optionally the frozen foodstuff (6) is separated, captured, collected and/or compacted. Independent claims are also included for: (a) frozen foodstuffs prepared by this method; (b) the ultra quick liquid freezer machine for carrying out this method; and (c) the use of this machine for freezing short shelf-life fresh liquid foodstuffs.

Description

Method for freezing fresh liquid foodstuffs as well as frozen foodstuffs obtained in this way,

The present application relates to a method for freezing daily fresh liquid foods.

In the food industry there is a continuing need for techniques to improve the shelf life of liquid foods, in particular of fresh daily liquid foods, such as milk and milk products, fruit juices and the like. Such techniques would allow the storage of these agents over time so that they can be buffered in a surplus period.

However, techniques currently used such as freeze drying and / or concentration, in which water is extracted from the product, have the drawback that after reconstitution (i.e. by re-adding water) the quality is considerably reduced compared to the original fresh food.

Freezing, for example, milk in a container takes too long, as a shift in the lactose concentration occurs and ice crystals are formed which damage the cell structure of the milk. Both phenomena again lead to an unacceptable loss of quality.

US patent 4,912,927 describes an apparatus and method for freezing liquid food products, in particular liquid egg. Here, drops of the liquid food product obtained from a "droplet dispenser" are frozen by dripping them onto a nitrogen-cooled roller, upon which they freeze as individual drops.

However, in this method, no two-phase nozzle is used to form the droplets, nor a freezing gas stream for freezing. The drops are also unilaterally introduced on / through the roller, which promotes shifting of the solids concentration; the further away from the freezing (rolling) surface, the higher this concentration becomes. Furthermore, the freeze-30 process according to this reference takes into account - given the number of revolutions of the roller (maximum 4 rpm) - at the smallest droplet size at least 60: 4 = 15 seconds. U.S. Patent 5,216,890 describes an apparatus and method for producing very fine frozen particles of a liquid material, especially 1007219 2 water, wherein the liquid is sprayed and then contacted with a cooling gas stream, such as low temperature nitrogen gas . Freezing of liquid food products such as milk is neither described nor suggested; the problems with regard to the loss of quality when freezing day-fresh liquid foods do not arise when freezing (pure) water.

U.S. Patent 4,848,094 describes an apparatus and method for forming substantially spherical frozen droplets of a liquid biological or organic material containing liquid. Here, the liquid is supplied under pressure to a feed nozzle to form a stream, which falls from some height into a bath of liquid nitrogen. Here, the liquid steam breaks up into droplets of about 0.6 to 5 mm in average diameter, which freeze in the liquid nitrogen bath and are collected at the bottom of the bath. H: The use of a two-phase nozzle nor the use of a freezing gas is described or suggested.

Similar methods using liquid nitrogen or a similar freezing medium are described in U.S. Patent Nos. 4,655,047, 3,932,943, 3,755,530, 3,721,725, 4,687,672, and 4,712,310. However, using liquid nitrogen as a freezing agent is expensive, cumbersome and not harmless.

The aim of the invention is therefore to provide a technique for freezing liquid, daily fresh foodstuffs without unacceptable loss of quality after reconstitution (i.e. thawing), even after long-term storage.

It has now been found that such a method can be provided by atomizing fresh liquid foodstuffs daily using a "two-phase" sprayer and then freezing very quickly using a freezing gas. Such a method is known per se for the formation of artificial snow by means of a snow cannon process, but has not previously been used in the freezing of foodstuffs.

The invention therefore relates to a method for freezing liquid foodstuffs, comprising: spraying the foodstuff using a two-phase sprayer to a droplet size of 30 to 200 µm: 1007219 3 contacting the sprayed foodstuff with a freezing gas flow, such that the droplets of the sprayed food are frozen within 10 seconds, preferably within 1 second, and optionally; - separating, collecting and / or compacting the frozen foodstuff thus formed.

The invention further relates to the frozen foods thus obtained, as well as to liquid foods obtained by reconstitution (in particular thawing) of the frozen foods of the invention.

In the figures - figure 1 is a drawing of the inborn foodstuff obtained according to the invention, showing the structure as well as the size distribution of spheres; figure 2 shows a schematic view of the embodiment of the invention in which snow cannons placed above a cone are used; and figure 3 shows a schematic view of the embodiment of the invention in which a cyclone is used, wherein figure 3a shows a top view and figure 3b shows a side view.

The invention is suitable for use with all liquid foods that are susceptible to quality loss upon freezing, and such agents will be apparent to those skilled in the art.

The invention is particularly suitable for freezing "fresh" liquid foodstuffs such as fruit juices and in particular for milk or liquid milk products. As is known, such "daily fresh" foods have a cell structure or a micelle structure, which can be affected by known freezing processes.

