Abstract:
An impregnator for mixing a nonaerated or only slightly aerated liquid (F) with gas (G), in particular for mixing a noneffervescent or only slightly effervescent beer precursor product, or a beer precursor product containing CO 2 , with CO 2 , includes a mixing cell, in particular tubular, which except for an incoming liquid inlet, an incoming gas inlet, and an outlet, is partitioned off from the surrounding, and at least one Impregnator body is disposed in the mixing cell in such a way that the flow through the mixing cell of the liquid (F) and gas (G) must necessarily take place through the impregnator body. Disposed in the mixing cell is at least one impregnator body, which includes a porous solid body, namely of a foam material, a sponge, a follow fiber module, or a sintered material.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an impregnator for mixing a nonaerated or only slightly aerated liquid with a gas. The invention also relates to a pressure compensator assembly for bar systems, an impregnator for inline gassing bar systems, and a bar system with a pressure compensator assembly. The invention further relates to novel uses of such an impregnator. The nonaerated or only slightly aerated liquid may be a soda, soft drink, water, juice, or a low-carbon-dioxide or carbon-dioxide-free beer precursor product. The gas be carbon dioxide or nitrogen. 
     2. Description of Related Art 
     Impregnation in terms of the invention is the release of gases into liquids, or in other words impregnating liquids with gases, as it is carried out in absorption columns in large-scale chemical systems. For example, according to the German Patent DE 25 03 681, a gas is conducted from the bottom of a column to the top of the column in counter current to a liquid, which flows from the top to the bottom, wherein the column is filled with a porous ceramic material. 
     Such impregnators are used in bar systems, so that liquids or beverage precursor products can be impregnated with gases, or gases can be released into the liquids and beverages ready to drink can thus be produced, but only once they are in the bar system. Examples of liquids to be impregnated, sodas (syrups) and in particular a low-carbonation or carbonation-free beer precursor product can be considered. Besides gases that contain flavorings, in particular carbonic acid (more precisely, CO 2 ) and nitrogen (more precisely, N 2 ) can be considered as impregnating gases, in particular for creating a bubbly soda and in particular a carbonated beer. 
     The term “carbonic acid” or “carbonated” is indeed usual in beverages, but more precisely, carbon dioxide (CO 2 ) is added, which by far predominantly bonds only physically in the liquid and does not enter into any chemical reaction to form carbonic acid (H 2 CO 3 ). 
     This physical bond upon the release of gases into liquids is a mass transfer process in accordance with the laws of physical absorption. This transfer process takes place at the gas-liquid phase boundary faces. The gas diffuses into the liquid. While nonpolar nonelectrolytes, such as oxygen and nitrogen, on becoming dissolved are incorporated primarily into the voids between the liquid molecules, polar electrolytes, such as carbon dioxide, in water form water bridges with the likewise polar water molecules, and these bridges cluster with other water molecules to form supermolecular assemblies. CO 2  molecules, for example, penetrate the microstructure of the water molecules quite well. The mass transfer of gases into liquids is described in simplified form in Fick&#39;s first law:
 
 Mi=A ( Ci*−C 1)=( Di/δi ) A ξ( Pi*−P 1).
 
In the equation,
 
     Mi stands for the mass flow of a gas from the gas phase into the liquid; 
     A stands for the area of the surface at which the mass transfer takes place; 
     (Ci*−C1) stands for the concentration gradient between the equilibrium concentration at the phase boundary face and the instantaneous concentration in the liquid; 
     δ stands for the length of the transportation course from the interior of the liquid to the phase boundary face; 
     Di stands for the diffusion coefficient for gases; 
     ξ stands for the absorption coefficient (of the solubility of gases) as a function of temperature, pressure, and material; and 
     (Pi*−P1) stands for the pressure drop between the partial pressure of the gas and the pressure applied at that instant in the liquid. 
     Accordingly, the speed (Mi) at which a state of equilibrium is established in a liquid depends on the concentration gradient, the diffusion coefficient for gas, the absorption coefficient, the surface area, the length of the transportation course, the prevailing pressure, and the temperature. 
     Efficient mass transfer systems must therefore have a large surface area where the mass transfer can take place, must create high turbulence for the shortest possible transportation courses, and must furnish both high pressure and low temperatures, so as to attain the most efficient and fastest possible mass transfer in one phase. 
     Besides known bubble-forming systems, such as agitation systems, loop reactors or injection systems, which are not very economical because of their vulnerability and in particular the high expense for equipment in injection systems (pressure vessel, pressure pump, cooling system) and the attendant high operating costs, carbonators or impregnators of the type defined at the outset have become established in the field of gassing beverages with carbonic acid in bars and pubs. 
     By means of a predetermined gas and liquid pressure—in the impregnation of an uncarbonated beer precursor product with CO 2 , a liquid pressure of 4 bar and a gas pressure of 5 bar, for instance, or a liquid pressure of 5 bar and a gas pressure of 5.5 bar, have proven suitable—the attempt is made to establish the desired ratio of gas to liquid in the mixing cell and an optimal pressure in the mixing cell, so that the desired dissolution of the gas in the liquid takes place. 
     However, such impregnators are often used in inline gassing bar systems, in which the beverage precursor product is conventionally pumped out of a tank with piston pumps and more recently also from a bag using diaphragm pumps, so that the impregnator is exposed on the inlet side to the pressure surges of the piston pump, and a constant fuel pressure cannot be attained. The volumetric flow discharging into the mixing cell per unit of time therefore depends substantially on the speed with which the bartender taps the beverage. If the tapping speed changes, the pressure drop from the gas infeed or liquid infeed side to the mixing cell changes as well, so that the degree to which the gas infeed and liquid infeed open fluctuates even though the external pressure is set to a fixed value. As a result, the volumetric flows discharging into the mixing cell change as well, so that the gas-liquid mixture ratio may deviate from the optimum for dissolution of the gas in the liquid at whatever pressure prevails in the mixing cell. 
     In bar systems, a beverage is pumped via a beverage infeed line from a beverage container to a dispensing tap, usually located at a higher level. In conventional bar systems, the beverage infeed line comprises a bar line; in bar systems with inline gassing, or pressure gassing stages in the bar, one or more impregnators may also be disposed in the beverage infeed line, and with them a beverage precursor product is enriched for instance with carbonic acid. In so-called postmixing bar systems, mixing valves for syrup with an inline-aerated water can be located in the beverage infeed line, along with a buffer container in which the water is aerated in a carbon dioxide atmosphere. 
     An impregnator, wherein water is impregnated with a carbon dioxide under a carbon dioxide atmosphere is disclosed in U.S. Pat. No. 636,162. The gas and the liquid pass through wire-cloth sieves and the impregnated liquid gas mixture is conducted in a buffer container. 
