METHOD AND APPARATUS FOR THE DIRECT HEATING OF A PROTEIN-ENRICHED DAIRY PRODUCT BY INTRODUCING WATER VAPOR INTO THIS DAIRY PRODUCT

Description

TECHNICAL AREA

[0001] The invention relates to a method for the direct heating of a protein-enriched dairy product by introducing steam into the product. During direct heating, the steam heats the dairy product to a high-temperature state to achieve a germ-free state. Prior to direct heating, the dairy product undergoes indirect preheating to a preheating temperature. This is followed, in the direction of flow through the dairy product, by a first holding period of the preheated dairy product for a defined and controlled time. Furthermore, in the direction of flow through the dairy product, a second holding period of a defined and controlled time is carried out after direct heating to the high-temperature temperature.Subsequently, water is removed from the heated, ultra-high-temperature dairy product by flash cooling through decompression to a lower pressure, in an amount corresponding to that of the previously added steam. The invention further relates to a system for carrying out the process, which, in addition to a direct heating device, includes a preheater upstream of the preheater with a first heating element located downstream of the preheater in the direction of flow of the dairy product. Downstream of the direct heating device, a second heating element is provided, which leads to a vacuum chamber.

[0002] In recent years, a trend towards the consumption of protein-enriched dairy products has been observed, which necessitates specific requirements for the necessary thermal treatment to extend their shelf life and durability. A protein-enriched dairy product is understood to be, for example, raw milk as the starting material for the heat treatment according to the present invention, which, as the following measured values ​​from three tests show, has a content of (acid-soluble) β-lactoglobulin in the range of 6.85 to 8.35 g / kg milk.

[0003] Out of [1]In contrast, A. Schmid and H. Mayer, Diploma thesis, Determination of furosin and other heating indicators in milk using HPLC, University of Vienna, May 2009, state that the mean value of the content of native β-lactoglobulin from seven raw milk samples examined, which come directly from farms or from organic shops labelled "raw milk", is 4.02 g / dm³ < milk (≈ 3.9 g / kg milk).

[0004] Protein-enriched dairy products are heat-sensitive and tend to scorch, particularly at temperatures above 100 °C. This means that under these conditions, deposits form on the walls of the process equipment used for heat treatment, conveying, and flow control of the dairy product. This deposit formation is also referred to as product fouling. Product fouling reduces the service life or operating time of the affected process equipment between cleaning cycles. In the following text, whenever dairy products are mentioned within the scope of the present invention, the feature "protein-enriched" should always be implied. STATE OF THE ART

[0005] Direct heating of dairy products using steam is a well-known and frequently used method. It serves to extend the shelf life of these dairy products and the end products derived from them. Heat treatment using steam as the heating medium (preferably saturated steam, but also superheated) can be carried out using a variety of methods, either direct or indirect ([2], Heinz-Gerhard KESSLER, Food Process Engineering, Focus on Dairy Technology, 1st edition, Munich - Weihenstephan, Verlag A. Kessler, 1976, pp. 154 to 159). Indirect processes include, for example, heating using various types of heat exchangers (recuperators: e.g., shell and tube heat exchangers; plate heat exchangers). Direct processes comprise two main groups, namely the injection process using steam ([2], pp. 154, 155) and the infusion process using steam ([2], p. 156).

[0006] The direct heat exchange between the steam and the dairy product heats it immediately, quickly, and efficiently. This rapid process reduces treatment time, resulting in less heat exposure and a dairy product that retains a higher quality level, particularly in terms of taste. The rapid and gentle heat treatment of the direct heating method comes at the cost of higher energy consumption compared to the indirect heating method.

[0007] In the injection process, the food product to be heated is conveyed through an injector. The steam is injected at a higher pressure directly into the food product for heating purposes; the food product preferably acts as the driving jet. The heat exchange between the mixing streams is completed in a so-called mixing chamber. ( DE 10 2007 017 704 A1 ).

[0008] In the infusion process, which utilizes infusion heating, the finely divided dairy product is heated in a steam chamber. The steam and product system pressures are nearly identical in this process. Therefore, the temperature difference between the heating medium and the dairy product is significantly smaller than in the injection process, resulting in gentler product handling. The disadvantages of the infusion process compared to the injection process are its more complex technology and higher investment costs. An overview of process concepts for the sterilization of food products, particularly considering direct heating methods of the type described above, is given by [3] Saskia SCHWERMANN Uwe SWEN-ZOW in "Process concepts for the production of ESL milk", article in three sections in Deutsche Milchwirtschaft, 11 / 2008 to 13 / 2008 (59th year).

[0009] EP 0 958 745 A2 discloses a UHT process for milk-based products in which the milk is preheated to 65-85 °C, the temperature is increased to 85-105 °C by means of steam injection, then held and stabilized at this temperature, and subsequently heated to a temperature of 140-145 °C in an infuser. After a holding time of 3-90 seconds, the product is transferred to a vacuum chamber, where it is depressurized and cooled, and an amount of water corresponding to the amount of steam supplied in the upstream sterilization process is removed from the product. In the further course of the process, the product is homogenized and cooled further.

