WO2018173090A1 - Process and devices for producing hydrogel membranes filled with a liquid - Google Patents

Abstract

The described process allows to obtain rapidly, i.e. the order of a few tens of seconds, calcium alginate membranes enclosing inside them spherical portions of food liquids of any kind and composition, including acidic liquids, or alcoholic liquids of any ABV grade, without altering its physical, chemical and organoleptic qualities. The invention also relates to a set of instruments and devices specifically developed for carrying out the procedure, either in a totally manual mode or in an automatic or semi-automatic mode, such as a positive displacement liquid exchange device with positive displacement pumps (3a, 4a).

Description

PROCESS AND DEVICES FOR PRODUCING HYDROGEL MEMBRANES

FILLED WITH A LIQUID

DESCRIPTION

Field of the invention

The present invention concerns a process for the production of hydrogel membranes filled with a liquid, as well as the devices for implementing such process. More particularly, the invention relates to a procedure, and the relative instrumentation, which allows to obtain in rapid times, that is, the order of a few tens of seconds, spherical membranes of edible or not edible gels, which enclose internally liquids of any kind and composition, including acidic liquids or alcoholic liquids of any alcohol content, without altering the physical, chemical and organoleptic properties of said liquids.

Background of the invention

As is known, spherification is a technique created in the frame of the avant-garde cuisine known as "molecular cuisine", which allows to encapsulate substantially liquid foods, such as juices, syrups or smoothies, in spheres or pearls with a solid external structure and liquid core, concentrating the flavors in small globules that burst into the mouth similar to caviar.

The technique was brought to popularity around 2003 by the Catalan chef Ferran Adria, who proposed in his well-known restaurant El Bulli dishes based on a variety of pearls and spheroids obtained from the elaboration of edible products, with original combinations of flavors. The technique is still used for the production of particularly eye-catching food preparations.

The formation of spherical structures is obtained with the help of a gelling agent, in particular, sodium alginate, and a second agent, generally a calcium salt such as calcium lactate or calcium chloride, which is able to exchange cations with the gelling agent. Sodium alginate is a polymer whose monomers consist of carbohydrates of various types, which share the

MB//A 17942 characteristic of having at least one carboxyl functional group bound to the monomeric ring. In sodium alginate the acid groups are salified with sodium, as shown in the followin structural formula.

Sodium alginate has a high solubility in water and tends to form more or less viscous aqueus solutions as the concentration of alginate changes. Sodium alginate is therefore used in the food industry as a gelling agent, i.e. as an additive which increases the viscosity of the preparation. It is also used in the pharmaceutical industry as a gastroprotector, thanks to its ability to form a film on the stomach walls, which makes up for the lack of the natural protective film.

An important feature of alginate is its great affinity for calcium, in its form of divalent cation. The latter is chelated by carboxyl (and hydroxyl) groups of different alginate chains, as schematized in the following formula. For this reason when a salt containing calcium ions is added to a sodium alginate solution, the calcium ions are exchanged with sodium ions to give a structure that takes the following form:

Such structure becomes progressively more compact than the previous one, due to the chelating action of the carboxylate groups on the Ca²⁺ ion, and there is a progressive stiffening of the structure.

In other words, as the same Adria then explained in the scientific insights on his work (H. Fu, Y. Liu, F. Adria, X. Shao, W. Cai, C. Chipot, From Material Science to Avant-Garde Cuisine. The Art of Shaping Liquids into Spheres, J. Phys. Chem. B, 2014, 1 18(40), 1 1747-1 1756), the gelling agent has the characteristic of forming a gel when it comes into contact with the calcium ions, thus forming a more compact structure, which the authors themselves called "egg box" spatial arrangement, schematically represented below.

The result of this cationic exchange is that the sodium alginate solution, initially liquid and slightly viscous, acquires a semi-solid and gelatinous consistency.

Accordingly, a given volume of sodium alginate solution dipped (e.g., poured drop-wise) in a solution containing calcium ions forms on its surface a gelatinous membrane of calcium alginate, more or less solid and elastic according to the concentration of sodium alginate and calcium ions in the two solutions. Therefore, when it is desired to enclose a (more or less viscous) liquid preparation in alginate spheres or beads, sodium alginate is mixed with the preparation to be spherified, and then the mixture thus obtained is put directly in contact with an aqueous solution of a calcium salt, for example, calcium chloride.

It should be noted that spherification does not start until the time when sodium alginate or other similar gelling substance (such as carrageenans (or carrageenins), gellan gum, agar-agar, locust bean gum, tragacanth, gum arabic, pectin and other polysaccharides which may have similar behavior) do not come into contact with the ion-exchange agent, or is not cooled below a certain temperature, depending on the type of gelling agent. From that moment on, a gel membrane forms at the interface between the drop of mixture to be spherified and the external bath. If the formed sphere is not separated from the bath, it continues to thicken gradually towards the interior, leaving the remaining encapsulated liquid in the core, until the process is complete and the liquid core has disappeared.

Using the instrumentation and techniques of molecular gastronomy, procedures have also been developed for the creation of cocktails and composite drinks that use spherification, as well as other procedures typical of molecular gastronomy. The relative sector is currently known as molecular mixology.

The spherification technique presents, as it may be deduced from the foregoing, various limitations due to the very nature of sodium alginate.

First of all, the spherification of excessively acidic substances is not possible. The carboxylic groups of alginic acid are weakly acidic, and the presence of other acids, even of weak strength, causes their protonation, which prevents the formation of complexes with calcium. When the pH drops to 1 .5, a milky precipitate, which does not contribute to the formation of the membrane, forms on the bottom of the bath. However, sodium alginate has a fair buffering power, and therefore by adding massive doses of alginate to an acidic solution its spherification becomes possible, but to the detriment of the acidity and of the preservation of the organoleptic properties of the starting solution. Alternatively, an acidity regulator can be added to the mixture, but still to the detriment of the original flavor.

In addition, many acidic drinks such as fruit juices or Coca-Cola also contain other chemical species, such as pectins or phosphates, which probably compete in the complexation of the calcium ions by alginate, thus making it impossible to obtain the membrane formation even with pH values higher than 1 .5.

Furthermore, the spherification of alcoholic solutions is currently possible up to a maximum alchol content of about 25 volume percent (ABV). The mixing of sodium alginate in solutions beyond this limit becomes slow and difficult to obtain and, where successful, would lead to an excessive increase in viscosity and difficulty in the formation of the membrane, which would become extremely fragile.

Since the procedures for making alginate spheres involve mixing alginate in the liquid or in the beverage to be spherified and the permanence of alginate inside the formed sphere, it is inevitable that there is a reduction in sapidity of the initial product, more or less less noticeable depending on the type of product.

