Soluble Coffee Powder

Abstract

The present invention relates to a coffee powder that provides a coffee beverage with crema. Further aspects of the invention are the use of the coffee powder for preparing a beverage, a beverage powder mix and a method for producing a freeze-dried coffee powder.

Description

Detailed Description of the Invention

[0001] [Technical field] The present invention relates to a coffee powder for providing a coffee beverage with crema. Further aspects of the invention are the use of the coffee powder for preparing a beverage, a beverage powder mix and a method for producing a freeze-dried coffee powder.

[0002] [Background technology] Soluble coffee or "instant" coffee is a phrase used to describe a powder that produces a coffee beverage upon reconstitution with water, thus avoiding the traditional complicated and time-consuming process of preparing a beverage from roast and ground coffee. Typically, soluble coffee is produced by first roasting, grinding the roasted beans, and extracting to produce a coffee extract, and then removing water from the extract to form a powdered product. Removal of the water is generally accomplished by freeze drying or spray drying.

[0003] However, unlike coffee beverages prepared from roast and ground coffee, coffee beverages prepared from soluble coffee do not typically exhibit a fine foam on the liquid surface when reconstituted with hot water. The foam that forms on the liquid surface of beverages prepared from roast and ground coffee is typically due to, and is generated, at least in part, by, the pressurized water and / or steam brewing machine.

[0004] This foam is known to have a positive impact on the mouthfeel of the product when consumed and is therefore highly desired by many consumers. Additionally, foam acts to retain more of the volatile aromas in the beverage so that they can be perceived by the consumer rather than being dispersed into the surrounding environment. Foam is often referred to as crema.

[0005] Several techniques are known for trapping gas in soluble coffee powder to form a cream upon reconstitution, but these techniques typically use spray drying, which aids in the formation of closed pores. EP 0839457 describes foaming a coffee extract by injection of gas, homogenizing the foamed extract to reduce the gas bubble size, and spray drying the homogenized extract.

[0006] In contrast to the closed porosity of such gas-treated spray-dried powders, conventional freeze-dried powders have primarily open porosity, which arise during drying of frozen extracts: the pores are areas originally occupied by ice crystals, and the open channels are the exit pathways for sublimated water.

[0007] Spray-dried coffee powders are perceived by some consumers to have an inferior aroma profile compared to freeze-dried powders because the spray-drying process results in a greater loss of coffee volatiles compared to freeze-drying. Although the quality of spray-dried coffee has improved significantly in recent years with the advent of improved aroma capture techniques, the perception of the superior quality of freeze-dried coffee remains for some consumers.

[0008] The process of freeze-drying coffee extracts usually involves gassing the extract to form a foam followed by freezing, as described for example in GB 1102587. This step is carried out to increase the drying rate and to control the density of the resulting powder. Such gassing processes do not produce soluble coffee that provides a large amount of crema.

[0009] WO 2017 / 186876 describes a freeze-dried coffee powder that produces some crema upon reconstitution and has a closed porosity of less than 15%. The production method involves slowly freezing a coffee extract to grow large ice crystals that result in open porosity when the extract is dried. However, longer freezing times reduce production efficiency.

[0010] However, many soluble coffee powders that produce foam still fall short in that the foam initially produced is not maintained during consumption, or the structure is coarse rather than the fine, smooth (velvety) foam ultimately desired by the consumer. Alternatively or additionally, the foam produced upon reconstitution of the powder may simply be insufficient and / or the foam may not cover the entire beverage surface.

[0011] Therefore, there remains a need in the art to find a better solution for providing a soluble coffee powder that produces crema upon reconstitution.

[0012] Any reference to a prior art document in this specification should not be considered as an admission that such prior art is well known or forms part of the common general understanding in the art. As used herein, the words "comprises," "comprising," and similar words should not be construed in an exclusive or exhaustive sense. In other words, they are intended to mean "including, but not limited to."

[0013] [Summary of the Invention] The object of the present invention is to improve upon the state of the art and to provide an improved solution to overcome at least some of the above mentioned disadvantages. This object is achieved by the subject matter of the independent claims. The dependent claims further develop the inventive idea.

[0014] Thus, the present invention provides in a first aspect a coffee powder providing a coffee beverage having crema, the coffee powder comprising particles having open and closed pores, the particles having an open pore volume mean diameter greater than 4 micrometers, a total open pore volume greater than 1 mL / g and a foamable porosity of 30% or greater.

[0015] In a second aspect, the present invention relates to the use of the coffee powder of the invention for preparing a coffee drink having crema.

[0016] A further aspect of the present invention is a method for producing a freeze-dried coffee powder comprising the steps of: Providing a coffee extract having a solids content of 50% to 70% by weight; adding gas to the coffee extract in an amount of 0.5 to 3 normal liters per kilogram of solids to provide a gas-containing coffee extract at a pressure greater than atmospheric pressure; cooling the gas-containing coffee extract to a temperature of between -10 and 10°C; applying a pressure reduction to the gas-containing coffee extract to form a foamed coffee extract; adding crystals of a sublimable material to the foamed coffee extract at a temperature between -10 and 10°C to form a mixture comprising the foamed coffee extract and the crystals of a sublimable material; cooling the mixture comprising the foamed coffee extract and the crystals of sublimable material to below -30°C to form a solid coffee extract; fragmenting the coffee extract solids; and exposing the solid coffee extract to conditions whereby the crystals of the sublimable material sublimate.

[0017] A high level of closed porosity creates foam in spray-dried coffee powders. However, the same approach has not been successfully applied to freeze-dried coffee powders. Freeze-dried coffee powders with a high level of closed porosity simply float to the top of the beverage, which is unattractive to consumers. This behavior is due to the slower dissolution of the freeze-dried powder.

