HEAT TREATMENT OF PIECE FOOD PRODUCTS

Description

[0001] The present invention relates to a method for carrying out heat treatment of lumpy foodstuffs, in particular the roasting of cocoa, nuts, coffee, grains or oilseeds. The scope of the invention is defined by the claims.

[0002] When processing foods that are in lumpy form, such as coffee beans, cocoa beans, seeds and nuts, various types of heat treatments play an important role, in particular drying, roasting or preservation processes such as sterilization or pasteurization of such foods.

[0003] During heat treatment, the food products are typically placed in a treatment chamber, such as a treatment drum. Heat is introduced into the product by supplying heat, for example, by introducing warm or hot air into the treatment chamber or, alternatively or simultaneously, by heating the treatment chamber from the outside. Efforts are made to distribute the heat as evenly as possible throughout the entire volume of the food products in the treatment chamber. This is achieved at a precisely defined temperature or through a sequence of different temperatures in multi-stage treatment processes. The duration of the heat exposure is also controlled.

[0004] A method for roasting coffee beans is known, for example, from WO 2015 / 110337 A1. Methods for drying pasta are known from WO 2009 / 150192 A2 or WO 2010 / 108806. Methods and equipment for drying rice are described, for example, in WO 2007 / 065279 A1 and WO 2005 / 017431 A1.

[0005] All known heat treatment methods share the common limitation that the moisture distribution within individual food products cannot be controlled. Consequently, with all methods used so far, moisture levels inevitably decrease at the surface of the products during heat treatment, leading to an increase in moisture content towards the product's core. However, the moisture distribution within the product, in conjunction with the prevailing temperature, significantly influences flavor development, intracellular structures (which correlate with product shelf life, for example), and morphological changes within the product.

[0006] Trabelsi S. et al.: "Nondestructive sensing of bulk density and moisture content in shelled peanuts from microwave permittivity measurements", Food Control, Butterworth, London, GB, Vol. 17, No. 4, 1 April 2006. Pages 304-311 describe the use of dielectric-based methods for the non-destructive and simultaneous determination of the bulk density and moisture content of shelled peanuts.

[0007] Garcia-Alamilla, in: "Moisture, acidity, and temperature evolution during cacao drying", Journal of Food Engineering, Barking, Essex, GB, Vol. 79, No. 4, 15 November 2006, pages 1159-1165, describe an estimation of the theoretical moisture and temperature evolution during fixed bed drying of cocoa.

[0008] Chmenki S. et al: "Modelling and simulation of drying behavior phenomena with rheological behavior" describe a modeling of water loss during the drying of food.

[0009] US 2009 / 0211274 A1 describes methods and devices for the pretreatment of fresh food.

[0010] Kemp, Ian C.: "Humidity effects in solids drying processes", https: / / journals.sagepub.com / doi / pdf / 10.1177 / 002029400704000901, January 1, 2007, reports on measurements of moisture in drying processes.

[0011] It is therefore an object of the invention to provide a method for the heat treatment of lumpy food products that enables improved control and regulation of the heat treatment and in particular of the heat and moisture distribution and moisture removal during the heat treatment.

[0012] This task is solved using the features of the claims.

[0013] A fundamental idea of ​​the present invention is to control the partial pressure of water in the atmosphere in which the food products are located during heat treatment, namely roasting the food products at a predetermined temperature. In particular, adjusting the partial pressure of water is intended to ensure a homogeneous moisture distribution within the individual food products during heat treatment.

[0014] Heat treatment involves roasting. Depending on the type of heat treatment, the temperature and duration are selected accordingly. For example, hazelnuts are roasted at approximately 130 °C. However, the temperature can reach or even exceed 230 °C, for instance, when roasting grains. Furthermore, processes often aim to quickly bring the product to a target temperature without drying. For example, in pasteurization, a temperature of approximately 95 ± 5 °C should be reached quickly before evaporation occurs. To achieve preheating as quickly as possible, moisture can be added to the warm air, thus adjusting the dew point of the air during the heating phase to, for example, 65 ± 5 °C and then 95 ± 5 °C.This setting prevents the products from drying because the water partial pressure is too low in this phase to induce drying, but allows for high energy transfer. This enables a speed increase of at least a factor of 2 while maintaining the same internal product moisture content.

