Optimized method of producing frozen vegetable and / or potato products

Abstract

The present invention relates to a method for producing frozen vegetable and / or potato products, comprising the following steps: - supplying an amount of vegetable and / or potato products; - washing the supplied vegetable and / or potato products to form base vegetable and / or potato products; - heat-treating the base vegetable and / or potato products in a housing to form heat-treated vegetable and / or potato products for at most 40 minutes; - freezing the heat-treated vegetable and / or potato products, wherein a dew point temperature for the air in the housing is set in the range from 70 °C to 99 °C for heat-treating the base vegetable and / or potato products (calculated in accordance with air temperature and relative humidity), wherein, during the heat treatment, the conditions of the air present in the housing are detected which are required to be able to determine the dew point temperature, and these conditions are adjustable in order to achieve and maintain the desired dew point temperature during the heat treatment.

Description

[0001] OPTIMIZED METHOD OF PRODUCING FROZEN VEGETABLE AND / OR POTATO PRODUCTS

[0002] The present invention relates, on the one hand, to a method for producing frozen vegetable and / or potato products, comprising the following steps: supplying an amount of vegetable and / or potato products; washing, preferably peeling and / or preferably cutting the supplied vegetable and / or potato products to form base vegetable and / or potato products; heat-treating the base vegetable and / or potato products in a housing to form heated vegetable and / or potato products for at most 40 minutes; and freezing the heated vegetable and / or potato products.

[0003] On the other hand, the present invention relates to frozen vegetable and / or potato products obtained according to the relevant method.

[0004] More specifically, the present invention relates to a method for producing, in particular on an industrial scale, frozen vegetable and / or potato products with improved sensorial and nutritional product properties compared to products obtained by using the conventional method. More particularly, the present invention relates to a method for producing products with an improved texture (e.g., bite), smell, colour, and taste experience on the one hand with regard to organoleptic properties, and to better retain vitamins, minerals and other bioactive components as regards the nutritional properties on the other hand.

[0005] In the context of the present invention, a large number of vegetables (or vegetable products) and / or potatoes (or potato products) may undergo the method according to the invention. Specifically, the method is suitable for processing the following product families: the nightshade family (Solanacae) of which the potato is part, the convolvulus family (Convolvulaceae), such as sweet potato, the Brassica family (Brassicaceae), for example broccoli and Brussels sprouts, the allium family (Alliaceae), for example leeks and onions, the umbellifer family, for example carrots and parsnips, the amaranth family, such as beetroot and spinach, the legume family (Fabaceae), such as chickpeas and green beans, and others (e.g., tomatoes). Small potatoes, sweet potatoes, potatoes, beans, (baby) carrots, beetroot, cauliflower, parsnips, pumpkins, broccoli, ... are preferred. Conventionally, when vegetables and / or potatoes (or potato products) are being processed to form a frozen product, the so-called IQF products (‘Individually Quick Frozen’) are inter alia heated by blanching them at a specific, mainly optimized blanching temperature for a certain time. The blanching temperature and blanching time depend on the product to be processed and the possible further processing steps, such as e.g., deep-frying or grilling. Blanching serves to stop the action of enzymes which may lead to a loss in taste, texture and colour.

[0006] During blanching, the supplied products are brought into contact with hot water for a certain period of time. In this case, use may be made of rotating drums, the so-called large-size drum blanchers with a helical shape on the inner periphery for supplying the products from one end thereof to the other along the drum, while hot water is conveyed in the opposite direction. In this case, the products float on the water. An alternative to the drum blancher is the belt blancher, where the products move through the blanching chamber by means of a belt or conveyor while hot water is continuously sprayed on the products. After blanching, the blanched products have to be cooled down quickly, often using iced water, in order to stop the heat treatment process and thus to prevent further uncontrolled heat treatment.

[0007] Despite its effect on the enzyme inactivation and resulting guarantee of quality during storage, the blanching process may nevertheless have some other, negative effects on quality.

[0008] A first drawback of blanching using water is that the solids may leach out of the product during the time that the products are being heat-treated in the water. This means that a certain percentage of the valuable food constituents (e.g. nutritional water-soluble components, such as for example vitamins) disappear in the blanching water. This also means that the dry matter of the product may be reduced during this step and that the components which are not soluble in water, such as, inter alia, the fibres, remain in the product, which may result in an end product having an unpleasant, fibrous texture.