[0018] The inventors have found that by gassing a high solids content coffee extract, the formation of foam-producing pores, e.g. closed pores, can be maximized. However, extracts with high solids content contain less water and therefore less ice is produced upon freezing during the production of freeze-dried coffee. With less ice formed, less open pores are produced and the freeze-dried powder tends to float rather than dissolve quickly. Floating particles do not produce good crema and are not aesthetically pleasing. The inventors have surprisingly found that by adding pre-formed ice crystals to the high solids extract after gassing, a freeze-dried coffee powder can be formed that has an improved level of closed pores, produces good crema, and dissolves quickly. The microstructure of the resulting powder shows a combination of a high level of foaming porosity and larger open pores sufficient to aid dissolution. [Brief description of the drawings]

[0019] [Figure 1] 1 is a plot of the time to 90% dissolution in seconds, t90 (x-axis), against the open pore volume in mL / g (y-axis) as measured by mercury intrusion at a pressure of 40 psia. [Diagram 2] 1 is a plot of the time to 90% dissolution in seconds, t90 (x-axis), against the median open pore diameter in micrometers (y-axis) as measured by mercury intrusion. [Diagram 3] Diagram of the apparatus used to measure the cream volume of the samples: (3.1) is a plastic scale to read the foam volume, (3.2) is the water reservoir, (3.3) is the lid of the reconstitution vessel, (3.4) is the connection valve, (3.5) is the reconstitution vessel, and (3.6) is the release valve. [Figure 4] FIG. 2 is a scanning electron microscope image of a coffee granule containing closed pores (a), voids due to ice sublimation (b), and voids due to ice crystal addition (c). [Diagram 5]FIG. 2 is a scanning electron microscope image of a coffee granule containing closed pores (a), voids due to ice sublimation (b), and voids due to ice crystal addition (c).

[0020] [Mode for carrying out the invention] The invention therefore relates in part to a coffee powder for providing a coffee beverage with crema, the coffee powder comprising (e.g. consisting of) particles (e.g. soluble particles) having open and closed pores, the particles having an open pore volume mean diameter (e.g. as measured by mercury porosimetry) of more than 4 micrometers, such as more than 5 micrometers, for example more than 6 micrometers, such as more than 7 micrometers, even such as more than 8 micrometers, a total open pore volume (e.g. as measured by mercury porosimetry) of more than 1 mL / g, such as more than 1.1 mL / g, for example more than 1.2 mL / g, such as more than 1.3 mL / g, even such as more than 1.4 mL / g, and a foamable porosity (e.g. as measured by mercury porosimetry) of 30% or more.

[0021] Coffee powder is a powder that produces a coffee beverage when reconstituted with water. An example of a coffee powder is a water extract of roast and ground coffee that is powdered and dried. The coffee powder may be instant soluble coffee. Typically, coffee powder consists of particles of coffee ingredients. Many food-related regulations prohibit ingredients other than coffee ingredients in soluble coffee. In one embodiment, the coffee powder may be free of insoluble roast and ground coffee.

[0022] In the context of the present invention, the term "open pores" is used to define voids present in the particle that have a connection to the surface of the particle. The term "closed pores" is used to define voids that are completely closed. Thus, liquids such as water cannot penetrate the closed pores before the particle dissolves.

[0023] "Volume mean diameter" is the average diameter on a volume basis, sometimes referred to as D[4,3]. Open pore volume mean diameter is the volume mean diameter of the open pores. Open pore mean diameter can be measured by mercury intrusion porosimetry. The inventors have found that the dissolution rate of the particles increases with the open pore volume mean diameter (see Example 3). In one embodiment the coffee powder comprises particles having an open pore volume mean diameter of 4 to 15 micrometers, such as 5 to 14 micrometers, further such as 6 to 9 micrometers.

[0024] In some coffee powders, individual particles aggregate with other particles to form agglomerates or granules. For example, the particles may be aggregated using a sintering process. In such agglomerates, there may be a bimodal distribution of open pore volume, i.e. smaller open pores in the original particles and larger open void spaces between the individual original particles in their aggregate structure.

[0025] In one embodiment the particles according to the invention have a bimodal open pore size distribution, the open pore volume mean diameter (e.g. as measured by mercury porosimetry) of the peak containing the smaller diameter is greater than 4 micrometers, such as greater than 5 micrometers, for example greater than 6 micrometers, such as greater than 7 micrometers, or even such as greater than 8 micrometers.

[0026] In one embodiment, the particles according to the present invention have a unimodal open pore size distribution.

[0027] Total open pore volume is the volume of open pores per gram of product in the size range 0.02 to 500 micrometers (corresponding to a mercury intrusion pressure of 9000 psia to 0.3 psia). In one embodiment the coffee powder comprises coffee particles having a total open pore volume of 1 mL / g to 1.8 mL / g.

[0028] As mentioned above, closed pores contribute to crema formation. Without wishing to be bound by theory, the inventors believe that open pores with an opening diameter of less than 2 micrometers also contribute to foam because the capillary pressure in these open pores is greater than the ambient pressure, which may allow foam formation. Foam porosity can be measured by a combination of mercury porosimetry and helium pycnometry. Foam porosity can be measured by mercury porosimetry, for example, as described in Example 3. The term "foam porosity" refers to the sum of closed pores and open pores with an opening diameter of less than 2 micrometers.

[0029]

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[0030] Closed pore volume V c can be measured by using a gas displacement pycnometer, for example, the skeletal (apparent) density of coffee powder can be determined by measuring the volume of a weighed amount of powder using a gas displacement pycnometer and dividing the weight by the volume. It is the ratio of the mass of the coffee powder to the total volume including closed (or obstructed) porosity. Skeletal density is a measure of density that includes the volume of any voids present in the powder that are sealed to the atmosphere and excludes the volume of any voids that are open to the atmosphere. The closed pore volume V c is determined by subtracting the inverse of the density of the coffee matrix from the inverse of the skeletal density, which is sometimes called the "true density" of the solid materials that form the coffee powder.

[0031] The density of the coffee matrix can be measured by grinding the coffee powder particles to open all the internal voids. For example, the coffee powder particles may be ground in a cryomill. A cryomill has the advantage that the low temperature helps to break up the particles and prevents thermal decomposition of the powder during grinding. The density obtained by pycnometry of the ground powder is the density of the coffee matrix. The volume V of the coffee matrix for a given weight of coffee powder is m is the density of the coffee matrix d m Another method to obtain the density of a coffee matrix is ​​to measure the density of liquid coffee at different concentrations and extrapolate to a density value for the coffee matrix at the relevant low moisture content.