· Finally, as anticipated, alginate spheres are not stable over time. Once the cation exchange has started, the calcium ions of the membrane spread towards the internal volume, which slowly leads to total gelation. The speed at which this occurs varies depending on the concentrations of the two solutions, on the temperature and the radius of the alginate sphere. This defect precludes the preventive preparation of the spheres and their storage for use in many preparations involving slow or delayed consumption.

For the reasons mentioned above, the spherification has been performed alternatively in a variant, known as reverse spherification.

In reverse spherification, a calcium salt (usually calcium lactate or calcium gluconate) is brought into solution directly into the liquid to be spherified, and subsequently this mixture is brought into contact with a sodium alginate solution. In this case, the two reagents of the classical spherification process are topological^ inverted, and the reaction between the alginate and the calcium ions takes place at the interface between the two liquids, but continues towards the outside of the formed sphere. Thanks to the presence of the calcium salt (which is tasteless) inside the sphere instead of alginate, the liquid contained within the sphere does not progressively change in flavor and consistency.

With reverse spherification it is therefore possible to produce spherified preparations of substances which are also strongly alcoholic. These preparations remain relatively stable over time.

While allowing to overcome some of the drawbacks arising in the classical spherification, however, reverse spherification is not free from some problems, the most notable of which being the following ones.

Times required for the express preparation are longer, as the spheres have to rest in the alginate bath for several minutes. The preparation is more difficult to handle, given the difference in viscosity between the liquid to be spherifed, which remains fluid, and the alginate bath, which is viscous. Freezing the liquid may help, but in the case of high alcohol content this requires expensive tools and materials, such as liquid nitrogen or ultra-freezers. Alternatively, the liquid product can be mixed with a thickener, but at the expense of flavor and organoleptic properties.

As in the classic spherification, also in reverse spherification the use of acidic substances is not allowed, unless the strength is buffered with an acidity regulator.

Finally, it should be noted that the spherified product contains moderate amounts of added calcium, and especially in the use of such products as a beverage risks for sensitive individuals cannot be excluded.

Some of the problems mentioned above have been addressed, for instance, in the European patent application EP2537420A1 (Biogades Food Tech. S.L.), which describes a method for the stabilization of food spheres with alcohol content. Such method comprises a first step of forming the spheres by reverse spherification, i.e. the preparation of a solution of the alcoholic liquid, a thickening agent (for example, xanthan gum) and calcium gluconolactate (which must be left to rest preferably for 24 hours), the preparation of a second solution of water and sodium alginate, and the consequent formation of the spheres by introduction of portions of the first solution in the second solution. Subsequently, the spheres are extracted from the bath and poured into a water bath to interrupt the gelling process, left to dry and then poured into a further "stabilizing solution" bath, consisting of a liquid with the same composition as the spherified liquid, but with a lower concentration of thickening agent. Once the internal and external concentrations of the thickener have equilibrated, the spheres can be kept soaked in the stabilizing solution for long periods without losing their characteristics.

It is evident that such a complicate methodology arises from the need to have spheres with an alcohol content that remain stable over time, but in any case the one above is not an "express" production, to be carried out directly il the place where the product is consumed.

The problem of the massive and express production of spherified liquids, both with the classical spherification technique and with the reverse spherification technique, is addressed in the international patent application WO2014/159678 (Lemniscate Innovations LLC), which describes an apparatus and a method for producing edible beads such as those of molecular cuisine or molecular mixology. However, the document does not focus on the chemical characteristics that raw materials must have in order to be processed with the classical or reverse spherification, but only concerns the problem of automation of the express sphere production procedure.

The apparatus described, therefore, is able to process only the products that are notoriously processable manually with classical or reverse spherification, and does not allow to obtain, for example, spheres of products with a high alcohol content, or of particularly acid products, like many fruit juices.

In the light of the described state of the art, therefore, it is evident that both in classical and in reverse spherification it is necessary to add to the liquid to be spherified sodium alginate, calcium salts, acidity regulators, thickeners and water, part of which, to a more or less critical extent depending on the case, remains in the spherified product, thus altering the physical, chemical and organoleptic properties of the product itself and making it less palatable. Moreover, in both techniques, the long and complex steps of the manufacturing process do not lend themselves to a rapid and massive express production for use directly in the production site.

It is therefore evident that there is a need to have systems capable of performing the preparation, expressly and directly to the public, and in a simple and fast way, of edible gel membranes containing liquids of any kind, including acidic or strongly alcoholic liquids, not modified or altered in consistency or taste. Summary of the invention

In the frame of the studies which led to the present invention, starting from the classical spherification technique with sodium alginate, it has been found that it is possible to produce spherical envelopes by means of a basic preparation composed of water, sodium alginate and possibly, but not necessarily, ethanol in predetermined proportions, which is placed in contact, in volumetrically defined portions, with a calcium salt solution to determine, at the interface, the formation of a calcium alginate membrane. In this process the obtained liquid spheres are rapidly emptied of their content, which is exchanged with a desired liquid content, of any type, thanks to a specially designed positive displacement liquid exchange device.

This procedure was designed to allow the formation of the alginate sphere superficial membrane in its optimal conditions and to replace its internal volume with a liquid that would not have allowed formation of the alginate sphere.

Further ingredients in addition to water, sodium alginate and possibly ethanol may be added to the basic preparation, which will also be referred to below as "Solution A", both to vary the mechanical properties of the membrane which will be obtained at the end of the procedure, and to aromatize the membrane itself with particular flavors, as long as the relative proportions of water and alginate do not vary excessively.

It has indeed been found, according to the present invention, that the mechanical properties of the membrane may change in the presence of excipients in Solution A. For example, the presence of mixtures of surfactant molecules such as soy lecithin, or fatty substances such as cocoa butter, olive oil or other edible fats make the membrane more elastic and delicate in its use, which in turn makes its consumption in gastronomy more pleasant. This effect can also be obtained with the use of polysaccharides not interacting with calcium such as agar, xanthan gum, guar gum, etc..

Furthermore, aromatized membranes can be obtained by adding syrups or aromatic powders or alcoholic liquids to Solution A. In this way it is possible to create many combinations of flavors by combining different ingredients in the membrane, and then it is possible to decide which liquid to use for the internal filling. It should be noted that if it is desired to aromatize the membrane with an alcoholic beverage, the amount of alcoholic beverage to be added to Solution A will have to change according to the alcohol content of the same, in order to maintain the total alcohol content of Solution A at about 20% in volume. Therefore, in these cases the optimal amount to be mixed should be calculated according to what is described below.

