Process and apparatus for quick-freezing of food products

Priority of a French patent application filed on April 25, 1977 under the number 77 12 339

The present invention relates to a method and apparatus for carrying out the rapid freezing of liquid or pasty food products for industrial use and for the manufacture of products intended for household consumption.

In the current state of the art, viscous food products or liquids are frozen in containers of variable volume, from 250 ml, for example, for concentrated fruit juices up to 10 or 20 liters for egg yolks, in plastic containers or other materials, and even 30 to 50 liters for orange juice packaged in plastic bags.

Freezing in flakes or platelets by cooled cylinders or scalyers is not suitable for the products considered.₅only suitable for low viscosity liquids ¹ like water for example. Viscous food products and liquids are therefore treated using the block freezing technique.

Block freezing of viscous food products and liquids, according to current industrial practice, has several drawbacks.

In all cases, the product subjected to the freezing treatment is packaged in a package. Any packaging. is expensive and all the more so since the unit volume is_Lo small.

On the other hand, freezing and thawing are slow. Thus, the freezing in bulk of bags of orange juice of 30 to 50 liters requires a stay of 24 to 48 hours in a cold room and that of eggs in a container about 48 hours During these prolonged periods of freezing, food products risk '' evolve and deteriorate during these operations. In the case of defrosting, an increase in the speed thereof can lead to overheating and cause a deterioration in the quality of the product, for example if it is a question of defrosting a block of soup with usual cooking means. .

In addition, it is necessary to thaw an entire block since it is difficult to fragment it, which prevents the practical use of small quantities of product. For the same reason, mixtures of frozen solid products are not feasible, whereas this technique should be able to be used to carry out different dosages of finished products or to be processed.

A process has been found which allows to overcome the disadvantages of block freezing. This new process which

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&lt;leads to the almost instant production of frozen granular products is suitable for industrial applications and for manufacturing for household consumption.

The rapid freezing of products, under regular and excellent cooling conditions, constitutes a guarantee for the consumer. The presentation in the form of particles of a frozen food product gives the consumer the possibility of withdrawing only the quantity intended for immediate use, it also assures him of a rapid de-freezing which eliminates any alteration in quality.

Thus, the user can take the quantity of frozen orange juice necessary for the preparation of a glass of fruit juice and, immediately after having extended water, consume the drink ready for use. In the case of block freezing of a can of orange juice, the consumer will have to wait approximately two hours before proceeding to dilute the juice; normal defrosting time for çôntgnu d.'uhè: box “t Similarly, the drawbacks of defrosting soups in blocks are eliminated.

The new technique allows mixing in the desired proportions of different constituents. You can make mixtures of fruit juices and concentrate and purees of several fruits and vegetables, as well as making soups based on various ingredients.

According to the process of rapid freezing of food product by mixing with dry ice, the liquid or pasty food product is frozen by kneading with the excess carbon dioxide snow.

According to an object of the invention, a carbon dioxide snow bed divided by mixing is formed in situ, then it is brought into contact with said bed of dioxide particles.

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-4LO of carbon the food product îi the liquid or pasty state, divided in contact with the snow of carbon dioxide until formation of granules of said food product.

Depending on its viscosity, the food product to be frozen can be introduced in mass and its division takes place in contact with the snow bed of carbon dioxide by the contact effect; it can also be divided over the dry ice bed.

The carbon dioxide snow and the food product are introduced continuously, while simultaneously withdrawing, continuously, the frozen product in granules and the carbon dioxide gas from the sublimation of the carbon dioxide snow.

The subLimation of solid carbon dioxide snow in contact with the viscous liquid product is very important; the freezing of the food product is extremely rapid and the food liquid feeds the already frozen particles which are in the mixing zone. The product makes it possible to obtain particles separated into granules of variable dimensions, the diameter of the granules being between 5 and 15 mm.

Carbon dioxide gas from the sublimation of carbon dioxide snow can be recycled after compression and liquefaction by cooling and then expansion.

The contact time of the product to be frozen with carbon dioxide snow and the speed of mixing depend on the desired size for the particles. It is therefore possible to vary the diameter of the granules by acting on the contact time or on the mixing speed: the particles are larger when the contact time increases and they are finer when the mixing is faster and vice versa. Advantageously, the contact time is' / λ

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Ι30 of the order of a few minutes, preferably between L to 10 minutes. An increase in the mixing speed of the order of 1 to 2 has a significant impact on the diameter of the granules. With a linear speed of the brewing organs of 0.80 meters / second, particles of 10 to 15 mm are obtained, while a double speed of 1.60 meters / second leads to smaller particles of 5 to 10 mm. . We choose a speed between 0.3 and 2 meters / second.