[0032] The expandable porosity of the particles according to the invention (e.g., as measured by mercury intrusion porosimetry) may be at least 30%, such as at least 32%, such as at least 35%, further such as at least 40%. The expandable porosity (e.g., as measured by mercury intrusion porosimetry) may be 30-60%, such as 32-50%, further such as 35-45%.

[0033] Closed pore volume V c , and their size distribution can be measured by X-ray tomography. X-ray tomography images are analyzed by image analysis software. For example, Geodict software (Math2Market) can be applied to high-resolution images to analyze the pore size distribution of closed pores. Pores can be distinguished from the wall by applying Auto-thresholding (OTSU method). Individual pore analysis may be performed using the "individual pores" function, selecting a threshold of 0% to consider only pores that are not connected to the outer surface. In this case, the volume average of closed pores

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[0034] In one embodiment, the volume mean diameter of the closed pores of the particles according to the invention

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[0035] The unique structure of the particles contained in the coffee powder of the present invention provides an advantageous balance between porosity that has the potential to produce cream upon dissolution of the powder and porosity that speeds dissolution to maximize the volume and quality of the resulting cream. Faster dissolution results in better surface foam coverage for the same foamable porosity. Slower dissolution results in particles floating to the surface, where they appear to the consumer as unattractive black specks and do not produce a satisfactory foam when finally dissolved.

[0036] In one embodiment of the coffee powder of the invention, the coffee powder provides a beverage with at least 2.5 mL, such as at least 3 mL, such as at least 4 mL, such as at least 5 mL, of crema when 5 g of coffee powder is used per 200 mL of deionized water at 85° C. The crema may be measured after 1 minute. The amount of crema produced can be measured with a simple device (FIG. 3) consisting of a reconstitution container connected to a water reservoir, which is initially closed with a valve. After reconstitution, the reconstitution container is closed with a special lid ending in a scaled capillary. The valve between the reconstitution container and the water reservoir is then opened, and the reconstituted beverage is pushed up by water (standard tap water) into the capillary, which makes it easy to read the crema volume. The crema may be at a temperature of 25° C. when its volume is measured. One embodiment of the invention is a coffee powder that provides a coffee beverage with a crema of at least 0.5 mL / g upon reconstitution with water, such as at least 0.6 mL / g, 0.8 mL / g or 1.0 mL / g upon reconstitution with water.

[0037] In one embodiment, the coffee powder is a freeze-dried coffee powder. Freeze-dried coffee powder is an instant coffee obtained by freeze-drying an extract (e.g., an aqueous extract) of coffee, usually roasted and ground coffee. The coffee may be arabica coffee (Coffea arabica), robusta coffee (Coffea canephora) or a blend of arabica and robusta coffee.

[0038] The extract can be provided by an extraction process that promotes some hydrolysis of the coffee. In roast and ground coffee, chemical transformations, such as hydrolysis, can occur during extraction, e.g., high molecular weight polysaccharides are cleaved and solubilized.

[0039] The coffee powder of the present invention has an attractive appearance and good solubility and does not require agglomeration. The coffee powder may be non-agglomerated. For example, the coffee powder may not have been subjected to a sintering process. In one embodiment, neither the coffee powder nor its components have been subjected to a sintering process. In one embodiment, the coffee powder is a non-sintered powder.

[0040] In one embodiment, the coffee powder has a dissolution time t90 (time for 90% dissolution) of 2 to 15 seconds.

[0041] The addition of preformed ice crystals to the coffee extract followed by freeze-drying produces freeze-dried coffee powder with a characteristic open pore structure. The voids left by the added ice crystals can be clearly observed in Figures 4 and 5 (shown as "c"). This open pore structure provides for fast dissolution. The size and shape of the voids left by the added ice can be measured by X-ray tomography. The X-ray tomography images are analyzed by image analysis software. Geodict software (Math2Market) can be used on low resolution images to analyze the 3D structure of the particles. The different pore populations are segmented as a function of sphericity value. First, a Non-Local Means filter is applied to the image. The pores are differentiated from the walls by applying Auto-thresholding (OTSU method). The function "flood fill large pores" (200 voxels) is then used to delineate the particle. Individual pore analysis is performed using the "individual pores" function, choosing a threshold of e.g. 14%. The identified pores are then filtered according to two criteria: a sphericity of less than 0.7 and an individual equivalent diameter of more than 25 μm. The resulting list of pores corresponds in appearance to the added ice. In one embodiment, the particles formed by the added ice have a volume mean diameter (e.g. as measured by X-ray tomography) of 50-1000 μm, such as 100-1000 μm, such as 200-500 μm, such as 90-250, such as 110-210 μm.

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[0042] Closed porosity contributes to crema formation in particles with suitable dissolution properties. In one embodiment, the particles have a closed porosity of 8% or more, such as 10% or more, such as 12% or more, such as 15% or more, such as 15.5% or more, such as 17% or more, or even 20% or more (e.g., as measured by helium displacement method). Closed porosity can be measured, for example, by measuring the skeletal density d s and the coffee matrix density d m The skeletal density d s can be measured, for example, by using a gas displacement pycnometer with helium gas, a measurement pressure of 134 kPag (kPa gauge), and a balance reference setting of 0.6895 kPag / min. m can be measured in the same way, except that the coffee powder particles are first ground to open all internal voids. The coffee powder particles can be ground using a cryomill for, for example, 8 minutes to open all internal voids.

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[0043] As discussed above, open pores with opening sizes less than 2 micrometers can contribute to foam generation upon dissolution. In one embodiment, the particles have an open pore volume (V:0<2μm ) is greater than 0.2 mL / g. For example, the particles according to the invention may have an open pore volume with openings less than 2 micrometers greater than 0.25 mL / g, such as greater than 0.3 mL / g. The particles according to the invention may have an open pore volume with openings less than 2 micrometers of 0.2 to 0.45 mL / g. The open pore volume with openings less than 2 micrometers (V 0<2μm ) can be measured, for example, by mercury intrusion porosimetry, as described above. In one embodiment, the particles have open pores with openings less than 2 micrometers, and the volume of the open pores with openings less than 2 micrometers is greater than 17%, such as greater than 19%, of the total volume of the open pores (e.g., as measured by mercury intrusion porosimetry).

