Field of the invention

The present invention concerns a capsule for use in a beverage preparation machine, and a method for manufacturing a capsule for use in a beverage preparation machine.

Background of the invention

Beverage preparation machines are well known in the food science and consumer goods area. Such machines allow a consumer to prepare at home a given type of beverage, for instance a coffee-based beverage, e.g. an espresso or a brew-like coffee cup.

Today, most beverage preparation machines for in-home beverage preparation comprise a system made of a machine which can accommodate portioned ingredients for the preparation of the beverage. Such portions can be soft pods or pads, or sachets, but more and more systems use semi-rigid or rigid portions such as rigid pods or capsules. In the following, it will be considered that the beverage machine of the invention is a beverage preparation machine working with a rigid capsule.

The machine comprises a receptacle for accommodating said capsule and a fluid injection system for injecting a fluid, preferably water, under pressure into said capsule. Water injected under pressure in the capsule, for the preparation of a coffee beverage, is preferably hot, that is to say at a temperature above 70°C. However, in some particular instances, it might also be at ambient temperature. The pressure inside the capsule chamber during extraction and/or dissolution of the capsule contents is typically about 1 to 8 bar for dissolution products, 2 to 12 bar for extraction of roast and ground coffee. Such a preparation process differs a lot from the so-called "brewing" process of beverage preparation - particularly for tea and coffee, in that brewing involves a long time of infusion of the ingredient by a fluid (e.g. hot water), whereas the beverage preparation process allows a consumer to prepare a beverage, for instance coffee within a few seconds.

The principle of extracting and/or dissolving the contents of a closed capsule under pressure is known and consists typically of confining the capsule in a receptacle of a machine, injecting a quantity of pressurized water into the capsule, generally after piercing a face of the capsule with a piercing injection element such as a fluid injection needle mounted on the machine, so as to create a pressurized environment inside the capsule either to extract the substance or dissolve it, and then release the extracted substance or the dissolved substance through the capsule.

When the beverage to be prepared is coffee, one interesting way to prepare the said coffee is to provide the consumer with a capsule containing roast and ground coffee powder, which is to be extracted with hot water injected therein. Different types of such capsules exist and it is known to introduce a protective gas inside the capsule to protect roast and ground coffee from air and specifically oxygen.

A particular system of a beverage preparation machine and capsules have already been described in EP 1472156 and in EP 1784344.

The capsules of this system are illustrated in Figure 1 and comprise typically :

- a hollow capsule body 2 defining a chamber and comprising walls extending axially towards a top opening and a bottom outlet,

- an injection membrane 3 closing the top opening. This injection membrane is impermeable to liquids and to air and is attached to the body and adapted to be punctured by e.g. an injection needle 4 of the machine,

- a bottom wall 5, provided inside the chamber so as to delimit with the injection membrane 3 the ingredient chamber,

- a bed of roast and ground coffee (RG) to be extracted provided in this ingredient chamber,

- an opening device 7 provided inside the capsule body and adapted to open the ingredient chamber by relative engagement of this opening device with the bottom wall 5 under the effect of the liquid pressure increase in the ingredient chamber during injection of liquid,

- optionally, means 10 configured to reduce the speed of a jet of fluid injected into the capsule and to distribute the fluid across the bed of roast and ground coffee at a reduced speed. Usually, these means are a wall or membrane comprising a multitude of openings passing through the said wall or membrane in such a way as to distribute the flow of fluid across the bed of substance.

During beverage preparation, the top membrane 3 is pierced by the liquid needle 4 and the liquid is injected. Pressure increases inside the chamber, which serves as an extraction means for extracting roasted and ground coffee contained inside the ingredient chamber and participates to the opening of the bottom wall by engagement of this wall with the opening device 7 which enables the dispensing of the extracted coffee through the bottom outlet. Yet a part of the liquid remains inside the capsule under residual pressure. After the beverage has been prepared and dispensed and when the liquid needle is removed from the top membrane, a jet of liquid - often referred to as "whale effect" - can spray out of the capsule injection membrane, through the hole pierced by the machine needle. Such a whale effect is represented in figure 2. Although such a phenomenon occurs randomly and infrequently, it is undesirable because hot liquid splashing out is messy. Moreover, in case said liquid is water mixed with an ingredient such a leakage of liquid from the capsule injection membrane is also undesirable for a cleanliness point of view as it could create some bacteria growth around or inside the machine, which forces the consumer to spend time cleaning the machine and its surroundings after usage. There exist solutions which reduce the whale effect. These solutions however require a complex design of the beverage preparation machine and/or of the capsule. For example, there is a capsule comprising a so called “soft distributor” having a very small number of holes (1 hole/cm2). This “soft distributor” is, however, disadvantageous, since it limits the extraction yield.