The solution based on calcium salts, in which the predetermined volume of the base preparation must be immersed, according to the procedure of the invention, in order to produce the calcium alginate membrane (which will also be referred to hereafter as "Solution B"), consists of an aqueous solution of calcium salts, preferably chloride or lactate. In the case where ethanol is also present in Solution A, Solution B will preferably have an alcoholic level similar to that of Solution A, so as to keep the ethanol concentrations in equilibrium during membrane formation.

With the procedure described, and making use of a hemispherical strainer which is part of the instrumentation specifically designed for the implementation of the present invention, it is possible to obtain spheres that are always the same and are rapidly prepared. Each of these spheres is then processed with a positive displacement liquid exchange device realized within the invention, which drills the sphere in a controlled manner and replaces the still fluid sodium alginate solution inside the membrane with a liquid of any type, carrying out a suction and an injection phase of the desired content in rapid succession.

After filling the sphere, in the fourth phase of the procedure the sphere is separated from the liquid exchanger device and immersed again, for a few seconds, in the calcium salt Solution B to seal the hole made by the device, and finally it is rinsed for a few seconds in water to remove calcium salt residues left on the membrane surface.

By providing and making possible the substitution of the alginate present inside the closed membrane already formed with any liquid content, the proposed procedure allows to solve in a simple and cheap way the problem of realizing hydrogel membranes stable and suitable for any use, achievable in extremely short times, without any physico-chemical alteration of the content and with little manipulation, and therefore lends itself optimally to an express production, also for food products.

The proposed procedure can be carried out in the same manner by using another gelling agent instead of calcium alginate, which agent is capable of giving gelation by ion exchange, and also, with minimal variations, using agents gelling upon temperature variation, such as agar. In the first case Solution A will have to contain a salt of the gelling agent with a counter-ion with which no gel is formed and Solution B will have to contain an ion with which the gel is formed, while in the second case Solution A will have to be at a temperature at which the substance employed does not gel and Solution B will have to be maintained at a temperature at which the gel is formed, and the operations of the third and fourth steps will have to be carried out at least at that temperature, as explained later on in the examples.

Brief description of the figures

The specific features of the invention, as well as the advantages of the same, will be more evident with reference to the accompanying figures, in which:

Figure 1a shows an orthogonal side elevation view of a strainer suitable for the execution of the second, third and fourth phases of a first embodiment of the present invention which employs a manual positive displacement liquid exchange device;

Figure 1 b shows an orthogonal side elevation view of a strainer suitable for the execution of the second, third and fourth phases of a second embodiment of the invention which employs a semiautomatic positive displacement liquid exchange device;

Figures 2a-2d schematically show the sequence of operations that are carried out in the second step of the process according to the invention, using for example the strainer of Figure 1 a, as well as the structure of the sphere thus obtained; Figures 3a-3d and 4a-4d schematically show the sequences of operations that are carried out in the third and fourth steps of the process according to the invention, as well as the structure of the sphere thus obtained, using for example the strainer of Figure 1 a and the manual positive displacement liquid exchange device, a portion of which is shown schematically, the procedure which makes use of the strainer of Figure 1 b and of the automatic or semiautomatic positive displacement liquid exchange device being equivalent;

Figure 5 shows an overall perspective view of a manual positive displacement liquid exchange device for the implementation of the third phase of the first embodiment of the process according to the invention;

Figures 6a-6d show the elevational views, front, rear, plan and side respectively, of the manual liquid volume exchange device of Figure 5;

Figures 7a-7d show the perspective views of four alternative needle types to be mounted in the center of the receiving chamber of the manual positive displacement liquid exchange device of Figure 5 or in a corresponding position in the semiautomatic positive displacement liquid exchange device of Figure 9 which follows;

Figure 8 schematically shows the connection of any one of the needles of Figures 7a-7d to the respective suction and liquid intake ducts of the positive displacement liquid exchange devices of Figure 5 and of the following Figure 9;

Figure 9 shows a perspective view of a positive displacement liquid exchange device for semiautomatic liquids for the execution of the third phase of a second embodiment of the process according to the present invention;

Figure 10 shows a partially exploded front perspective view of some of the components of the positive displacement liquid exchange device of Figure 9;

Figures 11a and 11 b show perspective views, respectively anterior and posterior, of the operating structure of the positive displacement liquid exchange device of Figure 9 without the two pumps;

Figures 12a and 12b show perspective views, respectively anterior and posterior, of the same operative structure of Figure 1 1 with the two positive displacement pumps in place;

Figures 13a and 13b show perspective views, respectively anterior and posterior, of the snap system for the exit of the needle in the positive displacement liquid exchange device of Figure 9;

Figure 14 shows a perspective view of the upper cover of the positive displacement liquid exchange device of Figure 9 and a side elevational view of the strainer of Figure 1 b in relation to the placement of the latter on the device during the third phase of the second embodiment of the process of the invention.

Detailed description of the invention

The present invention specifically provides a process for the preparation of closed hydrogel membranes containing a liquid, the process comprising the following operations:

1 ) preparing a first aqueous solution of a substance capable of gelling upon ion exchange, or upon temperature variation, and a second aqueous solution of the salt of a ion causes gelation of said substance, or a second solution cooled at least to the gelation temperature of the used substance;

2) introducing a predetermined volume of said first solution into a strainer and immediately immersing said strainer with said first solution in a bath of said second solution, keeping it soaked for a time sufficient to form a hydrogel membrane - using sodium alginate and a calcium chloride solution (preferred technique) the necessary time is between 3 and 10 seconds;

3) recovering the spheroid formed from the bath of step 2 by means of said strainer and exposing it, while contained in said strainer, to perforation by a two-way hollow needle connected to a positive displacement liquid exchange device, thus carrying out:

i) a first phase of aspiration of the liquid contained in the spheroid up to removal of most of it, followed by ii) a second step of introducing a desired liquid as filling of said spheroid, up to complete filling of the membrane, to obtain a sphere;

4) extracting said two-way needle from the membrane sphere containing the filling liquid, said sphere being still contained in said strainer and placing said sphere again in said bath of step 2 for sealing the hole, keeping it immersed for a time sufficient to seal it - when using sodium alginate and a calcium chloride solution (preferred technique) the time required is between 1 and 5 seconds - and finally washing the thus obtained filled sphere with water.

According to a preferred embodiment of the proposed process, the gelling takes place by cation exchange, and preferably said substance of the first aqueous solution is sodium alginate, while the second solution contains a calcium salt, preferably calcium chloride.

In order to have the maximum functionality in the operations of the second, third and fourth phases of the process according to the invention, said strainer is substantially semi-spherical, semi-ovoidal (or semi-ellipsoidal), or in any case it has a concave bottom with a curved surface.