[0015] To achieve a homogeneous moisture distribution within the food products, the partial pressure of water is adjusted according to the invention such that moisture loss from the food products is prevented during heat treatment. This is achieved by regularly or continuously determining the moisture content of the product during treatment, for example, as described in more detail below, by direct measurement or indirectly, for example, by comparing the moisture content of the supply and exhaust air into and from the treatment chamber. If the moisture content of the product being treated decreases, the humidity, and thus the partial pressure of water in the treatment chamber, is increased, thereby preventing a further reduction in the moisture content of the products.

[0016] This ensures that the initially homogeneous moisture distribution is maintained even as the individual food products heat up. Heat treatment, particularly roasting or thermal processes that alter morphology, can then take place once the temperature and moisture distribution within the product has become homogeneous. Upon reaching this state, the reaction proceeds uniformly throughout the entire food product for the duration of the heat treatment at a precisely defined moisture level. For example, drying can be initiated in a controlled manner. Specifically, if drying is started when the product reaches its glass transition temperature, the moisture can be removed more quickly without damaging the intracellular structures.Furthermore, in the case of roasting, the roasting temperature can be maintained at the target moisture content throughout the entire food product for the desired duration. Additionally, during a critical phase of morphological change, this condition can be better controlled, as a uniform moisture content can be established.

[0017] The water partial pressure is adjusted, for example, by measuring the relative humidity of the atmosphere surrounding the material in the treatment chamber. This can be done directly within the treatment chamber or indirectly by measuring the humidity of the warm air supply to the treatment chamber, which is used to adjust the temperature during heat treatment, and / or the exhaust air from the treatment chamber. The water partial pressure can also be adjusted by selectively adding steam to the atmosphere, for example, by adding it to the warm air stream.

[0018] Furthermore, the water partial pressure can be adjusted based on a determination of the moisture content of the food products. The density or density change of the food products can also be measured. For example, the product commercially available under the name HydroKen™ allows for the measurement of density and moisture using microwave radiation. Capacitive sensors can also be used to measure moisture. Direct moisture measurement can also be achieved, for example, using NIR radiation.

[0019] For certain types of heat treatment, selecting the dew point temperature during the process can be advantageous. To precisely and quickly achieve a specific product temperature without moisture loss, for example, during the pasteurization of food products, the atmosphere can be selected so that the dew point temperature is the desired preheating temperature for pasteurization. Due to the high energy input from the warm, humid atmosphere when using the dew point, it is possible to guarantee that the target temperature for the entire food product is reached during heat treatment, thus ensuring that treatments such as pasteurization are carried out at the desired temperature.

[0020] Furthermore, the choice of the glass transition temperature, i.e., the temperature at which the product transitions from a brittle to a viscoelastic state, can be advantageous. The warm, humid atmosphere can prevent the product from drying out, and the increased energy density allows the glass transition temperature to be reached more quickly. Once the glass transition temperature is reached, drying can be carried out, minimizing intracellular damage, which leads to increased shelf life of, for example, a nut, or reduces fat migration from the nut into the chocolate.

[0021] Heat treatment, especially the roasting of food products, is often followed by drying. During this drying process, the partial pressure of water in the atmosphere can be reduced to ensure uniform drying of the products. If a temperature at or above the glass transition temperature is chosen, the porous structure of the products allows for rapid drying due to increased water permeability, without damaging the product structure.

[0022] The present invention is described in more detail below with reference to the figures, wherein Fig. 1 schematically shows the distribution of moisture and temperature within a cocoa bean during conventional roasting (A) and during roasting according to an embodiment of the invention (B); Fig. 2 schematically shows the course of the glass transition temperature Tg as a function of moisture; Fig. 3 shows the time course of moisture during roasting and drying with conventional methods and a method according to the invention; Fig. 4 shows the time course of moisture during roasting after initial drying and a holding time at a specifically selected constant temperature with a method according to the invention in comparison with a conventional method; and Fig. 5 illustrates the yield gain during roasting with a method according to the invention with density measurement.

[0023] It is known that the effects of heat treatment, particularly on lumpy foods, depend not only on the temperature within the individual food products and the duration of this heat treatment, but also on and are influenced by the moisture content of the products. While previous methods aim to achieve the most homogeneous temperature possible, both within the treatment chamber as a whole and within the individual food pieces, these methods do not allow for adjusting the moisture distribution within the individual items. However, the outcome of the heat treatment is highly dependent on the humidity level during the process. Therefore, it is essential to ensure that the required temperature can be maintained within the food for the desired duration at a precisely defined humidity level.

