DESCRIPTION

Field of application

The present invention deals with a vacuum apparatus for the processing of food at low temperature. In particular, the invention deals with an apparatus for domestic use, for use in restaurants and in craft sector for the production of small batch of food and/or drink.

Prior art

In the food industry there are some processes that involve the boiling of the liquid portion of a food preparation. These processes are conducted in apparatuses comprising generally two chambers connected to each other, namely an evaporation chamber, where the food preparation is boiled, and a condensation chamber, where the vapors generated by the boiling are condensed. These apparatuses take the name of evaporators or distillers depending on whether the sequence of evaporation and condensation is needed to reduce the water content of a food preparation or to separate mixtures of liquids with different volatility, respectively.

The processes apt to reduce the water content of the food preparations essentially have the purpose of facilitating the transport and the storage of the same preparations, but also purposes related to the commodity because the reduction of water content may be an intrinsic characteristic desired for the final product, for example for the fruit nectars, the tomato concentrates or the condensed milk. The processes apt to separate mixtures of liquids with different volatility (or distillation processes) are widely used in the food industry for the production of alcoholic beverages and essential oils and for the extraction of natural flavors.

In the above mentioned processes the condensed vapors are collected in the condensation chamber, therefore separated from the food preparation. Others processes instead provide pouring part of the condensed vapors from the condensation chamber to the evaporation one; in that case, the condensed vapors go back into the food preparation forming a flowing back (or reflux).

The reflux processes are generally used in industrial field to improve the separation of volatile elements inside of distillers; otherwise in chemical laboratories to maintain a reaction mixture at a constant temperature inside of specific reflux apparatuses avoiding that the solvent runs out evaporating. On the contrary, these processes are not very common in the food industry, although the cooking of food preparation under a flowing back (known as reflux cooking) is very promising.

The vacuum evaporation is a widely used technology especially on an industrial scale, since it allows to lower the boiling temperature of a given liquid, and therefore to evaporate, distill or cook under reflux at temperatures lower than those that would occur at atmospheric pressure, which for water-based food preparations are equal to about 100 °C. Processing of food preparations at low temperature is particularly interesting when it is desired to preserve the original properties of the preparations themselves or for those cooking processes that cannot be carried out at too high temperatures.

The rotary evaporator is an apparatus commonly used in chemical laboratories for removing at low temperature a solvent by vacuum evaporation. A rotary evaporator is composed essentially of: (1 ) a first flask that works as evaporation chamber, containing the solution to be processed; (2) a water bath at a controlled temperature in which said first flask is plunged to heat the solution contained therein; (3) a condenser; (4) a second flask for collecting the condensed vapors connected to said condenser forming the so-called condensation chamber; (5) a motorized mechanism able to put in rotation the first flask and to connect it via a rotary connector to the condensation chamber; (6) a vacuum generation system, comprising a vacuum pump and connected to the condensation chamber.

The flask, the condenser and the connecting elements are made of borosilicate glass, which is a material able to resist to highly corrosive chemical substances, and all mounted system has a degree of gas tightness that allows it to reach pressures of some mbar. However, the leakage rate between the connecting elements of borosilicate glass is significant, therefore the vacuum generation system remains always connected to the condensation chamber. The rotary evaporator is used also in the kitchen both as evaporator to reduce the water content of food and distiller to extract the most volatile compounds of a particular food preparation, and only marginally to cook under reflux. Nevertheless it presents many limitations and problems.

First of all, the borosilicate glass with which the flasks are made is not a particularly suitable material because of its high brittleness and scarce manageability. Furthermore, in the kitchen the products to process are not as corrosive as the chemical ones, therefore, others materials are preferable such as the stainless steel.

Secondly, the water bath, through which the evaporation heat is supplied in an indirect way, although allows limiting the maximal temperature reachable and is very important in chemistry for avoiding to activate some unwanted reactions, is not suitable in the case of an apparatus designed for food processing, for which it is more practical to use a direct source of heat, for example an induction hob, a glass ceramics hob, a gas ring, an electrical hob, a woodstove, a fire or candles.

Thirdly, the apparatus has to stay connected to the system of vacuum generation during all processing time of the food preparation to limit the possible leaks between the connecting elements, and to the running water to guarantee the cooling of the condenser. An apparatus alternative to the rotary evaporator for the food processing and conceived for domestic use is described in RU2089086. This apparatus is made mainly in metal and comprises essentially: a first sealed container which works as evaporation chamber and within which the food is processed, equipped with a lid and with a steam jacket; a second sealed container which works as condensation chamber, placed over the first container and equipped with a heat exchanger; means for generating the vacuum, a pressure gauge and a valve. The heat exchanger, the means for generating the vacuum, the vacuum gauge are fixed on the lid of the condensation chamber. The heat exchanger is a coil cooled by a flow of running water and the means for generating the vacuum are a jet water pump or a manual pump.