As already noted, said first solution may contain one or more edible or non-edible substances having surfactant action, such as ethanol, soy lecithin, and/or one or more edible fats or oils, such as cocoa butter or oil olive. Such effect can also be obtained with the use of polysaccharides non-interacting with calcium such as agar, xanthan gum, guar gum, etc..

Furthermore, according to some of its variants, the first solution may contain one or more flavoring ingredients selected from aromatic powders or syrups, such as cocoa powder or mint syrup, and alcoholic beverages, such as for instance blue Curagao.

According to some preferred embodiments of the process of this invention, said first solution also contains a portion of ethanol not higher than 25% by volume, and said second solution contains a portion of ethanol substantially equal to the ethanol portion present in said first aqueous solution. Preferably, the first solution contains, based on 1 00 ml, from 1 to 2 g of sodium alginate and from 18 to 25 ml of ethanol. Optionally, the first solution may also contain from 5 to 15 ml of syrup, or from 1 to 5 g of flavoring agent powder, or an amount by volume of alcoholic beverage such as to bring the final alcohol content of said first solution to no more than 25% by volume, the rest being made up of water. In turn, according to the same preferred embodiments, the second solution contains, based on 400 ml, 2-4 g of calcium chloride and from 72 to 100 ml of ethanol.

By the term "positive displacement liquid exchange device" it is meant, according to the present invention, any device or apparatus, whether manual or semi-automatic or completely automated, which allows to transfer a defined volume of liquid out of a delimited space, replacing it with another liquid which occupies substantially the same volume of the extracted liquid. Given the nature of the "container" of the liquid and the potential miscibility of the two liquids to be exchanged in the present invention, the two "emptying" and "filling" operations must be carried out consecutively and in rapid sequence.

In a first variant thereof, the third phase (emptying and filling) of the invention process is carried out using a manual positive displacement liquid exchange device comprising:

- a cup-shaped housing for said strainer containing the spheroid formed in step 2, at the center of which housing said two-way hollow needle element protrudes;

- a plunger liquid suction device connected in fluid communication to a first suction path of said two-way hollow needle element;

- a plunger fluid injection device connected in fluid communication to a second delivery path of said two-way hollow needle element;

and in which, after having housed the strainer with said spheroid in said housing, said plunger suction device is manually operated until the membrane of said spheroid is almost completely emptied, and then said plunger injection device is manually actuated until said membrane is filled again, completely, with said desired filling liquid.

In a second variant, the third phase of the process of the invention uses a strainer provided externally, at the bottom, with an annular magnetic element, and is carried out using a semiautomatic positive displacement liquid exchange device comprising:

- a rigid container which encloses the components of the device;

- an annular housing for said strainer containing the spheroid formed in step 2, placed on a top surface of said container, at the center of which there is a hole from which said two-way hollow needle element may emerge, being preferably spring-actuated;

- a fluid aspiration device constituted by a first positive displacement pump, preferably a peristaltic pump;

- a fluid injection device consisting of a second positive displacement pump, preferably peristaltic;

- two tubular connection pipes, respectively from the suction of said first positive displacement pump and from the delivery of said second positive displacement pump, with a first suction way, of said two-way hollow needle element and with a second way, of delivery of said two-way hollow needle element;

- a retractable support device for said two-way hollow needle element, through which said needle element can translate vertically, preferably spring-actuated, between a first retracted position inside said container and a second extended position, in which it emerges from said hole, and in which, after positioning the strainer with said spheroid at said hole with the help of said annular magnetic element which is coupled with a corresponding magnetic element fixed to the upper surface of said container, the snap device is operated manually, effecting the two-way hollow needle element to emerge from said hole, then said first positive displacement pump is manually actuated until said membrane is almost completely emptied, and said second positive displacement pump is actuated until the membrane is completely filled again, with said liquid desired as stuffing. Said snap device is manually brought back into the initial phase by retracting the two-way needle out of the strainer and the obtained sphere.

According to some of its other aspects, the invention also relates to devices specifically designed for the positive displacement liquid exchange, both manual and semi-automatic, defined as above. The devices mentioned are specifically suitable for use in the production of closed hydrogel membranes based on sodium alginate or any ion exchange or gelation hydrogels caused by temperature variation and containing a filling liquid of any kind not causing the destruction of the reticular structure of the membrane.

The present invention will be described in detail below, by way of example, with specific reference to preferable embodiments thereof which use sodium alginate for the production of the membranes. These embodiments are also illustrated in the figures of the attached drawings.

STEP ONE: Preparation of Solutions A and B

Required tools

• Mixer

• Graded containers (in ml)

· Weight scale (specific at least at the tenth of a gram)

Preparation of Solution A- Estimated Time: 5 minutes

For 100 ml:

1 .25 g of sodium alginate is added in solution in 80 ml of water, mixing until completely dissolved; then 20 ml of ethanol is added and mixed until total homogenization.

The concentration of ethanol in the prepared solution is 19 volumes. Although it is possible to form membranes even with a simple sodium alginate aqueous solution, the addition of ethanol gives them a softer and more elastic consistency. Presumably, the effect is due to the lower hydrophilicity of ethanol compared to water, in fact it has a short aliphatic tail capable of forming poor interactions with the alginate chains, but which contributes to "clutter" them by distancing them and making the plot more loose; moreover, through its hydroxyl group it is able to form three hydrogen interactions per molecule, compared to four molecules per molecule formed by water.

Preparation of Solution B - extimated time: 5 munites

For 400 ml:

Solution B has an alcohol concentration of 20 volumes, similar to that of Solution A. This balance serves to maintain the percentage of ethanol in Solution A unchanged during membrane formation.

STEP TWO: Preparation of sphere - schematically shown in Figure 1 (tools) and 2 (Phases)

Extimated time: 10 seconds

Required Tools

• Strainer (shown in Figures 1 a and 1 b)

• Vessel with Solution A

• Vessel with Solution B

As shown in Fig. 2a, a few milliliters (on average 5) of Solution A are placed in a 35 mm diameter semispherical ladle or strainer (1 ), in order to avoid dispersion and to assist spherification. The amount of Solution A fed into the strainer determines the size of the spheres.

The strainer (1 ) is pierced on the surface to allow the Solution B to filter in it and completely wrap the Solution A, as shown in Fig. 2b. The immersion of the strainer (1 ) containing Solution A in Solution B causes the formation of the calcium alginate membrane, which almost instantly assumes a spherical shape, as shown in Figure 2c; this reaction takes on average 5/10 seconds to stabilize.

The sphere obtained, shown in Figure 2d, is therefore made up of a surface calcium alginate membrane and the internal sodium alginate solution remaining in original form since it has not yet come into contact with the calcium ions of the Solution B.