The dimensions of the granules are also a function of the viscosity of the product to be frozen; the granules are large and irregular when the product has a high viscosity. These dimensions are also a function of the product's ability to freeze; the grains are small when the product is difficult to remove. The process is applicable to a wide range of viscosity from aqueous low viscosity products to high viscosity products up to 60 poises. When the viscous liquid is frozen, the heat exchange with dry ice is reduced to an exchange between solids and it is possible to obtain a significant temperature difference between dry ice and the grains of frozen product. Although the sublimation temperature of carbon dioxide is - 78.9 ° C, grains of frozen food products, after temperature stabilization, can be extracted at temperatures of - 70 to - 18 ° C, for example, corresponding to the usual frozen storage temperatures.

The flow rate of the product to be frozen is high and varies according to the viscosity of the liquid to be frozen, decreasing when it increases. With aqueous products, it is possible to freeze 10 liters per hour per liter of capacity of the mixing device, for example 250 liters / hour for a mixer of 25 liters of capacity. The high flow makes

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-6that the abrasion of the frozen product is low during the operatiot

The carbon dioxide snow used in the process can be produced by expansion of liquid carbon dioxide. The trigger provides carbon dioxide gas and dry ice.

It is possible to envisage the use of carbon dioxide gas in a closed circuit, by means of a reliquefaction installation. This reliquefaction is carried out in a conventional manner by compression in two stages, up to 20 bars for example, then cooling to −20 ° C. by a conventional refrigeration installation with a refrigerant such as ammonia or a fluorinated hydrocarbon. .

According to a variant of the invention, it is possible to carry out a regulated additional supply of product to be frozen. This additional product is intended to sublimate the snow with excess carbon dioxide and to warm the temperature of the granules of frozen product before their extraction; it is regulated by the extraction temperature chosen. This supply of liquid to be frozen can be made, when the viscosity of the product allows it by spraying, either liquid alone, or liquid divided by carbon dioxide under pressure.

The freezing process by stirring the viscous product to be frozen is carried out at least in one zone.

According to an advantageous mode, the product is stirred in three zones.

In the first zone, called the freezing zone, the viscous food liquid is frozen by mixing.

in contact with dry ice. The flow of carbon dioxide snow into this first zone is regulated by the temperature of the second zone; dry ice is always in excess in the freezing zone.

- / The second zone is reserved for the separation of frozen granules of suitable size from fine snow and frozen fine particles. The fine particles which have been separated are returned to the freezing zone.

In a third zone, where the agitation is less than in the freezing zone, the carbon dioxide is recovered by sublimation of the excess carbon dioxide snow and the temperature of the frozen product is stabilized by an additional supply of product. to be frozen regulated by the extraction temperature chosen for frozen granules.

It is important to create a counter-current circulation between the small and large granules of frozen product, the small ones being sent back to the freezing zone and the large ones of suitable size oriented towards the temperature stabilization zone of the frozen product.

The process of the invention, which is simple and inexpensive to use, makes it possible to freeze into granules with a high hourly flow rate of liquid or pasty products. It is particularly applicable to the freezing of all fruit and vegetable juices from fruit pulps and nectars, such as peach, blackcurrant, apricot, currant, strawberry, raspberry, for the preparation of ice creams and sorbets. The process is particularly suitable for the preparation of coulis and tomato puree, mash of various vegetables such as carrots, the pectin and color of which remain intact, and spinach, onion, garlic. The process gives excellent results in the conservation of sauces, creams and soups as well as in egg yolks for baking. The process is also very advantageous in canning and food confectionery to absorb momentary overproduction when harvesting vegetables such as tomatoes and fruits for example.

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-810

The devices allowing the implementation of the process can be simple or sophisticated.

The simplest device is shown in vertical cross section in Figure 1 and axial in Figure 2, attached drawing. The mixer comprises a horizontal semi-cylindrical trough (1) fitted in the longitudinal direction with a rotor (2) provided with non-oriented arms (3) terminated by pallets (4); this rotary assembly being intended to carry out the mixing of the liquid or pasty food product. The gauge is externally insulated by conventional insulation (5), such as the injected polyurethane type.

The device is closed by the cover (6) into which arrives at (7) the tube for introducing the food product and at (8) the blower for supplying dry ice; the solenoid valve (9) controls the arrival of the liquid CC ^ conveyed in the pipe (10) ending in the blunderbuss; and the chimney (11) is provided for the evacuation of the CC ^ gas. An opening (12) is provided in the vertical outlet wall for the extraction of the frozen product and the excess carbon dioxide snow. At the exit of the device, a screen is provided to recover the finest products and excess dry ice, for recycling in the malaxei (This arrangement is not shown in the figures). At the lower part of the trough, the drain (13) is intended for the evacuation of the product remaining in the apparatus at the end of the operation.