[0010] WO 2018 / 115 131 A1 describes a plant and a process for heating liquid milk concentrates, wherein the product is preheated to a temperature of 5-75 °C, then subjected to direct steam heat treatment in an infuser, and kept hot on its way to a vacuum chamber. In the vacuum chamber, water is removed from the product by expansion and cooling in a manner known per se, and it is then cooled further.

[0011] A process and a plant of the generic type are described in EP 0 617 897 A1 , which is considered the closest prior art. The document discloses a method and a system for the direct heating of a milk-based product. In this process, the product is first preheated with steam before direct heating. After direct heating, the product undergoes indirect cooling before finally being cooled to its final temperature by flash cooling.

[0012] The following should also be mentioned as relevant to the state of the art: [4] KELLEHER, CM et al., A comparison of pilot-scale supersonic direct steam injection to conventional steam infusion and tubular heating systems for the heat treatment of protein-enriched skim milk-based beverages; Innovative Food Science and emerging Technologies, Vol. 52, 2019, S 282-290, - ISSN 1466-8564 and [5] LEE, AP et al., The influence of ultra-pasteurization by indirect heating versus direct steam injection on skim and 2% fat milks; Journal of Dairy Science, Vol. 100, 2017, pp. 1688-1701, - ISSN 0022-0302.

[0013] document [4] revealed in Figure 1 Flowcharts for the treatment of protein-enriched milk drinks by steam infusion and steam injection (see p. 283, right column, last paragraph; p. 284, Fig. 1 ; p. 285, Tab. 1; p. 285, left column to p. 286, left column, first paragraph; p. 286, Fig. 2 .

[0014] The document[5] A heating method for milk using direct steam heating can also be taken from this; here, the following is stated: Figure 1 , right side, referred to. Preheating of the milk is followed by direct heating with steam and then vacuum cooling.

[0015] The denaturation of some whey proteins in milk begins at temperatures as low as 65 °C. The main source of the released SH groups is β-lactoglobulin, which denatures completely at 130 °C and is responsible for the maximum formation of cooked milk flavor. This has a significant impact on the heating process and production time, as whey proteins increasingly denature and deposit on the heater walls at temperatures above 75 °C (≥ 75 °C). This product "fouling," as mentioned earlier, leads to the growth of an increasingly thick fouling layer over extended operating times, thereby continuously impairing heat transfer within the heater.

[0016] To prevent this effect, the dairy product is kept hot at 80°C to 90°C. A typical temperature-time combination is 90°C for 120 seconds. This or a similar measure is used in [3]not disclosed; however, it is to be regarded as prior art. ( EP 0 958 745 A2 ). Within this temperature range, a targeted denaturation of the whey proteins is forced, which then bind to a specific part of the caseins (κ-casein). Caseins make up approximately 80% of the total protein content in milk and are heat-stable compared to whey proteins.

[0017] In the case of protein-enriched milk or dairy products, which are the subject of the present invention, the protein content increases, and thus also the content of heat-unstable whey proteins.

[0018] A comparison between indirect and direct milk heating shows, with regard to the denatured fraction of β-lactoglobulin, that this is significantly higher in indirect milk heating at 83% than in direct milk heating at 66% (see [2], pages 132, 133).

[0019] The degree of denaturation in dairy products correlates with the degree and intensity of heat treatment, i.e., with the specific heat treatment applied. Today, the degree of denaturation is quantitatively assessed using so-called heating indicators. These heating indicators are primarily the acid-soluble β-lactoglobulin (undenatured β-lactoglobulin) and furosin. They serve as indicators for estimating and controlling the actual heat stress on extended-shelf-life dairy products. It is well-established that the degree of denaturation significantly determines the nutritional and sensory quality of dairy products. A clear correlation exists between the furosin content and the content of undenatured β-lactoglobulin when measured in the same, identically treated dairy product.An increase in furosine levels is associated with a decrease in β-lactoglobulin levels. The greater the heat stress (temperature and exposure time), the higher the furosine levels become, while the β-lactoglobulin levels decrease [1].

[0020] The object of the present invention is to provide a method of the generic type and an apparatus for carrying out the method, which effect a significant extension of the service life in the process or in the apparatus and thereby ensure a higher content of non-denatured whey proteins in the treated protein-enriched milk product compared to the prior art. SUMMARY OF THE INVENTION

[0021] This problem is solved by a method with the features of claim 1. Advantageous embodiments of the method according to the invention are the subject of the dependent claims. An apparatus for carrying out the method is the subject of dependent claim 6. Advantageous embodiments of the apparatus according to the invention are described in the dependent claims.