[0009] A second drawback of the present method of industrially processing vegetable and / or potato products to form frozen end products, is that using this blanching process may lead to a relatively large water consumption. In addition, the process is regarded as being less sustainable due to the pollution of the saturated (re-used) wastewater. It is therefore necessary to treat the wastewater at a certain point. This energy-consuming process should not be underestimated. In addition, heating the blanching water also requires a relatively large amount of energy.

[0010] An alternative heating method for traditional blanching in water to treat vegetable and potato products, is heat-treating them with steam (i.e. steaming). In this case, the supplied products are brought into contact with steam at a temperature of at least 100 °C for a certain period of time. Steaming has the advantage that the products are not submerged in water, so that more (health-promoting) nutrients are preserved. Just as with blanching with water, it is important to cool down the products after steaming quickly in iced water to stop the heat treatment process. Steaming has the drawback that the process requires a significant amount of energy. In addition, due to the high temperatures involved, evaporation of certain (useful) volatile components may occur. Bringing the heated products into contact with (iced) water after steaming also leads to a certain degree of leaching.

[0011] To remove the surface moisture in order to prepare the products for further processing, the blanched products are sometimes passed through a drier, at a drying temperature of approximately 80 °C. Drying often takes place using circulating hot air in special drying ovens or drying tunnels. The function of the drier is focussed on concentrating the solids which are still present in the product, to obtain a crunchy end product. However, this process has a relatively large energy requirement.

[0012] US patent publication US 2022 / 346586 Al describes a steam cooker and a steaming method which make it possible to create an unsaturated steam environment in the food chamber to prevent the food prepared in the steam cooker from having a squishy consistency due to the moist steam condensing and precipitating as water droplets on the surface of the food. In order to achieve this, the steam cooker described in US 2022 / 346586 Al comprises a control device which makes it possible to maintain the temperature in the food chamber at a temperature of 100 °C to 120 °C and to maintain the concentration of steam in the air in the food chamber below 100% relative humidity (RV) during the entire heat treatment process with a threshold concentration of 90% RV at 120°C. The device described in US 2022 / 346586 Al is a closed system in which the pressure is higher than the normal atmospheric pressure. Preparing food at elevated pressure can have a negative effect on the taste experience. In addition, the described method is difficult to implement on an industrial scale due to the fact that it requires a perfectly sealed device.

[0013] It is an object of the present invention to provide a method for producing frozen vegetable and / or potato products of optimized quality which is in particular suitable for use on an industrial scale, without leaching the solids out of the products, and which products may be heat-treated, for example, consuming no or hardly any water and whose end products have improved organoleptic and nutritional properties compared to vegetable and / or potato products obtained by means of the above-described blanching process, in particular as regards the concentration of vitamins, minerals, bioactive components, taste, texture, bite, shape, smell and colour. The invention furthermore also provides a method in which, in particular, no drying step is required anymore at relatively high temperatures (than ambient temperature) after heat-treating of the supplied products, in special driers or drying tunnels, but where cooling and / or drying may take place, for example, using ambient air.

[0014] The object of the invention is achieved by providing a method for producing frozen vegetable and / or potato products, comprising the following steps: supplying an amount of vegetable and / or potato products; washing the supplied vegetable and / or potato products to form base vegetable and / or potato products; heat-treating the base vegetable and / or potato products in a housing to form heat- treated vegetable and / or potato products for at most 40 minutes; freezing the heated vegetable and / or potato products, wherein a dew point temperature for the air in the housing is set in the range from 70 °C to 99 °C for heat-treating the base vegetable and / or potato products, and wherein, during the heat-treatment, the conditions of the air present in the housing are detected which are required to be able to determine the dew point temperature, and these conditions are readjusted in order to achieve and maintain the desired dew point temperature during the heat treatment, wherein the air in the housing during the heat treatment is an air / steam mixture having a relative humidity in the range of 30% - 100%, more particularly in the range of 55% - 100% and having a temperature in the range of 70 °C - 150 °C, in particular a temperature which is in the range of 85 °C - 125 °C, and more particularly a temperature which is in the range of 85 °C - 116 °C.

