NO136006B - - Google Patents

Description

Method and apparatus for producing dried puree with improved rehydration properties.

The present invention relates to pureed foodstuffs and a new apparatus for the production of dehydrated pureed foodstuffs which are suitable as food for young children and for nursing patients, especially after an operation, and which can advantageously be used to prepare soups, desserts

ter and other foods. More particularly, the invention relates to the production of dehydrati-

particularly stretched foodstuffs which may have a relatively high percentage of natural or added sugars and/or pectin-like substances, which can easily be rehydrated in cold water, milk or other water

solid liquids, and which, when cooled in a relatively dehydrated state, are free from agglomeration, whereby a free-flowing, easy-to-handle product is obtained.

During the production of so-called freeze-dried products, such as pears, peaches, apples, apricots, tomatoes, cranberries and the like in puree form, it is advantageous that the product is able to be "instant*

and fully rehydrated. In this connection, the term "momentary" is used

to describe a product that is able to be rehydrated within approx. 30 seconds, and within limits from approx. a few seconds to 1 minute, which hydration may take place in cold, lukewarm, hot or boiling water or other

liquid and is accompanied by a rapid increase in viscosity.

In order to reduce the weight and volume of the packaging, until now processes have been proposed to reduce the moisture content of fruits by freeze-drying them. Most freeze-drying processes consist of relatively slow drying, but certain factors during this process impair the desired rehydration properties of the product. Typical of such slow dehydration methods are processes that use the so-called tunnel or basting hydrators that have been in use for many years to dehydrate vegetables and fruit. When it comes to drying fruit purées, faster and cheaper drying can be achieved by guiding a slurry of purées onto a rotating drum whose outer surface is heated and which has a drying surface with good heat transfer capability and good release properties for particles, which increase the content of solids in puree

one from e.g. 9-30 percent to approx. 98-90 per cent solids, but preferably does not increase above the amount of solids where the taste, color and nutritional value deteriorate.

got.

During the performance of such drum drying, a number of difficulties are encountered which reduce the rehydration properties of the dried product. The partially dehydrated film of the product is plastic when removed

nes from the drum, and when it is removed by means of a scraper blade which acts tangentially on the smooth surface of the drum

len, the product can be retained on the ironing blades, so that when the product

nes from the drum, it acquires a wavy irregular surface with a partly crab-like appearance due to speed

the shrinkage of the film as it leaves the dryer. A build-up of this thickness of the product is detrimental to the rapid rehydration of the coated product.

Previous drum drying processes have been concerned with problems of protecting the product removed from a drum dryer from overheating. In conventional previous methods, it has thus been proposed to direct a blast of cold air at the wiping or scraping point, or to quickly remove from the vicinity of the drying surface the continuous film of the product brushed off from the drying surface. However, these previous methods did not give the thus dehydrated continuous film the desired rehydration and recovery properties. The previous methods only aimed to obtain an essentially continuous, uninterrupted tissue or film so that minimal time was lost when the film broke.

The previous drum drying systems which were used to dry films of e.g. foodstuffs, was also characterized by the fact that the continuous film passed over a long distance greater than 1 m, and usually 100-120 cm, from the point of removal (i.e. the wiping point) to the point at which the film first comes into contact with subsequent transport rollers. When the film being removed from the drum is quite hot, the former parts of the apparatus have tried to cool it as quickly as possible, and this was done by arranging a greater distance between the wiping point and the point of first contact with the subsequent transport rollers.

According to the present invention, an improvement is achieved in the drying technique of purees, puddings and similar products that have a relatively high content of natural or added sugars and/or pectin-like substances that are originally present, are added, or are released during cooking , in a way that satisfies the above-mentioned need for an instantly rehydratable product in film or flake form. For the sake of simplicity, products treated according to the invention will hereinafter be referred to as "purées", but this designation shall include soups, gruels and solutions containing solid particles, as all these materials form continuous stretches - mere films rather than powders when removed in concentrated form from a drying surface. The improvement comprises the placing of a puree which has finely divided solid food constituents in an amount of 9-30 per cent (but sometimes more), on a surface on which the puree is heated, concentrated and converted into a continuous film of syrupy viscose elastic properties when the film is in a heated state, and in this state the finely divided solid food ingredients are suspended in molten liquefied sugar and/or a pectin-like sugary molten carrier which gives the film a tensile strength which varies from product to product, but which in each case is sufficient for the product to retain its continuous adhesive character after it has been removed from the heating surface and while it has been stretched to an extent described later. The product is usually removed using such means as an impression sheet. Generally, the moisture content of the stripped film will be less than 12 percent and greater than 2 percent by weight of the film. The film is continuously removed in its molten state.

According to certain features of the invention, the apparatus for producing a dry stretched film can comprise a drying surface on which a continuous film of the material can be deposited, means for depositing this film on the drying surface, means for

to heat this drying surface whereby

the film deposited on the surface can be heated and dried to a stretchable state,

means for removing the film from said surface as a continuous film, a stretch roller by means of which the removed continuous film is subjected to a tension substantially greater than that required to prevent agglomeration during the removal of the film, but sufficiently great for stretching the film, sufficiently large to cause an arbitrary distribution of discontinuous surface breaks and voids in the film, and less than the breaking stress of the film, and an interrupted contact wheel which abuts said material film when the material passes over the stretching roll, whereby the stress during the removal of the film is maintained and the film is stretched while in the stretchable state.

A particularly advantageous feature of the method and the apparatus according to the invention consists in the fact that it is possible to subject the film sheet to tension over a short distance that extends from the wiping point to the first point of contact with the stretching roller. This stretch is as short as possible, preferably less than 1 m and usually 30 to 45 cm, but the stretch will vary with the change in the relative consistency of the stretched product under the atmospheric conditions of drying.