[0022] The invention is based on the process engineering of EP 0 617 897 A1 or on a known process for the direct heating of a liquid food product using steam, as described, for example, in EP 0 794 706 B1 (infusion process) or in WO 2011 / 101077 A1. ,which claims priority in DE 10 2010 008 448 A1 (infusion method; injection method). According to both documents, liquid food products, such as whey protein concentrates, baby food, liquid baby food concentrates, nutritious beverages, or cheese milk, are directly heated by steam to create a germ-free state, whereby water is removed from the liquid food product by pressure reduction to a lower pressure in an amount corresponding to that of the previously supplied steam. On the other hand, in the subject matter of the present invention, in contrast to the aforementioned prior art disclosed in the documents, the direct heating is preceded by a preheating step known per se and, in particular, by an additional, preferably defined and controlled, first holding period in the direction of flow of the milk product.

[0023] The problem underlying the invention is solved if the method of the generic type The preheated and kept hot milk product undergoes indirect cooling prior to direct heating by means of a recuperative cooling step from the preheating temperature to a cooling temperature with a temperature difference in the range of 5 K(elvin) to 10 K (ΔTK ≤ (5 to 10) K), the direct heating from the cooling temperature to the high-temperature heating temperature is controlled with direct heating parameters known per se, and according to feature (d) the milk product (P) is cooled by flash cooling from the high-temperature heating temperature to a necessarily required outlet temperature.

[0024] The inventive principle is therefore to preserve the nutritional and sensory quality of the treated dairy product, in the form of undenatured whey protein, to the greatest extent possible by providing a recuperative cooling step after the initial heating and before the ultra-high-temperature heating, using indirect cooling. This cooling step, from the pre-heating temperature to a cooling temperature, which involves a temperature difference in the range of 5 to 10 K (Kelvin), yields an unforeseen and surprisingly positive result because it reduces both the residence time of the dairy product at the ultra-high-temperature heating temperature and, consequently, further denaturation of the whey proteins.

[0025] The subsequent direct heating begins at the cooling temperature and heats the dairy product to the high-temperature heating temperature using variable direct heating parameters that are known per se. According to one embodiment of the process, these parameters are pressure, temperature, and the duration of steam exposure.

[0026] During flash cooling, the treated dairy product must be lowered to a necessary outlet temperature, depending on the additional supply of water vapor required by the indirect cooling process. This outlet temperature ensures that the treated dairy product returns to its water content level before the high-temperature heating process, i.e., before the supply of water vapor that causes the high-temperature heating.

[0027] At a high-temperature heating temperature, which can reach up to 140 °C, the cooling of the preheated and held milk product according to the invention from the preheating temperature to the cooling temperature comprises a temperature difference in the range of 5 K (Kelvin) to 10 K. The duration of the initial residence time of the milk product in the first holding phase prior to high-temperature heating can also influence the magnitude of the specific temperature difference.

[0028] The skilled person tasked with realizing the subject matter of the present invention will be able, without having to make an inventive effort, to optimize all the aforementioned influencing factors under the specific process conditions and product requirements with regard to the service life on the one hand and a high nutritional and sensory quality of the heat-treated, protein-enriched milk product on the other.

[0029] In the embodiment of the inventive method described in detail below, in which the present product requirements without the cooling step of the invention provide for a high-temperature heating from 85 °C to 137.5 °C, an optimization in the above sense was achieved by cooling or with a cooling step with a temperature difference of 10 K, wherein the first residence time of the first holding period is 30 seconds and the high-temperature heating is thus carried out from 75 °C to 137.5 °C.

[0030] A specific, effective cooling temperature depends on the particular process data of the direct heating. It is dimensioned such that, with the available and within a limited range variable direct heating parameters, such as pressure, temperature, and steam exposure time, the high-temperature heating from the achieved cooling temperature to the high-temperature heating temperature, which remains unchanged even after the cooling step according to the invention, is energetically ensured.

[0031] The process step according to the invention is advantageously applicable, as proposed, to direct heating by an infusion method known per se or an injection method known per se.

[0032] The cooling step according to the invention offers the following advantages in summary: Reduced denaturation of whey proteins (reduced cooking odor caused by the released SH groups); reduced Maillard reaction (browning); reduced furosine formation; significant extension of service life, with little to no product "fouling" after 5 hours of production and the maximum service life being two to three times longer than that of prior art processes or equipment.

[0033] Cooling energy is required for the aforementioned process and product improvements. The returning warm coolant (preferably cooling water) is used to improve the overall energy efficiency of the process, either in the mixing process or regeneratively for preheating.