The condensation chamber is connected to the evaporation chamber through a tube, to the means for generating the vacuum through the above-mentioned valve and to the pressure gauge directly. The operating principle of this apparatus is the following. The apparatus is placed on a stove, where the steam jacket surrounding the evaporation chamber and in turn the food preparation contained therein are heated; the vapor generated reaches the condensation chamber by passing through the tube that connects the evaporation chamber with the condensation chamber; the desired vacuum is obtained, then the valve which connects the means for the vacuum generation with the condensation chamber is closed and the evaporation occurs by manually adjusting the thermal power and the flow of cooling water so as the pressure indicated by the pressure gauge placed on the lid is kept constant. However, also the above-mentioned apparatus shows a series of limits. Firstly, it is very similar to the apparatuses used at industrial level and, therefore, maintains their complexity. Secondly, the several components forming it make it too expensive for most of restaurants and for any family. Also the cleaning is very complex, particularly the cleaning of the lid of the condensation chamber to which the means for vacuum generating, the pressure gauge, the valve and the heat exchanger are connected. Furthermore, it has to be kept always connected to the running water.

Lastly, this apparatus is conceived to work at pressure higher than 150 mbar, which corresponds to minimum boiling temperature of 55°C. On the contrary, the necessity of the avant-garde chef contemplates boiling temperatures close to room temperature, which means distilling pressures of about 20-15 mbar, which are ten times lower.

Another apparatus used for the vacuum processing of food is described in FR2684535. From the point of view of its design, this apparatus is very similar to a pressure pot and comprises a lid locked to the pot body, a manual relief valve and a thermometer mounted on the lid.

This apparatus allows steaming at a temperature between 60 °C and 80 °C, corresponding to pressures between 200 mbar and 470 mbar, and find domestic application because it does not require any type of vacuum pump. However, it has some limitations.

First of all, being a container close and locked, this apparatus can go overpressure. This makes necessary the presence of an additional security system able to limit the overpressure, for example a rupture disc. Secondly, this apparatus can be used only to steam at low temperature and it is not conceived to work as evaporator since it lacks of a condensation chamber.

Also the process used to generate the vacuum is inefficient because expels only partially the air contained into the apparatus. In fact, it contemplates to bring the water contained into the apparatus to the boil without waiting that all internal surfaces of the apparatus itself reach the boiling temperature of the water. The invention aims to solve all the mentioned disadvantages.

Summary of the invention The invention aims to provide a vacuum apparatus which is able to process food at low temperature, usually comprised between the room temperature and 90 °C; which can be used in the domestic sphere, in restaurants and for the artisanal production of small batch of food and/or drinks; which can be used either as evaporator, or as distiller, or to cook under reflux; which is of small dimensions; which is characterized by a simple and safe design which makes it cheap to be produced, convenient to handle, simple to clean and which needs to be kept connected neither to the running water nor to a vacuum pump during the food processing. The goal is reached by means of an apparatus for the vacuum processing of food according to the claim 1 .

This apparatus comprises a vessel equipped with an upper opening and a lid applicable on said opening in order to define a processing chamber inside said vessel, and it is characterized in that: said lid is vessel shaped in order to define a second chamber opened on the upper side and it is equipped with a bottom suitable to define the upper wall of said processing chamber when the lid is applied on the opening of the vessel; said apparatus comprises a valve having a closed position and an open position; said apparatus comprises a gasket placed on a contact border between said vessel and said lid and suitable to guarantee the seal between said vessel and said lid when the pressure inside the processing chamber is lower than the pressure of the external environment, gas-tight isolating said processing chamber from the external environment when the valve is in closed position. In the following, for convenience of reference, said vessel will be referred to as a pot.

Preferably said gasket is a separate element, being annexed neither to the pot nor to the lid, and it is applied to the pot or to the lid only at the moment of using the apparatus.

In other embodiments, said gasket is annexed to the pot and is placed on the border of the upper opening of said pot and the lid is apt to seal gas-tight on said gasket when the pressure inside the processing chamber is lower than the pressure of the external environment.

Preferably the bottom of said lid is curved, more preferably is concave-upward. According to a preferred embodiment, said lid is a vessel with bowl shape.

Preferably, the second chamber defined by said lid is a semi-sphere or part of a semi-sphere, for example a spherical cap.

Said lid is equipped with an upper border and said upper border identifies a flat surface tangent to the border itself which delimits said second chamber on the upper side. Preferably the upper border of said lid is tangent in each of its points to the flat surface which identifies; in other words, the upper border belongs to said flat surface. In other embodiments, instead, the upper border is tangent to the surface only in some points, while in other points it doesn't contacts it.