Furthermore, a key attribute to a beverage prepared from a capsule is the crema. The crema is typically a layer of creamy froth that forms on the top of a freshly prepared beverage such as a coffee, e.g. an espresso. With the crema, the prepared beverage makes a particularly fresh appearance. For example, with a crema in the correct quantity and with a specific colour (e.g. a tan colour) one can conclude that the prepared beverage fulfills certain quality criteria. Further, since the crema absorbs flavors of the prepared beverage, such as a coffee or an espresso flavor, the crema also improves the taste of the beverage. Thus, it is desired that the crema of the respective beverage is provided in a good quality, i.e. in particular in an optimal ratio of quantity and stability.

The crema is created in particular by extracting the beverage ingredient, such as ground coffee, at a high pressure. However, a beverage preparation machine has a limited extraction pressure, which is given by the pump and other machine properties. In particular, a high enough extraction pressure for creating the crema requires a relatively complex configuration of the machine such as of the pump. For example, an extraction pressure around 15 bars may create a good crema, whereas it is desired to have a beverage preparation machine with a maximum extraction pressure of at most 11 bars due to reasons for design and use of the machine.

Therefore, it is an object of the present invention to provide a capsule and a method for manufacturing a capsule, which overcome the aforementioned drawbacks. That is, it is in particular an object of the present invention to provide a capsule, which reduces the whale effect and has an improved crema.

These and other objects, which become apparent upon reading the following description, are solved by the subject matter of the independent claims. The dependent claims refer to preferred embodiments of the invention.

Summary of the invention

According to a first aspect of the invention, there is provided a capsule adapted for use in a beverage preparation machine, the capsule comprising :

- a hollow capsule body comprising :

. walls extending axially towards a top opening and . a bottom outlet,

- an injection membrane closing the top opening, said top membrane being attached to the body and adapted to be punctured for liquid injection into the capsule,

- a wall, provided inside the chamber so as to delimit with the top membrane an ingredient chamber,

- a bed of roast and ground coffee to be extracted provided in said ingredient chamber,

- an opening device provided inside the chamber and adapted to open the ingredient chamber by relative engagement of said opening device with the bottom/openable membrane under the effect of the liquid pressure increase in the ingredient chamber during injection of liquid, wherein the capsule is filled with a gas mixture of CO2 and at least one other protective gas, said gas mixture comprising :

- at least 35 vol. % CO2, and

- not more than 80 % CO2.

The relatively high amount of CO2 (carbon dioxide) in the gas mixture effects that a particularly large amount of the gas mixture escapes the capsule during the injection of the liquid and, thus, during the extraction process. The escape of the particularly large amount from the capsule during beverage preparation is in particular effected because CO2 dissolves well in the injected liquid (e.g. water), in particular better than N2 or air. That is, CO2 is chemically solubilized in the liquid, e.g. water, in the form of carbonic acid. Thus, during the preparation of the coffee beverage from the roast and ground coffee arranged in the capsule, a relatively large amount of the gas mixture, amongst others provided for maintaining a high quality of the capsule (shelf life, etc.), can escape the capsule. Consequently, after usage of the capsule, a reduced amount of the gas mixture and, thus, a reduced residual pressure remains in the capsule. Hence, due to the reduced residual pressure, there is a significantly reduced risk that a jet of liquid sprays, via the hole in the injection membrane pierced by the injection needle, through the injection membrane and out of the capsule. Thus the whale effect is significantly reduced. In particular, it is thus not required to provide specific means in the beverage preparation machine in order to reduce the whale effect, since the capsule as such provides means, namely the CO2 in said capsule, for reducing the whale effect. Further, since the capsule only requires the injection of a defined quantity of CO2 into the capsule, the capsule can be designed simply, in particular without specific and/or complex structures, in order to reduce the whale effect.

In sum, the capsule reduces the whale effect and, thus, the risk of capsule defects or of defects of the beverage preparation machine due this whale effect in a very cost-effective manner. For this reason, a gas mixture comprising : at least 35 vol. % CO2 is desirable against the whale effect.