As the two-phase sprayer (pneumatic atomizing nozzle), any device / technique known per se that can suitably spray the liquid foods to the required droplet size can be used, and such techniques / devices will be known to those skilled in the art, e.g. 30 image from snow cannon processes. In the method according to the invention, these techniques are used in an analogous manner for freezing the fresh liquid food.

Here, the food is preferably sprayed with an essentially inert gas that does not affect the properties of the food, such as air, nitrogen, carbon dioxide, or mixtures thereof. Compressed air is preferably used, which can optionally be pre-cooled.

The compressed air stream used in the two-phase nozzle is preferably pre-dried so that no additional moisture is added to the product by condensation. This is preferably performed by the compression / drying process described below, which is a further aspect of the application. Furthermore, contamination of the product is avoided as much as possible in the practice of the invention.

10 When spraying (atomizing), a droplet size should be reached from 30 to 200 μπι to allow rapid freezing. This droplet size can only be achieved with the above two-phase nozzles, and not with a "one-phase" nozzle.

The average size of the sprayed droplets is preferably in the range of 50-150 µm, in particular about 70 µm.

The skilled person will otherwise be able to carry out the spraying in a suitable manner, taking into account in addition to the droplet size to be achieved and throughput factors such as the self-cleaning aspect of, for example, fibrous liquids and freezing insensitivity.

The food sprayed in this way is then frozen using a freezing gas, which is understood to be a gas of such a temperature that the droplets of the sprayed food are rapidly frozen when they come into contact with the gas. This can be a substantially stationary gas, but is preferably a freezing gas stream, which is understood to mean a gas stream with a temperature and flow rate (relative to the feed of the food) which are suitable for rapid freezing of the liquid food such as described herein.

Again, any suitable gas may be used that does not adversely affect the properties of the food, such as air, nitrogen, carbon dioxide, or mixtures thereof, such as the same gas used to spray the food.

Cold ambient air is preferably used, i.e. air with a temperature of -15 ° C to -25 ° C. This air can be pre-dried again, for example in a manner known per se.

The sprayed droplets are frozen by the action of the freezing gas stream in less than 10 seconds, more preferably less than 3 seconds, most preferably in less than 1 second (with the residence time of the droplets in the freezing gas will be sufficient to achieve this freezing).

Due to this rapid freezing, no ice crystals will form, so that the cell structure of the liquid food is preserved and the moisture remains in the cells. Furthermore, the droplets of the food are frozen on all sides and evenly through the use of a freezing air stream, without this causing a shift in the solids concentration, such as when freezing on a (solid) surface, for example on a roller surface as described in United States Patent 4,912,927. This preserves the day-to-day character of the foodstuffs, even after long-term storage and reconstitution, in particular by thawing.

Using the method of the invention, small, frozen "pellets" or "spheres" of the food are formed, as shown schematically in the attached Figure 1. The formation of these pellets (which are essentially spherical, teardrop, oval or similar shape) can be easily determined by optical means.

The pellets formed can be compacted easily and without loss of quality by means of vibration, in contrast to indented products consisting of (ice) crystals. This allows a high density for storage to be achieved.

The food products thus frozen can be stored in a freezer 25 for a longer period of time without a significant loss of quality compared to the original daily fresh food after thawing - if carried out appropriately. In this storage, the storage temperature should be kept constant, especially at a constant temperature of -18 ° C or less.

Defrosting is preferably carried out in two steps, namely a first step using a temperature up to the freezing point of the food, followed by complete thawing to ambient or use temperature.

When freezing, storing and thawing are done as above 7? In addition, the storage times obtained, as well as the change in quality occurring, are almost identical to, for example, that of ice cream. Such results have not previously been obtained with daily fresh foods.

The method of the invention is preferably carried out in a refrigerated, enclosed space / device of suitable dimensions and design, such as a freezer containing the two-phase nozzles and means for collecting / collecting the inbound product. The food can herein be sprayed in the upper part of the space, for example by means of substantially horizontally arranged nozzles, after which the frozen product thus sprayed falls to the bottom of the space under the influence of gravity and is collected there.

Two special embodiments of the invention will be discussed below, which, however, do not limit the invention.

According to the first embodiment, the food is sprayed and frozen by means of a two-stage sprinkler-based snow cannon positioned above or on the periphery of a cone with an essentially vertical axis, such that the entrenched particles of the food which are ejected by the snow cannon, are collected in the cone and move under gravity to the bottom of the cone, where they are collected by means of collecting means provided under the cone.

For example, snow cannons can be used as used in the making of artificial snow; such devices are described, inter alia, in U.S. Patents 5,400,966; 5,230,218; 4,836,446; 4,813,598 and 4,383,646, the contents of which are incorporated herein by reference.