[0034] An apparatus according to the invention for carrying out the method according to the invention is based on EP 0 617 897 A1 or on the combination of the following features, which are known per se and are predominantly disclosed in the aforementioned EP 0 794 706 B1 (infusion system) or in WO 2011 / 101077 A1 (infusion system; direct heating device with injection device), wherein this prior art, as described in the publication, includes a first heating element, also known per se, between a preheater and a direct heating device. ( EP 0 958 745 A2 ) It cannot be determined: a direct heating device for the dairy product for direct high-temperature heating using steam to a high-temperature temperature, a preheater designed as a recuperator and arranged upstream of the direct heating device (viewed in the direction of flow of the dairy product) for indirect preheating of the dairy product to a preheating temperature, a first holding unit for first keeping the preheated dairy product hot, which is arranged between the direct heating device and the preheater, a first conveying device arranged downstream of the direct heating device for conveying the highly heated dairy product, a second holding unit arranged downstream of the first conveying device for second keeping the highly heated dairy product hot, and a vacuum device arranged downstream of the second holding unit in which the hot,Water is subsequently removed from the highly heated milk product by flash cooling through decompression to a lower pressure, in an amount corresponding to that of the previously added steam.

[0035] Starting from the generic system, the problem underlying the invention is solved in terms of system technology by arranging a cooler designed as a recuperator between the direct heating device and the first heating holder, which cools the preheated milk product from the preheating temperature to a cooling temperature by means of indirect cooling.

[0036] The arrangement of the cooler according to the invention is advantageously applicable, as proposed, to the direct heating device in the form of an infusion device known per se or in the form of an injection device known per se. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] A more detailed description of the invention will be provided in the following description and the accompanying figures of the drawing, as well as in the claims. While the invention is realized in various embodiments of a method of the generic type and in various embodiments of a system of the generic type for carrying out the method, a preferred embodiment of the method and system according to the invention is described below with reference to the drawing. The figures show... Figure 1 schematic representation of a plant for the direct heating of a protein-enriched dairy product by introducing steam into this dairy product according to the state of the art; Figure 2 in schematic representation and starting from the known system according to Figure 1 the system according to the invention with a cooler arranged according to the invention; Figure 3a block diagram of the process according to the state of the art (Attempt I); Figure 3a a block diagram of the inventive method with a cooling system ΔTK = 5 K (Attempt II); Figure 3b a block diagram of the inventive method with a cooling system ΔTK = 10 K (Attempt III); Figure 4 an excerpt from the plant according to Figure 2 in the area upstream of a direct heating device without cooling or cooling intervention of the preheated and kept hot milk product for carrying out the process according to the state of the art; Figure 5 the excerpt from the plant according to Figure 2 with the cooling of the preheated and kept hot milk product according to the invention by means of the cooler arranged according to the invention for carrying out the method according to the invention; Figure 6a graphical, normalized representation of the measured values ​​for the content of non-denatured β-lactoglobulin from a system according to the invention. Figures 2 , 4 and 5 treated protein-enriched dairy product, determined from Try I until III; Figure 7 a graphical, normalized representation of the measured values ​​for the furosine content from a system according to the invention. Figures 2 , 4 and 5 treated protein-enriched dairy product, determined from Try I until III and Figures 8a, 8b, 9a, 9b, 10a, 10b Photographic images of the product "fouling" or the "fouling" layer at the inlet of the second conveying unit located downstream of the direct heating unit after 5 hours of production time, wherein two vertically arranged images (8a, 8b; 9a, 9b; 10a, 10b) in the aforementioned order show the Try I until III are assigned and displayed.

[0038] A system 100 known from the prior art in printed form according to Figure 1 (Insofar as it concerns an infusion device and the further devices arranged downstream thereof) is disclosed, for example, in EP 794 706 B1 or WO 2011 / 101077 A1. Annex 100 contains, for carrying out an infusion process IFV, a direct heating device 8 designed in the form of an infusion device 80 for carrying out high-temperature heating HE within the framework of direct heating DE. The infusion device 80 may have a product inlet 28 in its headspace. ( WO 2010 / 086082 A1 ), via which a protein-enriched milk product P, which is to be heat-treated, is supplied to this infusion device 80, for example, and preferably centrally and in a circular shape.

[0039] For direct heating, the supplied milk product P is supplied, for example, and preferably, via an external and internal steam inlet 26, with steam D radially from the outside and simultaneously radially from the inside, thereby resulting in high-temperature heating HE from a preheating temperature T2 = TVE to a high-temperature heating temperature T4 = THE. The prior art knows of numerous other possibilities regarding the configuration of the supply of the milk product P and the steam D, which can also be applied within the scope of the present invention. The infusion device 80 receives a supply of a first coolant K1 via a first coolant inlet 40 to a coolant chamber on the bottom of the container for cooling the base of the infusion device 80. The first coolant K1 is discharged via a first coolant outlet 42.

[0040] An outlet opening at the lower end of the infusion device 80 is connected via an outlet pipe 30 to a first pumping device 10, for example, a rotary positive displacement pump or a centrifugal pump, which is connected via a third product line section 32 to a second heat holder 12 to a second heat holding chamber HH2 for maintaining the high-temperature heating temperature T5 = THE for a second residence time Δt2. The second heat holder 12 leads via a fourth product line section 34 to a vacuum chamber 14. The second pumping device 10 conveys the high-temperature milk product P, which is kept at the high-temperature heating temperature THE, from the infusion device 80 to the vacuum chamber 14. The vacuum chamber 14 is designed to cool the milk product P, which is being cooled by a pressure drop, by means of a so-called flash cooling system FK, by means of a quantity of water W as so-called vapors.The vapor is extracted from the infusion device 80 in the form of water vapor D and discharged via a vapor outlet 38, preferably located in the upper region. A milk product P treated in this way leaves the vacuum chamber 14 via a discharge line 36 located in its lower region on a tapered base, passing through a second conveying device 16 at an outlet temperature T6 = TA.