FIG. 3 of the appended drawing represents, in axial section, an improved apparatus in which the horizontal semi-cylindrical mixer has been lengthened and separated, in a more or less clear manner, into zones corresponding to the variant of the process in three stages: freezing, separation of frozen particles of suitable size and carbon dioxide snow fines and frozen product, sublimation of excess carbon dioxide snow and stabilization of the temperature of the frozen product.

The apparatus comprises a large, parallelipipedic tank (14) covered and insulated, with a cylindrical bottom.

Over the entire length, the device is equipped with a rotor (15) provided with arms (16) terminated by pallets (17) arranged in such a way that the movement of the product in the entry area has little orientation axial. In the central part of the device, the rotor arms carry a double series of pallets, at their end - a first series of peripheral pallets (18), oriented in such a way that the small particles of frozen product are directed towards the area previous, and closer to the center a second series of pallets (19) oriented in such a way that the large particles of frozen product are directed in the opposite direction towards the terminal part of the device. In this latter zone, the number of rotor arms is reduced compared to the input zone, and these only carry a series of pallets.

The central and terminal parts of the device are partially separated by a partition (20) and are in communication through the passage (21) formed in the partition.

In the entry area, the upper part of the apparatus is provided with the tubes for introducing the food product (22) evenly distributed around the blast of dry ice (23); the solenoid valve (24) controls the supply θ^{η C}° 2 ^^^ MLde circulating in the pipeline (25). The upper terminal part is equipped with a sprayer (26) to make up the liquid to be frozen, the gaseous carbon dioxide under pressure is introduced by (27), the central upper part is provided with a recovery device (28) carbon dioxide to a compression plant and

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-10llquéfaction by cooling then expansion, for recycling, not shown in the figure.

In the vertical end wall, there is provided the extraction airlock (29), the peripheral pallets of the central zone directing the fine particles towards the entry zone can be replaced by turns of suitable torsion.

The mixer can advantageously be tilted by raising the inlet zone relative to the outlet, in order to ensure the flow of large particles of frozen product in the direction of inclination of the mixer, the fine particles being brought back by the peripheral pallets. towards the entrance area.

As a variant, it is possible to use multiple mixers with double rotor or quadruple rotor; The different rotors being on the same horizontal plane which make it possible to increase the production capacity.

The appliances must be closed and the carbon dioxide discharged to the outside by a chimney in the case of use in waste gas, but it is possible to maintain an overpressure in the appliance, so that the air intakes can be completely avoided, which is favorable for the reliquefaction of carbon dioxide.

Examples are given below which illustrate the invention without implied limitation.

EXAMPLE 1

In a mixer, according to FIG. 3, in which the capacity of the first zone is 25 l, gelato juice concentrate is frozen. 14% of dry substance with a viscosity of 3 poises at 24 ° C, according to the following process. We pour carbonic snow, produced by relaxation and we stir until a bed of carbon dioxide snow is formed. Dry ice is introduced at the rate of 0.8 kg of snow per kg of tomato concentrate. Then pour on the snow bed The tomato concentrate juice with a flow rate of 2001 / h, which divides on contact with the dry ice bed.

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-11The linear speed of the mixer arms is 1.30 meters / second. Freezing is instantaneous and the residence time in the freezing zone is around 6 minutes. = / *

The granules from 10 to 25 mm, the snow and product fines are directed towards the separation zone where the temperature is of the order of -50 ° G. The external pallets return the fines less than 10 mm to the zone of freezing, while the central pallets direct the granules of suitable size 10 to 25 mm towards the corridor of communication with the temperature stabilization zone. We carry out a complete injection of the sprayer, with a flow rate of 10 L / h. The temperature. The grain size stabilizes at -20 ° C. and the frozen product is extracted. The carbon dioxide gas is recycled after compression and liquefaction.

EXAMPLE 2

In a type 1 mixer of 25 liters capacity, spinach puree of viscosity 40 poise is frozen at L5 ° C, under the following conditions:

Dry ice is poured into the mixer and stirred until a bed of dry ice is formed. Dry ice is introduced at the rate of 0.8 kg of snow per kg of spinach puree. Then pour the spinach puree at 15 ° C on the snow bed with a flow rate of L50 mg / hour; it divides on contact with the snow bed.

The linear speed of the mixer arms is 1.90 meters / second. Freezing is instantaneous and the residence time in the freezing zone is of the order of 8 minutes. The dry ice extracted from the mixer with the frozen spinach puree is smaller and more brittle so that the frozen spinach granules are separated by 6 mm to 6 mm and reintroduced the fine snow and small grains of spinach. / in the mixer. The snow is reused and the small grains grow by adding spinach puree which freezes on their surface. As n'-pcô ^ s - '. Have. nn + - = -. + --11 ^ - * ----- - ++ - - 5

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