[0015] Said dew point temperature is defined as the temperature at which air becomes saturated with water vapour, in other words the point at which water vapour starts to condense to form liquid water (dew, mist or condensation). The set dew point temperature is accurately and automatically aimed for by checking the relative humidity and the temperature in the housing. The method is optimized for various vegetable (products) and potato (products) with a view to achieving an optimum quality of the end product. In addition, the ranges of the parameters are defined within ranges which were empirically shown to have conditions which result in an end product of optimized quality.

[0016] The method according to the invention offers various advantages in the context of quality optimization of the resulting product after treatment of the vegetable or potato product by means of the inventive method according to the present invention. A first advantage is the fact that the temperature and the relative humidity of the air in the housing can be accurately controlled during the heat treatment (compared to for example a steaming process), resulting in more uniform heating, and thus higher quality products are obtained due to the creation of a stable heating environment during the planned period of time. Active control of the air flow in the housing during the heat treatment may improve the uniformity of the final product even further.

[0017] In addition, it is possible that due to specifically aiming for a dew point temperature, less condensation, if any, occurs. This has the advantage that the product is dry at the end of the process, consequently considerably reducing the need for a subsequent drying step, and that there is less risk of loss of moisture after defrosting the frozen products. This aspect also improves the quality of the end product (e.g. sensorial quality).

[0018] A third optimization of the product quality which can be brought about by means of the inventive method is the reduction of the leaching of (nutritionally) important components due to no direct contact with water during the heat treatment. Consequently, the balance of solids, sugars and fibres in the treated products is optimized, as a result of which the end products not only have improved nutritional, but also improved organoleptic properties, such as for example colour and texture, compared to products manufactured according to the prior art where blanching takes place during processing. In addition, the heating process according to the invention requires hardly any water.

[0019] According to the method of the invention, the base vegetable and / or potato products are heat-treated for at most 40 minutes, in particular at most 30 minutes, under the conditions selected in the housing. Heating will take place at normal atmospheric pressure (on average approximately 1013 hPa). This offers the advantage that no perfectly sealed housing is required in order to carry out the method, which allows the method to be applied on an industrial scale.

[0020] According to a specific method of the invention, the relative air humidity and the temperature of this air will be detected (measured) when detecting the conditions of the air present in the housing. Detection is carried out, for example, by means of detection means suitable for the purpose. In particular, detection of the air humidity, more particularly the relative humidity, in the housing is performed by means of a hygrometer. The temperature in the housing is detected, for example, by means of a thermometer.

[0021] On the basis of detected data, the actual dew point temperature of the air in the housing can be calculated (determined). This is achieved, for example, by means of a processing unit designed for the purpose. Subsequently, the actual dew point temperature can be compared to the set and / or desired dew point temperature and if this is different, then the dew point temperature in the housing can be adjusted. Readjusting (modifying) the dew point temperature in the housing is carried out, for example, by introducing an amount of steam into the housing for a certain period of time and / or by heating the air in the housing until the set dew point temperature is reached. Heating the air in the housing is preferably carried out by means of suitable heating means, such as for example heating means which are heated up by means of steam, the so-called steam coils. Alternatively, the heating elements may also be heated up electrically or by means of thermal oil. By the addition of steam in the housing and / or heating up the air in the housing, the dew point temperature in the housing will be adjusted.

[0022] During heating, the air in the housing is an air / steam mixture with a relative humidity in the range of 30% - 100%, in particular in the range of 55% - 100%. During heating, the air in the housing has a temperature in the range of 70 °C - 150 °C, in particular a temperature in the range of 85 °C - 116 °C. According to a specific method of the invention, during the heating treatment, the air actively (forced) circulates in the housing. To this end, the housing comprises, for example, ventilation means, more particularly in the form of one or more fans. During heating, the ventilation means will pass the air in the housing across the products to be heat-treated along a, for example, vertical and / or horizontal air flow. For example, this control of the air flow is adjustable, depending on the product and / or cut of the product.