[0041] The dairy product P to be thermally treated enters the system 100 via a dairy product inlet 18 into a preheater 2 for preheating VE to the preheating temperature T1 = TVE. The preheater 2 leads via a first product line section 20 to a first holding tank 4 for initial holding HH1 to maintain the preheating temperature T2 = TVE for a first residence time Δt1. The first holding tank 4 opens via a second product line section 22 and the subsequent product inlet 28 into the headspace of the infusion device 80. The preheater 2 is supplied with a preferably renewable heat transfer medium M via a heat transfer medium inlet 2a and a heat transfer medium outlet 2b.

[0042] The direct heating unit 8 of the plant 100 ( Figure 1 )Alternatively to the infusion device 80 described above, the injection device 800 can be configured as an injection device for carrying out an injection procedure IJV. In this embodiment, which is known per se, the milk product P enters the injection device 800 via the product inlet 28 for the purpose of high-temperature heating HE and preferably forms a motive jet there. The motive jet flows through a mixing chamber of the injection device 800, the flow of the heating medium, water vapor D, for the purpose of introducing it into the milk product P is caused by a pressure drop resulting from the velocity of the milk product P forming the motive jet. The water vapor inlet 26 also leads to the mixing chamber, and the water vapor D preferably impinges on the motive jet laterally there.

[0043] A system according to the invention 1000 ( Figure 2 )for the direct heating DE of the protein-enriched milk product P by introducing steam D into this milk product P proceeds in an identical manner from the known plant 100 according to Figure 1 The reference numerals are retained unchanged. To avoid repetition, only the differences that distinguish the inventive system 1000 from the known system 100 are described below.

[0044] A cooler 6, designed as a recuperator, is arranged between the direct heating device 8, 80, 800 and the first heating unit 4. The product side of this cooler is routed over the second product line section 22. The cooler 6 is supplied with a second coolant K2, preferably cold water, via a second coolant inlet 6a and a second coolant outlet 6b. Its function is to cool the preheated and heated milk product P by an indirect cooling K from the preheating temperature T2 = TVE to a cooling temperature T3 = TK.

[0045] Experiments were carried out with the inventive system 1000 to demonstrate that the objectives formulated in the inventive problem statement have been achieved. Three of these experiments, conducted on consecutive days, are described below, namely those with Attempt I, II and IIImarked, with regard to a selection of relevant results and measurements. Experiments I, II and III - Overview

[0046] First attempt (without cooling K), process control according to Figures 3 , 4 II second attempt (with cooling K), process control according to Figures 3a , 5 III third attempt (with cooling K), process control according to Figures 3b , 5

[0047] In the Attempt I ( Figures 4 and 3 ) The milk product P, preheated and kept hot to the preheating temperature T2 = TVE, is passed through the "inactive" cooler 6 via the second product line section 22 without cooling and fed to the direct heating device 8, designed as an infusion device 80, at the preheating temperature T2 = TVE.

[0048] In the Attempt II and III ( Figures 5 and 3a or Figures 5 and3b ) The milk product P, preheated to the preheating temperature T2 = TVE and kept hot, is guided through the "active" cooler 6 via the second product line section 22, where it undergoes indirect cooling K by the temperature difference. ΔTK on the cooling temperature T3 = TK, where the temperature difference ΔTK the Experiment II from that of the Experiment III The milk product P enters the direct heating device 8, designed as an infusion device 80, at the respective cooling temperature T3 = TK.

[0049] All relevant temperatures and residence times of the Experiments I to III the heat treatment of the protein-enriched milk product P from preheating VE in the preheater 2 with the preheating temperature T1 = TVE to the treated milk product P in the discharge line 36 with an outlet temperature T6 = TA ( Figure 1 , 2 )are in the following Table 1 compiled. The following applies to heat treatment, among other things: Attempt I: TVE - TA = 2 K; Attempt II: TK - TA = 1.5 K; Attempt III: TK - TA = 2 K. Table 1 Attempt TVE in °C Δ t1 in s TK in °C THE in °C Δt2 in s TA in °C I 85 30 - 137,5 1 83 II 85 30 80 137,5 1 78,5 III 85 30 75 137,5 1 73 Test results

[0050] A selection of the Try I until III The measured values ​​determined are in the above. Table 2 compiled. The relevant heating indicators, namely undenatured β-lactoglobulin and furosine, for estimating and controlling the actual heat stress on dairy products and their significance for the nutritional and sensory quality of these dairy products have been discussed above. The corresponding measured values, obtained from the Try I until III, are in Table 2 highlighted by grey marking.