[0044] In one embodiment, the particle comprises open and closed porosity, the open and closed porosity together having an overall pore size distribution with a volume median diameter Dv50 of 10-100 micrometers, such as 30-50 micrometers, such as 10-45 micrometers, such as 11-35 micrometers, such as 12-30 micrometers, such as 13-25 micrometers, such as 14-20 micrometers. The pore size distribution can be measured by X-ray tomography based on the void volume distribution. For example, low-resolution tomography of the particle may be performed using an X-ray beam energy of 12 keV, a sample-detector distance of 5 mm, and a detector with an effective isotropic voxel size of 1.625 μm. Geodict software (Math2Market) can be applied to the low-resolution image to analyze the microstructure of the open and closed porosity. First, a Non-Local Means filter is applied to the image. Pores are differentiated from walls by applying auto-thresholding (OTSU method) and a mask is applied to focus on the fully imaged particles. A granulometry method (PoroDict module) is performed to extract global diameter statistics of all pores.

[0045] In one embodiment the particles contain both open and closed pores with a pore size distribution characterized by a distribution span factor of 0.5 to 9, such as 1 to 8, for example 1.1 to 7, such as 1.2 to 6, for example 1.3 to 5, such as 1.4 to 4, for example 1.3 to 3, such as 1.4 to 2, further for example 1.5 to 1.9. The distribution span factor can be measured by X-ray tomography. The span of the distribution is calculated by the following formula:

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[0046] The inventors have found that a high percentage of open porosity with openings larger than approximately 4.4 micrometers results in rapid dissolution. Using mercury porosimetry, a pressure of 40 psia is required to penetrate the 4.4 micrometer pore openings. In one embodiment, the particles have a structure such that mercury porosimetry achieves intrusion of 60% or more of the particles at a pressure of 40 psia.

[0047] However, the inventors have found that for best crema production, a proportion of smaller pores should be present. In one embodiment, the particles have a structure such that mercury porosimetry can achieve 60-85% intrusion of the particles at a pressure of 40 psia. For example, the particles may have a structure such that mercury porosimetry can achieve 50-80%, such as 60-75%, or even 65-70% intrusion of the particles at a pressure of 40 psia. Such a desired structure can be formed by freeze-drying the coffee extract after the addition of ice crystals.

[0048] One aspect of the invention provides a pack, such as a single-serve pack, containing the coffee powder of the invention. The single-serve pack may be, for example, a capsule, a pod or a stick pack.

[0049] One aspect of the invention provides the use of the coffee powder of the invention to prepare a coffee beverage with crema, for example when 5 g of coffee powder is used per 200 mL of deionised water at 85° C., a coffee beverage having at least 2.5 mL of crema, such as at least 3 mL, for example at least 4 mL, such as at least 5 mL. The crema may be measured after 1 minute. The gas volume of the crema may be measured at a temperature of 25° C. One embodiment of the invention is the use of the coffee powder of the invention to provide a coffee beverage having at least 0.5 mL / g of crema upon reconstitution with water, for example at least 0.6, 0.8 or 1.0 mL / g upon reconstitution with water.

[0050] A further aspect of the present invention provides a beverage powder mix comprising the coffee powder of the present invention. The beverage powder mix may be, for example, a powder mix comprising ingredients selected from the group consisting of sugar, milk powder, "plant milk" powder (e.g. oat milk, almond milk, soy milk, coconut milk), creamer (including non-dairy creamers), and combinations thereof.

[0051] A further aspect of the present invention is a method for producing a freeze-dried coffee powder comprising the steps of: Providing a coffee extract having a solids content of 50% to 70% by weight; adding gas to the coffee extract in an amount of 0.5 to 3 normal litres per kilogram of solids to provide a gas-containing coffee extract at a pressure greater than atmospheric pressure (e.g., 50 to 400 bar gauge, further e.g., 150 to 350 bar gauge); cooling the gas-containing coffee extract to a temperature of between -10 and 10°C; applying a pressure reduction to the gas-containing coffee extract to form a foamed coffee extract; adding crystals of a sublimable material to the foamed coffee extract at a temperature between -10 and 10°C to form a mixture comprising the foamed coffee extract and the crystals of a sublimable material; cooling the mixture comprising the foamed coffee extract and the crystals of sublimable material to below −30° C. (e.g. below −40° C.) to form a solid coffee extract; fragmenting the coffee extract solids; and exposing the solid coffee extract to conditions whereby crystals of the sublimable material sublimate.

[0052] The coffee extract according to the invention may be an aqueous coffee extract suitable for further processing into pure soluble coffee. A coffee extract can be produced by extracting roasted coffee beans with water. The roasted beans are usually ground before being extracted with water. Grinding roasted coffee beans is well known in the art and the roasted coffee beans can be ground by any suitable method. The extraction can be carried out by any suitable method known in the art. Methods for extracting coffee beans are well known in the art of soluble coffee production, for example from EP 0826308, and usually involve several extraction steps at elevated temperatures. Once the desired degree of extraction is reached, the extracted roasted coffee beans are separated from the extract. The separation can be achieved by any suitable means, for example by filtration, centrifugation, and / or decanting. In conventional coffee extraction for the production of soluble coffee, the separation is usually achieved by carrying out the extraction in an extraction cell in which the coffee grounds are held by a filter plate or holding plate through which the coffee extract can pass. To avoid aroma loss, volatile aroma compounds may be recovered from the coffee beans and / or extract before and / or during extraction, for example by steam stripping and / or the use of a vacuum, and the recovered volatile compounds may be added back to the extract after extraction.

[0053] The coffee extract can be an extract of roasted Arabica or Robusta coffee beans, or a combination thereof. Coffee beans are the seeds of the Coffea plant. Arabica coffee beans refer to coffee beans derived from the Coffea arabica plant, and Robusta coffee beans refer to beans derived from the Coffea canephora plant.

[0054] The solids content of an extract is the weight of dry matter as a percentage of the total weight of the extract on a wet basis. Various methods are available for increasing the solids content of a coffee extract. For example, water may be evaporated from the coffee extract under vacuum, usually while capturing the aromas; water may be removed by membrane concentration; and / or additional solid coffee extract may be dissolved in the aqueous coffee extract. In one embodiment, dry pure soluble coffee is added to the aqueous coffee extract to obtain a coffee extract having a solids content of 50% to 70% by weight.