[0023] The dew point temperature set in the housing will vary for each product and depends on various factors, such as the type of product, the shape thereof, any further planned processing steps, such as e.g., deep-frying, grilling, .. which the heated products are to undergo after the heat treatment. The set dew point temperature will be that temperature which has been found, by empirical determination (to be determined separately for every vegetable and / or potato product), to result in an end product of optimum quality at a specific set (air) temperature and residence time. Thus, there will be a difference if the product to be treated still has to undergo or does not have to undergo a heating step, such as e.g. deep-frying or grilling. Said dew point temperature is in the range of 70 °C to 99 °C, in particular in the range of 80 °C to 99 °C, more particularly in the range of 80 °C to 90 °C and is most preferably approximately 85 °C. The respective dew point temperature range was confirmed by treating a number of products according to the method, and these were found to have an optimum quality with regards to sensorial and nutritional product properties following the treatment compared to products obtained by means of the conventional method. Since there is a correlation between the dew point temperature, the air temperature (in the housing) and the relative air humidity in the housing, it is also possible to set the air temperature and relative humidity for a well-defined vegetable and / or potato product. In practice, the specific dew point temperature, air temperature and residence time will be determined for every vegetable and / or potato product which will be produced by means of the method according to the invention and the air temperature and / or relative humidity will be monitored and readjusted during the process in order to maintain the set parameters.

[0024] After the heat treatment, the products are, for example, cooled down and / or dried by, for example, being exposed to ambient air, for example using ambient air of at most 35 °C, for a period of time which is sufficient to remove the surface moisture on the outside of the heat-treated products. In an alternative embodiment, drying may also be performed with the aid of a drier, if this is desirable for a specific product. The method according to the invention reduces the need for drying, due to the fact that the outer surface of the products is less moist at the end of their residence time in the housing. This is due to the fact that the dew point temperature is being used. A dry outer surface contributes to the adhesion of a possible coating to the product. The progress of the drying step is monitored, for example, by detecting the conditions, such as for example the temperature and dew point temperature of the air in the housing in which the drying step is carried out. In one possible embodiment, the drying step is performed in the same housing as the heat treatment, because this housing is provided with the necessary detection means.

[0025] In a more particular embodiment of the method according to the invention, a coating is applied to the base vegetable and / or potato products after these have been heat- treated, so that coated vegetable and / or potato products are formed. The coating is applied to impart a degree of crustiness to the product. In addition, the coating may give a neutral, spicy, sweet, or differently selected touch. In practice, the coating is often also chosen on the basis of the chosen final treatment (if applicable), in particular the heating step. If the products are to be deep-fried, the coating will be a specific batter, whereas if the products are to be grilled, the coating will preferably be an oil which is then usually sprayed over the respective products.

[0026] In a particular method according to the invention, the heated vegetable and / or potato products are prebaked in ovens which have a temperature of, for example, at most 180 °C, more particularly varying in the range from 165 °C to 175 °C, for, for example, at most 4 minutes, more particularly for between 1 and 2 minutes. According to a particular embodiment of the method according to the invention, the heat-treated vegetable and / or potato products, after having been heat-treated and before being frozen, are fried in oil. The oil has a temperature, for example, in the range from 165 °C to 175 °C.

[0027] According to an alternative embodiment of the method of the invention, the heat- treated vegetable and / or potato products are grilled after they have been heat-treated and before they are frozen. Grilling is carried out, for example, at a temperature in the range from 200 °C to 240 °C. According to a particular embodiment of the method of the invention, grilling will be carried out in the same housing as the one in which the products were heat-treated.

[0028] In a more particular method according to the invention, freezing the heat-treated and, if applicable, grilled or deep-fried, vegetable and / or potato products, to a temperature of at most -6 °C, for example to a temperature of at most -15 °C, and more particularly to a temperature of at most -18 °C is performed in order to increase the shelf life. Preferably, freezing is performed by using cold air on a conventional belt freezer.

[0029] According to a more advantageous method of the invention, the supplied vegetables are washed and peeled first before being heat-treated. Peeling is carried out according to one of the generally known techniques, for example by means of steam, in order to reduce the risk of damage and / or bacterial contamination as much as possible.

[0030] In a more particular method according to the invention, the supplied vegetable and / or potato products are calibrated and / or cut up.

[0031] Another aspect of this invention relates to frozen vegetable and / or potato products obtained by means of the method according to the invention as described above. The frozen vegetable and / or potato products obtained in this way have improved sensorial and nutritional product properties compared to products obtained by means of the conventional method, in particular blanching.