Further, the gas mixture with the defined amount of CO2 does not only achieve the reduction of the whale effect, but also achieves an improved quality of the crema of the coffee dispensed from the capsule. That is, the crema of the prepared coffee has amongst other an increased quantity and an increased stability. In particular, the capsule can provide a good quality crema even if used in a beverage preparation machine supplies liquid at a low extraction pressure only, such as a maximum extraction pressure of at about 11 bars. In other words, the gas mixture in the capsule provides a good crema of the dispensed coffee independent from the configuration of the beverage preparation machine. For example, even if the capsule is used in a beverage preparation machine with a simple or low-cost configuration, such as in a machine with a simply designed pump, the capsule effects in the dispensed coffee a crema with a good quality.

However, a too high content of CO2 in the gas mixture leads to a crema that is less dense and does not present the usual requested attribute of good cream quality. For this reason, a gas mixture comprising at most 80 vol. % CO2 is desirable for a good crema.

A plurality of methods may be used in order to determine or analyze the gas mixture in the capsule. For example, one possible method is to use micro gas chromatography in order to analyze and, thus, determine the composition of the gas mixture in the capsule.

Generally the capsule comprises a space between the bed (RG) of roast and ground coffee and the injection membrane, and preferably this space is at least partially delimited by a retaining element retaining roast and ground coffee out of the space.

The capsule may comprise one or more capsule side walls at least partially delimiting the chamber, wherein the space is at least delimited by at least part of the one or more capsule side walls and at least part of the injection membrane. In other words, the gas mixture is in direct contact with, amongst others, the one or more sidewalls and the injection membrane. Hence, the space and, thus, the gas mixture is arranged with respect to the bed of roast and ground coffee without requiring much space. This in particular for the reason that the one or more sidewalls do not only delimit a space (e.g. a compartment) dedicated for the bed of coffee, but also the space dedicated for the gas mixture. The capsule can thus be made very compact.

The retaining element ensures that the bed of roast and ground coffee remains in a space of the chamber, which space is dedicated for the bed of roast and ground coffee. Hence, the arrangement of the retaining element in particular ensures that the bed of roast and ground coffee is not moved or pushed towards the injection membrane during the injection of the liquid under pressure into the chamber. In addition, since the retaining element at the same time delimits the space dedicated for the gas mixture, a very compact arrangement of the retaining element in the chamber is achieved. For example, the retaining element may be adapted to allow a flow of liquid to pass through the retaining element and towards the bed of roast and ground coffee, but to prevent the bed of roast and ground coffee from flowing through the retaining element and into the space filled with the gas mixture. In particular, the retaining element may have a filter function and/or may be a filter element.

Preferably, the volume of the space is at least 40 % or at least 50 % or at least 60 % or at least 65 % or at least 70 % of the volume of the chamber, and/or the volume of the space is not more than 95 % or not more than 92 % or not more than 90 % or not more than 85 % of the volume of the chamber. Hence, a particular advantageous ratio of the gas mixture (filling out the volume of the space) with respect to the amount of the bed of roast and ground coffee is achieved for reducing the whale effect and improving the crema of the prepared coffee.

The gas mixture may comprise at least 40 vol. % CO2 or at least 50 vol. % CO2 or at least 60 vol. % CO2 or at least 65 vol. % CO2 or at least 70 vol. % CO2 or at least 75 vol. % CO2. These values of the CO2 concentration in the capsule, in particular in the volume of the space are particularly advantageous for reducing the whale effect.

The gas mixture may comprise not more than 75 vol. % CO2 or not more than 70 vol. % CO2 or not more than 60 vol. % CO2 or not more than 50 vol. % CO2.

These maximum values of the CO2 concentration in the capsule, in particular in the volume of the space guarantee a good quality of crema of the prepared coffee, that is a sufficient height of dense cream.

In a particularly preferred example, the gas mixture comprises from 55 to 70 vol. % CO2. This range was found to achieve a particularly advantageous reduction of the whale effect and a particularly improved crema of the prepared coffee.

The other gases of the gas mixture may be used for other advantageous effects such as for the improvement of the stability (e.g. the aroma stability and/or for preventing coffee from oxidizing) of the ground coffee. Preferably the gas mixture consists of CO2 and N2 only. In the preferred embodiment, this gas mixture comprises :

- between 40 % and 70 % in volume of CO2, and

- between 30 % and 60 % in volume of N2.