     For pumping the beverage or beverage precursor product through the beverage infeed line, a defined pumping pressure is necessary. In conventional bar systems, this pressure is furnished for instance via a compressed gas (such as carbon dioxide), whose pressure is exerted on a beverage keg or drink container, so that the beverage is forced upward to the dispensing tap via the dispensing line. In bar systems with a pressure gassing stage in the bar, which operate by the inline carbonation process and in which a so-called impregnator is provided in order to provide a low-carbonic acid or carbonic acid-free beverage precursor product in the bar system with carbonic acid or the like, conversely the beverage container is followed downstream by a pump, with which the beverage precursor product is pumped out of the beverage container to the impregnator and becomes carbonated there, or in other words mixed with carbonic acid (or more precisely, carbon dioxide), so that then it can be pumped as a beverage, with the carbonic acid dissolved in it, to the dispensing tap. 
     This requires a certain working pressure, which is above the keg pressure and the dispensing pressure. In inline gassing of beer, for instance, a pressure in the impregnator of 4 to 5 bar has proved suitable. 
     To enable adjusting the desired tapping speed of the dispensing tap, it is therefore necessary to artificially increase the pressure loss in the bar system, so that for instance an overly high pumping pressure, or the overpressure necessary for the inline gassing, is reduced, for instance to the keg pressure level that is usual in conventional bar systems. In conventional beer dispenser systems, for instance, a maximum of 1.5 to 3 bar, often 2.2 to 3 bar, of keg pressure is typical. 
     One possibility for this is to wind up the line in the form of a coil. So-called pressure compensators are also known, which today are usually directly integrated with the dispensing tap. In that case, a displaceable throttle restriction is disposed in the line leading to the dispensing tap, and its location can be adjusted by the bartender via an adjusting screw in such a way that the throttle restriction opens up an annular gap of a desired thickness, and the resistance can thus be varied and adapted to the desired conditions. With the adjusting screw, the bartender sets the dispensing tap to a desired flow rate, which is oriented for instance to whether he wants to fill large vessels, such as 1-liter steins, or small vessels, such as 0.25-liter soda glasses, and also depends on the liquid to be tapped, such as pale beer versus wheat beer. 
     Especially in bar systems with a pressure gassing stage in the bar, in which systems a working pressure in the impregnator is required that is above the keg pressure that is usual in conventional bar systems, the problem arises that regulating the quantity is no longer readily possible at the dispensing tap. If the bar system is used for beer, the beer “rips open”, or in other words begins to foam since carbonic acid is being released. This release is due to the fact that the dispensing tap pressure compensator is designed for a certain pressure range. If the line pressure is markedly higher than intended, the laminar flow is impeded, and eddies occur as a consequence of which carbonic acid is released. 
     If a compressed-air diaphragm pump is used at the dispensing tap, fluctuations in the pumping pressure can also occur. The tap pressure, however, should be constant, since otherwise, if pressure fluctuations occur, an unwanted release of carbonic acid can occur. 
     The U.S. Pat. No. 6,712,342 B2 and U.S. Pat. No. 6,138,995 disclose beverage dispensers, wherein hollow fiber membranes or bundles are provided. The hollow fiber membranes or bundles contain hydrophobic hollow fibers, which serve as impregnator bodies. CO 2  passes through the impregnator bodies and the liquid to be impregnated washes round the impregnator bodies. Only the gas can pass through the walls of the hollow fibers and impregnates thereby the liquid on the other side of the wall. 
     An impregnator of this kind is proposed for instance in German Patent Disclosure DE 198 51 360 A1. This involves a tubular sieve carbonator, in which many mixing sieves are lined up with one another in a mixing cell, embodied as a tube, to which the gas and liquid infeeds can be connected. The mixing sieves together offer the desired large surface area at which the mass transfer can take place upon dissolution of the carbonic acid in the beverage precursor product. A tubular sieve carbonator of this kind can also be found in German Patent Application DE 100 55 1371 A1. 
     In U.S. Pat. No. 3,761,066 as well, a tubular sieve carbonator of this kind is shown, in which the gas and water supplied has to flow through a plurality of wire cloth mixing sieves: Gas is fed in from the side and water from above. The gas passes through a filter and an adjoining nozzle or impact plate to reach a prevortexing stage that the liquid also enters, namely through openings in the circumference of a cylindrical perforated plate. The flow thus created passes through openings in a conical perforated plate to enter the actual impregnation stage. Cylindrical wire cloth rings are located there, and plates are disposed between the individual wire cloth rings, so that the flow experiences a slalom through the wire cloths and in the process is impregnated. The annular wire cloth elements may be formed of any material that has (liquid-) permeable properties and is suitable for use in the carbonator shown. 
     Such tubular sieve carbonators, however, are not only relatively expensive in terms of material costs because of the high number of metal sieves but are also expensive with regard to the correspondingly complex assembly. 
     Recently, bulk material carbonators have therefore also been proposed, for instance in German Patent Application DE 101 60 397 A1. From this reference, a bulk material carbonator is found, with a mixing cell that is filled with a bulk material that has a high surface area, such as quartz pellets or the like. Other granular materials have also been proposed as the bulk material, such as fine plastic pellets or fine steel pellets made by VA Stahl. The surface area attainable with the bulk material, however, is still limited. This is because floating of the bulk material out of the impregnator must absolutely be avoided, at least in the field of foodstuffs, and thus the bulk material, despite the requirement for a large surface area, cannot be allowed to be ground arbitrarily fine so as not to clog the requisite trapping systems for the bulk material. Nevertheless, clogging cannot be completely avoided over the course of time, and bulk material carbonators must therefore be replaced relatively often. It is also disadvantageous that such bulk material carbonators are relatively difficult to clean, so that at the cleaning intervals necessary for reasons of food hygiene, especially in connection with beverages containing starch or sugar, usually the entire bulk material carbonator has to be replaced. 
     SUMMARY OF THE INVENTION 
     It is therefore a first object of the present invention to create an impregnator of the type defined at the outset with which high gas release effectiveness is attained at low production and operating costs, and which is suitable for use in the food field and for producing beer, as well as a bar system equipped with such an impregnator, as well as to improve the production of beer and other beverages. 
     These objects are attained with not only with regard to an impregnator, a pressure compensator assembly, and a bar system, but also with regard to beer and beverage production by the use of an impregnator. 