[0032] The invention will now be explained in more detail by means of the following description. The sole aim of this description is to give an illustrative example and may thus by no means be interpreted as a limitation of the area of application of the invention or of the patent rights defined in the claims.

[0033] In this description, reference numerals are used to refer to the attached drawings, in which:

[0034] Fig. 1: is a diagrammatic representation of a device in which supplied vegetable and / or potato products are heat-treated by means of a dew point temperature controller.

[0035] The present invention relates to a method with a specifically defined range of conditions for producing high-quality frozen vegetable and / or potato products, comprising at least the following steps: supplying an amount of vegetable and / or potato products; washing, optionally also peeling and / or cutting, the supplied vegetable and / or potato products to form base vegetable and / or potato products; heat-treating the base vegetable and / or potato products in a housing (1) to form heat-treated vegetable and / or potato products; and freezing the heat-treated vegetable and / or potato products.

[0036] The innovative aspect of the method according to the invention is that before and during the heating of the base vegetable and / or potato products, a desired dew point temperature, chosen within a specific range, is set for the air in the housing (1), wherein the conditions of the air present in the housing (1) are detected during the heat treatment, more particularly the temperature and the relative humidity, which are required in order to be able to determine the dew point temperature, and wherein these conditions can be regulated to reach and maintain the desired and set dew point temperature during heating. Detection preferably takes place by means of detection means (8) which are designed for the purpose. The detection of the temperature in the housing (1) will be carried out, for example, by means of a thermometer, whereas the detection of the air humidity, for example the relative humidity, of the air in the housing will be carried out, for example, by using a hygrometer. On the basis of the detected data (temperature and relative humidity), the actual dew point temperature in the housing (1) can be calculated. This is preferably carried out with the aid of a processing unit (7). Subsequently, the actual dew point temperature can be compared to the set and / or desired dew point temperature and if this differs, it is possible to adjust the dew point temperature in the housing (1), if desired. Adjusting the dew point temperature in the housing (1) is effectuated, for example, by introducing an amount of steam (2) in the housing for a certain period of time and / or by heating the air in the housing until the set and / or desired dew point temperature is reached. Heating the air in the housing is carried out, for example, by means of suitable heating means (3), such as for example heating elements which are heated up by means of steam, the so-called steam coils. Alternatively, the heating elements may also be heated up electrically or by means of thermal oil. By the addition of steam (2) in the housing (1) and heating up the air in the housing (1), the dew point temperature of the air in the housing (1) will be adjusted in accordance with the desired setting in the processing unit (and in accordance with the ideal heat treatment parameters pertaining to the respective product which have been optimized beforehand). The heat treatment parameters (dew point temperature, air temperature, residence time) which result in a product of optimum quality will be determined separately for each product. However, the set heat treatment parameters will always be within the range as indicated in the respective claims.

[0037] Due to the fact that the dew point temperature in the housing is mainly determined by two important, but different factors, the air temperature in the housing (controlled by heating the air present in the housing) and the humidity (controlled by adding steam), the heat process can be controlled much better and a stable heating environment is created, as a result of which the products introduced into the housing can be heat- treated evenly and uniformly during the set period of time. Treatment of vegetable and / or potato products by means of the method according to the invention makes it possible to optimize the quality of the frozen end products. This method offers the following advantages:

[0038] (i) absence of condensation by working at a specific dew point temperature, which benefits the quality of the end product (e.g. improved texture, taste perception),

[0039] (ii) possibility of homogenous heat treatment, which benefits the quality and perception of the end product, (iii) absence of the risk of leaching of, inter alia, nutritional components into the water, which does occur with conventional blanching,

[0040] (iv) working in pre-set ranges of modifiable conditions (i.e. air temperature, dew point temperature and residence time), wherein the range of the dew point temperature is set to between 70 °C and 99 °C, more particularly to between 80 °C and 99 °C which is regarded as optimum for the quality of vegetable and / or potato products.