For larger scale production, multiple nozzles can be used simultaneously, evenly distributed on the periphery of the top ring of a cone, the size of which is determined by the required pitch of the snow cannons. This throw depends on the throughput / production to be achieved, and is related to factors such as the freezing air temperature, the water content and the droplet size, coupled with the minimum required speed. One skilled in the art will be able to control these factors appropriately.

In this embodiment, the process can advantageously be performed as a combination of one or more snow cannons in combination with a vibrated 1007219 7 collection cone, which is placed as a whole in a freezer. It is possible to work in an existing standard freezer room.

This embodiment can for instance be carried out as indicated in figure 2, in which (1) represent the snow cannons, which comprise a sprinkler (2) as well as 5 high-pressure fans (3); (4) is the cone, (5) is the spray mist sprayed with the carrier flow (freezing air), (6) is the snow collected in the bottom of the cone and (7) is a vibratory conveyor. The nozzles (2), to which the liquid and the dried and pre-cooled compressed air are supplied, are mounted on the outlet periphery of a high-pressure tube-10 fans (3) of the snow cannons (1). These fans are in turn, widely distributed, mounted in a cooled room (freezer), with a temperature of about -18 ° C. The room air is drawn in by these fans (3) and blown out at such a speed that the foodstuffs sprayed by sprinklers (2) are kept in a floating state long enough until the largest droplets to be expected (200 µl) are frozen. This process is essentially analogous to known snow cannon processes. The spray mist (5) collects as snow (6) at the bottom of cone (4) and is discharged by means of vibrator (7).

In the second embodiment, which is intended to limit the process dimensions, the food sprayed through the two-phase nozzles comes into a mist in a rotating freeze air stream where the sprayed droplets are frozen.

Here, the freezing gas stream is in the form of an eddy current or cyclone, as shown in Figures 3a and 3b, wherein (8) are the two-phase nozzles 25 located in near dead space (9); (10) is the freezing gas cyclone; (11) are freezing gas jets; (12) is the wall of the cyclone; (13) is a high pressure fan for drawing air from the freezer; (14) is the space for collecting / collecting the food; (15) represents the central recirculation channel for the freezing air stream leaving the cyclone, (16) are means for removing small particles from the freezing air stream; (17) is the collected frozen food and (18) is a vibrator. The whole is placed in freezer silo (19).

The food is sprayed from (the nozzle of the two-phase) 8 nozzles (8), which are located in almost dead space (9). These nozzles (8) are placed above cyclone (10) such that the sprayed food falls under gravity into cyclone (10), where it comes into contact with the rotating freezing air in the cyclone (10) and freezes.

This freezing air is supplied to cyclone (10) by jets (11), and can for instance be drawn in from silo (18) by means of high pressure fans (13) which are connected to jets (11) via a ring channel. The freezing air exiting the cyclone is removed from space (14) via central channel (15), and can be stripped of particles by means of particle removers (16) if it exits again to silo (19).

The frozen food particles slowly move from cyclone (10) under gravity to the bottom of space (14), where they are collected and collected as snow / powder (17), which can optionally be compacted by means of vibrator (18), and can be discharged by means of a drain (not shown).

In this case it is preferred to work in such a way that the drops of the food do not touch the cyclone wall (12), so that the drops are prevented from freezing on them. In order to achieve this, the freezing air is preferably supplied along the periphery of the cyclone via jets (11), so that an air film is created which moves at high speed along the cyclone wall (12). This prevents drops in the frozen state from hitting the cyclone wall (11).

The dimensions of the cyclone are again determined by the above-mentioned factors of freezing air temperature, water content, droplet size and minimum required speed, whereby the cyclone can advantageously be designed for large-scale production.

The gas flows used in the invention are preferably reused after use. In the first embodiment as described above, this is achieved, for example, in that the gas, which may have been slightly heated up, rises from the cone and is cooled there again by coolers present in the room. In the second embodiment this can be achieved in that the gas is discharged via the cyclone discharge and subsequently cooled by the space coolers.

The ambient air used in the invention as carrier gas and / or freezing air is maintained at 1007219 9 by means of standard fin air coolers and a normal cooling machine. The compressed air used is preferably dried so that no additional moisture is added to the product by condensation. This is preferably performed by the compression / drying process described below, which is a further aspect of the application.

Conventional piston and screw compressors are generally not suitable because they contain lubricants such as oil, which can get into the food product and also because they heat the air strongly through the compression process.

According to the invention, therefore, an oil-free liquid ring compressor known from the vacuum technique is preferably used, the liquid of which is strongly supercooled. The air, which is therefore drawn in via a biocell filter, is therefore removed from the production process. A table salt solution cooled to the same temperature as the process air is used to maintain the liquid ring. The low vapor pressure and temperature of this solution guarantee a dry atomizing air, so that the subsequent switching of a compressed air dryer is not necessary. A so-called compact separator ensures that the air is supplied drip-free to the atomizers.