     In a first aspect of the invention, an impregnator body is disposed in a mixing cell of the impregnator, into which cell a gas inlet and a liquid inlet discharge and from which an outlet for the liquid and gas mixture leads outward, the impregnator body being disposed in such a way that the flow of liquid and gas through the mixing cell must necessarily take place through the impregnator body, and the impregnator body comprises a porous material or in other words is a porous solid body. The porous solid body, or solid body that has pores, can comprise any material that has pores and a large surface area, such as sintered materials, woven, knitted, mesh or felted solid bodies, or sponge or foamed materials, or the like. A hollow fiber module comprising hollow plastic fibers, which can be fabricated in the size of a human hair, would also be conceivable. These materials are inexpensive, and particularly the sintered solid bodies can be produced with high uniformity in terms of pore size and pore arrangement, so that advantages are attained not only in terms of commercial aspects but also in terms of the quality of impregnation or carbonation of the liquid to be impregnated with a gas and in particular to be carbonated. 
     All the materials listed above are suitable as material for the impregnator bodies. However, it has been found that embodiments in which the impregnator body, or one of the impregnator bodies, is produced from a sponge, from foamed material or foam, or from a body that comprises hollow fibers has especially many advantages, since these materials have high porosity, with a relatively high number of pores that can be adjusted depending on the material and a relatively high average pore size and thus have large phase boundary faces with low flow resistance and adequate resistance to being washed away. In a preferred embodiment, the at least one impregnator body comprises a polyester or polyether filter foam with a pore size of 90-100 PPI (pores per inch), corresponding to a pore size of approximately 250 μm and approximately 90,000 cells/cm 3  (open-pore cells). Especially advantageously, the foam has the cellular structure of a reticulated filter foam, which is virtually 100% open-celled. Because of the reticulation, the cell membranes are removed virtually entirely; that is, only a skeleton remains behind. This assures a pronounced low flow resistance. The phase boundary faces are accordingly no longer located at pores that are completely surrounded by walls of material but rather at otherwise open-walled cells that are surrounded by only a skeleton of material. 
     For attaining an even smaller pore size, the foam in the carbonator is advantageously compressed, in particular from originally 150 mm to 80 mm in length. As a result, the foam impregnator body is compressed, and the number of cells rises to approximately 170,000 cells/cm 3 . 
     With sintered materials as well, however, large phase boundary faces and great turbulence in the flow can be generated. Depending on the desired gas and liquid and on the desired composition of the starting mixture, various sintered materials with different pore sizes are available, so that the impregnator can be adapted to particular specifications by the selection of the suitable material for the impregnator body. Depending on requirements made of the impregnator body, including durability and food safety, a sintered material of glass, ceramic, plastic, or metal may be used. 
     Advantageously, the impregnator body is embodied as a disk that fills the diameter of the mixing tube, so that the liquid, but also the gas, must necessarily flow through the impregnator body and enters into solution at the large surface area of the pores of the solid body. It is advantageous here that this solid body can be introduced easily into the mixing cell but also removed easily from it again, so that both economical production and maintenance of the impregnator at the intervals prescribed by hygiene laws are easily possible. Bulk material is thus effectively prevented from washing away, without the high cost, complicated engineering, and complex assembly of a tubular sieve carbonator. 
     However, it would also be conceivable to provide the impregnator body with a mounting—for instance of plastic—and thus to form an impregnation cartridge that fills the diameter of a mixing cell that is advantageously embodied as a mixing tube. 
     If it proves necessary for the impregnator body to be additionally fixed in the mixing cell, then suitable fixation means may be provided, such as a perforated plate or a lattice, which holds the impregnator body in position and with which the impregnator body is optionally compressed. 
     A further advantageous refinement pertains to a high-frequency or ultrasonic vibrator, which acts on the interior of the mixing cell and thus serves as a supplementary impregnator or impregnation reinforcing device. The vibrator could be mounted on the wall of the mixing cell, for instance, or have ultrasound generators distributed over the entire circumference of the mixing cell and/or an ultrasound unit disposed in the mixing cell. As a result of the oscillations generated per high-frequency vibration and the resultant cavitation, high turbulence and hence short transportation courses in the mass transfer are attained in the mixing cell. It is especially advantageous that the use of ultrasound is done at the pressure prevailing in the mixing cell of the carbonator or impregnator (such as 3 to 5 bar) and with the medium flowing through it. 
     One method for releasing gas in a liquid with the aid of ultrasound is described in European Patent Disclosure EP 0 661 090 B1. 
     The invention is not limited to an impregnator with an impregnator body. On the contrary, a plurality of impregnator bodies may be connected in series in the mixing cell. Each impregnator body or some of the impregnator bodies may comprise different materials, so that the mixing properties of the impregnator can be adapted even better to the particular liquid or gas or desired starting composition. 
     Also advantageously, a head piece that seals off the gas and liquid infeed side of the mixing cell from the surroundings is provided that is provided with one connection for a liquid infeed line and one connection for a gas infeed line. The impregnator can thus be installed in existing systems in a simple way. 
     Preferably, the impregnator is produced as a one-piece end product, such as a one-piece injection-molded component with an integrally welded impregnator body. Alternatively, the impregnator may instead be constructed such that it can be broken down into its individual parts and cleaned, which also makes easy replacement of the impregnator body or impregnator bodies possible. Especially advantageously, the entire impregnator (except for the impregnator body or bodies) or at least the housing of the mixing cell is made from a plastic that does not swell and that can be shaped with sufficiently precise tolerances. 
     If the head piece is screwed to the mixing tube, the gas inlet discharges centrally into the mixing tube, and the liquid channel is eccentric or annular, the gas outlet may for instance be provided on a truncated tube screwed onto the head piece in the interior of the mixing tube. 
     For mixing in a second gas, a second gas infeed line connection can also be provided on the mixing cell. It would be equally conceivable for that purpose to connect a plurality of impregnators in series in such a way that the outlet of the preceding impregnator communicates with the liquid inlet of a downstream impregnator, in order to create an impregnating system for mixing a liquid with a plurality of gases. Such impregnators with a plurality of gas connections can advantageously be used for mixing a beer precursor product that does not contain CO 2  or contains only little CO 2  with CO 2  and nitrogen. Nitrogen is added to beers—at least in foreign countries that do not have the German Reinheitsgebot or purity law—for the sake of better foam holding, while conversely CO 2  has to be added to beer precursor products that contain no or only little CO 2 . 
     Further advantageous uses of the impregnator according to the invention are obtained upon mixing a beverage precursor product with flavorings, since flavorings or fragrances are often in gaseous form. This use is especially suitable for substance or materials that are not durable for very long once they are mixed or when they are at low concentrations and which therefore have to be freshly prepared on an ongoing basis. For instance, an apple juice could be mixed with cherry flavor or the like. Another advantageous use has already been addressed in conjunction with the impregnator that has two gas inlets. Naturally, impregnators according to the invention that have only one gas inlet can also be especially advantageously used for mixing a noneffervescent or only slightly effervescent beer precursor product, or one contains no or only little CO 2 , with CO 2 . On the other hand, they can also be used to mix beer or a beer precursor product with nitrogen. 