[0055] In one embodiment, the coffee extract is subjected to high pressure (e.g., 50-400 bar gauge, further such as 80-300 bar gauge, further such as 120-250 bar gauge) by a high pressure pump. Gas may be added to the coffee extract before and / or after the high pressure pump. The gas may be added by a gas addition line, where the gas is at a pressure above that of the coffee extract (e.g., slightly (e.g., up to 10%) above the pressure of the coffee extract). The gas may be selected from the group consisting of nitrogen, air, argon, nitrous oxide, and carbon dioxide. Nitrogen is preferred because it tends to form smaller, more stable bubbles. The gas is dissolved in the coffee extract, for example by ensuring a sufficient residence time in the coffee extract. For example, the gas may have a residence time of at least 60 seconds before the gas-containing coffee extract is depressurized. Although the term "gas" is used herein for ease of explanation, it is noted that gases such as nitrogen are in the form of supercritical fluids under some conditions of the present method.

[0056] The gas is added to the coffee extract in an amount of 0.5 to 3 normal liters per kilogram of coffee extract solids, for example 1 to 2.8 normal liters per kilogram of coffee extract solids. The amount of gas in 1 normal liter is the amount that occupies a volume of 1 liter at 20° C. and 1 atmosphere (101.325 kPa) pressure. The amount of gas added affects the amount of gas bubble voids in the final coffee powder.

[0057] The gas-containing coffee extract is cooled to a temperature of -10 to 10°C (e.g. -7 to 8°C, e.g. -6 to 7°C, e.g. -5 to 7°C, further e.g. 0 to 6°C). Preferably, the gas-containing extract is cold enough not to cause excessive melting of the sublimable material crystals when these are added. The gas-containing coffee extract may be cooled to a temperature above the freezing point of the coffee extract. The gas-containing coffee extract may be cooled, for example, to a temperature of 3°C below the freezing point of the coffee extract to 5°C above the freezing point of the coffee extract. Cooling the gas-containing coffee extract may be performed before or after depressurizing the gas-containing coffee extract to form a foamed coffee extract. Cooling may be performed, for example, using a scraped-surface heat exchanger. Depressurizing the gas-containing coffee extract after cooling helps control the foam structure as it reduces the opportunity for gas bubbles in the foam to coalesce. Depressurization may be performed via sparging or spraying nozzles.

[0058] The sublimable material according to the present invention may be water or carbon dioxide. In one embodiment, the sublimable material crystals may comprise, for example consist of, water ice.

[0059] The crystals of the sublimable material are added to the foamed coffee extract at a temperature of −10 to 10° C. (e.g. −7 to 8° C., e.g. −6 to 7° C., e.g. −5 to 7° C., further e.g. 0 to 6° C.). The crystals of the sublimable material may for example be added to the foamed coffee extract at a temperature of from 3° C. below the freezing point of the coffee extract to 5° C. above the freezing point of the coffee extract.

[0060] The crystals of the sublimable material may be added to the foamed extract in the mixer. Sufficient shear is necessary to effectively mix the crystals into the foamed extract, but care should be taken to limit damage to the foam structure and to avoid heating the mixture. In one embodiment, the crystals of the sublimable material are at a temperature of -40°C to -10°C when added to the foamed coffee extract. The addition of the crystals may reduce the temperature of the gas-containing coffee extract. For example, the gas-containing coffee extract may be cooled by adding the crystals of the sublimable material, for example, while mixing the crystals of the sublimable material with the gas-containing coffee extract under moderate shear. The shear rate applied during mixing may be at least 50 s -1 , for example at least 100 seconds -1 , for example at least 200 seconds -1 Porous spray-dried particles of dried coffee extract having a high level of closed porosity (e.g. greater than 20% closed porosity) may be added to the foamed coffee extract to contribute to the closed porosity of the coffee powder obtained by the method of the present invention.

[0061] The mixture including the foamed coffee extract and the sublimable material crystals is cooled to below -30°C to form a solid coffee extract, e.g., a frozen coffee extract. The solid coffee extract has structural rigidity. The mixture may be cooled by placing it on a tray that moves between cold rooms or other zones held at different temperatures. The mixture may be cooled by passing it through a heat exchanger or cooling drum. The mixture may be cooled from a temperature of -5°C to a temperature of -30°C for a time of less than 30 minutes, e.g., less than 20 minutes, e.g., less than 10 minutes, e.g., less than 6 minutes. Rapid cooling ensures that the larger crystals in the solid extract are primarily derived from added crystals. For crystals that grow during cooling rather than being added, rapid cooling produces smaller crystals. The rate of crystal addition and cooling can be controlled to optimize the microstructure of the freeze-dried coffee powder.

[0062] The solid coffee extract may be fragmented before and / or after being subjected to conditions that cause the crystals of the sublimable material to sublime.

[0063] The condition under which crystals of a sublimable material sublime can be a vacuum. Sublimation is the process by which a solid changes directly to a vapor, for example, ice changes directly to water vapor without passing through a liquid phase.

[0064] In one embodiment, the ratio of sublimable crystals to coffee extract is in the range of 5-40% by weight, for example in the range of 10-30% by weight. The ratio is calculated on a wet basis coffee extract weight. This ratio is set to control the balance between added crystals and crystals that grow during freezing in order to optimize the microstructure in terms of dissolution rate and maintenance of foaming pores.

[0065] In one embodiment, the sublimable material crystals are ice, the solid coffee extract is a frozen coffee extract, and the sublimation is carried out under vacuum. The coffee extract may be placed on a tray in a cabinet under a vacuum of less than 1 mbar for a period of up to 7 hours.

[0066] In one embodiment, the ice has a volume mean diameter of 45-2000 μm, such as 50-1700 μm, such as 50-1500 μm, further such as 150-1000 μm. The ice may have an average aspect ratio b / l3 of 0.5-0.7. The volume mean diameter and average aspect ratio can be measured, for example, by laser diffraction. The ice can be prepared, for example, by using an ice shaver to generate small water ice particles from ice blocks. The ice may be crushed and sieved to obtain the desired size and shape.