,It was discovered a long time ago that the various methods and previously used apparatus parts were unsatisfactory as they did not allow to obtain a product which can easily be rehydrated. Many modifications of the apparatus were found and many attempts were made to construct a proper apparatus, but until now no apparatus was constructed which would allow a product with the above-mentioned better properties to be obtained.

In the preferred embodiment of the invention, the apparatus may comprise a double drum dryer, a stretching roller for stretching the sheets of material removed from the dryer, and a contact or gripper wheel which facilitates the formation of the tension in the film and thereby contributes to the achievement of the necessary stretching the film.

During the use of this new combination of apparatus it was noted that the contact wheel should preferably be a single cylindrical wheel, although it was thought that a series of spaced shorter rollers might be satisfactory. In many, possibly most cases, both constructions will function satisfactorily. However, in the case of certain very sticky foodstuffs, it has been found that the film passing between the removal or stretching roller and the contact, tension or intermediate wheel will adhere to the latter wheel and thus interrupt the operation of the machine. This effect is particularly noticeable when it comes to foods of the following type: peaches, pears, tomatoes, etc.

The tension should be sufficient to stretch and thereby elongate the film, whereby the solid food constituents become thinly and separately dispersed in the still molten sugar-containing carrier, and whereby the fibrous and other insoluble solid food constituents appear to the naked eye as randomly distributed and unoriented particles. Films of peach and pear purées and, to a lesser extent, apple and tomato purées will have a greater tensile strength than pudding films due to the fact that fruits contain more pectin materials. As a result, such fruit purees will usually need a higher tension than puddings. In this connection, the temperature of the drawn film will influence its extensibility and although a rapid cooling of the stretched film is desired, the film should be sufficiently melted at least in the initial stages of elongation to provide the here mentioned stretching mode. However, the temperature of the product will not usually exceed 100° C during the stretch. Usually this state of stretching will be felt by an arbitrary distribution of discontinuous openings, surface scratches and voids in the stretched film, and in many natural fruit purées it will be felt by minimal blisters or blisters that are almost invisible to the naked eye and that in many cases causes the formation of a number of "pimples" of which some are open and some are intact.

Under a strong microscope it can be seen that the stretched chilled product comprises a translucent substrate layer or phase which is continuous and comprises dispersed solids or agglomerates, as the surface of the product is also translucent and as the above-mentioned discontinuous openings, surface scratches and voids in the product appear in the continuous phase, this indicates loss of elasticity at spaced points in the sugar-containing carrier for the solid food ingredients.

The thickness of the product film after stretching will vary from product to product depending on the product's stretchability and the degree of stretching required to make the product instantly rehydratable. Typically, the removed film will have a thickness reduced to less than 0.125 cm and up to approx. 0.0125 cm.

The voltage used according to the invention to remove the film from the heating surface is thus greater than that normally required to prevent agglomeration of the product and rapid removal of the film from the drying surface, but lower than the voltage at which the film will completely fail, which can is felt by a complete break in the film resulting in a break in the film's continuity.

The stretching may take place by any adjustable means of accelerating the speed of movement of the removed film relative to the speed of movement of the film at the point of removal. Due to the desired film properties, such stretching means must be able to provide this speed increase uniformly without causing excessive tension but at the same time providing such a great tension that it is sufficient to obtain and to maintain a high degree of dispersion of the solid food ingredients in the molten carrier.

Due to the condition of the film created by the stretch, an ideal distribution of water-soluble and water-insoluble solid food ingredients is achieved in the film, and the film has attractive colors and a fresh aroma when reconstituted. The majority of the water-soluble solid food ingredients appear to be in the continuous phase, the majority of the water-insoluble solids being thinly and separately dispersed in this phase in the form of a discontinuous phase. Most of the surface of this thin film is also covered by the continuous phase. Although the water-soluble solids will quickly dissolve in cold water, due to this arrangement and the condition of the water-soluble and water-insoluble solid food ingredients, this will not happen at the expense of the water-insoluble solids which are ideally dispersed and have the greatest chance of being rehydrated without clumping.

Flakes formed by breaking the film will be broken into different sizes depending on the rehydration properties of the particular mash to be dried. For most fruit purees and puddings, the film will preferably be shredded to a specified size, with 100 percent of the product passing through a 10 mesh U.S. sieve series (0.375 mm wire), but there can be produced flakes of a larger size with usable rehydration properties. Without further treatment according to the method according to the invention, the film should not be broken into very fine particles, e.g. under 40-mesh U.S. series sieve, as the particles when broken tend to form lumps during handling or storage, forming confection-like balls that do not hydrate instantly in cold water.

The meaning of the above-described stretching will. is understood when one takes into account that in the case of a plastic but nevertheless stretchable film of a puree that has not been stretched to the extent and in the manner described above and from which the heat can spread, a wrinkled puree will have relatively weak rehydration properties, e.g. it will take 3-10 minutes when the product is reconstituted in cold or lukewarm water (4.4-26.7° C) before the desired smooth, even structure and viscosity is achieved. In the case of the aforementioned stretched film and fluff according to the invention, the puree product has rehydration properties that can be appropriately described as "instantaneous" and it has the ability to be reconstituted to the appropriate viscosity in cold to lukewarm water (4.4 - 26.7° C) for less than 60 seconds depending on the product, usually 1-30 seconds. Apple purées are rehydrated the fastest and this phenomenal rehydration is noticeable by the "blooming" of the product after reconstitution in water. In the case of light bulbs, a slight delay is noticed by e.g. 5 seconds before the bloom takes place. In each case, these rehydration properties occur in a wide variety of fruits, and the term "fruit" in the description and claims means any plant that has a naturally high sugar content, e.g. 13 percent by weight of solids, and represented by such common fruit species as apples, cranberries, peaches, pears, apricots and the like.