     In a further aspect of the invention, a gas inlet valve and a liquid inlet valve are provided, which are arranged for opening and closing the gas and liquid inlets in accordance with the magnitude of a pressure drop from the inlet side to the mixing cell, and the gas inlet valve has a gas inlet closing element, disposed in a gas inlet channel, and the liquid inlet valve has a liquid inlet closing element, disposed in the liquid inlet channel, and the gas inlet closing element and the liquid inlet closing element are coupled to one another in such a way that the gas inlet valve opens the gas inlet to a predetermined degree of opening, depending on the degree of opening of the liquid inlet at the time. 
     By way of coupling the degree of opening of the gas inlet with the degree of opening of the liquid inlet, in accordance with the invention, it is thus successfully possible for various tapping speeds to establish a mixture ratio suitable for the impregnation process in the interior of the mixing cell. Depending on the liquid and gas selected and on the optimal ratio of the two to one another at the applicable pressure, the coupling may increase linearly or degressively or progressively with the pressure. If the liquid inlet opens widely, then the gas inlet opens correspondingly widely as well, and hence the necessary carbonic acid for impregnating a carbonic acid-free beer precursor product, for instance, flows in. If the degree of opening of the liquid inlet is reduced, conversely, then the degree of opening of the gas inlet lessens accordingly, so that once again, a mixture ratio of gas and liquid that is suitable for the impregnation process in the mixing cell is established. 
     In this way, it is successfully possible to compensate both for the effects of pressure fluctuations on the mixing cell side on the ratio of the inflowing gas to inflowing liquid and for the effects of pressure fluctuations on the liquid inlet side. This is because, if the pressure in the mixing cell drops, the liquid inlet closing element reduces the degree of opening of the liquid inlet, and thus the gas inlet closing element coupled with it reduces the degree of opening of the gas inlet accordingly. The same is true if the pressure rises in the mixing cell; then the gas inlet closing element either reduces the degree of opening to the same ratio or in obedience to the principles (mixture ratio course over the pressure) suitable for the particular impregnation process, in the same way as is predetermined by the liquid inlet closing element. 
     Conversely, if pressure surges occur on the liquid inlet side, surges that as addressed above can be caused by the use of piston pumps, then the liquid inlet valve will open the liquid inlet to a defined degree, as a function of the pressure drop existing at the particular time from the liquid inlet to the mixing cell, and via the coupling of the gas inlet valve, the gas inlet is likewise opened correspondingly wide. 
     Advantageously, the liquid inlet closing element is prestressed toward the liquid inlet side and is joined integrally to the gas inlet closing element, so that a displacement of the liquid inlet closing element is transmitted to the gas inlet closing element. The unit thus formed can be embodied on the order of a piston slide, if the mixing cell head or the head piece of the impregnator is constructed like a T element, or in other words if the liquid inlet and the gas inlet are aligned with one another. It is thus possible in a structurally simple way to define both the inflowing liquid flow rate and the inflowing gas flow rate as a function of the pressure drop from the liquid inlet side to the mixing cell. 
     Alternatively, an electrical coupling of the closing elements could also be provided. In addition, a piston slide unit on the order of a multiposition valve, comprising the gas inlet closing element and the liquid inlet closing element, could also be used in a mixing head in which two parallel inlet channels lead into the interior of the mixing cell. For that purpose, a closing position could for instance be provided in which the piston slide seals both the gas inlet channel and the liquid inlet channel, as well as an opening position, in which the piston slide is thrust with one or more openings penetrating it in front of both the liquid inlet opening and the gas inlet opening, so that the applicable opening is uncovered. However, in this arrangement one additional provision is necessary in order to actuate the piston slide as a function of the pressure drop from the liquid inlet side to the mixing cell, such as a suitable bypass line to a face end of the piston slide from the liquid inlet side, and a prestressing device acting on the other face end of the piston slide. However, that construction is relatively complicated. 
     What is therefore preferred is a mixing head in the shape of a T, with an aligned liquid inlet channel and gas inlet channel, in which the piston slide, formed of the liquid inlet closing element and the gas inlet closing element, is seated directly in the liquid inlet channel and the gas inlet channel and, by a displacement in the direction toward the gas inlet opens both the gas inlet and the liquid inlet to the desired extent. Conversely, a displacement toward the liquid inlet closes both the gas inlet and the liquid inlet. 
     In a first embodiment, this response to the pressure drop from the liquid inlet to the mixing cell could be accomplished by providing that the gas inlet closing element is a piston, which widens conically toward the gas infeed side and which is located in a likewise conically widening gas inlet channel portion and communicates with the liquid inlet closing element via a piston slide portion. The liquid inlet closing element can be a slide that tapers conically toward the liquid infeed side and is located in a liquid infeed, likewise tapering conically toward the liquid infeed side, and that is prestressed, on its side toward the liquid infeed side, toward the liquid infeed. 
     Because of its simple and more-economical construction, however, an embodiment is preferred in which the liquid passage extends from the liquid infeed side into the mixing cell through the liquid inlet closing element, and the gas infeed is effected through the gas inlet closing element. To that end, the liquid inlet closing element may be a hollow body surrounded on multiple sides and open toward the liquid infeed side, and in the walls that surround the hollow body on multiple sides, at least one passage opening for the liquid is provided. In the closing position, in which the liquid inlet closing element fills the liquid inlet blocking portion, no passage of liquid therefore occurs. However, if the liquid inlet closing element is put in an opening position, in which it protrudes into a volume located on the mixing cell side, the liquid passage is at least partially uncovered, and the beverage precursor product flowing into the hollow body from the liquid infeed side can flow into the mixing cell. 
     The gas inlet closing element can in this case as well be provided as a conical slide element in a conical gas inlet channel. However, it is advantageous for a hollow body to be provided also on the gas inlet side, as a gas inlet closing element, but this hollow body is open toward the mixing cell and in a closing position fills the gas infeed channel, and in an opening position it is thrust so far into a volume on the gas infeed side that at least one gas passage opening for the gas is uncovered, through which the gas can flow from the gas infeed side into the mixing cell interior. 
     It is understood that in the event that the force acting from the gas side on the piston slide is greater than the force acting from the liquid side, it is also possible to provide the hollow body on the liquid side with an opening toward the mixing cell and with closable liquid passages to the liquid infeed side, if the gas inlet closing element is at the same time open toward the gas side and is closable toward the mixing cell. 