[0041] The housing (1) itself, where the heat process will take place, is diagrammatically illustrated in Fig. 1. The housing (1) is made, for example, from stainless steel and of elongate design. The housing delimits a heat treatment space. The heat treatment space consists of one, two or more zones. In case there are two zones, in a first embodiment, the set and / or desired dew point temperature is identical in both zones or, in a second embodiment, the set and / or desired dew point temperature is different in both zones. In case there are several, i.e., more than two, zones, the set and / or desired dew point temperature in the various zones may be identical or the set and / or desired dew point temperature may be different in at least a number of the various zones. The housing (1) comprises an entry, via which the products to be treated are supplied, and an exit via which the heat-treated products leave the housing (1). Supplying and discharging the products takes place by means of a transport medium (4), preferably a conveyor belt, which extends throughout the housing (1). The heating process itself may take place in a continuous or discontinuous way.

[0042] The housing (1) comprises supply means (5), suitable for supplying steam to the housing (1), and heating means (3), for example in the form of electrical helical coils, suitable for heating up the air in the housing (1). The housing (1) furthermore also comprises ventilation means (6) configured to generate horizontal and / or vertical air circulation in the housing (1).

[0043] The set dew point temperature in the housing (1) varies for each product which is being processed and depends on various factors, such as the type of product, the shape of it, and any aftertreatment which the heat-treated products still have to undergo after the heat treatment. Thus, there will be a difference depending on whether the product to be treated does or does not still have to undergo a heating step, such as e.g., deep- frying or grilling.

[0044] The Applicant has already determined the suitable parameters (dew point temperature, air temperature in the housing, residence time) for a number of products, for example: the dew point temperature for sweet potatoes which are to be deep-fried after the heat treatment is preferably between 79 °C and 84 °C, at an air temperature of approximately 90 °C, and is preferably 81 °C, for a heat treatment time of approximately 5 to 6 minutes. The dew point temperature for carrots which are to be deep-fried after heat treatment is preferably between 92 °C and 96 °C, and is preferably 94 °C, at an air temperature of approximately 100 °C for a heat-treatment time of approximately 7 to 8 minutes. For parsnips which are to be deep-fried after heat treatment, at an air temperature of approximately 96 °C, the ideal dew point temperature is, for example, between 80 °C and 88 °C, and in particular 85 °C, and for 4.5 to 9 minutes. For diced potato which is not to be deep-fried after heat treatment, the ideal dew point temperature, at an air temperature of approximately 100 °C, is preferably between 90 °C and 95 °C, and is preferably 93 °C for a heat treatment time of 4 to 6 minutes.

[0045] By heat-treating the supplied products in a different way than was hitherto customary when producing frozen vegetable and / or potato products, the Applicant has empirically found that there was an improvement in taste, colour, bite, smell, shape and texture of the supplied products. In addition, the products are also drier than with the conventional blanching process after they exit the housing, at the end of the applied method. In addition, by avoiding contact with water during the heat treatment, the risk of leaching of solids from the cell of the product is reduced. This results in an improved retention of the following characteristics: colour: better preservation, or even more accentuation, of the natural colour; cut or natural shape (new potatoes, baby carrots): is retained to a greater extent. With the known technology using blanching, the shape / cut is sometimes slightly deformed; taste: the natural, typical taste of the product is preserved to a greater degree; texture: by specifically optimizing the product using, according to the inventive method, a process which is controlled by the dew point, condensation is prevented, resulting in a texturally better end product. Less watery, less fibrous and crunchier defrosted frozen vegetable and potato products are obtained. During internal tasting sessions, a test panel already noticed the difference of an improved texture (less woody, fibrous, sticky). In addition, this controllable method ensures uniform heating, improving the uniformity of the end product which improves the perception; nutritional value: nutritional components, such as (water-soluble) vitamins and minerals and other health-promoting bio-active components, are not leached into the water, resulting in an end product of better nutritional quality.

[0046] After the heat treatment, the products are, for example, cooled down and / or dried further by exposure, for example, to ambient air, for example to ambient air of at most 35 °C.

[0047] The processing step, in particular the heat-treating of vegetable and / or potato products in a closed housing, cannot be performed on an industrial scale at pressures higher than atmospheric pressure. In order to investigate the effect of elevated pressure conditions on the taste, tests at laboratory scale were performed internally by the patent applicant, which will be described below.

[0048] The tests were performed on three different raw materials, in particular parsnips, carrots and green beans. The parsnips and carrots underwent further processing after the heat treatment and were made into deep-fried products with dimensions of 11 x 11 mm. The carrots and beans were prepared respectively as slices of 5 - 7 mm and as whole vegetables in a kitchen appliance (Rational electrical combi-steamer) which is suitable for operating both at ambient pressure (as is the case with an industrial housing) and at elevated pressure.