The term "stretchable" used in the description and claims denotes the plastic state that prevails when the moisture content of the puree is reduced to slightly more than 90 percent of solids and is between 90 and 98 percent of solids, the upper limit of the moisture content being limited of properties of the plastic state and of properties of the product itself which, when it contains a very high percentage of solids, can be damaged during excessive heat treatment. It has been observed that 2-10 percent of moisture in the stretchable mass is advantageous, but an even higher moisture content of up to 15 percent can be used in the invention. In natural fruit purées that do not contain additives, a moisture content greater than 10 percent will be characterized as soupy. However, by modifying thickening agents, such as starches, gums, covering agents and the like, which are capable of increasing the tensile strength of the puree, it will of course be possible to change the moisture content. at which the desired stretchability will occur.

A very good rule of thumb for determining the degree of stretchability to be used is that the product should be stretched to such an extent that many minimal surface scratches appear on the film surface.

The stretching is preferably carried out by allowing the water-containing film of the product to travel in a substantially uncompressed manner over wiping means by means of which the material film is caused to move at a greater speed than that at which it is removed from the hot film-forming surface.

In order to achieve a suitable flocking of the film, it is necessary to regulate the product's humidity and/or temperature, depending to a large extent on the nature of the treated material. The product should be in a brittle, fragile state and should remain in this state after fizzing to retain its free-flowing, "instantly" rehydratable character. This brittle state is achieved and maintained by exposing the stretched concentrated product blanket to regulated atmospheric conditions and humidity.

Products coming from stretchers under varying operating conditions may, but need not, be cooled to such a temperature, and their moisture content should be adjusted to such an extent that the blanket of solids can be easily fluffed under normal atmospheric conditions to provide an instantaneously rehydratable material . Under conditions of high relative humidity, certain products, particularly many of the above-mentioned fruit purees and puddings, will absorb atmospheric moisture due to their hygroscopic nature. Other products, e.g. applesauce and tomato paste, even under ideal atmospheric conditions, i.e. at a low swirl temperature, will need a further downward adjustment of the product's moisture content. Even when a product blanket is dehydrated to the point where it will pill, i.e. do not want. are bundled together during processing on a conveyor, there will be situations where the temperature must also be lowered, even if a temperature lowering takes place when the product is stretched.

For example applesauce puree will be removed from the dryer with 7 per cent moisture and it can be dried in a stretched cold state with approx. 5 percent humidity. Nevertheless, when the same product is removed from the drying roll under atmospheric conditions of relatively high humidity and temperature, with a moisture content much lower than 7 percent, and when stretched with a still lower moisture content than 5 percent, it will not fray effectively and retain their free-flowing and rehydratable properties after storage, if the product blanket is not exposed to dehumidified air and preferably to cooled dehumidified air. Dehumidification and cooling will usually be necessary at relative humidities above approx. 60 per cent and temperatures above 26.7° C: The film of the product to be stretched will generally have a moisture content between 2 and 7 per cent before stretching (usually about 4.5 per cent) and a moisture content between 5 and 3 per cent. after stretching (usually below 4.5 per cent). When the products contain a high percentage of sugars, starches and acids, it is preferable to refrigerate them the duct blanket by using recycled cooled air with a temperature below 21.1° C and a relative humidity below 45 per cent, but as mentioned above certain usable products can be obtained when using slightly higher relative humidities and air temperatures. When ie processed products are fruit purées 0?; puddings, chilled pieces of these products will not be stored in a room that has an air temperature of e.g. — 14° to — 23° C, tend to form lumps and will not be able to be processed for a period of approx. 24 hours. It is therefore a very big advantage and necessary for most fruit purées that conditions are used in which the product has a temperature below 21.1° C when it enters the pulping device and below 26.7° C when it leaves the pulping device, because it resulting fluffy product will be free-flowing and well-workable after it is stored and then wrapped as needed. In accordance with the most preferred cooling fluffing method, conventional refrigerants using recycled dehumidified air of less than 1.1°C will dehumidify before fluffing and at the same time cool the stretched product blanket to the desired degree. On the other hand, other means can be used to carry out such a treatment continuously during the fluffing and a preferred modification of the apparatus, which will be described later, consists in a screw conveyor which is enclosed with the exception of an entrance opening for the screw, being a source of recycled dehumidified cold air is introduced into the enclosed conveyor in countercurrent to the product's direction of movement. In such a conveyor, the product carpet will be slightly broken, but the fluffing will take place when the product is introduced into the fluffing apparatus, which is also enclosed and located below the conveyor. The creasing device may comprise any suitable well-known creasing apparatus capable of breaking a sheet of product and passing it through a sieve. Such a winnowing device typically uses a series of powered vanes that push the product through, a screen of a U.S. sieve series below 40 mesh.

The product can then be stored in a suitably cooled atmosphere or directly packaged either in an inert gaseous atmosphere or under normal atmospheric conditions. Thus, the product can be wrapped in sterile airtight containers, e.g. tin box in an inert gaseous atmosphere, eg, nitrogen. A less expensive packaging system which is, however, ideal and particularly suitable for the stretched flounder purées according to the invention, consists in packing and curing these products in a frozen state (-h 17.8° C) in any conventional food packaging .

In the following, the invention will be described in more detail on the basis of photomicrographs of various chilled flounder samples and of an apparatus for carrying out the invention. Figs. Ai, Aii and Aiii are photomicrographs of apple-apricot purees that have been unstretched, stretched to a medium degree, and stretched to a maximum degree after drying. Fig. Bi, Bii and Biii, fig. Ci, Cii and Ciii and fig. Di, Dii and Diii are corresponding photomicrographs of other purees, namely pears, applesauce and vanilla puddings. The photomicrographs designated by (i) represent non-stretched dehydrated products, and photomicrographs designated by (ii) and (iii) represent the medium-stretched and maximally-stretched dehydrated purées according to the invention. Fig. 1 is a schematic diagram showing an apparatus by means of which the puree is stretched and the product blanket is removed and fluffed. Fig. 2 is a view, seen from above, of that in fig. 1 shown apparatus. Fig. 3 shows from the side what in fig. 1 shown apparatus. Fig. 4 is a schematic ground plan of transport and fluffing means and shows the means for recirculating dehumidified cooled air in counter-flow to the flow of the stretched products to the fluffing device, and fig. 5 is an enlarged view with cut away parts of film breaking agents shown in fig. 1.