[0024] The present invention makes it possible to achieve a homogeneous moisture distribution within the individual food products.

[0025] In Figur 1 This is shown schematically using the example of roasting a cocoa bean.

[0026] In Figur 1A The distribution of temperature and relative humidity within a schematically represented cocoa bean during a roasting process is shown, wherein Fig. 1A -a represents the situation of the starting product. Within the cocoa bean, there is an essentially homogeneous temperature distribution, the storage temperature of the starting product, and a homogeneous humidity of, for example, about 7%. During convective and / or conductive roasting ( Fig. 1A -b') Heat is applied to the surface of the cocoa bean, which inevitably leads to an increase in the surface temperature of the cocoa bean. At the same time, the moisture content will decrease where the temperature is initially increased, which will only occur inside the cocoa bean once the temperature there has also increased over time ( Fig. 1A -d). As a result, the desired low moisture content of, for example, 2% is achieved throughout the entire cocoa bean at the end of the roasting process, and the temperature distribution within the cocoa bean is also homogeneous at the desired roasting temperature. However, it is evident that during the roasting process, and especially at the beginning, conditions prevail inside the cocoa bean that differ significantly from the surface to the kernel, and therefore it cannot be guaranteed that the same results can be achieved throughout the entire volume of the cocoa bean during roasting.

[0027] In Fig. 1B The corresponding process is shown when applying the method according to the invention. Starting from the same initial conditions (Fig. 1B-a), the temperature in the treatment chamber is again increased, so that the temperature at the surface of the cocoa bean initially rises again (Fig. 1B-b). However, by adjusting the water partial pressure according to the method according to the invention, it is ensured that no water escapes from the product during this heating phase, so that the moisture content inside the cocoa bean remains constant at the initial level throughout the volume of the cocoa bean, for example, at about 7%. Only when the desired temperature is reached throughout the entire cocoa bean and is maintained for the desired duration of the heat treatment, e.g., roasting (Fig. 1B-c), is it ensured that the temperature effect has occurred throughout the entire cocoa bean at a precisely defined moisture content.Only then does the drying of the cocoa bean begin, during which the moisture content decreases uniformly throughout the entire volume of the cocoa bean until the desired final state (Fig. 1B-d) is reached. During roasting and at the beginning of drying (Fig. 1B-c), the temperature is, for example, uniformly around 120°C throughout the entire bean, and the moisture content is uniformly around 7%.

[0028] To ensure the water partial pressure is correctly set, the humidity inside the treatment chamber can be monitored, and additional steam can be introduced into the chamber atmosphere based on these measurements. Humidity monitoring can be achieved, for example, by measuring the humidity of the warm air introduced during convective heat treatment and / or the humidity of the exhaust air. Direct measurement of the humidity inside the treatment chamber is also possible.

[0029] Alternatively or additionally, the density or density change of the products being treated can also be monitored, for example using microwaves. The moisture content within the products can also be measured directly.

[0030] Control of the water partial pressure is also possible empirically by determining, through appropriate series of experiments, how the steam supply must be adjusted at which temperatures during the process in order to achieve the desired result.

[0031] In the roasting process previously described in more detail using cocoa beans as an example, which can also be used in the processing of coffee, nuts, or grains, the method according to the invention enables the targeted adjustment of temperature and humidity within the products being treated, which can then be reliably maintained at the selected values ​​for a specific period of time. The Maillard reactions that occur during roasting, which are responsible, among other things, for the development of flavor and color, can only be precisely controlled if the humidity, morphological state, and homogeneity of the product with respect to humidity and temperature can be accurately controlled, which is made possible by the method of the invention.To achieve the desired homogeneous state in the products, as described above, steam / water injection is used in a warm air stream, which heats the interior of the treatment chamber, or in the externally heated "closed space" of the treatment chamber. This allows for controlled heat treatment of the entire product while maintaining homogeneous consistency. Heating the product with controlled moisture loss is possible. After reaching the target temperature of, for example, approximately 120°C, the product moisture content of, for example, 5% can then be maintained for, for example, ten minutes, whereas previously roasting inevitably led to drying, which also occurred unevenly across the product.The invention enables precise control, which significantly influences aspects such as flavor development and appearance, including color development, as well as shelf life. For example, when roasting nuts, such as hazelnuts or peanuts, the desired color can be achieved by precisely controlling the drying speed and final moisture content.

