HEAT TREATMENT OF BULKY FOOD PRODUCTS

Abstract

A method for carrying out a heat treatment, in particular roasting of bulky food products, in particular cocoa, nuts, like almonds, hazelnuts, pecans or walnuts, coffee, seeds, cereals, malt, peanuts, brans, grains or oilseeds such as sunflower seeds, wherein the food products are subjected to a predetermined temperature for heat treatment. During the heat treatment, the partial pressure of water in the atmosphere where the food products are located is controlled such that during the heat treatment a substantially homogeneous moisture distribution forms in the food products. In particular, the partial pressure of water is adjusted such that during the heat treatment the escape of moisture from the food products is avoided.

Claims

1. A method for carrying out a heat treatment of bulky food products, in particular cocoa, nuts, like almonds, hazelnuts, pecans or walnuts, coffee, seeds, cereals, malt, peanuts, brans, grains or oilseeds such as sunflower seeds, the method comprising: subjecting the food products to a predetermined temperature for heat treatment, and controlling a partial pressure of water in an atmosphere where the food products are located during the heat treatment such that a substantially homogeneous moisture distribution occurs in the food products during a duration of the heat treatment.

2. The method according to claim 1, wherein the partial pressure of water can be adjusted such that during the heat treatment a deliberate moisture escape from the food products can be adjusted.

3. The method according to claim 1, wherein the partial pressure of water is controlled on a basis of a measurement of a relative air moisture in the atmosphere and/or a moisture content and/or a density of the food products, wherein the measurement of the moisture content or the density is carried out by using microwave radiation or capacitive sensors.

4. The method according to claim 1, wherein hot air is supplied to the atmosphere to achieve and/or maintain the predetermined temperature, and the partial pressure of the water is controlled on a basis of a moisture of a supply air and/or an exhaust air of a hot air stream.

5. The method according to claim 1, wherein the control of the partial pressure of the water takes place before and/or during the heat treatment by deliberately supplying vapor to the atmosphere.

6. The method according to claim 1, wherein, during the heat treatment, a substantially homogeneous distribution of the temperature in the food products prevails.

7. The method according to claim 6, wherein the temperature maintained during the heat treatment is one of a dew point temperature or a glass transition temperature of the food products.

8. The method according to claim 1, wherein the duration of the heat treatment is controlled on a basis of a density measurement of the food products.

9. The method according to claim 1, wherein the food products are dried after the heat treatment, and the partial pressure of water in the atmosphere is lower during the drying than the partial pressure of water in the atmosphere during the heat treatment.

10. The method according to claim 1, wherein the food products are dried after the heat treatment, and the partial pressure of the water in the atmosphere is controlled during the drying on a basis of a density change in the food products.

11. A device for carrying out the method according to claim 1, wherein the device comprises a treatment chamber, in particular a roasting chamber or roasting drum, a supply air duct for supplying hot air into the treatment chamber, an exhaust air duct and means for supplying vapor into the supply air duct, wherein the device further comprises at least one of the following measuring means: means for determining a density of the food products, means for determining a moisture content of the food products, means for determining a relative air moisture in the treatment chamber, means for determining a supply air moisture, and means for determining a exhaust air moisture.

12. A device for carrying out the method according to claim 1, wherein the device comprises a roasting chamber or a roasting drum, a supply air duct for supplying hot air into the roasting chamber or the roasting drum, an exhaust air duct and means for supplying vapor into the supply air duct, wherein the device further comprises at least one of the following measuring means: means for determining a density of the food products using microwave radiation, means for determining a moisture content of the food products using microwave radiation, means for determining a relative air moisture in the treatment chamber, means for determining a supply air moisture, and means for determining a exhaust air moisture.

13. The method according to claim 6, wherein the prevailing temperature in the food products is between 90 C. and 230 C.

14. A method of carrying out roasting of bulky food products which comprises one of cocoa, nuts, almonds, hazelnuts, pecans, walnuts, coffee, seeds, cereals, malt, peanuts, brans, grains, oilseeds and sunflower seeds, the method comprising: subjecting the food products to a predetermined temperature for heat treatment thereof, and controlling a partial pressure of water, in an atmosphere where the food products are located during the heat treatment, such that a substantially homogeneous moisture distribution occurs within the food products during a duration of the heat treatment.

15. The method according to claim 14, further comprising adjusting the partial pressure of water such that during the heat treatment a deliberate moisture escape from the food products is adjustable.