Figs Ai, Bi, Ci and Di show control samples removed from the stripping blades of a conventional atmospheric double-drum dryer by means of a conventional take-off roll, where the product is wound loosely over a take-off roll on which a blanket of product is cooled as it is drawn off the friction between the product and the roller surface. These specimens have a corrugated crayfish-like appearance, and when viewed through a strong microscope with greater magnification than 200 diameter, one sees that they comprise thick balled-up agglomerates on the surface of the crayfish-like flakes, arranged in furrows that have a unidirectional organized direction. It is assumed that these agglomerates consist of soluble solids from puree cells in the case of fruits, see fig. Ai, Bl and Ci. It can be seen that the support structure for these furrows contains numerous fibers and fibrils, apparently derived from the plant's pith fibers and cell walls. When it comes to

vaniij epudding (fig. Di) this ground layer contains a few starch granules with polarized properties that resemble raw gelatinized starch and one could not observe any cellular character or other distinguishing features.

Figs Aii, Bii, Cii and Dii show medium-stretched samples of pears, apple-apricots, applesauce and vanilla pudding purées which have been stretched or elongated in the above-mentioned manner by means of the apparatus described later. These "medium-stretch" samples show a clear dilution of the sample. When viewed through a strong microscope, one sees that surface agglomerates are scattered in clearly visible clumps that lie on a translucent substrate layer, and which, in the case of fruit purées, contain numerous fibers and fibrils apparently from plant pith remains and cell walls. These fibers and cell remains show the effects of the severe distortion and breakage caused by the mechanical treatment. As seen on photomicrographs, the base layer is beginning to show signs of ice breaking, and some open areas show that the breaking has taken place. The increase in surface areas between the product series (i) and the medium-stretched samples of series (ii) is large and very important for the formation of instantly rehydratable purées. With regard to photomicrographs of series (iii), the maximally stretched samples of purées show more clearly the effect that can be seen in the medium stretched samples. It will be understood that the preferred strained purees according to the invention are the maximally strained products, but for certain products the medium strained sample will be usable, depending on the raw material and the composition of the entire puree, e.g. applesauce, in contrast to pears and peaches, will require a higher degree of stretching of the species represented by type (iii). When you look again under a strong microscope, you see that the ground layer or the continuous phase is translucent and that the cell remains are broken and shredded to a greater extent. Fig. Aiii, Biii and Ciii show that fractures and tearing are numerous and large. Under a strong microscope you can see that the agglomerates on the surface of the product are more spread out and that they are smaller in the case of series (iii) than in the case of series (ii).

The above description of products of series (ii) and. (iii) shows tremendous pulling, tearing and shearing of the sub-stratum with a resultant movement of the cell contents to the surface of the supporting basal layer composed of cell debris (in the case of fruit). Although biochemical and biophysical forces presumably acted during the stretching process and caused the greater rehydratability of products of series (ii) and (iii), compared to series (i), they explain physical changes at least in part the achieved improvement of rehydratability, the enormous surface increase and reduction of sheet thickness as well as the movement in a dispersed discontinuous phase of agglomerates of the solid food constituents in a base mass of amorphous carbohydrates and other constituents, which also help to form an ideal rehydratable structure. Although these agglomerates of solid food ingredients may be termed "dissolvable", these products are usually termed rehydratable and suspendable materials. The continuous phase usually comprises sugars or carbohydrates in solid amorphous form as a result of the rapid cooling that takes place during stretching.

The composition of this continuous phase is of course dependent on the raw materials from which the puree is made. Thus, the puree can be composed of finely divided solid fruit components and fruit juices and their mixtures which can be combined with vegetable solids and juices, with solid meat and finely ground vegetable-meat mixtures, if desired, most of which in a concentrated state can be stretched according to the present method.

However, as shown by the composition of fig. Di.Dii and Diii, the puree can consist of other foodstuffs, such as puddings which are rich in starch and sugars and which have a sticky, stretchy, viscous character, to which category belong various spicy puddings such as vanilla, chocolate, orange puddings and the like, as the starch in these agents is formed from potatoes, salep, sago, maize etc., either gelatinized or partially gelatinized. A substantial proportion of the non-aqueous components of the pudding puree will be of a starchy character and origin, and will be gelatinized to a gel-like consistency due to the heat treatment to which the puree is subjected as the solids content of the puree increases on the drum to make the puree film-forming and stretchable.

Typical of the usable thickeners or "modifiers" which have a starchy character but not a starchy origin, and which can be used to make the concentrated puree stretchable, are polysaccharides and cellulose ethers, such as pectin, algin, Irish moss extract , gum arabic, gum acacia, alkali metal salts of carboxymethylcellulose (CMC) and other nonionic ethers of cellulose, ionic ethers of cellulose, such as ethyl cellulose, methylcellulose, methylethylcellulose, hydroxypropylmethylcellulose and hydroxyethylcellulose. The present method also relates to puree mixtures which can be obtained by mixing one or more of the aforementioned gelatinous polysaccharides with proteinaceous substances of animal or vegetable origin, preferably isolated in a gel-forming heat-denaturable state, e.g. with alkali or ethanol extracted soy protein, peanut protein, fish protein and the like.