[0032] In various applications, the choice of the so-called glass transition temperature Tg of the products to be treated is particularly advantageous. At this temperature, the deformability of the workpieces changes. Below this temperature, the material behaves like glass, i.e., brittle, while above this temperature it is viscoelastic. The glass transition temperature changes, as described in... Figur 2 This is shown to be dependent on the product's moisture content. Selecting the appropriate glass transition temperature during heat treatment minimizes intracellular damage, for example, by at least 25% in hazelnuts. This reduced damage to cellular structures, in turn, leads to a longer shelf life, for example, three times longer compared to conventional roasting processes. It also results in less fat migration from nuts into chocolate, for example.

[0033] Specifically, by adding steam or water to the atmosphere surrounding the material to be treated, the glass transition temperature can be reached quickly due to the higher energy density of moist, warm air, without negatively affecting the properties of the material.

[0034] Furthermore, at or above the glass transition temperature, the product has a "porous structure", which weakens the retention of water in the matrix of the material to be treated and results in increased water permeability of the material.

[0035] Fig. 3 The graph shows the time course of the moisture content within the workpiece to be treated during a conventional roasting process (curve "STD") and a roasting process using the present invention (curve "New"). As shown in Fig. 3 As shown, when using the method according to the invention, the moisture content within the product being treated initially remains constant (within the shaded rectangle shown) until the glass transition temperature is reached. In contrast, in the case of conventional roasting, where no steam is added, the moisture content in the food product decreases continuously. Compared to conventional roasting processes, the entire process using the present invention can be carried out more quickly because, although no drying takes place in the first step, the product can be brought to the target temperature more rapidly. The subsequent drying can then occur more quickly at or above the glass transition temperature due to the product properties, as indicated by the shaded rectangle in the figure. Fig. 3 This is symbolized. Due to the increased water permeability of the product, drying can be achieved faster without structural damage to the product.

[0036] Maintaining moisture during roasting allows the raw material texture to be preserved despite the roasting process, thus achieving the roasted flavor while maintaining the same product texture.

[0037] Furthermore, it can be advantageous to carry out heat treatment, in particular roasting, at a specific temperature and humidity for a specific, defined period of time. This is exemplified in the Fig. 4 shown. Here, starting from a humidity of approximately 14%, the temperature is first increased, while the humidity simultaneously decreases. According to an embodiment of the invention, which is represented by the curve labeled "New" in Fig. 4 As shown, when the desired temperature is reached during the process through the frame in Fig. 4 The symbolic duration of the water partial pressure is controlled, for example, by adding water or steam to the treatment chamber, so that the product moisture remains constant at a constant temperature. Only after the desired holding time has elapsed, as previously mentioned with reference to the Figur 3 The drying process is described. Compared to conventional methods (curve "STD" in Fig. 4 During the holding time, when using the method according to the invention, not only the temperature but also the overall product moisture content and the moisture content within the individual product units remains constant.

[0038] When roasting certain products, such as coffee or grain, significant morphological changes can occur during a specific step of the heat treatment process, leading to significant changes in flavor, such as the so-called "crack" in coffee roasting. Furthermore, roasting processes involving an exothermic reaction carry the risk of pyrolysis, which can result in yield loss ("black malt"). Such a reaction can also be controlled by selectively adjusting the water partial pressure according to the present invention and monitored and prevented online using the sensors employed according to the invention, in particular a density sensor, which can lead to an increase in yield.

[0039] Fig. 5Figure 1 illustrates the yield achieved ("Extract Dry") during roasting using conventional methods ("STD") and using a method according to the invention ("New") at different temperatures. The desired yield is indicated by the shaded rectangle. With conventional methods, the yield is dependent not only on the duration of the treatment but also strongly on the temperature used. As shown, even a slight temperature increase of, for example, only about 5 °C can drastically reduce the yield in conventional methods. This is because at higher temperatures, the risk of a pyrolysis reaction, which renders the affected goods unusable, is increased.