[0051] In Figure 6is the normalized content of non-denatured β-lactoglobulin L / Lo [1] in the treated milk product P for the Try Figures I to III are shown. Here, L represents the respective measured value (β-Lg) for the non-denatured β-lactoglobulin in g / kg protein (*) in the treated milk product P, which is referenced to Lo, where Lo, as the reference value for normalization, denotes the respective measured value for the non-denatured β-lactoglobulin in the untreated milk product P (raw milk). Result

[0052] The test results (Table 2) show that the indirect cooling K according to the invention is evident from the Experiment II (ΔTK = 5 K → L / Lo = 0.34) and the Experiment III (ΔTK = 10 K → L / Lo = 0.42) to a desirable, unexpected and surprising increase in the content of non-denatured β-lactoglobulin compared to the Attempt I (without cooling K; ΔTK= 0 K → L / Lo = 0.25) leads to, under the given other process conditions in plant 1000, the cooling by ΔTK = 10 K in Attempt III delivers an optimal result ( Figure 6 ).

[0053] In Figure 7 is the normalized content of furosine F / Fo [1] in the treated milk product P for the Try I to III The figure represents the respective measurement value for furosine in mg / 100g protein in the treated dairy product P, which is referenced to Fo, where Fo, as the reference value for normalization, denotes the respective measurement value for furosine in the untreated dairy product P (raw milk). Result

[0054] The test results (Table 2) show that the indirect cooling K according to the invention is evident from the Experiment II (ΔTK = 5 K → F / Fo = 3.38) and the Experiment III(ΔTK = 10 K → F / Fo = 3.14) to a desirable, unexpected and surprising reduction in the furosine content compared to the Attempt I (without cooling K; ΔTK = 0 K → F / Fo = 3.55) leads to, under the given other process conditions in plant 1000, the cooling by ΔTK = 10 K in Attempt III delivers an optimal result.

[0055] However, whether the increase in the β-lactoglobulin content and the decrease in the furosin content are solely attributable to the indirect cooling K according to the invention prior to direct heating DE cannot be determined by the Experiments I until IIIThis cannot necessarily be proven. It cannot be ruled out that the observed differences, which are desirable, unexpected, and surprising, are predominantly due to the indirect cooling K according to the invention and, if at all, to a rather small extent to the necessary stronger cooling of the protein-enriched milk product P during flash cooling FK (different outlet temperatures of 78.5 °C and 73 °C for the Experiment II or III each compared to TA = 83 °C for Attempt I) are attributable to.

[0056] This lack of knowledge, however, does not appear to be essential to the invention, especially since the Experiment II and III inevitably among themselves and each other AttemptThe different outlet temperatures TA must result. The latter necessarily result from the condition set by feature (d) in the preamble of claim 1, and ultimately the indirect cooling according to the invention is also the cause of this fact and its possible effects.

[0057] The fulfillment of characteristic (d) is only possible depending on the respective direct heating DE in the Attempt I to IIIThe supplied amount of water vapor (preferably saturated steam) inevitably results in correspondingly different outlet temperatures TA. Flash cooling FK also includes the removal of the amount of water that is necessarily required as compensation for the respective indirect cooling K from the preheating temperature TVE to the cooling temperature TK (enthalpy reduction), in the form of an adequate amount of water vapor D during the direct heating DE from the cooling temperature TK to the high-heating temperature THE (enthalpy increase).

[0058] The Attempt I to III assigned outlet temperatures TA (see Table 1) In order to fulfill the condition set by feature (d) in the preamble of claim 1, they must necessarily be different for the following reasons. Attempt I (without cooling)

[0059] In order to remove the amount of water W from the superheated milk product P during flash cooling FK, which corresponds to the amount of water vapor D previously supplied for heating from the preheating temperature TVE = 85 °C to the superheating temperature THE = 137.5 °C, a vacuum device 14 (see Figure 2 ) to set a saturation pressure ps or a corresponding absolute pressure (negative pressure compared to atmospheric pressure) that causes the milk product P to boil at a saturation temperature Ts(ps) = 83 °C, which also corresponds to the outlet temperature TA. Attempt II (with cooling; cooling from TVE = 85 °C to TK = 80 °C; ΔTK = 5 K)

[0060] Cooling the milk product P by a temperature difference ΔTK = 5 K requires a corresponding heat removal or enthalpy reduction from or within the milk product P. This enthalpy reduction in Attempt II During direct heating DE, additional supply of steam, preferably saturated steam, is required. Attempt Imust be compensated to achieve the same high-temperature heating temperature THE as in Attempt I to reach (THE = 137.5 °C).