     In this respect, a sealing element is advantageously provided between the gas inlet closing element and the gas inlet blocking portion. 
     It is also advantageous if the liquid passages are bores distributed over the wall of the liquid inlet closing element, or in other words are relatively small in proportion to the diameter of the liquid inlet blocking portion but in turn are present in high numbers. The same is true for the gas passages. The ratio of the diameter of the closing element to the passage bore is advantageously over 1:10 and preferably over 1:20. In this way, the number of passage bores available for the gas and liquid passage can be allocated precisely, to suit the position of the valve piston slide. 
     It is especially advantageous in this respect if the liquid and/or gas passage bores are provided in the form of a chain of bores located spirally around the side wall of the respective closing element. This is because in that case, the available number of bores for the passage of liquid and gas does not increase or decrease suddenly, but instead increases and decreases incrementally upon displacement of the piston slide, by one bore each, so that the desired gas and liquid flow rate can be adjusted still more precisely as a function of the pressure drop from the liquid inlet side toward the mixing cell. 
     Additional advantageous refinements will become apparent from the following description. 
     Within the scope of the invention, it is understood to be possible to combine the various characteristics freely, to the extent that this appears useful. It is understood that the aforementioned characteristics and those still to be explained below can be employed not only in the combination indicated but also in other combinations or on their own, without departing from the scope of the invention. Nor is the invention restricted to the uses described herein. 
     For instance, the use of any suitable impregnator for mixing beer with nitrogen or for mixing a beverage precursor product with gaseous flavorings or for mixing beer precursor products that contain no CO 2  or only little CO 2  with CO 2  could be made the subject of an independent patent application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Individual advantageous embodiments of the invention will be described in further detail below in conjunction with the accompanying drawings. Shown are: 
         FIG. 1 , a sectional view of a solid body impregnator in accordance with a first embodiment of the present invention; 
         FIG. 2   a , a sectional view of an impregnator in a further embodiment of the present invention; 
         FIG. 2   b , a sectional view, corresponding to  FIG. 2   a , of a further embodiment of the present invention; 
         FIG. 3 , a sectional view along the axis of the gas and liquid inlet channel in  FIG. 2   b , perpendicular to the sheet direction; 
         FIG. 4 , a sectional view along the line IV-IV in  FIG. 3  of a slightly modified form of the embodiment of the invention shown in  FIG. 2   b;    
         FIG. 5 , a view corresponding to  FIG. 4  of a slight modification of the embodiment shown in  FIG. 2   b;    
         FIG. 6 , a sectional view of an impregnator in a further embodiment of the invention; and 
         FIG. 7 , a perspective view of a valve slide in  FIG. 6 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First, reference will be made to  FIG. 1 . Reference numeral  1  designates a tubular mixing cell. In the mixing cell  1 , disklike impregnator bodies  11 ,  13 ,  15  are press-fitted in series and in succession, so that the liquid flowing through the mixing cell  1  and the gas, or the already premixed gas-liquid mixture, flowing through the mixing cell  1  must pass through the impregnator bodies  11 ,  13 ,  15  and thus enter into solution at the surface of the pores marked with dots. The first impregnator body  11  in order from the infeed side is made of a sintered material with finer pores than the two impregnator bodies  13 ,  15  that follow it. 
     The impregnator bodies are adjoined by a calming portion marked  10 , in which the gas-liquid mixture emerging as a turbulent flow from the outlet-side impregnator body  15  is calmed to a laminar flow before exiting the impregnator through an outlet opening  7  and being conducted for instance to a dispensing tap in the dispenser system. 
     The outlet tube  7  is provided in a cap that is screwed onto the mixing tube  1  and is sealed off from the mixing tube  1  by an O-ring. On the inlet side, the mixing tube  1  is likewise closed with a screwed-in component, which is a head piece  21 , and sealed off with an O-ring. 
     The gas infeed G on one side—at the left in the drawing—and the liquid infeed F on the other—at the right in the drawing—can be connected to the head piece  21 . To that end, the head piece  21  is penetrated by a gas infeed channel, which discharges into the mixing cell via a truncated tube  3 , and a liquid passage channel, which discharges into the mixing cell  1  eccentrically at a point marked  6 . Both on the gas infeed side and the liquid infeed side, threaded bores are provided in the head piece, and respective connection pieces  33 ,  31  are screwed into them, each connection piece receiving a respective check valve  29 ,  27 , with which the gas and liquid infeed channels are secured against a reverse flow from the mixing cell  1 . A connection tap  23  is screwed in turn into the connection piece  33  on the gas infeed side and can be connected in plug-in fashion to a gas infeed line, while conversely on the liquid infeed side, a connection tap  25  is screwed into the connection piece  31  there, and a hose for liquid can be slipped onto this connection tap with a suitable plug part. The gas infeed channel, in the region of the connection tap  23  on the gas infeed side, has a cross-sectional constriction marked  22 , which acts as a pressure limiting nozzle  22 . With the pressure limiting nozzle  22 , it is assured that the gas pressure will not become so high that the gas positively displaces the liquid in the mixing cell; the gas pressure and furthermore the mixing operation nevertheless remain adequately controllable. 
     The truncated tube  3  mentioned above, into which the gas infeed channel that penetrates the head piece discharges centrally, has a plate  5  or an encompassing shoulder  5  on its side facing away from the head piece  21 , and on its side facing toward the head piece  21  it is screwed into the gas infeed channel, which is provided with a female thread and extends centrally to the center axis A of the mixing tube. Between the plate  5  and a corresponding encompassing stop on the head piece  21 , a preimpregnation sleeve  17  is fastened in place. The preimpregnation sleeve  17  is sealed off from the head piece on the head piece side by a sealing ring, embodied as an inner shoulder on a bucket wheel  19 , and is sealed off on the other end against the plate  5  of the truncated tube  3 ; in the drawing, the truncated tube  3  is shown in a state in which it has not yet completely entered the threaded bore in the head piece. The bucket wheel  19  has guide buckets over its circumference, which impart a turbulent spiral flow to the liquid discharging into the mixing cell  1  at the liquid inlet  6 . The truncated tube  3  that forms the gas inlet into the mixing cell  1 , conversely, on its circumferential surfaces has two oblong slots  4 , through which the gas can pass from the gas infeed channel through the preimpregnation sleeve  7  into the mixing cell  1 . 