16. The method according to claim 14, further comprising controlling the partial pressure of water on a basis of a measurement of at least one of a relative air moisture in the atmosphere, a moisture content of the food products or a density of the food products, and carrying out the measurement of the moisture content or the density by one of using microwave radiation or capacitive sensors.

17. The method according to claim 14, further comprising supplying hot air to the atmosphere for one of achieving and maintaining the predetermined temperature, and controlling the partial pressure of the water on a basis of at least one of a moisture of a supply air and/or an exhaust air of a hot air stream.

18. The method according to claim 14, further comprising controlling the partial pressure of the water, by deliberately supplying vapor to the atmosphere, at least one of before and during the heat treatment.

19. The method according to claim 14, further comprising, during the heat treatment, achieving a prevailing temperature distribution in the food products of between 90 C. and 230 C.

20. The method according to claim 14, further comprising using one of a dew point temperature of the food products or a glass transition temperature of the food products as the temperature during the heat treatment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In the following the present invention will be described with reference to the Figures, wherein

[0019] FIG. 1 schematically shows the distribution of moisture and temperature within a cocoa bean during a conventional roasting (A) and during a roasting according to an embodiment of the invention (B);

[0020] FIG. 2 schematically shows the course of the glass transition temperature T.sub.g depending on the moisture;

[0021] FIG. 3 shows the time course of the moisture during roasting and drying with conventional methods and a method according to the invention;

[0022] FIG. 4 shows the time course of the moisture during roasting after initial drying and a hold time at a deliberately chosen constant temperature with a method according to the invention compared to a conventional method and

[0023] FIG. 5 shows the yield during a roasting with a method according to the invention with density measurement.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] It is known that the effects of a heat impact in particular on bulky food do not only depend on and are influenced by the temperature in the individual food products and the time during which said temperature acts but also the moisture of the products. Whereas conventional methods aim at achieving a temperature as homogeneously as possible both in the entire treatment chamber provided for the heat treatment and within the individual bulk food, it is not possible with the conventional methods to adjust the moisture distribution within the bulk goods. The result of the heat treatment, however, is especially dependent on the moisture prevailing during the heat treatment. Thus, it has to be ensured that the required temperature can have an impact within the food for the desired time at an exactly defined moisture.

[0025] The present invention enables achieving a homogeneous moisture distribution within the individual food products.

[0026] This is schematically shown in FIG. 1 with the example of the roasting of a cocoa bean.

[0027] FIG. 1A illustrates the distribution of the temperature and the relative moisture within a schematically depicted cocoa bean during a roasting process, wherein FIG. 1Aa depicts the situation of the initial product. Inside the cocoa bean a basically homogeneous temperature distribution prevails, the storage temperature of the starting product, and a homogeneous moisture of, e.g. about 7%. During a convective and/or conductive roasting (FIG. 1A-b), heat is supplied to the cocoa bean at the surface, which inevitably leads to a temperature increase at the surface of the cocoa bean. At the same time, the moisture decreases where the temperature is at first increased, which will not take place inside the cocoa bean until the temperature has increased here as well over time (FIG. 1A-d). As a result, at the end of the roasting, the desired low moisture within the whole cocoa bean of, e.g. 2% is obtained, and the temperature distribution, too, inside the cocoa bean is homogeneous at the desired roasting temperature. However, it is apparent that during the course and especially at the beginning of the roasting, conditions prevail inside the cocoa bean which differ significantly from the surface to the core and therefore it cannot be guaranteed that the same results can be achieved with the roasting over the whole volume of the cocoa bean,

[0028] FIG. 1B shows the corresponding course when the method according to the invention is used. Taking the same initial conditions as the starting point (FIG. 1B-a) the temperature in the treatment chamber is increased so that again at first the temperature at the surface of the cocoa bean increases (FIG. 1B-b). By adjusting the partial pressure of water according to the method of the invention it is, however, guaranteed that during said heating phase no water leaks out of the product so that the moisture inside the cocoa bean remains constant at the initial level throughout the volume of the cocoa bean at, e.g. about 7%. Only when the desired temperature within the whole cocoa bean is reached and maintained for the desired period of time during the heat treatment, e.g. the roasting (FIG. 1B-c) is it ensured that the temperature impact has taken place at an exactly defined moisture throughout the whole cocoa bean. Only then will the drying of the cocoa bean be started, wherein the moisture decreases homogeneously through the whole volume of the cocoa bean until the desired final state (FIG. 1B-d) is reached. During the roasting and at the beginning of the drying (FIG. 1B-d) the temperature is, e.g. homogeneously at about 120 C. through the whole bean and the moisture homogeneously at, e.g. 7%.