The maximal distance existing between said flat surface and said bottom of the lid is preferably at least 4 cm, said distance being orthogonal to the flat surface. This distance corresponds to the maximal depth of said lid with vessel shape. Preferably said maximal distance existing between said flat surface and the bottom of the lid is at least 1/5 of the distance which separates two points at maximal distance inside the second chamber, preferably it is at least 1/4 of said distance, more preferably it is at least 1/3. Said two points at maximal distance are the farthest points inside the second chamber. For example, in cases in which the second chamber is semi-spherical, said two points have a distance equal to the diameter of the sphere; in cases in which the second chamber is a spherical-cap, said two points have a distance equal to the diameter of the base of said cap.

According to a preferred embodiment the valve is placed on the bottom of the lid.

In other embodiments, said valve is placed on one of the walls of the pot. The food preparation contains at least a liquid fraction. The term "liquid fraction" includes both the added cooking liquids (for example broth, water, oil) and the liquid contained inside the food itself (for example the water contained into the vegetables or into the meat). Said liquid fraction comprises the most volatile components of the food preparation. The use of the apparatus is essentially the following. A pressure lowering is produced inside the processing chamber, up to reach a desired vacuum degree. This pressure lowering can be obtained with an external vacuum pump and/or by evaporating and successively condensing a liquid contained into the processing chamber, according to various embodiments, as it will be better described in the following.

The term "vacuum generation" will be used to indicate a lowering of the pressure down to a desired value.

As said, the vacuum generation inside the processing chamber causes the isolation of the chamber itself, as a result of the sealing between pot and lid, when the valve is in closed position.

During the real processing stage, the second chamber defined by the lid is preferably filled with a refrigerant, while the processing chamber contains the food preparation to be processed. Furthermore heat is supplied to the processing chamber with a suitable heating source.

Preferably, said refrigerant is water or ice or a mixture thereof. Said heat source is for example an induction hob, a stove, a gas hob or an electrical hob. Due to the presence of the refrigerant, the bottom of said lid, namely the surface which delimits the processing chamber on the upper side ("ceiling" of the chamber), represents a condensation cold surface of the vapors which are generated inside the processing chamber itself and works as heat exchanger. The food preparation is heated up to a temperature suitable to bring at least part of its liquid fraction to the boil generating vapor; said vapor condenses when enters into contact with the cold surface.

The fact that the bottom of said lid, therefore said cold surface, is preferably curved allows to increase the heat exchange surface compared to that of a lid with flat bottom. Furthermore, the curved shape of the bottom of said lid tends to direct and to drain the condensate in a precise point of the bottom. In some embodiments, the bottom of said lid can have a shape with singularities, for example pinnacles, apt to create preferential dripping areas of the condensate.

In some embodiments of the invention, the condensed vapor returns to the food preparation realizing a reflux cooking; in other embodiments the condensate is collected and thus the apparatus of the invention operates as evaporator or distillatory.

As a result of the vacuum, the boiling temperature of the liquid fraction is lower than the boiling temperature at atmospheric pressure, allowing a low temperature cooking or a process close to room temperature. Low temperature cooking means a cooking carried out at temperatures not exceeding the 90 °C, preferably comprised between 60 and 90 °C in case of cooking of vegetables and between 50 and 70 °C in case of cooking of meat and fish.

In the embodiments in which the condensate returns to the food preparation, the processing chamber works as evaporation chamber, while the cold surface of the bottom of said lid works as heat exchanger of the condensation chamber.

During the cooking or the processing, due to the pressure difference between the processing chamber and the external environment, the lid and the pot are gas-tight sealed from the external environment and it is possible to maintain a vacuum condition (that is pressure lower than the atmospheric pressure) inside the processing chamber itself.

At the end of the cooking or at the end of the processing of the food preparation, the vacuum present inside the processing chamber is broken, acting preferably on the valve placed on the walls of the pot or on the bottom of said lid. Advantageously said valve is put in open position, allowing the outside air to enter and bring the pressure inside the processing chamber back to the atmospheric value. Consequently, the lid is separated from the pot allowing accessing to the food preparation cooked or conveniently processed.

Preferably said valve is a check valve which commutes between a close position and an open position as a result of the pressure difference existing between the processing chamber and the external environment.

For example said check valve has a moving plug equipped with a gasket which, in the abovementioned condition of pressure into the processing chamber lower than the external pressure, is pushed from the external pressure in a gas-tight closed position.

The use of the apparatus contemplates a heat source and a refrigerant means. An aspect of the invention contemplates to maintain the boiling temperature inside the processing chamber at a constant value. This can be done by a control system which generates a signal apt to regulate at least one of the thermal power supplied to the processing chamber by said heat source and the thermal power subtracted from the processing chamber by said refrigerant. In some embodiments of the invention said control system acts only on the heat source, for example when the refrigerant is a mixture of water and ice at constant temperature of 0 °C. In other embodiments the control system acts on the refrigerant means, for example the refrigerant means is an evaporating liquid, for example water, and the control system regulates a fan placed to promote the evaporation rate of the liquid. Preferably said control system is of closed loop type and more preferably uses a Proportional-lntegral-Derivative controller, known as PID.