STEP THREE - Processing of the sphere - schematically shown in Figures 3a-3d

Extimated time: 30 seconds manually, 5 seconds automatically

The created sphere undergoes rapid processing by an operator, which uses the positive displacement liquid exchanger (manual or automatic, Fig. 5 and Fig. 9 respectively) described below. This process is used to replace the Solution A of sodium alginate inside the sphere of Fig. 2d with any liquid to be introduced.

The process of processing the spheres obtained from phase two of the process must take place within 10 minutes after their creation, as they, prepared as such, are not stable and are gradually gelling.

As previously described, step three can be performed by means of a manual, semi-automatic or automatic device.

Manual positive displacement exchange device - shown in Figures 5 and 6a-6d

Frame (2): its function is to provide support to the other parts of the instrument, in order to guarantee its mechanical stability during processing. The frame (2) allows the insertion of two 50 ml syringes (3 and 4). The same frame is equipped with extensions (5), always in stainless steel, for an ergonomic grip.

Two 50 ml polypropylene syringes (3, 4) without needles: a syringe (3) is given the task of aspirating the alginate solution from the sphere, to the other syringe (4) has to inject the liquid chosen inside it. The two syringes are designed to be connected to the respective suction (6) and injection (7) silicone tubes through the couplings (8) and the standard Luer threaded connections (9).

Receiving compartment (10) of the sphere: it is a hemispherical compartment (10) with a diameter of 35 mm in polypropylene or stainless steel, in which the sphere is introduced for processing. It has a central hole through which a needle passes (1 1 ).

The sphere is inserted inside the receiving compartment (10) by affixing the strainer (1 ) above it to be pierced by the needle (1 1 ).

The processing therefore consists of two phases: STEP A - Manual Aspiration

By means of the action of the suction syringe plunger (3) the sphere is emptied of the internal solution which, passing through the suction holes, exits the suction path (6). Aspiration proceeds until the internal solution of sodium alginate is almost completely removed.

STEP B - Manual injection

Through the action of the injection syringe plunger (4) the membrane is filled with the previously selected liquid and loaded into the syringe (4). The filling liquid passes into the injection route (7) to the needle (1 1 ). It is preferred to inject a slightly larger volume than the aspirated one, to give a slight turgidity to the finished sphere.

Semiautomatic positive displacement exchange device - shown in Figures 9-14

The semiautomatic positive displacement exchanger is a device with which the spheres are processed in the third step of the process according to the invention in order to replace the internal solution of sodium alginate with a liquid of any type.

The procedure with this instrumentation proves even faster and easier than the manual one.

The operation of the semiautomatic positive displacement liquid exchanger coincides with that of the manual positive displacement liquid exchanger previously described, except that some of the operations that were performed manually take place in this case in semiautomatic mode through the use of positive displacement pumps (3a and 4a in Figures 10 and 12) .

The main differences between the manual and the semi-automatic positive displacement liquid exchange device are the following:

• The receiving compartment (10) is no longer present: in its place a strainer (1 in Fig. 1 b) is used, separated from the device, which hooks onto the device through a magnet (12) placed at the base of the strain (1 a) itself, in correspondence with a housing (10a) located on the upper lid of the device, in the center of which there is a hole from which the needle (1 1 ) can emerge. • The syringes used in the previous embodiment are replaced by two peristaltic positive displacement pumps (3a and 4a), connected to two buttons (13 and 14 in Fig. 9) placed on the lid (15) of the machine, with which they can be activated manually suction and injection procedures. It is also possible to use a third embodiment of the fully automated positive displacement liquid exchange device, in which the timing of the suction and injection phases is controlled by a programmable electronic controller, for example Arduino.

The suction pump (3a in Fig. 10) extracts the alginate from inside the membrane, pouring it out through a special tube (16) into a dedicated container. The injection pump (4a) draws, from a dedicated external container through a special tube (17), the liquid to be inserted in the sphere just emptied.

In processing, the alginate extracted from the membrane is transferred through a tube connected to the side path (18 in Figures 1 1 a, 12a and 13b) of the two-way needle element (1 1 ), while the injection pump (4a) inserts the liquid selected through the vertical path (19 in Figures 1 1 a and 13) of the same two-way needle element (1 1 ).

The processing therefore consists of two phases:

STEP A - Semiautomatic Aspiration

Through the action of the suction pump (3a) the membrane is emptied of the internal solution which, passing through the suction holes of the needle, exits the sphere through the suction path (16). Aspiration proceeds until the internal solution of sodium alginate is almost completely removed.

STEP B - Semiautomatic Injection

Through the action of the injection pump (4a) the membrane is filled with the previously selected liquid and loaded into a suitable external container. The filling liquid passes through the injection route (17) to the needle, through which it fills the sphere. Also in this case it is preferred to inject a slightly larger volume than the aspirated one, to give a slight turgidity to the finished sphere. Needles typology

Needle attack technical description

The two-way needles (1 1 ) can be of different types, and are mounted so as to form a removable body from the rest of the positive displacement liquid exchanger, whether manual or semi-automatic. In this way they can be replaced according to the needs of product realization. The replacement takes place through the connections placed at the ends of the injection and suction path of the chosen needle. The special suction and injection tubes can be inserted by pressure on the needle attachments, being of elastic material, and their elasticity allows a perfect seal during the operations necessary for processing the product.

Single Needle - shown in Figure 7a

This is a stainless steel needle that penetrates inside the receiving compartment (10) (in the case of use on the manual positive displacement liquid exchanger) for 10 mm. Its upper end (20) is closed and rounded to prevent the upper part of the membrane from accidentally drilling during the suction phase.

Further down, about 3 mm from the bottom of the receiving compartment (10) four holes (21 ) are made distributed crosswise around the needle (1 1 ), which constitute access to both the suction and the injection. Their cross arrangement is necessary to obtain a homogeneous aspiration from all sides of the spheroid. The position of the holes (21 ) in relation to the bottom of the receiving compartment (10) is calibrated so that the suction, even if it has to take place from below to guarantee an optimal removal of the sodium alginate solution, leaves a small quantity in the near the needle entry hole to allow the membrane to close at the end of processing.

Moreover, the holes (21 ) are made with an angle of incidence on the surface of the needle (1 1 ) of 45 ° upwards, so that in the injection phase they push the flow of the injected liquid upwards to assist the swelling of the membrane.

Double needle - shown in Figure 7b

This is an asymmetrical double needle in stainless steel. Its shorter part (22) is dedicated to the suction phase and penetrates into the receiving compartment (10) (in the case of use on the manual positive displacement liquid exchanger) for 5 mm. In this part of the needle there is a suction window

(23) about 3 mm from the base of the receiving compartment (10), through which the sodium alginate is aspirated from the sphere. The window is obtained on the whole semi-circumference of the needle (1 1 ) to allow a suction as homogeneous as possible of the liquid contained.