[0067] In one embodiment, the sublimable material crystals may be ice, which may be added in the form of a frozen aroma extract, for example a frozen aqueous aroma extract obtained (e.g. recovered) during the processing of a coffee extract. The frozen aroma extract may contain some coffee extract solids, for example 5-15% by weight of coffee solids.

[0068] Those skilled in the art will understand that all features of the invention disclosed herein can be freely combined. In particular, features described for the product of the invention can be combined with the method of the invention, and vice versa. Furthermore, features described for different embodiments of the invention can be combined. Where known equivalents exist for specific features, such equivalents are incorporated herein as if specifically mentioned.

[0069] Further advantages and features of the invention are apparent from the drawings and non-limiting examples. EXAMPLES

[0070] Example 1: Preparation of coffee powder The coffee liquid extract was transported and pressurized to approximately 220 bar with a high pressure piston pump. Nitrogen was injected immediately after the high pressure pump. The gassed extract passed through a specified length of pipe to ensure sufficient residence time (e.g., more than 60 seconds) to dissolve the nitrogen. The extract was passed through a spray nozzle to release the pressure to atmospheric pressure and form a foam.

[0071] The foamed extract was cooled above its freezing point without the addition of gas using a scraped surface heat exchanger.

[0072] An ice shaver was used to generate small water ice particles from the ice blocks. The ice was then crushed and sieved using an Urschel CC slicer equipped with an SL8 head. The ice powder was stored in a cold room at temperatures below -40°C until required.

[0073] The size and shape of the ice powder before addition was evaluated using a Camsizer X2 instrument (Retsch) fitted with an X-Jet module. The powder was kept at -20°C and the ice was introduced directly into the air dispersion unit (300 kPa, 9 mm gap) via a spoon, without the use of a tray to avoid melting of the particles before measurement. At least 1 million particles were recorded by the system. The volume mean diameter D 4,3 (M by Camsizer software v3 ) and the average aspect ratio b / l3 were extracted from the Camsizer software.

[0074] Volume mean diameter of ice D 4,3 was 590 μm and the average aspect ratio b / l3 was 0.619.

[0075] A weighed amount of ice powder was added to the foamed extract and mixed. A moderate level of shear was applied, sufficient to ensure good mixing but not to promote significant ice melting. The temperature of the foamed extract was reduced during the mixing of the ice. The foamed extract with added ice was then further cooled to below -40°C to form a frozen layer. This frozen extract was milled and then freeze-dried using an Atlas freeze dryer. Final particle size was measured using laser diffraction. All samples had a d50 particle size in the range of 2.0-2.5 mm.

[0076] The process parameters for the seven samples are given in the table below.

[0077] [Table 1]

[0078] Example 2: Method for measuring closed porosity by He porosimetry Skeletal density d of coffee particles of sample A s was measured using a gas displacement pycnometry system (AccuPyc 1340, Micromeritics). The pycnometer measurement cell was filled to two-thirds of its volume and the sample weight was recorded. The following parameters were used: 10 purges, purge and measurement pressure of 134 kPag; average of three. The volume of gas penetrating the measurement chamber was used to calculate the g / cm3 by the instrument. 3 This allows the calculation of the unitary skeletal density. Skeletal density is a measure of the density of a material including the closed voids within the particles but excluding all voids open to the atmosphere (open porosity and interparticle voids). Skeletal density was first measured using a gas displacement pycnometer with nitrogen gas, as nitrogen has a lower tendency than helium to diffuse into the matrix material making it easier to achieve a strict equilibrium criterion. The equilibrium criterion for nitrogen was set at 0.0345 kPa / min (referred to as the "equilibrium rate" in the instrument software). With this setting, the skeletal density of sample A was 1.201 g / cm 3 The sample was then measured with helium gas, which is more commonly used for pycnometry. The equilibrium standard setting was 0.6895 kPag / min. The skeletal density of sample A measured with helium was 1.203 g / cm. 3 It was.

[0079] Next, the skeletal density d s is the density of the coffee matrix, d m Estimate the closed porosity of the sample by dividing by

number

[0080] The density of the coffee matrix was measured by grinding the samples in a SPEX Sample Prep 6875 freezer mill for 8 minutes and then performing the helium displacement method as described above.

[0081] Coffee matrix density is 1.540g / cm 3 and the skeletal density is 1.203 g / cm 3 The closed porosity of Sample A was calculated to be 21.9%. The closed porosity of other samples was measured in the same manner and is listed in the table below, along with the closed porosity of a commercially available freeze-dried coffee advertised as producing crema (Prior Art i).

[0082] [Table 2]

[0083] Example 3: Measurement of pore structure by mercury intrusion method An AutoPore IV 9520 was used for the structural characterization (Micromeritics Inc., Norcrose, GA, USA). The operating pressure for Hg injection was 0.4 psia to 9000 psia (0.4 psia to 40 psia low pressure port and 20 to 9000 psia high pressure port). The pore diameters under this pressure ranged from 500 to 0.01 micrometers. Data on total pore volume and pore volume (mL / g) at different pore opening diameters (μm) were recorded. Approximately 0.1 g to 0.4 g of sample was accurately weighed and loaded into a penetrometer (3.5 mL capacity, 0.3 mm neck or capillary stem diameter, and 0.5 mL stem capacity).

[0084] After inserting the penetrometer into the low pressure port, the sample is initially pumped at 1.1 psia / min, switched to a medium rate of 0.5 psia, and then to a high rate of 900 μmHg. Aim for pumping at 60 μmHg. After reaching the target, pumping is continued for 5 min, after which Hg is introduced.

[0085] Measurements are taken with a set time equilibration, i.e., pressure points at which data is acquired and time spent at that pressure, in a set time equilibration (10 seconds) mode. Approximately 140 data points are collected over that pressure range.

[0086] The volume of open pores per gram of product in the diameter range 1-500 micrometers gives the "open pore volume."

[0087] Baseline values ​​were obtained by running a corresponding empty penetrometer under the same operating conditions of pressure for Hg intrusion, i.e., 0.4 psia to 9000 psia, without containing any sample.