Products according to the invention can best be used in foodstuffs for young children or as geriatric food, where the digestibility and the advantageous appearance and aroma as well as the resemblance to fresh fruit make the products desirable. The term "fruit" here includes tomatoes, pears, apples, apricots, peaches, prunes, cranberries and similar fruit-like materials. Mixtures of these fruits will also taste good, e.g. apple-apricots, pear-apples, etc.

Products that can be used as foodstuffs or soups for young people can also be produced according to the invention. Thus, concentrated soups of tomatoes, asparagus, beans and the like can be prepared from the cooked pureed vegetables. Many of these vegetables will not possess an inherent elastic character, so that they will not usually have the stretchable character described here. However, many of these materials contain natural pectinous or pectin-like materials, e.g. cooked tomato paste, which are sufficiently elastic in concentrated puree form to be stretched as a film into products having the above-mentioned properties. As regards the materials which do not have sufficient inherent elasticity, modifying agents can be added to the puree before the puree is concentrated to a viscous form, so that films can be stretched from it. For example when pectin or algin is added to a bean puree, a sheet product removed from the drying roller will have sufficient stretchability.

Typical of other materials that can be treated in a similar way are materials that contain a significant amount of fat associated with either meat or milk products, such as milk or butter. In these cases, mixtures of starch, vegetables, fruits, and/or meat with such fat components will give a concentrate that is wiped off from a suitable drying surface, a sticky, elastic character, and the concentrate can be extended into a film with reduced thickness, which will quickly cool. A product resulting from such stretching, e.g. a puree composed of carrots, bacon, celery and rice flour will be stretchable under the above-mentioned conditions and will be instantly reconstituted.

Purées of the foregoing types are best concentrated by using drying equipment which concentrates the product to a solids content whereby the concentrate adheres to the drying surface but can be easily removed, whereby a film of concen-. the funnel can be wiped off and continuously stretched using manual or mechanical means. Typically, one or two chrome-plated atmospheric drum dryers associated with wiper blades that grip the concentrate will be used in combination with appropriate means for uniformly stretching the film or product blanket in a controllable manner. Stretching means are of course a very important feature of the present process. Their construction and location will. be to some extent dependent on the type of drying apparatus used to produce the film processed on the apparatus. The stretching means should be able to exert a continuous tension on the product arriving or being removed from the drying area, and they should also be able to transport the product in the form of a thin film blanket suitable for subsequent treatment, which treatment will usually consist of a dehumidification of the stretched film, preferably by means of chilled air. Preferably, the stretching means should only serve to accelerate the movement of the film relative to a portion of the film. During the performance of such stretching and acceleration, it is advantageous to avoid that the product acquires a highly calendered densified form.

Ideally, such stretching means can comprise a stretching roller which has a friction surface over which the idler wheels are mounted. The necessary degree of stretching requires means which cause a sheet movement corresponding to the peripheral speed of a tension roller or roller, and this effect is achieved by positive contact with the take-off roller or roller of intermediate wheels or intermediate rollers of such a size, number and location that they provides an easy grip contact. Although such intermediate wheels are preferred, other means known to those skilled in the art will provide the same stretching effect, but of course with less tension continuity. The removal roller can be suitably arranged so that it exerts a suction effect on the contact surface of the sheet passing on the roller, which in turn ensures a positive movement of the product in accordance with the peripheral speed of the roller or roller and at the same time causes a withdrawal of both heat and moisture. Such a modification would comprise a roller provided with a series of perforations communicating with a vacuum, so that suction is exerted on the periphery of the roller only by the arc of contact necessary to achieve the desired tension.

Example I.

As shown in fig. 1-4, a preferred embodiment of the invention comprises a pair of counter-rotating chrome-plated drums 20 and 22, with a diameter of 60 cm, which are driven at 1.5 revolutions per my. and which is heated from the inside with steam at an excess pressure of 1.4 kg/cm<2>, each drum having a drying surface of 2.32 m2, and means for wiping, stretching and fluffing are shown at 24, 26 and 28. These wiping, stretching and fluffing means are shown connected with only one drum, e.g. 22, <:>whereas similar means used for the drum '20 are not shown. As shown in fig. 3, a puree is introduced using any means known in the drum drying technique, e.g. shuttle feed to the bit between the drums 20 and 22, where the product is concentrated by about 35 percent by weight, until it has a solids content of more than 85 percent. Generally, the thickness of the dried sheet, as the product passes the bit between the drum and the periphery of the sheet, be dependent on the distance between the drums, on the drum speed, the nature of the mash and the steam pressure in the drums. The operation and setting of the device will be described for

■an applesauce which is processed by boiling, cooling and straining to form a puree having a solids concentration close to 17% by weight and which is introduced into the bite at 26.7° C. The drum distance for applesauce is close to 0.15 — 0.31 mm, preferably 0.25 mm. As the drums rotate, part of the liquid passes through the bite between the drums, forming a thin film with a thickness of 0.25 mm on the drums. This film is carried around on the drying surface of the drum.

and during this time it dries by the heat that develops inside the drum. The moisture content can then be lowered from the char moisture content of approx. 65 percent to a dry moisture content of approx. 15 per cent. The stretchable puree concentrate is formed at a rate of 3 kg/m<2> of the drying surface per hour and is brushed at 24 and passed over a perforated stretching roller 30 with a diameter of 15 cm which is formed from woven wire or expanded metal.

The peripheral speed of the stretching roller is sufficient to obtain the above-mentioned tension in the film. Although it is possible to mechanically connect the tension roller to the rotary drum dryer, or to allow the two to rotate at the same number of revolutions per minute, it is preferable to drive the tension roller independently. The stretching roller may be larger or smaller than the drum drying rollers, but in each case it will rotate at an approximate speed which makes its circumferential speed sufficiently great to give the film the above-mentioned degree of stretching.