     The mixing operation thus proceeds as follows: 
     From a connected gas infeed G, the gas is carried via the gas infeed channel that penetrates the head piece  21  to the oblong slots  4  in the truncated tube  3  and emerges there. The gas that has emerged necessarily diffuses through the preimpregnation sleeve  17  received in sealed fashion on both ends, and as a result the gas flow entering as a gas stream is converted into a large-area, turbulent gas jet, distributed over the surface toward the mixing cell  1  of the preimpregnation sleeve  17 , at the surface of the porous material from which the preimpregnation sleeve  17  is formed, before the gas flow enters the mixing cell  1 . 
     Simultaneously, from a connected liquid infeed F, liquid passes eccentrically to the center axis A of the mixing tube through a liquid infeed channel, which penetrates the head piece  21 , and enters the mixing cell  1  at the point  6 . There, the liquid flow meets the guide buckets  41  of the bucket wheel  19  and is subjected by them to a swirl in the direction crosswise to the inflow direction, so that the inflow of liquid is also initially braked and made turbulent. Because the preimpregnation stage  17  comprises an only semipermeable, hydrophobic material, the liquid inflow cannot, however, reach as far as the gas outlet openings  4 . A first premixing of the turbulent gas inflow, distributed over a large surface area, and of the turbulent liquid inflow in the mixing cell  1  thus takes place in the inlet region in the vicinity of the head piece  21 . 
     The preimpregnation stage  17  and the prevortexing stage (bucket wheel  19 ) could also be omitted. Alternatively to the preimpregnation stage  17  and the prevortexing stage (bucket wheel  19 ), an ultrasonic vibrator could also be provided, in order to bring about preimpregnation. As an alternative to that, the ultrasonic vibrator could also be downstream of the impregnator bodies  11 ,  13 ,  15  described below. Instead of an ultrasonic vibrator, a high-frequency vibrator could also be provided. Within the scope of the invention, “high-frequency” is understood to mean frequencies above 12000 Hz. 
     The flow, comprising the gas already premixed with the liquid, in its further course enters the first impregnator body  11 , which comprises a fine-pore material. The surface of the porous solid body impregnator body  11  is formed not only by its outer surface but also by the surface of the pores in the interior of the impregnator body  11  and is therefore very large in area, so that high turbulence in the flow passing through occurs, along with dissolution of the gas in the liquid because of the large phase boundary face. The first impregnator body  11  can be adjoined by two further impregnator bodies  13 ,  15 , with which the fine adjustment of the mixture ratio of the gas-liquid mixture is done. The impregnator bodies  11 ,  13 ,  15  are made in disklike shape from a porous sintered material and are stuffed into the mixing tube  1 , so that they close off its diameter completely, and the incoming flow is forced to diffuse through the material comprising the impregnator bodies  11 ,  13 ,  15 . The two impregnator bodies  13 ,  15  have a lesser number of pores than the impregnator body  11  located farthest upstream. 
     The sintered solid bodies  11 ,  13 ,  15  may, however, as has recently been demonstrated, also be replaced by foam impregnator bodies, and in particular by polyester or polyether filter foams, preferably reticulated. 
     After the passage through the main impregnation stage, which is formed by the impregnator bodies  11 ,  13 ,  15 , the gas-liquid mixture reaches a calming zone  10 , which is separated from the rest of the mixing cell  1  by the impregnator bodies  11 ,  13 ,  15  and in which the turbulent flow is braked and converted into a laminar flow that can emerge from the mixing cell via the outlet opening  7 . 
       FIG. 2   a  shows an embodiment of the impregnator of the invention in which the impregnation is done by the same principle as in the impregnator of  FIG. 1 , but now on the inlet side of the mixing cell a valve assembly is provided, in which a gas inlet closing element  121  and a liquid inlet closing element  127  are coupled, while conversely on the outlet side of the mixing cell, a pressure compensator assembly is provided. Even under highly fluctuating pressure conditions and mass throughputs, a constantly good outcome of impregnation can be attained, and at the same time the dispensability of the beverage produced can be assured. The valve assembly on the inlet side of the mixing cell and the pressure compensator assembly on the outlet side of the mixing cell supplement one another in terms of absorbing fluctuations in pressure or quantity both at the inlet side and on the dispensing tap side. This highly important, especially for gassing beer with CO 2  in a bar, since beer is a beverage that starts foaming readily. However, if the beer or beer and gas mixture in the dispenser system rips open, forming foam, it is no longer possible to achieve a satisfactory outcome at the tap. 
     The liquid flows through the liquid inlet F and the gas flow through the gas inlet G into the mixing head  121 , and there it is carried onward into the mixing cell  1 , in which the actual impregnation operation takes place. The gas inlet closing element  129  is in the shape of a piston that tapers to a point conically toward the gas inlet G, while the liquid inlet closing element  127  is a piston that tapers on the order of a truncated cone toward the liquid inlet, and the two closing elements  127 ,  129  are joined into a valve slide unit by way of a connecting portion  128  embodied in needle-like fashion in some portions. The liquid inlet closing element  127  is prestressed counter to the liquid inlet by an annular spring  134 , which is braced on one end on the back side of the liquid inlet closing piston  127  and on the other on a wall of the liquid inlet channel and surrounds the connecting portion  128 . 
     If a force, which is greater than the contrary force resulting from the internal pressure of the mixing cell on the inside of the liquid inlet closing element  127 , the spring force, and the gas pressure on the gas inlet closing element  129 , is exerted by the inflowing liquid on the liquid inlet closing element  127 , then the liquid inlet closing element  127  opens the liquid inlet, and—via the connecting portion  128 —the gas inlet closing element  129  opens the gas inlet. The conical course of the gas inlet closing element  129  and of the gas inlet blocking portion surrounding it is adapted to the frustoconical course of the liquid inlet closing element  127 , and of the liquid inlet blocking portion surrounding it, in such a way that for every pressure drop between the liquid inlet and the mixing cell, the optimal ratio of the flow rate of gas to the flow rate of liquid for the impregnation operation is established. The gas infeed G takes place through a preimpregnation body  117 , along which the liquid infeed F flows annularly. To compensate for pressure fluctuations on the inlet side of the mixing cell, a compressible balloon  26  may also be provided, as a volumetric compensation body. 
     The impregnator is in an upside-down position; that is, the mixing head  121  is located at the bottom, and the mixing cell  1  with the impregnator bodies  13  has a vertically upward-oriented flow course. Any gas bubbles B still present in the mixing cell  1  after passage through the impregnator bodies  13  can rise in this way and be intercepted in the calming zone  10  of the mixing cell  1 , without entering the pressure compensator assembly at the mixing cell outlet and thereby causing turbulence at the dispensing tap. 
     As an alternative to this, the mixing head  121  may also be disposed at the top. This is because even better results are then attained, as has been demonstrated. This is due to the fact that the carbonated liquid, before exiting (at the bottom) from the mixing cell, is still in a kind of calming tub. Moreover, unbound gas, especially CO 2 , in the liquid has the tendency to rise, or in other words to ascend backward in the direction of the proportional valve, so as to be bound into liquid there. 