The longest part (24) of the double needle penetrates 10 mm into the receiving compartment (10). Its top is closed and rounded to prevent the upper part of the membrane from accidentally drilling during the suction phase. Near the top there are three holes (25) distributed uniformly along the semi-circumference of the needle, which constitute the access of the injection route. This arrangement of the holes (25) is necessary to obtain an injection which is as homogeneous as possible on all sides of the sphere. The holes (25) are made with an angle of incidence on the surface of the needle of 45 ° degrees upwards, so that in the injection phase they push the flow of the liquid injected upwards to assist the membrane's swelling .

Catheter needle- shown in Figure 7c

This is a redesigned two-way catheter needle re-designed in order to carry out the working process (suction-injection) in the best way. It penetrates inside the receiving compartment (10) (in the case of use on the manual positive displacement liquid exchanger) for 10 mm. The catheter (26) of FEP is of large caliber (G14/G16) and within this the steel needle is replaced with a needle (27) of lower caliber (G20). The difference in diameters thus generates a gap between the inner wall of the catheter (26) and the outer one of the steel needle, which flows into the suction path. On the catheter (26) there are four holes (28) distributed crosswise on the circumference of the catheter itself, which constitute access to the inter-cavity; while the normal hole at the top of the needle is sealed.

The holes (28) are 3 mm away from the bottom of the receiving compartment (10), as the suction, even if it has to take place from below to guarantee an optimal removal of the sodium alginate solution, must nevertheless leave a small amount of sodium alginate near the entrance hole of the catheter needle into the sphere, to allow it to close at the end of processing. The cross-shaped arrangement of the holes (28) is necessary in order to obtain a homogeneous suction on all sides.

The steel needle (27) instead crosses with the top (29) the sealing of the catheter, to inject into the environment of the emptied spheroid the chosen liquid. It is connected to the injection way, besides it is devoid of the usual oblique cut tip, in order to avoid that the upper part of the membrane is perforated during the emptying phase because of its possible reclining on the end of the needle.

Needles in series - shown in Figure 7d

The catheter needle described above presents an important problem: a strong resistance in suction and injection, there is therefore the need to use powerful thrusts and needles with a wider section (14G), which nevertheless leave a large hole in the membrane to such an extent that make it difficult to close. This is due to the simultaneous presence of two needles one inside the other, in which the wall of the internal one subtracts much of the section useful for the passage of liquids.

A system of needles has been realized which keeps the coaxiality composed of two needles with a smaller diameter (18G) than the previous ones (14G, 16G), arranged in series. The plastic catheter is replaced by a steel needle (30a) 18G, which is able to pierce the membrane of the sphere due to its rigidity. The steel needle (30a) is connected to a "T" fitting (31 ) typical of the two-way catheter needles. The lateral pathway (18) (shown also in Figures 1 1 a, 12a and 13b) will be that of aspiration. In the vertical path (19) (shown also in Figures 1 1 a and 13), instead, another needle (30b) 18G is hooked by means of a threaded connection, the end of which ends one millimeter before the needle (30a) previously mentioned begins.

By arranging the needles (30a and 30b) in this way, the sucked liquid proceeds through the first steel needle and flows into the T-piece thanks to the millimeter of space left by the second needle, then flows into the suction pipe towards the pump (3a), from which the suction force comes from. The injected liquid, instead, runs through the tube coming from the injection pump (4a), arrives at the second needle (30b) and, once run across, it flows into the T-piece (31 ), covering that millimeter of space that brings it to the first needle (30a), and ending directly in the alginate membrane.

Thanks to this arrangement of the elements, the resistance opposed by the small section of the needle decreases drastically, as it is efficiently exploited the entire section of the same, which was not previously done as most of the section was occupied by the wall of the internal needle. Suction and injection, therefore, can be conducted at extremely high speeds, and the effort required for suction and injection is greatly reduced.

A disadvantage of the system with needles in series consists in the possibility of contamination of the base of alginate aspirated by the liquids injected in the previous processes. This base can not be reused.

The advantages and disadvantages of each type of needle are listed briefly in the table below.

Single needle

ADVANTAGES DISADVANTAGES

Smaller diameter Greater alginate residue in sphere

Greater ease of implementation Possibility of obstructions due to

reactions between injected liquid and alginate residue in the needle

Necessary use of taps that block the direct flows from the injection tank to the suction tank

It only supports liquids with a density lower than Solution A

Double needle

ADVANTAGES DISADVANTAGES

Minimal possibility of obstructions Asymmetry of aspiration and injection

Relatively simple realization Larger diameter or considerably

slower suction Possibility of tearing the outgoing

membrane

It only supports liquids with a density lower than Solution A

Catheter needle

ADVANTAGES DISADVANTAGES

Minimum alginate residue in Larger diameter (minimum 16G for sphere (maximum exchange the catheter)

efficiency)

Minimal possibility of obstructions It only supports liquids with a density

lower than Solution A

Needle in series

ADVANTAGES DISADVANTAGES

High flow rate Contamination of Solution A removed from spheres with injected liquids

Minimum resistance

Relatively simple realization

Supports all density of liquids as

long as the suction and injection

operation take place quickly

In the case of use on the semi-automatic positive displacement liquid exchanger, the series system of needles (30a and 30b) penetrates and subsequently emerges from the membrane to perform the emptying and filling operations by means of a vertical snap system shown in particular in Figures 13a and 13b. The snap system is regulated by a spring-loaded piston (32) and assisted by ball bearings (33), and is operated by the push-button (34) on the upper cover (15) of the illustrated device.

STEP FOUR: Stabilization and rinsing of the sphere - schematically shown in Figures 4a-4d

Extimated time: 5 seconds

Once the filling has been completed, the formed sphere is removed from the positive displacement liquid exchanger by means of the strainer (1 ) and again immersed in Solution B to seal the needle entrance hole, which closes thanks to the small volume of alginate solution of sodium remained near the hole.

The procedure ends with the rinsing of the sphere, always transported through the strainer (1 ), in water, for the elimination of calcium chloride residues remaining on the membrane surface.

On the stability of the finished product

The spheres worked through the positive displacement liquid exchanger do not undergo modifications over time. The internal volume, no longer constituted by a solution of sodium alginate, can not be continued in gelation. These spheres can be inserted in preparations that foresee a slow consumption, and it is allowed to be stored preferably in the short term (5 hours) and at temperatures close to the freezing threshold of the internal liquid.

The spheres prepared in step two are compatible with filling with moderately acidic liquids. In this regard, leak tests were carried out with different hydrochloric acid solutions, up to a concentration of 1 molar (pH = 0). It is assumed that the acid, coming into contact with alginate chains already complexed with calcium, sees its ability to protonate the carboxyl groups slowed by the compact structure assumed by the gel. It is therefore probable that an initial protonation of the inner surface of the membrane occurs, which however fails to proceed immediately. Currently there are no published scientific studies that confirm this hypothesis.