Providing N2 (nitrogen) in the space particularly avoids that ground coffee is subject to oxidation. Hence, N2 effects that a good quality of the bed of roast and ground coffee maintains over a long time. With these values of the N2 concentration in the volume of the space an improved quality of the bed of roast and ground coffee (less oxidation, etc.) is achieved, while still having a reduced whale effect and an improved crema.

According to a further aspect of the invention, there is provided a method for manufacturing a capsule being adapted for use in a beverage preparation machine, such as for manufacturing a capsule such as described above, the method comprising the following steps :

- providing a hollow capsule body,

- introducing an opening device in said body,

- attaching a wall above said opening device to the internal wall of the body,

- introducing roast and ground coffee in the body,

- optionally attaching a retaining element above coffee to the internal wall of the body,

- attaching an injection membrane to the top opening of the body, wherein, at least from the step introducing roast and ground coffee in the body, the steps are processed under a gas atmosphere, and wherein said gas atmosphere comprises CO2, and wherein the content of CO2 in said gas atmosphere is set so that the capsule comprises a gas mixture of at least 35 vol. % CO2 and not more than 80 vol. % CO2 after one day, preferably two days, from the step of attaching the injection membrane.

This method implements the usual steps of assembling the different components of the capsule such as described above. In addition, in order to have the capsule filled with the gas comprising the requested ratio of CO2, all or a part of these steps are implemented under the atmosphere of a gas mixture comprising CO2 and at least one other protective gas so that this gas atmosphere is enclosed in the capsule when the injection membrane is sealed in the latest step.

This gas atmosphere is preferably used at least from the step of introducing roast and ground coffee in the body in order to benefit from its protection against ambient air and oxygen.

Depending on the type and/or the quantity of roast and ground coffee introduced in the capsule, and in particular the freshness of this roast and ground coffee, this coffee may release some gases, in particular CO2, inside the produced and closed capsule during the hours following the production, which can modify the composition of the gas atmosphere trapped inside the capsule at the moment of attaching the injection membrane. For this reason, the content of CO2 in the gas atmosphere that is used during the manufacturing process is set so that the capsule comprises a gas mixture of at least 35 vol. % CO2 and not more than 80 vol. % CO2 when the capsule will be used in a beverage preparation machine. Generally, the release of CO2 by ground coffee happens until 24 to 48 h after grinding.

Preferably, the method comprises an additional step of providing roast and ground coffee by grinding roasted coffee beans, and the content of CO2 of the gas atmosphere is set in function of the time elapsed between said grinding operation of said roast and ground coffee and the step of introducing said roast and ground coffee in the capsule body.

By taking into account the fact that fresh ground coffee releases CO2 during the hours following its finding operation, the content of CO2 of the gas atmosphere is set lower when the roast and ground coffee has been recently ground, for example less than 4 hours before filling coffee in the capsule, and this content is set higher when the roast and ground coffee has been ground for more than 4 hours before filling coffee in the capsule.

Since the freshly ground coffee releases CO2, the bed of roast and ground coffee enclosed in the sealed capsule modifies the composition of the gas enclosed inside the capsule, in particular by increasing the CO2 content.

The quantity of released CO2 can depend on the quantity of coffee in the capsule and the time elapsed since the grinding operation at the moment the capsule is closed with the injection membrane.

In one preferred embodiment, the time elapsed between the grinding operation of said the and ground coffee and the step of introducing said roast and ground coffee in the capsule body is of at least 8 hours, and the content of CO2 of the gas atmosphere is of at least 3§5 vol. % CO2 and not more than 80 vol. % CO2.

Actually after 8 hours, the release of CO2 by roast and ground coffee becomes negligible.

What has been said above with respect to capsule applies analogously to the method. Thus, the method in particular achieves that a capsule is provided, which reduces the whale effect in a very cost-effective manner and which, at the same time, provides an improved crema of the coffee beverage prepared from the capsule. Brief description of the drawings

Additional features and advantages of the present invention are described in, and will be apparent from, the description of the presently preferred embodiments which are set out below with reference to the drawings in which :

Figure 1 is schematic profile cut view of a capsule according to the prior art at the beginning of liquid injection therein;

Figure 2 is a view similar to figure 1 , showing the backflow of liquid under pressure after the injection needle has been removed from the injection (i.e. top) membrane;

Figure 3 is a schematic profile cut view of a capsule according to the invention, showing the capsule shortly after the injection needle pierced the injection membrane;

Figures 4 is a diagram showing different exemplary compositions of a gas mixture filled in the (head) space of the capsule;

Figure 5 is a diagram showing the impact on the whale effect by different CO2 concentrations in the gas mixture filled in the (head) space;

Figure 6 is a diagram showing different crema heights effected by different CO2 concentrations in the gas mixture filled in the (head) space, respectively;

Figure 7 is a diagram showing the impact on the crema density effected by different CO2 concentrations in the gas mixture filled in the (head) space; and

Detailed description of the invention

The capsule 1 illustrated in figure 3 is adapted for use in a beverage preparation machine. The capsule 1 comprises a chamber, which may be defined or delimited by a capsule body 2. The chamber is a closed chamber. The chamber is adapted to enclose roast and ground coffee.