     If the liquid or beverage, impregnated for instance with carbon dioxide in the impregnation or mixing cell  1 , and in particular the now-carbonated beer, reaches the inlet of the pressure compensator assembly, then it presses with the operating pressure in the mixing cell  1  against the throttle restriction  108 . This pressure is counteracted by the prestressing force of the spring  109 , which presses on the back against the throttle restriction  108  and which can be adjusted via an adjusting screw  9   a . The pressure on the outlet side A also acts counter to the working pressure in the mixing cell. If the bartender opens the tapping line or dispensing tap adjoining the outlet side A, the pressure on the outlet side A drops, and the throttle restriction  108  is forced upward far enough that the impregnated liquid in the mixing cell  1  can flow through the pressure compensator assembly to the dispensing tap. 
     The gap width between the sleeve  102  and the throttling tap  108  determines the flow speed and hence the 
     flow rate and at the same time has an influence on the pressure loss at the pressure compensator assembly. If the bartender wants a large quantity of impregnated beer ready to tap, for instance, then the pressure on the tapping side drops sharply, and the throttle restriction  108  opens over a wide gap width. If the pressure on the tapping side drops less sharply (because the bartender is asking for a smaller quantity), the throttle restriction  108  opens over a lesser gap width. 
     The pressure compensator assembly acts in this process on the inlet valve assembly as well, since with the pressure compensator assembly, pressure changes in the mixing cell that result from the different tapping speeds are buffered, and as a result, the gas metering problems that have to be dealt with via the inlet valve assembly at different pressure drops between the liquid inlet and the mixing cell are lessened, since the pressure fluctuations become less. 
     A further embodiment of the invention is shown in  FIG. 2   b . The throttle restriction  108  shown in  FIG. 2   a  and correspondingly the sleeve  102  are somewhat slimmer than the respective body  8  and sleeve  2  shown in  FIG. 2   b , so that the friction losses overall are somewhat less. Moreover, the sleeve  102  is received entirely in the stopper  120  that closes off the mixing cell on the outlet face end, to which stopper the outlet piece  130  is flanged with an outlet A extending to the side and is sealed off from the sleeve  102  with an O-ring. The stopper  120  is also sealed off with an O-ring and a flat seal, inserted at the face end, from the side walls of the mixing cell. 
     The pressure compensator assembly thus has a line segment  2 ,  30 ,  12 , which is screwed into a (female-) threaded flange  20  of an impregnator that forms the closing wall of the mixing cell  1 . The line segment  2 ,  30 ,  12  has an inlet-side sleeve  2 , which is press-fitted into a corresponding receiving opening in the wall of the threaded flange  20  that closes off the mixing cell on the outlet face end. A throttle restriction or throttle tap  8  is disposed in the sleeve  2 ; it comes to a point toward the inlet side and thus corresponds to the widening at that location of the sleeve  2 . Acting on the tap  8  is a spring  9 , which forces the tap  8  toward the inlet to the sleeve  2 , so that the inlet of the sleeve  2  or line segment  2 ,  30 ,  12  is closed when no pressure is acting on the tap  8  from the inlet side. To that end, the spring  9  is braced on an annular shoulder  16  in the tubular piece  30 , and the tubular piece  30  is screwed in sealed fashion into the female thread of the threaded flange  20  and keeps the sleeve  2  in the receptacle in the threaded flange  20  and with it forms one continuous line that is sealed off from the surroundings. On the outlet side, a connection piece  12  is inserted into the tubular piece  30 , so that the impregnator can be connected via the pressure compensator assembly to the bar line. 
     The pressure compensator assembly in  FIG. 2   b  is thus distinguished from the embodiment shown in  FIG. 2   a  essentially in that the beverage emerges here through the annular spring  9  and then flows vertically upward without kinks in the flow, while in  FIG. 2   a , conversely, a lateral beverage outlet connection is provided. Although the inlet valve assembly is more fundamentally different from the embodiment shown in  FIG. 2   a , nevertheless as in the pressure compensator assembly, similar reference numerals are used as in  FIG. 2   a  for components that are functionally similar or identical. 
     The liquid inlet closing element  227  is again braced against the liquid inlet pressure via an annular spring  234 , which surrounds a connecting portion  228  that combines the liquid inlet closing element  227  with the gas inlet closing element  229  to make a piston slide unit that can be displaced in the aligned gas inlet channel and liquid inlet channel. The hollow cylinder that forms the liquid inlet closing element  227  is opened toward the liquid inlet and is closed toward the mixing cell by an end wall, while conversely the hollow-cylindrical needle that forms the gas inlet closing element  229  is closed toward the gas infeed side by an end wall and, has a plurality of openings, not shown in  FIG. 2   b  (see reference numeral  232  in  FIGS. 3 and 4 ), toward the mixing cell  1  that are distributed over its circumference. The hollow cylinder that forms the liquid inlet closing element  227  is received with little play in a bore forming a liquid inlet blocking portion, and the hollow-cylindrical needle forming the gas inlet closing element  229  is received with little play in a bore that forms a gas inlet blocking portion; a gas seal  239  is provided between the bore and the hollow-cylindrical needle, and the two bores are aligned with one another. 
     Reference numeral  236  identifies a chain of liquid passage openings, spirally surrounding the circumferential side wall of the liquid inlet closing element  227 , and reference numeral  238  identifies a chain of gas passage openings, spirally surrounding the circumferential side wall of the liquid inlet closing element  227 . Now, if a suitably high pressure is exerted from the fluid inlet side on the liquid inlet closing element  227 , then the entire piston or valve slide assembly shifts to the left in the drawing, causing the liquid inlet closing element  227  to protrude, with its sides toward the mixing cell, into an open volume  237 . As a result—depending on the liquid pressure, the gas pressure, and an internal pressure in the mixing cell that are applied—at least some of the liquid passages  236  are opened, so that the flow rate of the liquid flowing into the mixing cell is adjusted accordingly. 
     The gas flow rate flowing into the mixing cell is established in a similar way: When the gas inlet closing element  229 , via the connecting portion  228 , is shifted to the left, it protrudes with its end toward the gas infeed into a free volume  235 ; some of the gas passage bores  238  corresponding to the opened portion of liquid passages  236  are uncovered, so that for the flow rate of each inflowing liquid, the optimal gas flow rate to suit the impregnation operation is established. 