Freezing can be used to guarantee long-term storage. In the case of non-alcoholic substances this can take place in a normal freezer, whereas in the case of high-graded alcohol, temperatures up to -100 °C may be necessary. It should be noted that frozen membranes are very fragile and sensitive to thermal shock from thawing. Their fragility decreases as the alcohol content of the internal drink increases. EXAMPLES

Below are some variations for the preparation of Solution A referred to STEP ONE.

EXAMPLE 1

Preparation of Solution A flavored with alcoholic beverage

Ingredients:

^• Three cases are possible:

• The alcoholic beverage has an alcohol content of less than 20 volumes: an amount of ethanol must be calculated to bring the final mixture to 20 volumes. The addition of water is not necessary as it is already present in the flavoring drink.

• The alcoholic beverage is already at a volume of 20 volumes, or next to it: this drink can be considered ready for mixing with sodium alginate, avoiding adding ethanol or water to it.

· The alcoholic beverage has a gradation higher than 20 volumes: a quantity of water must be calculated to obtain a final solution of 20 volumes. It is not necessary to add ethanol, as it is already present in the flavoring drink.

Calculation

The amounts of water and ethanol to be added to flavored membrane drinks can be calculated using the equations expressed below to obtain 100 ml of base solution.

Given the following parameters:

B = maximum amount of usable aromatizing drink (ml)

E = 95% volume of food ethanol to be added (ml)

A = volume of water to be added (ml)

G₀ = alcohol percentage by volume of the flavoring drink

G_f = alcohol percentage in final volume of the mixture If Go < G_f there can be used an amount of beverage equal to:

100(l00-G/)

(100-Go) (1 )

To bring the ABV to G_f, ethanol must be added in the following quantity:

E = 100 - B

If instead G₀ > G_f there can be used an amount of beverage:

(2)

Go

To bring the ABV to G_f water will have to be added in the amount of:

A = 100 - B

It should be noted that equations (1 ) and (2) do not take into account the fact that food ethanol is usually found at a concentration of 95% by volume. The value of G_f will be slightly inaccurate as G₀ decreases for each Go less than G_f. The correction factor would make the formula more complex in front of an insubstantial benefit. In case it is necessary to have avaialble ethanol at percentages by volume lower of 95% the discrepancy should be corrected.

In the event that a beverage has a particularly intense flavor it may be diluted bearing in mind that the amount of ethanol in the beverage will also be diluted, so its value of G₀ will be recalculated on the basis of the dilution made by the operator. Once the new value of G₀ is found, it can be entered in the appropriate equation.

Below is a table showing the application of the equations to obtain 100 ml of base mixture 20% by volume of ethanol (the most suitable for processing) with alcoholic beverages of some exemplary gradations..

Beverage Beverage Additional Additional Final graduation Maximum volume Ethanol (ml) Water (ml) ABV (% (% vol) (ml) Vol)

0 80.00 20.00 0.00 19.00

10 88.89 1 1 .1 1 0.00 19.44 20 100.00 0.00 0.00 20

30 66.67 0.00 33.33 20

40 50.00 0.00 50.00 20

50 40.00 0.00 60.00 20

60 33.33 0.00 66.67 20

70 28.57 0.00 71 .43 20

80 25.00 0.00 75.00 20

90 22.22 0.00 77.78 20

100 20.00 0.00 80.00 20

There are three possibilities:

Beverages with a gradation of less than 20% by volume:

• the sodium alginate is brought into solution until completely dissolved · the ethanol is added and mixed until total homogenization.

Beverages with a gradation equal or close to 20% by volume;

• the sodium alginate is brought into solution directly into the mixture, this operation will require a longer and more vigorous stirring, since the dissolution of the alginate in a 20% by volume solution of ethanol is not immediate and leads to the formation of lumps that must be brought into solution.

Beverages with a gradation higher than 20 volumes:

• the sodium alginate is added in solution in the volume of water calculated by mixing until total dissolution;

· the drink is added slowly, mixing until total homogenization;

• if the calculated volume of water is excessively reduced for mixing, it is possible to proceed by mixing first the drink and the water and then adding the alginate and mixing as in the case of a 20% by volume drink. EXAMPLE 2

Solution A with four ingredients

Ingredients:

Preparation:

- 0.16 g of soy lecithin are added in solution in 20 ml of ethanol, mixing until complete dissolution;

- 1 .25 g of sodium alginate are added in solution in 80 ml of water, mixing until complete dissolution;

- the two preparations are mixed until total homogenization.

EXAMPLE 3

Solution A with five ingredients

Ingredients:

Preparation:

0.16 g of lecithin and 0.8 ml of olive oil are added in solution in 20 ml of ethanol, mixing until complete dissolution;

1 ,25 g of sodium alginate are added in solution in 80 ml of water, mixing until complete dissolution;

-the two preparations are mixed until total homogenization.

EXAMPLE 4

Solution A for membranes flavored with cocoa powder

Ingredients: Water 80 ml

Ethanol 95% vol. 20 ml

Sodium alginate 1 .25 g

Cocoa powder 4 g

Preparation:

- - 1 ,25 g of sodium alginate are added in solution in 80 ml of water, mixing until complete dissolution;

- - 20 ml ethanol are added and mixed until total homogenization;

- - 4 g of aromatic powder are added and mixed until total homogenization. EXAMPLE 5

Solution A for membranes flavored with mint syrup

Ingredients:

Preparation:

- - 10 ml of syrup are mixed with 70 ml of water;

- - 1 .25 g of sodium alginate are added to the solution of water and syrup, stirring until complete dissolution;

- - 20 ml ethanol are added and mixed until total homogenization.

EXAMPLE 6

Solution A based on agar for membranes obtained with temperature variation

As it is known, agar is a carbohydrate extracted from red algae (Gelidium, Gracilaria, Gelidiella, etc.) soluble in water at high temperatures (90-100 °C) which forms a hydrogel after cooling because it is not soluble cold.

Ingredients:

Water 100 ml

Agar 7 g Preparation:

- - 100 ml of water are brought to boil;

- - mix 7 g of agar with 100 ml of water until completely dissolved (the solution must be clear) keeping the water temperature at 100 °C;

The solution obtained remains in a liquid and viscous state between

100 and 50 °C, in this state it is possible to create a sphere as in STEP TWO described in the detailed description of the invention. The process includes:

- - to immerse a selected volume of the mixture obtained in a cold water bath at a preferable temperature of 10 °C for an average time of 3 seconds.