In the preferred embodiment, the stretch roller will have a friction or roughened surface which provides friction as the stretchable film passes over it. The roughened surface may be perforated or mesh-shaped, but in the preferred embodiment the surface of the tension roller will comprise sections of expanded metal - ribs wrapped around a support which, if desired, may be perforated. These ribs will preferably lie so that when the roller rotates, the surface edges of the ribs will be directed in the direction of rotation, thereby achieving a fixed and positive tension effect on the film which is placed in contact with the surface of the stretching roller. The stretching roller may also suitably be provided with means which exert a suction effect on the contact surface of the film or sheet passing over the roller, to draw away heat and moisture. Such a modification may comprise a roll which has a plurality of perforations in contact with a central vacuum means, whereby the suction effect is exerted on the periphery of the roll at the contact arc of the film and the stretch roll.

The product sheet is kept in contact with

the roller by means of a series of hard rubber contact wheels 32 which engage the roller 30 at the point shown, and which are pivotally mounted on the machine frame, to grip the product blanket and cause it to move with the tension roller substantially with the circumferential direction of the roller speed. In the case shown, the roller was driven

with approx. 35 revolutions per my. and the resulting blanket of product was stretched to that of fig. Ciii showed degree, as the product was stretched from a thickness at the squeegee blade of approx. 0.1—0.12 cm to a thickness of 0.037—0.05 cm.

It is an essential feature of the invention that the apparatus in the preferred embodiment comprises an interrupted contact-ener tension wheel which preferably consists of a wheel with a number of surfaces which are designed as a single cylindrical wheel or a roller with recessed parts of the surface, or as a plurality of independent non-interconnected and spaced wheels.

In the preferred embodiment, the contact wheels are placed on a single contact line, the total length of the contact wheel surfaces touching the contact line on the tension rollers being from 10 to 50 percent of the length of the line. The distance between these wheels is such that they fall within a small angle of preferably not more than 30°, measured from the surface of the tension roller. Regardless of whether the contact or tension wheel is a simple cylinder with an uninterrupted surface or several separate wheels, the distance between the parts that come into contact with the traveling film field must be such that the sheet is evenly stretched without any local bunching of the material, and that there is evenly tense. It has been found that the preferred length of each of these contact wheels should be approx. 2.5-10 cm. If they have a greater length, they tend to cut the film, and the operation will require a very large number of wheels to stretch the sheet satisfactorily. The surface layer of these wheels preferably consists of a flexible material, such as hard rubber or neoprene, which provides the necessary flexibility and a sufficient coefficient of friction.

The blanket of product falls into a cooled conveyor and fluffing means 28. The means 28 comprises an upwardly inclined screw conveyor 34 mounted for rotation within an insulated tube 36, and driven by a variable speed motor through a gear 38 by means not shown . The blanket of the stretched product is deposited in the tube 36 through an opening 40 of a sufficient size to accommodate the blanket of product. Mounted above the opening 40 is a filling funnel and switch assembly 42. As shown in fig. 5, this hopper and switch assembly consists of a hood provided with an elongated slot 46 which is placed in the hood to receive the product blanket through the slot, with guide springs or wires 48 which serve to introduce the sheet in a substantially flat condition under a series of switch arms or fingers 52, fixedly mounted on the shaft 54 which is rotatably driven and supported.

Recycled and dehumidified cold air flows upwards in the hood and will thereby cool the product that passes through the slot 46. The cooled product is broken by rotating arms 52, passes under guide springs or threads 48, flows over openings 56 and 58 arranged at the lateral ends of the hood to allow cold air to escape under pressure from the hood, instead of through the slot 46, which would cause difficulty in maintaining product flow from the draw roll through the slot 46 to the guide wires.

Broken product that passes through the switch assembly is led through the inlet opening 40 in the path of the rotating wings of the screw 34, and is led upwards along the sloping pipe 36. In connection with the ends of the pipe 36 is an inlet opening for cold air 60, and an outlet opening for cold air 62, by means of which cold air circulates in countercurrent to the product flow by means of the schematics in fig. 4 showed funds. Spent product transported past the inlet opening 60 falls in cascades from the upper end of the pipe 36 into the path of the rotating vanes 64 which are driven by suitable means not shown through the transfer 66, the vane 64 being located within the saturation funnel 68 which forms a circumferential grid corresponding to to the path of movement of the free edges of the vane.

As shown in fig. 4, the preferred cooling air system comprises an air separator, preferably of the cyclone type 70, a silica gel air dryer 72, a series of indirect heat exchange units of the cooling coil type 74, an electric heating unit 76 and a ventilator 70 which recirculates the cooled dehumidified air countercurrently to the material: as passes from the drum dryer to the fluffer. The silica gel dryer is of conventional construction, and although silica gel is mentioned as an absorbent material, any absorbent material may be used during the operation of the dryer. Cooling units 74 cool the partially dehumidified air in many cases to temperatures below freezing, thereby condensing the remaining moisture that has not been removed by means of the inorganic absorption material in the dryer. After the moisture in the cooling unit has been removed, the substantially dehumidified air is heated again in the heating unit, denoted by 76, where by a gradual heating and expansion of the air volume, the relative ability of the air to absorb larger amounts of moisture is significantly increased. The thus dehumidified air, which is now not only dry but due to the partial reheating also hydrophilic, is recirculated by means of the blower fan 78 through the system in countercurrent contact with the product particles.

Example II.

According to a specific example for a method using the apparatus according to the invention, a pear puree (to which 3% by weight of tapioca starch had been added) with a moisture content of 86-88 percent is introduced into a mass of pear puree which was in the bite of a double drum dryer. The clearance between the drums was 0.175 — 0.2 mm. The rollers 20 and 22 of the dryer had a diameter of 60 cm and each of them had an effective heating surface (chrome-plated) of approx. 2.3 m<2>.