[0061] So that the milk product P is affected by the additional steam supply in the Attempt II To prevent the milk product P from becoming "diluted," a quantity of water in the form of vapors corresponding to the additional amount of water vapor must be removed from the milk product P in vacuum chamber 14 by means of so-called flash cooling FK. This process takes place when the milk product P is saturated. Attempt III (with cooling; cooling from TVE = 85 °C to TK = 75 °C; ΔTK=10 K)

[0062] Cooling the milk product P by a temperature difference ΔTK = 10 K requires a corresponding heat removal or enthalpy reduction from or within the milk product P. This enthalpy reduction in Attempt III During direct heating DE, the additional supply of steam, preferably saturated steam, is required to achieve an even higher level of efficiency compared to other methods. Attempt I and accordingly also to a greater extent compared to Attempt IImust be compensated to achieve the same high-temperature heating temperature THE as in Attempt I or in Attempt II (each THE = 137.5 °C) to reach.

[0063] So that the milk product P is affected by the additional steam supply in the Attempt III not to an even greater extent than in Attempt II To prevent the milk product P from becoming "diluted," a quantity of water in the form of vapors corresponding to the additional amount of water vapor must be removed from the milk product P in vacuum chamber 14 by means of so-called flash cooling FK. This process takes place when the milk product P is saturated.

[0064] The Figures 8a, 8b, 9a, 9b and 10a, 10b qualitatively show the extent of the product "fouling" or the "fouling" layer in the usually most critical area of ​​the system 1000, namely downstream of the outlet from the direct heating device 8, 80 and here from a disassembly point of view in the easily accessible suction nozzle of the second conveying device 10 ( Figure 2 ), for the Experiments I until III after 5 hours of production time each. The photographic recordings of the Figures 8a, 8b are the Attempt I, those of Figures 8a, 8b dem Attempt II and those of Figures 10a, 10b dem Attempt assigned to III.

[0065] The Figures 8a, 8b (Attempt I, Without cooling (K), a closed "fouling" layer PF of significant thickness is observed after 5 hours of production, impairing heat transfer and the overall functionality of the plant components in the relevant high-temperature areas. A production stoppage and cleaning of plant 1000 is necessary after approximately 10 hours of production.

[0066] The Figures 9a, 9b (Attempt II, with cooling K; ΔTK= 5 K) show extensive colonization of the wall of the areas in question by a "fouling" layer PF of very moderate thickness, characterized by numerous island-like interruptions. This layer hardly impairs the heat transfer and general functionality of the plant components in the relevant high-temperature areas, so that an interruption of production and cleaning of the plant 1000 is only necessary after a production time of up to 20 hours (production time approximately 2-3 times longer than in Attempt I) is necessary.

[0067] The Figures 10a, 10b (Attempt III,with cooling K; ΔTK = 10 K) show an island-like, area-wise very limited colonization of the walls in question by a "fouling" layer PF of moderate thickness, which hardly impairs the heat transfer and the general functionality of the plant components in the relevant high-temperature areas, so that an interruption of production and cleaning of the plant 1000 is only necessary after a production time of up to 20 hours (production time about 2-3 times longer than in test I).

[0068] The black and white depiction of the Figures 9a to 10b The darker areas visible on the front surface of the suction nozzle are minor deposits of the highly heated milk product P with brown or reddish-brown discolorations, which are presumably caused by minor leaks at the flange connection and indicate a Maillard reaction MR of the milk product P.

[0069] The facts and results presented above with regard to the direct heating device 8 designed as an infusion device 80 can be applied analogously to a direct heating device 8 designed as an injection device 800. ( Figure 1 , 2 ). A person skilled in the art tasked with solving the problem described in the invention, a process engineer or technologist specializing in dairy science, food processing engineering or dairy technology, will be able to apply the teaching of the present invention to an injection process not detailed in this application and optimize it with regard to the process parameters to be determined, without having to make an inventive contribution. LIST OF ABBREVIATIONS USED

[0070] Figure 1 (State of the art) 100 State-of-the-art system 8 Direct heating unit 80 Infusion unit 800 Injection unit 2Preheater 2aHeat transfer medium inlet 2bHeat transfer medium outlet 4. First heating unit 10. First conveying unit 12. Second heating unit 14. Vacuum unit 16. Second conveying unit 18. Dairy product inlet (for dairy product P to be treated) 20. First product line section 22. Second product line section 26. Steam inlet 28. Product inlet 30. Outlet pipe 32. Third product line section 34. Fourth product line section 36. Discharge line (for dairy product P treated) 38. Vapor outlet 40. First coolant inlet 42. First coolant outlet D Steam DE Direct heating FK Flash cooling HE High-temperature heating HH1 First holding heat HH2 Second holding heat IFV infusion procedure IJV injection procedure K1 first coolant M heat transfer medium P milk product (protein enriched) TAOutlet temperature (= T6) TVEPreheat temperature (= T1, T2) THEHigh heat temperature (= T4, T5) VE preheating water Δt1 first dwell time Δt2 second dwell time Figures 2 to 4 1000 plant 6 Radiator 6a Second coolant inlet 6b Second coolant outlet Cooling K2 second coolant TK Cooling temperature (= T3) ΔTK Temperature difference ps Saturation pressure Ts Saturation temperature Figures 6 to 10b I First attempt (without cooling K) II Second attempt (with cooling K) III Third attempt (with cooling K) Table 1 Attempt TVE in °C Δ t1 in s TK in °C THE in °C Δ t2 in s TA in °C I 85 30 - 137,5 1 83 II 85 30 80 137,5 1 78,5 III 85 30 75 137,5 1 73 FFurosin (measured value in mg / 100 g protein) FoFurosin (measured value, reference value for normalization) F / FoFurosin (normalized measured values ​​in [mg / 100 g protein] / [mg / 100 g protein] = [1]) L-non-denatured β-lactoglobulin (measured value in g / kg protein) Lowird (measured value, reference value for normalization) L / Lo-non-denatured β-lactoglobulin (normalized measured values ​​in [g / kg protein] / [g / kg protein] = [1]) MRMaillard reaction (browning) PF "Fouling" layer (product "fouling"; deposit formation)