As shown in figure 3, the capsule 1, e.g. the capsule body 2, comprises capsule sidewalls extending axially towards a top opening. The capsule body comprises a bottom outlet 23. The capsule sidewalls 2 at least partially delimit the chamber, in which the coffee is contained. The capsule 1 further comprises an injection membrane 3 pierceable by an injection needle 4 of the machine which is adapted to inject an extraction liquid under pressure inside or into said chamber. The injection membrane 3 may be a top membrane 3. The capsule 1 further comprises a wall 5, which may be a bottom wall. The wall 5 is not limited to a specific material. For example, the wall 5 is made of aluminium and is, thus, preferably, an aluminium membrane.

In the course of the present description, the injection membrane 3 may also be identified as a "top membrane" and the bottom wall 5 as the "bottom membrane" 5 , these two membranes being located on the opposite sides of the capsule. This definition is such that "top" and "bottom" membranes are defined whatever the position of the capsule within the machine, when both capsule and machine are engaged in a functional manner.

As illustrated in figure 3, the capsule 1 further comprises an opening device 7 adapted to open said chamber by relative engagement with the bottom wall 5 under the effect of the liquid pressure increase in the chamber during injection of said liquid. This opening device 7 means may comprise a rigid plate 71 comprising spikes or pyramids 72 on its surface turned towards the wall 5. The rigid element 71 may be generally referred to as "pyramid plate". Upon liquid injection inside the capsule compartment, pressure builds up, which deforms the wall 5 against the spikes 72 of the pyramid plate 71 , until said wall 5 is pierced, giving way to the beverage coffee inside the capsule towards the outside of the capsule, inside a cup (not illustrated). Coffee beverage can flow to the bottom outlet 23 by flowing through the radial circumference of the rigid plate 71 and/or through traversing holes provided in the rigid plate 71. Piercing of said wall 5 with the opening device may be also facilitated with piercing or opening elements other than the rigid plate 71 and/or the spikes 72.

As illustrated in figure 3, a space (head space) 8 is provided in the chamber and between the roast and ground coffee and the injection membrane 3. Usually, the capsule 1 comprises a retaining element 10. The retaining element 10 is in particular adapted to retain the roast and ground coffee out of the space 8. For example, the retaining element 10 is arranged between the space 8 and the bed of roast and ground coffee RG. The retaining element 10 may extend horizontally and/or parallel to the injection membrane 3. The retaining element 10 generally provides a filter function. Thus, the retaining element 10 may permit the flow of liquid through the retaining element 10, but not permit the flow of particles of the bed of roast and ground coffee RG through the retaining element 10. Preferably, the retaining element 2O is a perforated element. The retaining element 10 may be made of a thin element, such as of a foil. If the retaining element 10 is present, the retaining element 10 may at least in part delimit the space 8. Thus, the boundary between the space 8 and the bed of roast and ground coffee RG may be at least in part provided by the retaining element 10.

The space 8 has a volume, and the chamber has a (total) volume. The (total)volume of the chamber may consist of the volume of the space 8 and the volume of the coffee. The volume of the space 8 is preferably at least 40 % or at least 50 % or at least 60 % or at least 65 % or at least 70 % of the volume of the chamber. Preferably, the volume of the space 8 is in the range from 50,000 to 10,000 mm ³ , preferably in the range from 40,000 to 15,000 mm ³ , more preferred in the range from 35,000 to 20,000 mm ³ .

According to the invention, the capsule, and preferably the space 8, is filled with a gas mixture 11 (i.e. a gas composition), which comprises CO2 and at least one other protective gas, said gas mixture comprising :

- at least 35 vol. % CO2, and - not more than 80 % CO2.

Thus, the volume of the space 8 is completely filled with the gas mixture.