     Between the sleeve  2  and the head piece  221 , an impregnator body  213  can be press-fitted into place, through which the flow has to pass. The impregnator body  213  is dimensionally stable to such an extent that no further securing means are needed; for instance, it comprises a dimensionally stable hollow fiber module. Except for the calming zone  10 , it completely fills the mixing cell  1 . Once again, it has been demonstrated that the impregnator is best operated in a position in which the mixing head is at the top, or in other words a position rotated by 180° compared to the drawing. 
       FIGS. 4 and 5  each show modifications of the embodiment shown in  FIG. 2   b.    
     In  FIG. 4 , section lines shows an open position of the valve slide, comprising the liquid inlet closing element  227 , the connecting portion  228 , and the gas inlet closing element  429 . It can be seen that the chain of gas passages  438  extends with a slight slope around the lateral circumferential wall of the gas inlet closing element  429 . Per unit of length by which the valve slide is displaced into the open position, a greater number of gas passages is opened than in the embodiment shown in  FIG. 2   b . Therefore the embodiment shown in  FIG. 4  can be used for instance for producing a different beverage from that of the embodiment shown in  FIG. 2   b , for instance for producing wheat beer from a carbonic acid-free wheat beer precursor product and carbon dioxide in contrast to the production of pale beer from a carbonic acid-free barley beer precursor product and carbon dioxide. 
     In the embodiment shown in  FIG. 5 , conversely, the entire circumferential side walls of both the liquid inlet closing element  327  and the gas inlet closing element  329  are perforated with passages  336  and  338 , respectively. 
       FIG. 6  shows a further embodiment of the impregnator of the invention, and  FIG. 7  shows the valve slide of this impregnator, the slide comprising the liquid inlet closing element  527 , the connecting portion  528 , and the gas inlet closing element  529 . Functionally similar or identical parts have been identified with similar reference numerals. 
     The gas passages  538  extending as a chain around the circumference of the gas inlet closing element  529  have a diameter of 0.2 mm; only the first gas passage on the side of the gas inlet is somewhat larger, that is, in the embodiment shown here, 0.3 mm. By comparison, the liquid passages  536  disposed as a chain around the circumference of the liquid inlet closing element  527  have a diameter of 2.2 mm. The diameter ratio is thus in a range from 1:9 to 1:11, which overall appears to be suitable for beer production with proportional valves for impregnators of the type according to the invention. 
     The gas flows through the gas passages  538  into an inner bore  540 , which is shown in  FIG. 6 , that extends along the gas inlet closing element  529  and otherwise is closed off from the gas inlet side. From the inner bore  540 , the gas flows via two outlet openings  532  (diameter 2.2 mm) on the circumference of the connecting portion  528  into the mixing cell. 
     The inner bore  540  may be in contact with the liquid side but need not be. In the example shown, it is drilled from the liquid side into the valve slide, so that the latter can be fabricated in one piece. Because of the higher gas pressure (for instance, 5.5 bar compared with 4.5 bar of liquid pressure), a liquid flow to the gas inlet side is suppressed in every case, even if the slide is open, and an adequate gas flow in the direction into the mixing cell is assured in every case. Nor can the gas pass very far toward the gas inlet side, since it is carried along with the quantitatively much greater liquid flow through the liquid passages  536 . 
     The embodiment shown in  FIGS. 6 and 7  moreover differs from the embodiments shown in  FIGS. 2   b  through  5  essentially only in the following aspects: In its upper region, the mixing cell is filled completely by a compressed foam solid body  513 , acting as an impregnator body, which is pressed into position and held there by a perforated plate  514 . The perforated plate  514  in turn is held in position on its outer circumference by a threaded stopper  520 , with which the mixing cell is sealed off on the outlet side. The impregnator body is in particular of polyester or polyether filter foam with a pore size of 90 to 100 PPI (pores per inch), measured for instance by the PPI measuring method. This is equivalent to a pore size of approximately 250 μm and approximately 90,000 cells/cm 3  (open-pore cells). The cellular structure is that of a reticulated filter foam, or in other words is virtually 100% open-celled. Alternatively to the retention of the impregnator body by means of the perforated plate  514 , an impregnator body that fills the entire mixing cell could also be provided. For the reasons already given above, the impregnator is installed in the position shown in  FIG. 6 , with the head piece seated at the top. 
     The compensator tap  508  is also disposed in the threaded stopper  520 , in a suitably shaped recess  502  that conically tapers toward the mixing cell. 
     It is understood that deviations from the embodiments shown are possible without departing from the scope of the invention. Moreover, the characteristics of the embodiments shown may be combined arbitrarily. 
     For instance, in the impregnators shown in  FIGS. 2   a  through  7 , it is indeed especially advantageous that both impregnation solid bodies and the inlet-side proportional valve and the outlet-side pressure compensator be used. For instance, because impregnation solid bodies are used, clogging or malfunction of the pressure compensator is prevented, and by means of the inlet proportional valve, the pressure fluctuations at the pressure compensator are reduced, and vice versa. However, within the scope of the invention, embodiments of an impregnator would be equally conceivable that each have the characteristics shown only with regard to the filling of the mixing cell or inlet or outlet or in which only two of these aspects of the invention are implemented. 
     Besides beer and soda, with the impregnator of the invention such beverages as cider, sparkling wine, champagne, apple juice mixed with carbonated water, and cola can be produced by carbonation from a suitable precursor product that is low in carbonic acid or is carbonic acid-free. As an alternative to the coupling of the gas inlet closing element and liquid inlet closing element shown in  FIGS. 2   a  through  7  and claimed in claims  11  through  20 , within the scope of the invention control or regulation of an impregnator having the characteristics of the preamble to claim  21  may also be provided, with which the CO 2  content in the beverage generated with the impregnator of the invention is regulated by way of the inlet-side gas pressure as a controlling variable. For instance, if one wishes to have less CO 2  in the beverage than what is on hand at the moment, the gas pressure is reduced, for instance from 5.5 bar to 5 bar. If more CO 2  in the beverage is wanted, then the gas pressure is increased, for instance to 6 bar. Thus the desired, beverage-specific CO 2  content can always be adjusted via the gas pressure, although also always as a function of the liquid pressure at the time. The higher the liquid pressure, the lower is the CO 2  concentration in the beverage produced, if the gas pressure stays the same. To obtain the same CO 2  concentration in the beverage produced when the liquid pressure is increased, for instance from 5.5 bar to 6 bar, the gas pressure would have to be corrected upward as well, until the ratio is again correct. The CO 2  concentration in the beverage produced can be measured, and the gas pressure can be set in accordance with a suitable regulating algorithm. When the liquid pressure is known, the suitable gas pressure may, however, also be read off from a performance graph of the particular impregnator and the particular beverage and adjusted accordingly.