Since water emerges during the compression process, the salt concentration is maintained by means of dosing equipment known per se.

In both processes it is possible that the smallest drops of the sprayed and frozen foodstuffs are entrained in the heated gas and thus not caught. These will float uncontrollably in the room, especially when using snow cannons, and possibly be drawn in by the air coolers. In order to prevent the air coolers from slamming, a special heat exchanger can be connected, whose surface temperature is above 0 ° C. This will cause the snow to settle and melt. The required heat is preferably supplied from the refrigerant condensate. The supercooling of this refrigerant condensate improves the cooling capacity. Since the absolute mass of drifting snow is very small, the supercooling range of the coolant is large enough to fully recover the heat of melting. Because of contamination, this melt can usually no longer be reused.

For application of the special cyclone, a heat exchanger arranged on the discharge of the cyclone, preferably as described above, is preferably used as a demister.

i007219 10

The person skilled in the art will further be able - with the aid of the present description - to properly carry out and control the method of the invention, on the basis of factors such as the nature of the liquid food, the desired throughput, the equipment used, the drop size, the flow rates used and the temperature of the freezing gas; any changes and / or adjustments required for this will fall within the scope of the invention.

The invention further relates to a device for carrying out the method according to the invention. This "ultra quick liquid freezer" is preferably designed as described in the above-described preferred embodiments and the figures, ie in the form of a cone above which one or more snow cannons on the basis of two-phase nozzles for feeding, spraying and freezing the liquid food, or in the form of a fluidized bed device, above which one or more two-phase nozzles for supplying and spraying the food are placed.

The invention finally relates to the use of these devices in the freezing of fresh liquid foodstuffs.

10072 1 9

Claims (15)

A method of freezing liquid foodstuffs, comprising: spraying the foodstuff using a two-phase sprayer to a droplet size of 30 to 200 μτη: contacting the sprayed foodstuff with a freezing gas, preferably a freezing gas stream, such that the droplets of the sprayed food are frozen within 10 seconds, preferably within 1 second, and optionally; 10. (separating, collecting, collecting and / or compacting the frozen food thus formed. 2. A method according to claim 1, wherein the liquid food is a "daily fresh" liquid food, preferably milk or a liquid milk product. A method according to any one of the preceding claims, wherein the food is sprayed in the two-stage sprayer pre-cooled and dried compressed air. 20 A method according to any one of the preceding claims, wherein the freezing gas is air with a temperature of -15 ° C to -25 ° C, preferably about -18 ° C. A method according to any one of the preceding claims, wherein the liquid food is sprayed and introduced by means of one or more devices known per se as snow cannons, which are arranged on the upper periphery of a cone, preferably a vibrated cone, and / or drains of the frozen food. 30 A method according to any one of claims 1 to 5, wherein the food sprayed by the two-phase nozzles is frozen in a rotating freeze air stream, in particular in a cyclone. 1007? 19 A method according to any one of the preceding claims, carried out in a freezer room which is kept at a temperature of preferably less than -18 ° C. A method according to any one of the preceding claims, wherein the frozen food is stored at an essentially constant temperature of -18 ° C or less. A method according to any one of the preceding claims, further comprising the step of reconstituting the liquid food from the frozen food, in particular by thawing. A method according to claim 9, wherein the thawing is carried out in two steps, namely a first step up to a temperature below the freezing point of the foodstuff, and a second step up to ambient or use temperature. 11. A method according to any one of the preceding claims, wherein the freezing gas stream is recirculated and wherein particles of the frozen foodstuff, which are not collected, are removed from the recirculated gas stream by means of a lamella heat exchanger, which is used for any in the recirculation circuit. existing air cooler is installed. 12. Frozen foodstuff obtained or obtainable according to the method of any one of claims 1-7. 13. Device for carrying out the method according to any one of claims 1-5, comprising a cone present in a freezing cell, above which one or more snow cannons based on two-phase nozzles for supplying, spraying and freezing the liquid foodstuff are placed in such a way that the particles of the sprayed and frozen food, which are ejected from the snow cannons, can be collected in the cone. 1 007212 Apparatus for carrying out the method according to any one of claims 1 to 4 and / or 6, comprising a fluidized bed device present in a freezer cell, above which one or more two-phase nozzles for supplying and spraying the liquid food are placed, such that the droplets of the sprayed food product exiting the two-phase sprayer can be collected in the fluidized bed device. Use of a device according to claim 13 or 14 in freezing fresh liquid foodstuffs. 10 *** 10072 0