The other gas is preferably a gas that provides the roast and ground coffee with a protection against ambient air, specifically oxygen, and that does not interact with coffee beverage contrary to CO2. Any gas able to protect roast and ground coffee, that does not interact with coffee beverage and that is food agreed can be used such as nitrogen, argon or helium. This gas is preferably N2.

Preferably, the one or more further gaseous substances do not include any O2 (oxygen), or at least include a volume percentage of O2, which is, compared to the volume percentage of O2 in air (such as about 2O vol. %), reduced. Thus, the impact of O2 on the bed of roast and ground coffee, in particular on the roast and ground coffee, is reduced so that the degradation of the bed of roast and ground coffee is reduced, too.

It is preferred that the gas mixture 11 comprises at least 40 vol. % CO2 or at least 50 vol. % CO2 or at least 60 vol. % CO2 or at least 65 vol. % CO2 or at least 70 vol. % CO2.

Preferably, the gas mixture 11 comprises not more than 75 vol. % CO2 or not more than 70 vol. % CO2 or not more than 60 vol. % CO2 or not more than 50 vol. % CO2.

With the concentration of at least 35 vol. % CO2, and the above-specified preferred concentrations of the CO2, in the gas mixture 11 , both the whale effect is reduced and the quality of the crema is improved. This is apparent from, in particular, figures 4 to 7.

Figure 4 illustrates the composition of four different mixtures of CO2 and N2 present in capsules such as illustrated in Figure 1. Four different series of capsules were produced : for the four series the capsule was identical and comprised the same quantity of roast and ground coffee and the same capsule components. The capsules corresponded to Nescafe Dolce Gusto Espresso Intenso except that the gas mixture was modified. The four series differed one from the other only by the composition of the gas mixture inside the closed capsule. Precisely :

- the composition "Ref" corresponds to a capsule where the gas mixture of N2 and CO2 comprised 11.4 % vol. CO2.

- the composition "Level 1" corresponds to a capsule where the gas mixture of N2 and CO2 comprised 54.4 % vol. CO2.

- the composition "Level 1" corresponds where the gas mixture of N2 and CO2 comprised 77.6 % vol. CO ₂ . - the composition "Level 1" corresponds to a capsule where the gas mixture of N2 and CO2 comprised 98.7 % vol. CO2.

Figure 5 shows the impact of the CO2 concentration on the whale effect. In the diagram of figure 5, the whale effect is quantified with a “whale effect score”, which ranges from 0 to 3. A whale effect score of 3 means that the whale effect is fully present, as in the capsule shown in figure 2. A whale effect score of 0 means that the whale effect is almost not present. As shown in figure 5, already with a CO2 concentration of 54.4 vol. % in the gas mixture 11 , around 50% of all capsules tested show a whale effect score of 0, such that the whale effect is significantly reduced. Further increasing the CO2 concentration in the gas mixture 11 , such as to 77.6% or 98.7%, even further reduces the whale effect. For example, at 77.6% CO2 concentration around 70% of all capsules tested show a whale effect of 0, and at 98.7% CO2 concentration even around 90% of all capsules tested show a whale effect of 0.

As shown in figure 6, the CO2 concentration in the gas mixture 11 according to the invention also has a positive effect on the crema height. In particular, the CO2 concentration of 54.4 vol. % effects a higher crema height (more than 3mm) than a capsule having only a 11.4 vol. % CO2 concentration in the gas mixture in the (head) space (crema height: 3mm). With a CO2 concentration of 77.6 vol. % the crema height is even further improved, i.e. increased to more than 4mm. With a CO2 concentration of 98.7 vol. %, a crema height of even about 5mm can be reached.

In figure 7, the diagram indicates the stability of the crema, effected by different CO2 concentrations in the gas mixture 11 . The stability of the crema is particularly effected by the density of the crema so that the indication of the crema stability indicates at the same time the crema density. In order to quantify the stability of the crema, the sugar test is used. In the sugar test, it is measured for how long an espresso spoon of sugar (between 3 and 6 grams of sugar) can be supported by the crema. Thus, in the sugar test the time (measured in seconds [s]) is measured, which lapses until the crema is traversed by the espresso spoon of sugar. In figure 7, it can be seen that for CO2 concentrations of at least 45 vol. % CO2, the crema stability is in the range from about 14s to about 2OS. Thus, the CO2 concentration in the gas mixture 11 also provides a good quality with respect to the crema stability.

The addition of (pure) N2 to the gas mixture 11 is advantageous since N2 effectively prevents the bed of roast and ground coffee RG, in particular roast and ground coffee, from degrading.