Steam was introduced into the interior of the drums with an overpressure of 1.4 kg/cm 2 , and the drums were rotated at 0.8 revolutions per revolution. my. The puree formed a film on the drum and as the hot drum rotated the film was dehydrated to 2.5% - 5% moisture. After passing approximately 225° of the drum surface, the material film was removed from the drum by means of a wiping blade 24 which was arranged substantially tangentially to the surface of the drum. The removed film passed substantially horizontally over a short distance to the stretching roll. During the short passage time it was only slightly cooled and it was stretchable or plastic.

The coated film was passed over a stretching roller 30, with a diameter of 15 cm, and provided with a perforated surface formed of expanded metal. The tension roller rotated at 1.33 revolutions per my. and the film sheet of the pear puree was stretched as it passed over the roller. A contact wheel ul 32 pressed lightly on the film as it passed over the tension roller 30 and ensured a positive and even tension.

The pear puree film had a sheet thickness of 0.125 - 0.175 mm (unit weight 70 g per m<2>) and was characterized by a discontinuous perforated surface. The thus stretched film passed downwards into the stretch roller hopper 42 which contained breaker arms or fingers 52 firmly mounted on the shaft 54 and which broke the film into smaller pieces which then passed in an insulated pipe 36 containing a screw conveyor 34. Here the dried mash came into contact with dry air flowing downward through the screw conveyor as the pieces moved upward through it under the action of the screw conveyor. The temperature of air in the conveyor was -r- 8° C and the air temperature out of the conveyor was 3° C.

The material left the screw conveyor at its upper end and passed into the threshing apparatus comprising rotating vanes 64 (driven by suitable means not shown) which lightly pressed pear puree pieces through holes in a screen to obtain a product of the desired size.

The dehydrated puree-shaped product obtained by means of the device according to the invention is characterized by its essentially "momentary" — up to 5 seconds — rehydration in contact with a liquid to give the desired puree.

Example III.

In another example, 450 g of tomato puree is brought into contact with the surface of counter-rotating drums 20 and 22, so that the puree flows to the bite between the drums operated at a drum steam pressure of 1.4 kg/cm and a drum speed of 0.8 rev. per my. The tomato puree is concentrated by evaporation until the solids content is over 85 per cent, preferably approx. 90 per cent. The thickness of the sheet that is dried on the surface of drying drums will depend on the gap or distance in the bite between the drums where the puree is deposited on the surface of the drums, on the speed of the drum, the steam pressure in the drum and the nature of the dried puree. In the case of tomato puree, the sheet thickness on the drum surface before stretching is from 10-19 thousandths of a 1 cm. After the removal by means of the wiping blade and the passage between the stretching roller 30 and the contact wheels 32, the thickness of the product will be reduced to 6.2-8.5 thousandths of a cm, and the moisture content to approx. 4 percent. The distance between the drums used during the processing of the tomato puree is preferably 25 thousandths of a cm, but it can be as low as 17 thousandths of a cm, and still give a usable product.

The partially dried sheet of tomato puree is removed from the drum by wiping, passed over a tension roll 30 of woven wire mesh with a diameter of 15 cm, and held on this roll by means of contact rollers 32 with a diameter of 10 cm. The speed of the stretching roller is approx. 1.25 revolutions per my. The sheet of the partially moist product is held against the surface of the stretching roller by means of 8 spaced hard rubber contact wheels which grip the product tissue and press it downwards to increase the tension and thereby partially break the sheet. It is noted that when the product sheet is removed from the drum with the help of an eraser blade, it folds up and exerts a refraction effect in the system.

The stretched product is then passed through the cooling fluffing apparatus described in the preceding examples. The cooled and fluffy product, formed by the apparatus and by means of the procedure, is dehydrated to a stable moisture content of approx. 2 percent and has a free-flowing character and the ability to quickly rehydrate with good aroma properties.

The refined and cooled product formed by the device is dehydrated to a stable moisture content of approx. 2 percent and has the fresh aroma and color of the fruits from which the puree is obtained. Due to the new stretching method, the continuous film of the concentrated product does not need to be dehydrated or exposed to temperatures at which the flavor and color will be lost during storage. When the spoiled product is stored at -17.8° C it will retain its instantaneous rehydration properties for a long time despite the presence of significant amounts of sugars and the otherwise hygroscopic nature of the puree, which causes the product to ball up during storage. Thus, although for many products it is advantageous to mix powdered sugar with the fluffy puree, the product can also be composed of large amounts of sugar, which is higher than the amount naturally present, and which amounts to approx. 30 percent by weight of the fibers.

Although the benefit of the instant rehydration and the desired flavor and color will be retained by most products when stored under refrigeration, many products will retain their instant rehydration character and they will not lose any flavor and color during storage. Typical of these products is tomato puree which does not have to be stored under refrigeration, but which will nevertheless quickly rehydrate, i.e. in less than 3 minutes, and obtain a final viscosity that is higher than the viscosity of tomato purees that have been dehydrated using other processes to a stable moisture content. Although products according to the present invention can most advantageously be used for the production of chilled purées,

the invention is not limited to these products, as products other than tomatoes will also instantly rehydrate and can be well stored without refrigeration.