Additional preferred characteristics are described in the following.

Preferably, the pot and the lid portion which compresses the gasket have smooth borders and without irregularity so that the thickness of the gasket is small and the compression, under the effect of the external pressure, big and uniform. A benefit correlated with this characteristic is a better gas-tight sealing of the gasket and therefore a lower risk of leaks which could compromise the vacuum seal over the time. According to a preferred embodiment, said apparatus comprises a temperature sensor that generates a signal which, once processed, gives the temperature value reached by the food preparation inside the processing chamber.

Preferably, said temperature sensor is positioned outside the apparatus and is in contact with the external wall of the pot, from the temperature of which it is possible to go back to the boiling temperature of the liquid fraction present inside the processing chamber because of the convective heat transfer from the boiling food preparation.

Preferably, the temperature sensor and the external surface of the pot close to the temperature sensor are thermally insulated with respect to the external environment in order to guarantee a more accurate measure of the temperature.

The fact of measuring the boiling temperature without inserting a thermometer inside the processing chamber reduces the number of possible leaks sources and allows simplifying the apparatus. Preferably, the signal generated by the temperature sensor is transmitted by means of a cable or using a wireless technology to a peripheral device which shows the temperature value. In the embodiments in which the food preparation has to be processed at a precise and constant temperature, the signal generated by the temperature sensor is transmitted advantageously to a closed loop control system which uses the signal generated by the temperature sensor as feedback signal. Said closed loop system controls the boiling temperature of the food preparation using for example a PID controller, as already mentioned.

The boiling temperature can be controlled for example regulating the power of the heat source or regulating the evaporation rate of the water contained in the lid. In the first case, the closed loop control system comprises a micro-controller and uses the signal generated by the temperature sensor and a temperature value selected as reference (set-point) by the user as input signals to compute the output amplitude of the signal which will regulate the power supplied by the heat power. The computation of the output amplitude is processed by said micro-controller according to a control algorithm.

In the second case, the closed loop control system is connected for example to a fan positioned over the surface of the water contained in the second chamber defined by said lid. The control system regulates the working velocity of said fan which, moving the air above the water surface, produces a higher evaporation rate of the water and therefore increases the heat flow removed from the processing chamber.

For embodiments in which the condensate is collected and separated from the food preparation, the apparatus comprises a collecting container placed inside the processing chamber. In this case, the evaporation chamber is delimited by the inner walls of the pot and by the outer walls of the collecting container, while the condensation chamber is delimited by the bottom of the lid and the inner walls of the collecting container. Hereinafter the aforementioned condensate will be referred to as a distillate.

Preferably, said collecting container is bowl shaped. Preferably, said collecting container is equipped with a holder which keeps it raised with respect to the bottom of the pot.

Preferably, said collecting container is formed by a set of walls made with different materials. More preferably, the outer wall of said container, being exposed to the vapors generated by the processing of the food preparation, is made of metal in order to guarantee an uniform temperature, while the inner part of said container, being in contact with the distillate, is preferably made of glass or plastic or ceramic or any other material suitable to come in contact with the distillate and characterized by a low thermal conductivity. In fact, it is preferable to reduce at the minimum the transfer of heat through the walls of the collecting container, from the vapor present in the boiling chamber to the distillate collected into the condensation chamber, as it could produce an evaporation of the distillate with the resulting saturation of the condensation capacity and therefore reduce the efficiency of the distillation separation. Another object of the present invention is a lid applicable on the upper opening of a vessel or pot for the vacuum processing of food, according the claims. Preferably said lid is a concave vessel opened on the upper side, for example with bowl shape.

Said lid is particularly adapted to be used in a process of vacuum processing of food, using for example the apparatus described above.

Another aspect of the invention deals with a process for the vacuum processing of a food preparation comprising at least a liquid fraction using the above described apparatus, according to the attached claims.

The process of vacuum processing according to an embodiment of the invention comprises the following steps:

(a) placing the food preparation inside said pot;

(b) applying said lid to said pot in order to define a processing chamber inside said pot;

(c) lowering the pressure inside said processing chamber, producing the squashing of said gasket by said lid and consequently gas-tight isolating said processing chamber from the external environment; (d) heating, by means of a suitable heating source, said pot bringing at least part of the liquid fraction contained in said food preparation to the boil and obtaining the passage of at least part of said liquid fraction to the vapor state;

(e) cooling the bottom of said lid in order to condense at least part of said vapor generated by the boiling in step (d). Preferably, the steps d) and e) take place simultaneously and represent the real processing stage of the food preparation, during which the food preparation is processed at the desired temperature for the desired time.