Claims

1. Method for directly heating (DE) a protein-enriched milk product (P) by introducing steam (D) into said milk product (P), (a) wherein during the direct heating (DE) the steam (D) heats the milk product (P) to form an aseptic state by a direct high heating (HE) to a high-heating temperature (THE), (b) wherein prior to the direct heating (DE), an indirect pre-heating (VE) of the milk product (P) to a pre-heating temperature (TVE) and, viewed in the flow direction of the milk product (P), a first heat-holding (HH1) following the pre-heating (VE) of the pre-heated milk product (P) with a defined and controlled first residence time (Δt1) is carried out, (c) wherein, viewed in the flow direction of the milk product (P), after the direct heating (DE) to the high-heating temperature (THE), a second heat-holding (HH2) of the high-heated milk product (P) with a defined and controlled second residence time (Δt2) is carried out, and (d) wherein water (W) is subsequently extracted from the heat-held, high-heated milk product (P) by a flash-cooling (FK) by means of expansion to a lower pressure in an amount corresponding to that of the previously supplied steam (D), characterized in that • the pre-heated and heat-held milk product (P) prior to the direct heating (DE) undergoes an indirect cooling (K) by a recuperative cooling step from the pre-heating temperature (TVE) to a cooling temperature (TK) with a temperature difference (ΔTK) in a range of 5 K(elvin) to 10 K (ΔTK ≤ (5 to 10) K), • the direct heating (DE) from the cooling temperature (TK) to the high-heating temperature (THE) is controlled with direct-heating adjustment variables known per se, and • in accordance with the provision of feature (d), the milk product (P) is cooled by the flash-cooling (K) from the high-heating temperature (THE) to an inevitably necessary exit temperature (TA).

2. Method according to claim 1, characterized in that the temperature difference (ΔTK) is 10 K (ΔTK = 10 K).

3. Method according to one of claims 1 or 2, characterized in that the direct-heating adjustment variables are pressure, temperature, and exposure time of the steam.

4. Method according to any of the preceding claims, characterized in that the direct heating (DE) is realized by an infusion method (IFV) known per se.

5. Method according to any of claims 1 to 3, characterized in that the direct heating (DE) is realized by an injection method (IJV) known per se.

6. Apparatus (1000) for directly heating (DE) a protein-enriched milk product (P) by introducing steam (D) into said milk product (P), according to any of claims 1-5, comprising in a manner known per se • a direct-heating device (8; 80, 800) for the milk product (P) for a direct high heating (HE) by means of steam (D) to a high-heating temperature (THE), • a pre-heater (2) arranged upstream of the direct-heating device (8; 80, 800), viewed in the flow direction of the milk product (P), configured as a recuperator for an indirect pre-heating (VE) of the milk product (P) to a pre-heating temperature (TVE), • a first heat-holding device (4) for a first heat-holding (HH1) of the pre-heated milk product (P), which is arranged between the direct-heating device (8; 80, 800) and the pre-heater (2), • a first conveying device (10) arranged downstream of the direct-heating device (8; 80, 800) for conveying the high-heated milk product (P), • a second heat-holding device (12) arranged downstream of the first conveying device (10) for a second heat-holding (HH2) of the high-heated milk product (P), • a vacuum device (14) arranged downstream of the second heat-holding device (12), in which water (W) is subsequently extracted from the heat-held, high-heated milk product (P) by a flash-cooling (FK) by means of expansion to a lower pressure in an amount corresponding to that of the previously supplied steam (D), characterized in that • between the direct-heating device (8; 80, 800) and the first heat-holding device (4), a cooler (6) configured as a recuperator is arranged, which cools the pre-heated and heat-held milk product (P) by an indirect cooling (K) from the pre-heating temperature (TVE) to a cooling temperature (TK).

7. Apparatus according to claim 6, characterized in that the direct-heating device (8) is configured in the form of an infusion device (80) known per se.

8. Apparatus according to claim 6, characterized in that the direct-heating device (8) is configured in the form of an injection device (800) known per se.