Claims (21)

1. Process for the production of a dried puree with improved rehydration properties, where a puree containing finely divided water-soluble and water-insoluble solids of a foodstuff is concentrated to a state that is stretched bar at a moisture level not greater than 15 per cent, preferably less than 12 per cent, and a film of said concentrated puree is produced in which said water-insoluble solid nutrient particles are suspended in a molten carrier medium, characterized in that said film is stretched under tension to a sufficient extent to distribute the water-insoluble solids of the food randomly, thinly and separated as a discontinuous phase in a continuous phase of water-soluble solids without breaking the continuity of the film. 2. Method as stated in claim 1, characterized in that the stretching of said film under tension is carried out in such a way that the distribution of said water-insoluble solids in said continuous phase is accompanied by the formation of many small cracks in the film, but without the continuity of said film breaks. 3. Method as stated in claim 1 or 2, where said film after its formation has a thickness of less than 1.25 mm and greater than 0.125 mm, characterized in that the film is then stretched under atmospheric conditions and, if desired, the stretched film is exposed to a drying atmosphere to further reduce its moisture content before subsequent breaking up into flakes. 4. Method as stated in one of claims 1-3, characterized in that the material film is cooled to a brittle state. 5. Method as stated in one of claims 1-4, characterized in that after said film of concentrated puree has been prepared and peeled off in a hot state, it is stretched under tension to a thickness of 0.38 to 0.51 mm, whereby the water-insoluble solid food particles are randomly, thinly and separately dispersed as a discontinuous phase in a continuous phase of water-soluble solids. 6. Method as stated in claim 5, characterized in that the stretched puree film is cooled to a temperature substantially below 21° C, and broken up into flakes. 7. Method as stated in claim 6, characterized in that the film breaks up into flakes in the presence of dry air at a temperature lower than — 1° C. 8. Apparatus for carrying out the method as stated in claim 1, comprising a rotating drum (20, 22) on which a film of the puree material can be deposited, a supply device for liquid material for depositing said material film on the said rotating drum (20, 22), a drum surface heater for heating said rotating drum (20, 22), whereby the deposited film can be heated and dried to a stretchable state, a scraper blade (24) lying against the outer surface of said drum and which removes said film from the drum as a continuous film, characterized by a stretching roller (30) serving to subject said removed continuous film to tension substantially beyond that which is necessary you to prevent agglomeration during said removal and large enough to stretch the film, and further large enough to induce random distribution of discontinuous surface defects and openings or voids in the film, and less than the breaking strength of the film, and an interrupted draw wheel or several distinct draw wheels ( 32) arranged to rest against said material film, as it passes over said stretching roller (30), and which maintains a positive tension or stretch during removal of the film and stretches it while it is in a stretchable state. 9. Apparatus as in claim 8, characterized in that said stretching roller (30) is a cylinder mounted close to and parallel to said rotating drum (20, 22) and whose periphery is designed to provide a friction-giving surface, the upper part of said cylinder's periphery lies in the same horizontal plane as said scraper blade (24), and which is positively driven in relation to said rotating drum (20, 22) to stretch said film between said rotating drum (20, 22) and the cylinder, as the part of said film which is located between said rotating drum (20, 22) and said cylinder is essentially held horizontally. 10. Apparatus as stated in claim 8, characterized in that said interrupted traction wheel f32V has several surfaces. 11. Apparatus as stated in claim 10, characterized in that said interrupted traction wheel (32) consists of a cylindrical wheel where parts of the cylindrical surface have been cut away. 12. Apparatus as stated in claim 8, characterized in that said interrupted traction wheel (32) consists of a cylindrical wheel with parts of the cylindrical surface cut away, said interrupted traction wheel touching said stretching roller (30) along a single contact line, which line is parallel with the axis in said stretch roller (30). 13. Apparatus as stated in claim 12, characterized in that said interrupted traction wheel (32) touches 10-15 percent of the length of the contact line between said interrupted traction wheel (32) and said stretching roller (30). 14. Apparatus as stated in claim 13, characterized in that said line of contact is parallel to the axis of the stretching roller (30) and is offset along the latter's circumference to 30°—60° from the vertical. 15. Apparatus as stated in claim 8, characterized in that said interrupted traction wheels (32) comprise 4-10 separate traction wheels each having a length of 2.5-10 cm, the total length of all said wheels being 10-50 % of the length of the contact line between the tension roller (30) and the traction wheels. 16. Apparatus as set forth in claim 8, characterized in that said stretching roller (30) is provided with a surface of expanded metal sheet placed with its sharp edges pointing in the direction of rotation of the stretching roller, which helps to subject said removed continuous film to tension substantially above that required to prevent agglomeration during said removal, large enough to stretch the film, large enough to induce random distribution of discontinuous surface defects and voids throughout the film, and less than the tensile strength of the film. 17. Apparatus as stated in any of claims 8 to 16, designed for the production of a flaky puree from a stretched puree film, characterized in that said apparatus also comprises a substantially horizontal line (36) with a material inlet end (40) and a material outlet end (68), a screw conveyor (34) inside said conduit for transporting said material from said inlet end of said conduit to said outlet end of said conduit, an inlet (60) for introducing conditioned gas to one end of said conduit , an outlet (62) for extracting gas from the other end of said line, said gas during the passage through said line coming into contact with said material therein, and a material receiver (69) for collecting said material at the outlet end of said wire. 18. Apparatus as stated in claim 17, characterized in that said conditioning equipment comprises a gas dryer (72). 19. Apparatus as stated in claim 18, characterized in that said conditioning equipment comprises a gas cooler (74). 20. Apparatus as stated in any of claims 8 to 16, designed for the production of a cooled, flake-shaped product from a dried and stretched puree film, characterized in that said apparatus also comprises a sloping line (36) with a material inlet end (40) and a material outlet end (68), a screw conveyor (34) inside said conduit which occupies less than its overall cross-section to convey said material from the inlet end to the outlet end in said conduit and to stir said material while it is conveyed from the inlet end of said line to its outlet end, an inlet (60) for the supply of cooled air to one end of said line, said air during passage through said line coming into contact with said material traveling through it, whereby said material substantially simultaneously cooled and transferred to flakes, and a material receiver (69) for collecting said cooled flaky material. 21. Apparatus as stated in any of the claims 8 to 20, arranged for the production of a flaked product from a downwardly running band of dried material, characterized in that it also comprises a switch assembly (42) for breaking up the band of material that is supplied to it.