Preferably, the cooling of the step (e) is generated by a refrigerant means placed inside the second chamber defined by the lid. Said refrigerant means is preferably water or ice or a mixture thereof. During the processing stage, it is possible to add or to remove a quantity of refrigerant means, if necessary, for maintaining an optimal quantity of said refrigerant.

At the end of the processing stages (d) and (e) the vacuum is broken in order to remove the lid from the pot and to have access to the processed food preparation. Preferably, the breaking of the vacuum is obtained with the manual opening of the valve.

If the food preparation to process is at the liquid state, during the step (a) bodies apt to facilitate the boiling are preferably added , which represent local points of triggering for this phenomenon. For this purpose, for example sphere or chips of glass are employed.

The step (c) of pressure lowering inside the processing chamber can be implemented using various procedures. According to a first embodiment of the invention, the pressure is lowered by means of expulsion of gases, usually air, contained in the processing chamber by the vapor generated at atmospheric pressure into the processing chamber and successively condensed. In more detail, according to this embodiment, the step (c) of the process described above comprises:

(i) heating the pot bringing at least part of the liquid fraction of the food preparation to the boil producing vapor;

(ii) keeping the liquid fraction boiling for a fixed time during which the produced vapor expels a given quantity of air, or more generally gas, from the processing chamber;

(iii) cooling the processing chamber introducing a refrigerant into the second chamber defined by the lid, obtaining the condensation of at least part of the vapor contained therein, the lowering of the internal pressure, the squashing of said gasket by said lid and the gas-tight isolation of said processing chamber from the external environment.

During the above mentioned steps (i) and (ii) the vapor which is generated in the processing chamber has a pressure at least equal to the atmospheric pressure and has the effect of expelling the air contained in the processing chamber, for example through the lid border. In fact in this condition the lid is not sealing the pot since the pressure into the processing chamber is at least equal to the atmospheric pressure. As a result of the air expulsion, the processing chamber reaches a condition in which the internal pressure is essentially due to the vapor partial pressure. The step (iii) of cooling occurs suddenly as a result of the refrigerant introduced into the second chamber, which is preferably water, ice or a mixture thereof. As a consequence, the vapor contained into the processing chamber, contacting the cold surface of the bottom of the lid, condenses causing a decreasing of the vapor fraction and therefore a lowering of the pressure, as a result of which the lid starts sealing the gasket impeding air from the outside to enter. If for example the valve of the apparatus is a check valve, it closes as a result of the described pressure lowering inside the processing chamber, and the processing chamber results gas-tight isolated from the external environment. In this way the cooling of the processing chamber has the effect of achieving a certain vacuum degree inside the same chamber.

As a result of the pressure lowering in the processing chamber, the boiling temperature of the liquid fraction present into the food preparation decreases and the evaporation rate increases. Furthermore, the convective heat transfer from the food preparation to the refrigerant contained into the second chamber increases and said refrigerant, absorbing heat, condenses the vapor released from the boiling of the liquid fraction. As a result, the food preparation cools down and the refrigerant warms up dissipating heat into the environment and evaporating otherwise it is kept at constant temperature, provided the refrigerant is water or a mixture of ice and water, respectively.

In any case the stationary processing temperature of the food preparation is reached once the thermal power absorbed by the refrigerant (plus that possibly dissipated into the environment through the walls of said pot) equals the thermal power supplied to the pot from the direct source of heat. Regulating the thermal power supplied or that absorbed by the refrigerant, for example with a control system as described above, it is possible to control the boiling temperature.

According to a further embodiment of the invention, the above mentioned step c) doesn't contemplate to heat the food preparation up to the boiling temperature (at the atmospheric pressure) of the liquid fraction. More specifically, the pressure is lowered with a vacuum pump. Preferably, said vacuum pump is connected to the valve, by means of an external connector, once the lid is placed on the pot, in order to evacuate the air before starting heating the food preparation. Said external connector comprises a cylindrical body, through which the pump is connected to the valve, and an aspiration tube. Preferably, said valve is a check valve and is characterized by a cracking pressure lower than 20 mbar (in case the liquid fraction of the food preparation is water) and assembled in order that the air can be evacuated from the processing chamber connecting the body of the external connector of the vacuum pump to the valve, but at the same time the air can't flow back into the processing chamber once said body of the external connector is disconnected from said valve.

The pressure reached at the end of the step c) depends on the evacuating degree of the air of the processing chamber, on the temperature reached by the inner walls of the processing chamber, hence on the temperature reached by the liquid fraction of the food preparation.