[0049] The process conditions applied during the heat treatment step were selected in such a manner that in each case at least one sample was prepared at elevated pressure. As a result thereof, it was possible to make a direct comparison between samples prepared at elevated pressure and samples prepared at atmospheric pressure, in which case the effect of the variety in raw materials was excluded. The following table shows the various set parameters for the various examined products.

[0050] The samples obtained in this way were assessed by a panel of selected test subjects. The assessment was a blind assessment, with the samples being assessed for taste, texture and appearance for each product group and in an arbitrary order.

[0051] It was noticed that, in the case of parsnip and carrot fries, the samples prepared at atmospheric pressure were generally found to be superior in all sensorial aspects. By contrast, for the carrot slices and the beans no particular preference was found; in these cases, some samples prepared at elevated pressure (dew point temperature in this case over 100 °C) were deemed to be better than the samples prepared at atmospheric pressure.

[0052] Nevertheless, it could be concluded that, in the case of preparation at atmospheric pressure, the process conditions within the industrial housing can be optimized in such a way that an end product is obtained which is sensorily preferred to products prepared at elevated pressure. This is configured by the presence of samples which, despite having been prepared at atmospheric pressure, were deemed to be better than their counterparts prepared at higher pressure.

[0053] It can therefore be deduced that vegetable products, in particular vegetable fries, prepared under atmospheric conditions with a suitable combination of air temperature and humidity, may be of superior quality within the described dew point temperature range (< 99 °C).

[0054] For other products, such as carrot slices and green beans, the trend was more ambiguous. However, it was found that by specifically controlling process parameters, it is possible even at atmospheric pressure to obtain products which are sensorily preferred to products prepared at elevated pressure.

Claims

CLAIMS1. Method for producing frozen vegetable and / or potato products, comprising the following steps: supplying an amount of vegetable and / or potato products;- washing the supplied vegetable and / or potato products to form base vegetable and / or potato products; heat-treating the base vegetable and / or potato products in a housing ( 1 ) to form heat-treated vegetable and / or potato products for at most 40 minutes; freezing the heat-treated vegetable and / or potato products; characterized in that a dew point temperature for the air in the housing (1) is set in the range from 70 °C to 99 °C for heat-treating the base vegetable and / or potato products, wherein, during the heat treatment, the conditions of the air present in the housing (1) are detected which are required to be able to determine the dew point temperature, and these conditions are readjusted in order to achieve and maintain the desired dew point temperature during the heat-treatment, wherein the air in the housing (1) during the heat treatment is an air / steam mixture having a relative humidity in the range of 30% - 100% and having a temperature in the range of 70 °C - 150 °C.

2. Method according to Claim 1, characterized in that when detecting the conditions of the air present in the housing (1), the air humidity and the temperature of this air are detected.

3. Method according to Claim 1 or 2, characterized in that steam (2) is fed into the housing (1) and / or the air in the housing (1) is heated up in order to readjust the dew point temperature of the air in the housing (1).

4. Method according to one of the preceding claims, characterized in that, during the heat-treatment, the air in the housing (1) circulates actively.

5. Method according to one of the preceding claims, characterized in that the heattreatment takes place at atmospheric pressure.

6. Method according to one of the preceding claims, characterized in that, after the heat-treatment the base vegetable and / or potato products and before freezing them, a coating is applied to the heat-treated vegetable and / or potato products so that coated vegetable and / or potato products are formed.

7. Method according to one of the preceding claims, characterized in that freezing takes place at a temperature of at most -6° C, preferably at a temperature of at most -18 °C.

8. Method according to one of the preceding claims, characterized in that the heat- treated vegetable and / or potato products are dried with the aid of ambient air after heat treatment and before freezing.

9. Method according to one of the preceding claims, characterized in that the heat- treated vegetable and / or potato products, after being heat-treated and before being frozen, are fried in oil.

10. Method according to one of Claims 1 to 8, characterized in that the heat-treated vegetable and / or potato products, after being heat-treated and before being frozen, are grilled.

11. Frozen vegetable- and / or potato products obtained by means of the method according to one of the preceding claims 1 to 10.

Images