[0029] In order to achieve that the partial pressure of water is suitably adjusted, the moisture can be monitored within the treatment chamber and, on the basis of said measurements, additional vapour can be supplied into the atmosphere in the treatment chamber, if need be. The moisture in the treatment chamber is monitored, e.g. by measuring the moisture of the hot air supplied in case of a convective heat treatment and/or measuring the moisture of the exhaust air. A direct measurement of the moisture within the treatment chamber is also possible.

[0030] As an alternative or in addition, the density or the density change of the products to be treated can be monitored which is, e.g. possible by using microwaves. The moisture inside the products can also be measured directly.

[0031] A control of the partial pressure of water is also possible empirically by determining through corresponding test series how to adjust the vapour supply at a certain temperature during the course of the procedure in order to achieve the desired result.

[0032] As regards the roasting exemplarily described before in view of cocoa beans, which can also be used for the treatment of coffee, nuts or cereals, the method according to the invention enables the deliberate adjustment of temperature and moisture within the products to be treated which can then be reliably maintained for a certain duration at the chosen values. The Maillard reactions occurring during roasting, which are, i.a. responsible for the flavour and colour development, can only be deliberately controlled when the moisture, the morphological status and homogeneity of the product with regard to moisture and temperature can be exactly controlled, which is enabled by the method of the invention. In order to obtain the desired homogeneous status in the products, a vapour/water-injection into a hot air stream is provided, as described above, through which the inside of the treatment chamber is heated or in the closed room of the treatment chamber heated from the outside. Thus, the heat treatment in the whole goods can be controlled and at the same time the homogeneous status can be maintained. Heating the goods with deliberate moisture loss is possible. After having reached the target temperature of, e.g. about 120 C., the moisture of the goods of, e.g. 5% can be maintained deliberately for, e.g. ten minutes, whereas so far the roasting has inevitably led to a drying which was additionally inhomogeneously through the bulk goods. The invention enables the exact control, which decisively influences the flavour development and appearance, e.g. colour development and shelf-life. For example, when roasting nuts, e.g. hazelnuts or peanuts, the desired colour can be achieved by exactly controlling the drying velocity and final moisture.

[0033] In various applications, it is particularly advantageous to choose the so-called glass transition temperature T.sub.g of the products to be treated. At this temperature the deformation capability of the bulk goods to be treated changes. Below said temperature, the material behaves in a glassy manner, i.e. brittle, and above said temperature it is viscoelastic. The glass transition temperature changes, as shown in FIG. 2, depending on the moisture of the product. The choice of the glass transition temperature in a heat treatment leads to the minimisation of the intracellular destruction of, e.g. at least 25% in case of hazelnuts. This reduced destruction of the cellular structures in turn leads to a longer shelf-life, e.g. by a factor of 3 compared to conventional roasting processes. Thus, a reduced fat migration of, e.g. nuts in chocolate can be achieved.

[0034] In more detail, the glass transition temperature can be achieved quickly by supplying vapour or water into the atmosphere surrounding the goods to be treated due to the higher energy density of moist-warm air without negatively influencing the goods' properties.

[0035] Furthermore, the product has a porous structure at or above the glass transition temperature, wherein the retaining capability of water in the matrix of the goods to be treated is reduced and the goods have an increased water permeability.

[0036] FIG. 3 shows the time course of the humidity within the bulk good to be treated during a conventional roasting (curve STD) and a roasting according to the present invention (curve New). As is shown in FIG. 3, when the method according to the invention is used the moisture within the goods to be treated remains initially constant (within the drawn shaded rectangle) until the glass transition temperature has been reached. Contrary thereto, in case of the conventional roasting, where no vapour is supplied, the moisture in the food product decreases continuously. Compared to conventional roasting processes, the entire process can be carried out altogether faster when using the present invention since, although there is no drying in the first step, the roasting product can be brought faster to the target temperature. The subsequent drying can take place faster at or above the glass transition temperature due to the product properties, which is symbolised with the patterned rectangle in FIG. 3. Due to the increased water permeability of the product, the drying can be achieved faster without structural damages to the product.

[0037] Maintaining the moisture during the roasting ensures that the raw material texture can be further maintained despite the roasting, whereby the roasting flavour can be obtained while the texture of the products remains the same.