The surface of the aforesaid volume cooling gels and forms an agar and water membrane while maintaining a hot and liquid solution of the same compound inside. Subsequently and quickly it is necessary to carry out the emptying and filling procedure of the membrane described in PHASE THREE of the detailed description of the invention, before the internal temperature falls below 50 °C to avoid that the gelling process extends to the whole volume inside the sphere obtained due to the lowering of the temperature. Once the two-way needle has been extracted from the sphere following the filling procedure, the hole will close by simply lowering the temperature of the residual internal agar solution near the hole itself. In these circumstances it is possible to realize a sphere containing any desired liquid, as in the previous examples. In the case described above it is necessary to thermostat the suction path of the used positive displacement liquid exchanger at a temperature of 60 °C.

The present invention has been described with reference to some of its specific embodiments, but it is to be understood that variations or modifications may be made to it by those skilled in the art without thereby departing from the relative scope of protection.

Claims

1 . A process for the preparation of closed hydrogel membranes containing a liquid, which process comprises the following steps:

1 ) preparing a first aqueous solution of a substance able to gel upon ion exchange or upon temperature variation, and a second aqueous solution of a ion salt which causes gelation of said substance, or a second solution cooled at least at the gelation temperature of the substace used;

2) dropping a predetermined volume of said first solution in a strainer (1 ) and immediately immersing said strainer with said first solution in a bath of said second solution;

3) retrieving the spheroid so formed from the bath of step 2 by means of said strainer (1 ) and exposing it, while contained in said strainer, to perforation by a two-way hollow needle element (1 1 ) connected to a displacement liquid exchange device, thereby carrying out:

i) a first step of aspiration of the liquid contained in the spheroid, up to removal of most of it, followed by

ii) a second step of introduction of a liquid desired as a filling of said spheroid, up to complete filling of said membrane, to obtain a sphere;

4) extracting said two-way needle element (1 1 } from the sphere containing the filling liquid, still contained in said strainer (1 ), placing it again in said bath of step 2 and, finally, washing the filled sphere thus obtained with water,

2. A process according to claim 1 , wherein said substance of the first aqueous solution is able to gel upon anionic exchange, and said second solution contains a salt of a ion with which said substance gels.

3. A process according to claim 2, wherein said substance of the first aqueous solution is sodium alginate, and said second solution contains a calcium salt, preferably calcium chloride.

4. A process according to claim 2, wherein said substance of the first aqueous solution is based on polysaccharides gelling upon variation of temperature, as, for example, agar.

5. A process according to any one of the preceding claims, wherein said strainer (1 ) is substantially semi-spherical, semi-ovoidal or has a curved- surface concave bottom.

6. A process according to any one of the preceding claims, wherein said second solution contains one or more edible substances having surfactant action, selected from ethanol, soy lecithin and/or one or more edible fats or edible oils, such as cocoa butter or olive oil.

7. A process according to any one of the preceding claims, wherein said first solution contains, one or more flavoring ingredients selected from powders or aromatic syrups and alcoholic beverages.

8. A process according to any one of claims 3-7, wherein said first solution also contains a quote of ethanol no more than 25% by volume, said strainer having said first solution is immersed in step 2 for a period of time comprised between 3 and 10 seconds, said second solution contains an amount of ethanol substantially equal to the amount of ethanol present in said first aqueous solution and said sphere achieved in step 4 is immersed for a period of time comprised between 1 and 5 seconds.

9. A process according to claim 8, wherein said first solution comprises, based on 100 ml, from 1 to 2 g of sodium alginate, form 18 to 25 ml of ethanol and optionally, from 5 to 15 ml of syrup, or from 1 to 5 g of a flavoring powder, or a volume quantity of an alcoholic beverage such as to bring the final alcohol by volume (ABV) of said first solution to no more than 25% by volume, the remainder being water.

10. A process according to any one of claims 3-9, wherein said second solution contain, based on 400 ml, 2-4 g of calcium chloride and, optionally, from 72 to 100 ml of ethanol.

1 1 . A process according to any one of claims 1 -10, wherein said third operation is carried out using a manual displacement liquid exchange device comprising:

- a cup shaped housing (10) for said strainer (1 ) containing said spheroid formed in step 2, at the center of which housing said two-way hollow needle element (1 1 ) protrudes;

- a plunger fluid suction device (3) connected in fluid communication to a first suction path (6), of said two-way hollow needle element (1 1 );

- a plunger fluid injection device (4) connected in fluid communication to a second delivery path (7), of said two-way hollow needle element (1 1 ); and in which, after having housed the stainer (1 ) with said spheroid in said housing (10), said plunger suction device (3) is manually operated until the membrane of said spheroid is almost completely emptied, and then said plunger injection device (4) is manually actuated until said membrane is again filled, completely, with said desired filling liquid.

12. A process according to any one of claims 1 -10, wherein said strainer (1 ) is externally provided, at its bottom, with an annular magnetic element (12), and said third step is carried out using a semi-automatic fluid displacement exchange device comprising:

- a rigid container that encloses the components of the device;

- an annular housing (10a) for said strainer (1 ) containing said spheroid formed in step 2, placed on a top surface (15) of said container, at the center of which there is a hole from which said two-way hollow needle element (1 1 ) may emerge, being preferably spring-actuated;

- a fluid aspiration device consisting of a first positive displacement pump (3a), preferably a peristaltic pump;

- a fluid injection device consisting of a second positive displacement pump (4a), preferably a peristaltic pump;

- two connecting pipes, respectively from the suction of said first positive displacement pump (3a) and from the delivery of said second positive displacement pump (4a), to a first suction path (18), of said two-way hollow needle element (1 1 ) and to a second delivery path (19), of said two-way hollow needle element (1 1 );

- a retractable support device (32, 33) for said two-way hollow needle element (1 1 ) through which said needle element (1 1 ) can move vertically, preferably spring-actuated, between a first retracted position inside said container and in which, after positioning said strainer (1 ) with said spheroid aligned with said hole with the help of said annular magnetic element (12) coupling with a corresponding magnetic element fixed to the upper surface of said container, the retractable device (32, 33) is manually actuated, causing the needle element (1 1 ) to emerge from the hole, then said first positive displacement pump (3a) is operated until almost completely emptying said membrane, and then said second positive displacement pump (4a) is actuated until said membrane is again filled, completely, with said desired filling liquid.

13. A manual positive displacement liquid exchange device as defined in claim 1 1 , for use in the production of closed edible hydrogel membranes based on sodium alginate and containing an edible filling liquid of any kind..

14. A semi-automatic positive displacement liquid exchange device as defined in claim 12, for use in the production of closed edible hydrogel membranes based on sodium alginate and containing an edible filling liquid of any kind.