Preferably the pressure reached at the end of the step c) is lower than 700 mbar for boiling temperatures lower than 90° C, lower than 200 mbar for boiling temperatures lower than 60°C, lower than 40 mbar for boiling temperatures lower than 30 °C.

According to certain embodiments, the evacuation degree of the air from the processing chamber is bigger than 80%, more preferably bigger than 90%, even more preferably bigger than 99%.

Some embodiments of the invention comprises a stage of introduction of a second food preparation inside of the processing chamber, said stage being performed downstream of the stage c) of pressure lowering inside the processing chamber and, according to the cases, upstream or during the real processing stage represented by the steps d) and e).

Said second food preparation is in the liquid state. A food preparation in the liquid state is meant to be a liquid food preparation or substantially liquid, namely a food preparation which has been previously filtered, for example with a strainer. Said second food preparation can have the same composition of the food preparation added during the step a) or a different composition. The introduction of the second food preparation occurs via the opening of the valve in order to connect the processing chamber with the second food preparation, said second food preparation being contained in a chamber placed outside of said processing chamber, and in order to obtain the transfer of said food preparation inside the processing chamber.

The valve is opened manually. Preferably, the valve in open position connects the external chamber containing the food preparation with the lower part of the processing chamber by means of an hollow body or a tube, by ensuring the food preparation is transferred (or "sucked in") from the external chamber to the bottom of the processing chamber taking advantage of the pressure difference between the external environment and the processing chamber.

Preferably, said external chamber with respect to the processing chamber containing the second food preparation is the second chamber defined by the lid. According to the aforementioned embodiment, the valve is placed on the bottom of said lid.

By using a process comprising the above-mentioned stage of introduction of a second food preparation it is possible to realize several operations.

In case of reflux cooking, for example, the introduction of a second food preparation downstream of the step c) having a different composition with respect to that previously introduced during the step a) gives the possibility of adding a specific ingredient without breaking the vacuum and removing the lid of the pot.

In case of a distillation process of a food preparation at the liquid state, the possibility of introducing an additional fraction of the food preparation downstream of the stage c) inside the processing chamber allows reducing the amount of glass spheres apt to promote the boiling.

Furthermore, by using the above-mentioned process it is possible to use the food preparation introduced during the step a) to generate vapor at atmospheric pressure and later condense said vapor in order to lower the pressure inside the processing chamber, then to introduce the second food preparation downstream of the step c) so that it can be processed at low temperature.

The processes of vacuum processing described above can be used for the reflux cooking at low temperature of certain food preparations, during which the condensed vapor returns inside the food preparations themselves.

For example, these processes can be used to cook a tasty broth, since the perfumes generated during the cooking condense on the internal surface of the lid and reflux inside the broth. Furthermore, the vacuum allows cooking the broth at low temperature (for example comprised between 60 °C and 90 °C) and guarantees the air-tight sealing of the apparatus, in such a manner that the most volatile components can reflux in the broth and not be dispersed in the environment. Finally, the fact that the second chamber is filled with a refrigerant means, such as water and/or ice, generates a good reflux rate, which allows mixing continuously the most volatile components with the least volatiles ones.

Another application of these processes of vacuum processing is the low temperature distillation, namely the extraction of the most volatile components contained in certain food preparations, wherein the distillate is collected inside the collecting container described above. For example, this process can be efficiently used to extract the aroma from liquid bases, such as fruit and vegetable juices, or from solid bases, such as wood, soil, hay, wool after initial infusion in a suitable solvent, or to separate essential oils dissolved in alcohol at the end of an enfleurage process used to capture the aromas from particularly delicate flowers, or still to distill aromatic alcohols, but also to clarify broths.

Another application of these processes of vacuum processing is the low temperature evaporation, namely the reduction of the water content in a liquid food preparation, in which the evaporated water is condensed and collected inside the collecting container described above. For example, this process can be efficiently used to reduce sauces, to obtain gravies starting from broths or syrups starting from sweet wines, to concentrate fruit and vegetable juices.

A further application of these processes of vacuum processing is the low temperature frying, namely the reduction of the water content of the solid fraction of a food preparation. During the frying processes, at least part of the cooking liquid (which falls within the definition of liquid fraction of the food preparation) consists of oil, which allows transmitting the necessary heat for the evaporation of the water from the above-mentioned solid fraction. The evaporated water is successively condensed and collected inside the collecting container described above.

For example, this process can be used for frying in an optimal way the potatoes, obtaining crispy potatoes with low contents of acrylamide, substance suspected to be carcinogen, generated by the high temperature frying. The vacuum apparatus of the present invention can be implemented also in chemical laboratories, as it can replace the rotary evaporator, especially when the solvents to evaporate are not particularly dangerous or corrosive.

The advantages of the present invention will emerge even more clearly with the aid of the detailed description that follows, and which deals with certain preferred embodiments.