[0088] The bulk volume of the granule is obtained from the initial volume of the mercury and the sample holder. The volume of the open pores with an opening diameter of more than 2 micrometers is obtained after intrusion of mercury to a diameter of 2 micrometers. (A mercury intrusion pressure of 90 psi is required to penetrate the pores of 2 micrometers.) This volume is subtracted from the bulk volume of the granule to obtain the new volume of the granule, including the closed pores, the open pores with an opening diameter of less than 2 micrometers, and the volume of the coffee matrix. The volume of the closed pores and the open pores with an opening diameter of more than 2 micrometers of the granule is obtained by subtracting the volume of the coffee matrix from the new volume of the granule. The volume of the coffee matrix is ​​obtained from the weight of the sample and the coffee matrix density (see Example 2). The foamable porosity is the ratio of the volume of the closed pores and the open pores with an opening diameter of less than 2 micrometers to the new volume of the granule.

[0089] Reconstitution kinetics were evaluated by conductivity. A 10 Hz conductivity probe (Pt1000 / B / 2 0-70 °C, Metrohm) was used in combination with an acquisition module (module 856, Metrohm). The probe was placed horizontally in a double-walled glass container thermostated at 80 °C. The experiment was started after pouring 10 g of coffee powder into 400 mL of demineralized water heated to 80 °C. The solution was stirred at 500 rpm using a magnetic stirrer and at 100 rpm using an overhead stirrer to ensure rapid immersion of all particles. The time t corresponds to the time between the first change in conductivity and the time when the conductivity is equal to 90% of the final solution conductivity. 90 It was recorded.

[0090] The sample results are listed in the table below.

[0091] [Table 3]

[0092] To investigate the effect of pore structure on dissolution, a series of porous freeze-dried coffee powders with the same particle size were prepared. The time to 90% dissolution (t 90 ) was found to be lower for coffees with higher indentation at a pressure of 40 psia (Figure 1), and the time to 90% dissolution was found to be lower for coffees with higher median open pore size (Figure 2).

[0093] Example 4: X-ray tomography Multi-resolution X-ray tomography of coffee particles was performed at the TOMCAT beamline of the Swiss Light Source (SLS) at the Paul Scherrer Institut (PSI). For each sample, five coffee particles were stacked in a 4 mm diameter Kapton tube mounted on a brass sample holder. Polymer foam was placed as spacer between the particles.

[0094] A detector with an effective isotropic voxel size of 1.625 μm was used to perform low-resolution tomography of each particle. A high-quality microscope (Optique Peter, Lentilly, France) with a 4x objective was used to couple a PCO.edge 5.5 sCMOS camera (PCO, Kelheim, Germany) to a 100 μm thick LuAG:Ce scintillator. The camera has 2560 × 2160 pixels giving an effective field of view of 4.16 mm (horizontal) × 3.51 mm (vertical). The X-ray beam energy used was 12 keV and the sample-detector distance was 5 mm.

[0095] High-resolution tomography was then performed using a detector with an effective isotropic voxel size of 0.325 μm. A PCO.edge 5.5 sCMOS camera (PCO (Kelheim, Germany)) was coupled to a 20 μm thick LuAG:Ce scintillator using a high-quality microscope (Optique Peter (Lentilly, France)) with a 20x objective. The camera has 2560 × 2160 pixels giving an effective field of view of 0.83 mm (horizontal) × 0.7 mm (vertical). The X-ray beam energy used was 12 keV and the sample-detector distance was 3 mm.

[0096] For each configuration, darkfield (no X-ray beam) and flatfield (no sample in the beam) images were also recorded to correct for camera noise and background intensity non-uniformity. Phase retrieval of the projections using the Paganin algorithm [D. Paganin et al., Journal of Microscopy-Oxford 206 (2002)] was performed before tomographic reconstruction [F. Marone et al., J. Synchrotron Rad. 19 (2012)]. Data of reconstructed tomographic slices were saved in 16-bit TIFF.

[0097] Geodict software (Math2Market) was used on low-resolution images to analyze the microstructure of open and closed pores. First, a Non-Local Means filter was applied to the images. Pores were differentiated from the walls by applying Auto-thresholding (OTSU method) and a mask was applied to focus on the fully imaged particles. Granulometry (PoroDict module) was performed to extract the overall size statistics of all pores. The volume mean diameter D of pores (both open and closed) in the sample was calculated. v The 50 are listed below with their spans.

[0098] [Table 4]

[0099] Example 5: Crema volume measurement The amount of crema produced by the different samples was measured with a simple device (Figure 3), consisting of a reconstitution vessel connected to a water reservoir, which is initially closed by a valve. After reconstitution of 5 g of coffee powder with 200 mL of deionized water at 85 °C, the reconstitution vessel is closed with a special lid ending in a graduated capillary. The valve between the reconstitution vessel and the water reservoir is then opened, allowing the reconstituted beverage to be pushed up by the water (standard tap water at 25 °C) into the capillary, which allows an easy reading of the crema volume at 25 °C.

[0100] The sample results are listed in the following table.

[0101] [Table 5]

[0102] Example 6: Measurement of ice crystal void space The size and shape of the voids left by the ice were measured by X-ray tomography which was analysed by image analysis software.

[0103] Low-resolution X-ray tomography was performed as described in Example 4. Geodict software (Math2Market) was applied to the low-resolution images to analyze the 3D structure of the particles. The different populations of pores were segmented as a function of sphericity value. First, a Non-Local Means filter was applied to the images. Pores were differentiated from the walls by applying Auto-thresholding (OTSU method). The function "flood fill large pores" (200 voxels) was then used to delineate the particles. Individual pore analysis was performed using the "individual pores" function, selecting a threshold of 14%. The identified pores were then filtered according to two criteria: sphericity less than 0.7 and individual equivalent diameter greater than 25 μm.

[0104] D obtained for pores with a sphericity of less than 0.7 and an individual equivalent diameter of more than 25 μm 4,3 The data is listed in the following table. [Table 6]

[0105] Various features and embodiments of the present invention are described with reference to the following numbered paragraphs.