[0038] Furthermore, it can be advantageous to conduct a heat treatment, in particular a roasting, at a certain temperature and moisture for a certain defined period of time. This is exemplarily shown in FIG. 4. In this example, starting from a moisture of about 14%, the temperature is at first increased, wherein at the same time the moisture decreases. According to an embodiment of the invention, which is illustrated in FIG. 4 with the curve New, upon reaching the desired temperature during the period of time symbolised with the frame, the partial pressure of water is, e.g. controlled such by supplying water or vapour into the treatment chamber that the product moisture remains constant at a constant temperature. The drying takes place only after termination of the desired hold time, as described before with reference to FIG. 3. Contrary to conventional methods (curve STD in FIG. 4), not only the temperature but also the product moisture remains constant as a whole and also within the individual bulk goods during the hold time when the method according to the invention is used.

[0039] When certain products are roasted, e.g. coffee or cereals, significant morphological changes in a specific process step of the heat treatment can occur, leading to significant flavour changes, such as for example the so-called crack during coffee roasting. Moreover, roasting processes having an exothermic reaction involve the risk of pyrolysis processes, which may lead to a yield loss (black malt). Such a reaction, too, can be controlled by deliberately controlling the partial pressure of water according to the present invention, and be monitored online and avoided by means of the sensors according to the invention, in particular a density sensor, which may result in a yield increase.

[0040] FIG. 5 illustrates the obtained yield (Extract Dry) through a roasting with conventional methods (STD) and using a method of the invention (New) by applying various temperatures. The desired yield is illustrated by the shaded rectangle. In conventional methods, the obtained yield is not only dependent on the duration of the treatment but also strongly on the temperature used. As shown, already a minor temperature increase of, e.g. only about 5 C. can massively reduce the yield when conventional methods are used. This is due to the fact that a higher temperature involves the danger of a pyrolysis reaction, which renders the affected goods useless.

[0041] This can he avoided by controlling the partial pressure of water according to the present invention. By means of a treatment in a moist atmosphere, the desired roasting can also be carried out at significantly different temperatures without considerable yield loss. Through additionally monitoring the density of the goods, a starting pyrolysis can be moreover detected and avoided by increasing the moisture in the treatment chamber.

[0042] Moreover, the method according to the invention enables a precise and fast adjustment of a certain product temperature without moisture loss by making use of the dew point, i.e. the conditions are set such that the water condenses at the desired temperature. This can he in particular important regarding methods for preservation, i.e. pasteurisation and sterilisation, wherein it has to be ensured that the whole product is subjected sufficiently long to a certain temperature. The application of moist hot air enables a fast transmission of energy to the goods. This high energy yield guarantees a simultaneous homogeneous temperature within a treatment chamber which can be used for controlling the roasting profile or also for the deliberate sterilisation. In a convective roasting, the adjustment of the dew point can be effected as described before via a vapour supply into the hot air stream. By correspondingly choosing the dew point at, e.g. 955 C. for the pasteurisation so that the water condenses at this temperature and the faster heat transition takes place, it is ensured that the desired temperature prevails also in the whole bulk good. Thus, the long hold time in conventional methods can be avoided where, e.g. higher temperatures have to be used for a longer duration in order to ensure the achievement of the necessary temperature within the bulk good.

[0043] The moisture-based control of the heat treatment processes, in particular the roasting processes, according to the present invention can thus lead to a better shelf-life. The Maillard reactions, which are decisive particularly for the flavour development of the product, can be better controlled. Furthermore, an improved yield can be achieved by controlling morphological changes via controlling the drying and avoiding pyrolysis processes. Further, a faster roasting can be achieved through using a higher energy density during heating and subsequent drying when the glass transition temperature has been reached. The colour development of the product can be controlled independently of the initial temperature and the desired product temperature can be adjusted without drying effect. This method enables the product roasting and at the same time maintaining the raw material texture, wherein a reduced fat migration, e.g. in chocolate, can be achieved by gentle roasting.

[0044] The method according to the present invention can be conducted in particular in a conventional treatment device comprising a treatment chamber, in particular a roasting chamber or roasting drum, a supply air duct for supplying hot air into the treatment chamber, an exhaust air duct and a device for supplying vapour into the supply air duct. The products Solano or Tornado by Bhler Barth GmbH are, e.g. particularly suitable. The used device further has to comprise at least one of the following measuring systems:

[0045] means for determining the density of the food products, in particular using microwave radiation,

[0046] means for determining the moisture content of the food products, in particular by using microwave radiation,

[0047] means for determining the relative air moisture in the treatment chamber,

[0048] means for determining the supply air moisture and

[0049] means for determining the exhaust air moisture.

[0050] Thus, it has to be ensured that a corresponding controlled vapour supply is possible and the parameters for monitoring the moisture can be measured by corresponding sensors.