Brief description of the drawings

Fig. 1 a shows a vacuum apparatus for application in the reflux cooking of food, according to a first embodiment of the invention.

Fig. 1 b shows a lid applicable on the pot for the vacuum processing of a food preparation.

Figs. 2a e 2b show details of a vacuum apparatus according to another embodiment of the invention. Fig. 3 shows a vacuum apparatus for application in the reflux cooking of food according to a further embodiment of the invention.

Fig. 4 shows a vacuum apparatus for application in the distillation or evaporation at low temperature, according to an embodiment of the invention. Fig. 5 shows a vacuum apparatus wherein a second food preparation is introduced inside the processing chamber already vacuum-sealed for application in the distillation or evaporation at low temperature.

Detailed description of preferred embodiments

The vacuum apparatus 1 showed in Fig. 1 a comprises essentially a vessel or pot 2 and a lid 4 of closure for said pot 2. Said lid 4 is showed separately in Fig. 1 b.

Said pot 2 is equipped with an upper opening and a gasket 3 on the border of said opening. Said lid 4 is applicable on the upper opening of the pot 2 so as to define a processing chamber 6 inside which a food preparation 7 is cooked. In the embodiment of the Figs. 1 a and 1 b, said lid 4 is a concave vessel opened on the upper part with bowl shape apt to delimit a second chamber 21 with a shape substantially semispherical.

Said lid 4 is equipped with an upper border 4c. Said upper border 4c identifies a flat surface 4d, which is tangent to the border in each of its points; this means said border 4c belongs to said surface 4d. Said flat surface delimits the second chamber 21 on the upper part.

Furthermore said lid 4 is equipped with a bottom 4a concave upward which defines the upper wall of the processing chamber 6. The maximal distance which separates said flat surface 4d and said bottom 4a is indicated with the reference letter d, as showed in Fig. 1 b.

In the example of the Figs. 1 a e 1 b, said distance d is about half of the distance c/2 which separates two points positioned at maximal distance inside the second chamber.

The bottom 4a of the lid comprises a flat portion 4b, on which a valve 5 is positioned. Said valve 5 is preferably a check valve and has two working positions, one opened and one closed. When the pressure inside the processing chamber 6 is lower than the external pressure the valve 5 is in the closed position and the processing chamber 6 results gas-tight isolated from the external environment.

The working process of the apparatus 1 of Fig. 1 is described below. A food preparation 7 comprising a liquid portion 7a is introduced into the pot 2 and the lid 4 is placed to close the pot 2 by means of the gasket 3, determining the processing chamber 6.

The pot 2 is heated by means of a direct source of heat, for example a induction cooker 8, to a temperature apt to bring at least part of the liquid portion 7a of the food preparation 7 to the boil, generating vapor 10 at atmospheric pressure.

The liquid portion 7a is kept boiling for a pre-defined time during which the generated vapor 10 removes air from the processing chamber 6.

As a result of the air expulsion by the vapor 10, the pressure inside the processing chamber 6 is due essentially to the vapor 10 of the liquid fraction 7a, the air content being substantially negligible.

At this point, the second chamber 21 defined by the lid 4 is filled with a refrigerant means 9, in this case water, cooling down, and the vapor 10 generated into the processing chamber 6 condenses in contact with the bottom 4a of the colder lid. Consequently, the pressure inside the processing chamber 6 decreases and the vacuum is generated. As a consequence of the pressure lowering inside the processing chamber 6, the valve 5 placed on the bottom of the lid 4 closes and the chamber 6 is gas-tight isolated from the external environment.

Furthermore, as a consequence of the pressure lowering, the boiling temperature of the liquid 7a of the food preparation 7 decreases. The liquid 7a is kept boiling for time enough to cook the food preparation 7 and the water present in the lid 4 absorbs the heat transferred by the food preparation 7, condensing the vapor 10 released from the boiling liquid. The condensed vapor 1 1 drips from the bottom 4a of the lid and refluxes inside the food preparation 7.

Finally both the heating source 8 and the refrigerant means 9 are removed. Successively, the valve 5 is opened in order to remove the lid 4 from the pot 2 and to have access to the food preparation 7 processed with method of reflux cooking.

As alternative to the lowering of the pressure by means of air expulsion by the vapor 10 generated at atmospheric pressure inside the processing chamber 6 and successive condensation of said vapor 10, another embodiment of the invention provides for connecting the valve 5 to a vacuum pump in order to evacuate the air before starting the heating of the food preparation.

Fig. 2a shows the connection between the vacuum pump through a specific external connector 30 and the valve 5. In particular, the connector body 31 is placed around the valve 5, which opens, and the air is evacuated from the processing chamber 6 passing through the aspiration tube 32.

Referring to Fig. 2b, once completed the aspiration phase, the external connector 30 of the vacuum pump is disconnected from the valve 5 and said valve 5 closes by the effect of the external pressure.