[0040] This can be avoided by controlling the water partial pressure according to the present invention. Treatment in a humid atmosphere allows the desired roasting to be carried out even at significantly different temperatures without substantial loss of yield. Furthermore, by additionally monitoring the density of the goods, the onset of pyrolysis can be detected and prevented by increasing the humidity in the treatment chamber.

[0041] Furthermore, the inventive method enables precise and rapid temperature control of a specific product without moisture loss by utilizing the dew point, i.e., by adjusting the conditions so that water condenses at the desired temperature. This can be particularly important in preservation processes, such as pasteurization and sterilization, where it is essential to ensure that the entire product is exposed to a specific temperature for a sufficient duration. The use of moist warm air facilitates rapid energy transfer to the product. This high energy input ensures a consistent, homogeneous temperature within a treatment chamber, which can be used to control the roasting profile or for targeted sterilization. In convective roasting, the dew point can be adjusted, as previously described, by adding steam to the hot air stream.By selecting a suitable dew point for pasteurization, for example 95 ± 5 °C, so that water condenses at this temperature and faster heat transfer occurs, it is ensured that the desired temperature is maintained throughout the entire product. This avoids the long holding times of conventional methods, where, for example, higher temperatures must be used for a longer period to ensure that the required temperature is reached within the product.

[0042] The humidity-based control of heat treatment processes, particularly roasting processes, according to the present invention can therefore lead to improved shelf life. The Maillard reactions, which are crucial for the product's flavor development, can be better controlled. Furthermore, improved yield can be achieved by controlling morphological changes through drying control and the avoidance of pyrolysis. Faster roasting can also be achieved by utilizing a higher energy density during heating and subsequent drying upon reaching the glass transition temperature. The product's color development can be controlled independently of the initial temperature, and the desired product temperature can be set without any drying effect.This process makes it possible to roast products while maintaining the texture of the raw materials, thus achieving reduced fat migration, for example in chocolate through gentle roasting.

[0043] The method according to the present invention can be carried out, in particular, in a conventional treatment device comprising a treatment chamber, especially a roasting chamber or roasting drum, an air supply duct for supplying warm air to the treatment chamber, an exhaust air duct, and a device for supplying steam to the air supply duct. The products "Solano" or "Tornado" from Bühler Barth GmbH are particularly suitable, for example. The device used must further comprise at least one of the following measuring devices: a device for determining the density of food products, in particular using microwave radiation, a device for determining the moisture content of food products, in particular using microwave radiation, a device for determining the relative humidity in the treatment chamber, a device for determining the moisture content of the supply air and a device for determining the moisture content of the exhaust air.

[0044] It must therefore be ensured that a corresponding controlled steam supply is enabled and that the parameters for monitoring humidity can be measured by appropriate sensors.

Claims

1. A method for 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 certain temperature for roasting, wherein the partial pressure of water in the atmosphere where the food products are located during the roasting is controlled such that a substantially homogeneous moisture distribution occurs in the food products during the duration of the roasting, wherein the control of the partial pressure of the water takes place by deliberately supplying vapour to the atmosphere, wherein the moisture of the bulk is determined during roasting and wherein the moisture and thus the partial pressure of the water is increased in the atmosphere when it is determined that the moisture of the bulk decreases.

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

3. The method according to at least one of the preceding claims, wherein hot air is supplied to the atmosphere to achieve and / or maintain the predetermined temperature, wherein the partial pressure of the water is controlled in particular on the basis of the moisture of the supply air and / or the exhaust air of the hot air stream.

4. The method according to at least one of the preceding claims, wherein moisture is supplied to the atmosphere to control the partial pressure of water before and / or during the roasting.

5. The method according to at least one of the preceding claims, wherein, during the roasting, a substantially homogeneous distribution of the temperature in the food products prevails, in particular a temperature of 90°C to 230°C.

6. The method according to claim 5, wherein the temperature maintained during the roasting is the dew point temperature or the glass transition temperature of the food products.

7. The method according to at least one of the preceding claims, wherein the duration of the roasting is controlled on the basis of a density measurement of the food products.

8. The method according to at least one of the preceding claims, wherein the food products are dried after the roasting, wherein the partial pressure of water in the atmosphere is preferably lower during the drying than the partial pressure of water in the atmosphere during the roasting.

9. The method according to at least one of the preceding claims, wherein the food products are dried after the roasting, wherein the partial pressure of the water in the atmosphere is controlled during the drying on the basis of the density change in the food products.