[0106] Paragraph 1. A freeze-dried coffee powder providing a coffee beverage having crema, the coffee powder comprising particles having open and closed pores, the particles having an open pore volume mean diameter of more than 4 micrometers, such as more than 5 micrometers, for example more than 6 micrometers, such as more than 7 micrometers, for example more than 8 micrometers (e.g. when measured by mercury intrusion porosimetry), for example an open pore volume mean diameter of between 4 and 15 micrometers, such as between 5 and 14 micrometers, further such as between 6 and 9 micrometers, and a closed porosity of 15.5% or more (e.g. when measured by helium displacement porosimetry).

[0107] Paragraph 2. The freeze-dried coffee powder of paragraph 1, wherein the coffee powder provides a beverage having at least 2.5 mL, such as at least 3 mL, such as at least 4 mL, for example at least 5 mL, of crema when 5 g of product is used per 200 mL of deionised water at 85°C.

[0108] Paragraph 3. The freeze-dried coffee powder according to paragraph 1 or 2, wherein the particles have a total open pore volume, as measured by mercury porosimetry, of more than 1 mL / g (such as more than 1.1 mL / g, such as more than 1.2 mL / g, such as more than 1.3 mL / g, further such as more than 1.4 mL / g).

[0109] Paragraph 4. The particles comprise open pores formed by the added ice, the open pores having a volume mean diameter D of 50 to 1000 μm, for example 100 to 1000 μm, for example 200 to 500 μm, for example 90 to 250, for example 110 to 210 μm (e.g. as measured by X-ray tomography). 4,3 4. The freeze-dried coffee powder according to any one of paragraphs 1 to 3, having

[0110] Paragraph 5. The particles comprise pores having a sphericity of less than 0.7 and an individual equivalent diameter of more than 25 μm, and the open pores having a sphericity of less than 0.7 and an individual equivalent diameter of more than 25 μm have a volume mean diameter D of 50 to 1000 μm, for example 100 to 1000 μm, for example 200 to 500 μm, for example 90 to 250, for example 110 to 210 μm, as measured by X-ray tomography. 4,3 5. The freeze-dried coffee powder according to any one of paragraphs 1 to 4, having

[0111] Paragraph 6. A freeze-dried coffee powder according to any one of Paragraphs 1 to 5, wherein the particles have open pores with openings less than 2 micrometers and the volume of the open pores with openings less than 2 micrometers is greater than 17% of the total volume of the open pores as measured by mercury porosimetry.

[0112] Paragraph 7. A freeze-dried coffee powder according to any one of Paragraphs 1 to 6, wherein the particles comprise open and closed pores, the open and closed pores together having an overall pore size distribution with a median diameter by volume Dv50 of 10 to 100 micrometers, such as 30 to 50 micrometers, such as 10 to 45 micrometers.

[0113] Paragraph 8. A freeze-dried coffee powder according to any one of Paragraphs 1 to 7, wherein the particles have a structure such that mercury intrusion porosimetry achieves 60% or more of the particles at a pressure of 40 psia.

[0114] Paragraph 9. Use of a freeze-dried coffee powder according to any one of paragraphs 1 to 8 for preparing a coffee drink having crema.

[0115] Paragraph 10. A beverage powder mix comprising the freeze-dried coffee powder of any one of Paragraphs 1 to 8.

Claims

1. A coffee powder for providing a coffee beverage having crema, wherein the coffee powder contains particles having open pores and closed pores, and the particles have an open pore volume average diameter exceeding 4 micrometers, a total open pore volume exceeding 1 mL / g, and a foaming pore ratio of 30% or more.

2. The coffee powder according to claim 1, wherein the coffee powder is freeze-dried coffee powder.

3. The particles contain pores having a sphericity of less than 0.7 and an individual equivalent diameter exceeding 25 μm, and the pores having a sphericity of less than 0.7 and an individual equivalent diameter exceeding 25 μm have a volume average diameter D of 50 to 1000 μm when measured by X-ray tomography. ４，３ The coffee powder according to claim 2.

4. The coffee powder according to any one of claims 1 to 3, wherein the particles have a closed pore ratio of 8% or more.

5. The particles have open pores having an opening less than 2 micrometers, and the volume of the open pores having an opening less than 2 micrometers exceeds 17% of the total volume of the open pores. The coffee powder according to any one of claims 1 to 3.

6. The particles contain open pores and closed pores, and the combination of the open pores and the closed pores has an overall pore size distribution having a volume median diameter Dv50 of 10 to 100 micrometers. The coffee powder according to any one of claims 1 to 3.

7. The coffee powder according to any one of claims 1 to 3, wherein the particles have a structure such that 60% or more of the particles are penetrated under a pressure of 40 psia by mercury intrusion porosimetry.

8. The coffee powder according to any one of claims 1 to 3, wherein the particles have an open pore volume average diameter of 4 to 15 micrometers.

9. Use of the coffee powder according to any one of claims 1 to 3 for preparing a coffee beverage having crema.

10. A beverage powder mixture comprising the coffee powder according to any one of claims 1 to 3.

11. A method for producing freeze-dried coffee powder, comprising: preparing a coffee extract having a solid content of 50% to 70% by weight; adding a gas to the coffee extract in an amount of 0.5 to 3 normal liters per kilogram of solid content to provide a gas-containing coffee extract at a pressure higher than atmospheric pressure; cooling the gas-containing coffee extract to a temperature of -10 to 10°C; reducing the pressure of the gas-containing coffee extract to form a foamed coffee extract; adding crystals of a sublimable material to the foamed coffee extract at a temperature of -10 to 10°C to form a mixture comprising the foamed coffee extract and the crystals of the sublimable material; cooling the mixture comprising the foamed coffee extract and the crystals of the sublimable material to below -30°C to form a solid coffee extract; fragmenting the solid coffee extract; placing the solid coffee extract under conditions where the crystals of the sublimable material sublimate.

12. The method according to claim 11, wherein the ratio of the sublimable crystals to the coffee extract is in the range of 5 to 40% by weight.

13. The method according to claim 11 or 12, wherein the crystals of the sublimable material are ice, the solid coffee extract is a frozen coffee extract, and the solid coffee extract is dried under vacuum.

14. The method according to claim 13, wherein the ice has a volume average diameter of 45 to 2000 μm.

15. The method according to claim 13, wherein the ice is added in the form of a frozen aroma extract.

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