The vacuum apparatus showed in Fig. 3 comprises a temperature sensor 12 which measures the temperature value of the external wall of the pot 2, from which it is possible to go back to the boiling temperature of the liquid fraction 7a present inside the processing chamber 6, and transmits it to a peripheral device13. In the example of Fig. 3, the apparatus also comprises a closed loop control system 14. Said sensor 12 generates a signal which is processed and transmitted to the control system 14, while said peripheral device 13 transmits to the same a particular value of temperature selected by the user (set-point). The control system 14 uses the signal received by the sensor 12 as feedback signal to control the boiling temperature of the food preparation 7 so as to reach the temperature value selected by the user (set-point) regulating the evaporation rate of the refrigerant means 9, in this case water, contained inside the lid 4. In particular, said control system 14 is connected to a fan 15 positioned over the surface 16 of the water contained in the second chamber 21 and regulates its working speed. Said fan 15, moving the air above the surface 16 of the water, produces a higher evaporation rate of the water, therefore the release into the environment of a bigger heating flow and the consequent lowering of the processing temperature of the food preparation.

The apparatus showed in Fig. 4 comprises a collecting container 17 of the condensed vapor 1 1 in the processing chamber 6. Said collecting container 17 defines a condensation chamber in its inside and an evaporation chamber outside. Said chambers are connected by a passage 33 between the bottom 4a of the lid and said container 17.

The collecting container 17 is equipped with a holder 18 which keeps it raised with respect to the bottom 19 of the chamber 6, where there is the food preparation 7 to process. In the example showed in figure, said collecting container 17 is bowl shaped. The apparatus of Fig. 4 is used for processes of distillation or evaporation, namely for extracting the more volatile components contained in certain food preparation or, respectively, for reducing the water contents in certain food preparations, during which the condensed vapor 1 1 is separated and collected in the collecting container 17, instead of refluxing and flowing back into the food preparation.

The refrigerant 9 used in the apparatus of Fig. 4 and placed into the second chamber 21 is a mixture of water and ice, which allows reaching boiling temperatures, during the distillation and evaporation processes, close to room temperature.

The apparatus showed in Fig. 5 comprises a tube 20 which connects the valve 5 to the bottom of the processing chamber 6. Said tube 20 feeds a second liquid food preparation 27 from the second chamber 21 to the processing chamber 6, inside which is the pressure has already been lowered or the vacuum generated.

Examples

Test 1: Control of the boiling temperature through a fan connected to a closed loop control system (Fig. 3)

It has been used an apparatus 1 comprising a pot 2 with a diameter of 24 cm and provided with a lid 4 composed of a semispherical bowl with a diameter of 28 cm. The fan 15 used to displace the air on the surface 16 of the water moves, at the maximal rotation speed, less than one m ³ of air per minute. The direct source of heat used is a commercial induction hob.

The reflux rate and the temperature range within which it is possible to regulate the boiling temperature of the food preparation 7 with an accuracy of ± 0.2 ° C are given in Table 1 for different values of the thermal power provided by the direct source of heat used to heat the pot 2.

Electrical power Thermal power Temperature Reflux rate

[Watt] [Watt] range [°C] [litri / ora]

200 About 170 50 - 60 About 0.25

400 About 300 60 - 70 About 0.45 600 About 450 70 - 80 About 0.70

800 About 600 80 - 90 About 0.90

Table 1

Test 2: Control of the boiling temperature and of the distillation rate of an apparatus used in a distillation process (Fig. 4)

They have been used: a vacuum pump, provided with an external connector 30, able to reach a final pressure lower than 1 mbar; a pot 2 with diameter of 24 cm and height of 21 cm able to process up to two liters of food preparation 7; a collecting container 17 with a capacity of about one liter. The direct source of heat used is a commercial induction hob. The bowl that forms the lid 4 has been kept full of ice and water throughout the test series. A water mixture, flavored and colored with turmeric powder has been used as food preparation 7, where glass spheres have been added to facilitate the boiling of the same. In this way it has been possible to prove that the apparatus is able to produce a crystal clear and transparent distillate.

The evaporation rate and the boiling temperature of the aqueous food preparation are showed in the Table 2:

Table 2 Test 3: Control for comparison of the time required to evacuate efficaciously the air contained into the processing chamber by the vapor generated at atmospheric pressure and later condensed according to an embodiment of the step c) showed in the text (Fig. 5) It has been used an apparatus 1 comprising a pot 2 with a diameter of 24 cm. To reach performances similar to those obtained using a vacuum pump (Table 2), some water has been kept boiling for 20 minutes (duration of the point ii) showed in the text.

From the data showed in the above tables 1 e 2 it is noted that the lower the temperature the lower the distillation or reflux rate.