WO2025131367A1 - Method for treating pistachios - Google Patents

Abstract

The invention relates to a method for treating in-shell pistachios by means of the following steps: a) wetting the pistachios with water, in particular with a salt brine; b) heating the wetted pistachios for pasteurisation and/or for a roasting process. In the method according to the invention, during the wetting with water, in particular the salt brine, and/or immediately following this, the pistachios are treated with ultrasound, and/or the heating of the wetted pistachios comprises a step of heating the pistachios in a planar, preferably single-layer, spread-out bed by irradiating with short-wave infrared radiation having a wavelength of λ ≤ 1.4 µm, in particular a wavelength λ of 1.2 µm ≤ λ ≤ 1.4 µm, and/or the heating comprises shock-like heating of the pistachios using hot air at a temperature of 300-600°C for a period of 10 to 60 seconds.

Description

Process for treating pistachios

The invention relates to a method for treating pistachios.

Pistachios are known to be latently contaminated with Salmonella. Prevalence rates range between 0.5 and 3%, depending on origin, variety, harvesting method, and processing immediately after harvest and before shipping.

Pistachios are stone fruits whose kernels are encased in a hard, woody shell and consumed. As they ripen on the tree, the shell opens, providing a gap-like access to the kernel. Pistachios can become infected with Salmonella while still on the tree through contact with contaminated aerosols or through other transmission routes. Due to their peritrichous flagellation, Salmonella is capable of active movement and can therefore penetrate the ripe fruit once the shell has opened on the tree. Salmonella attacks the kernel of the pistachio by attaching itself to the surface of the exposed cell structure and then migrating into the pores.

Salmonella can cause severe, and in particularly severe cases even fatal, infections in young children, frail, or elderly people. People with weakened immune systems, as well as healthy individuals who become infected with Salmonella, often suffer from Severe fever, sometimes bloody, diarrhea, nausea, vomiting, and excruciating abdominal pain. In rare cases, Salmonella infection can cause the pathogen to enter the bloodstream and cause more serious illnesses, such as arterial infections, including aneurysms, endocarditis, and arthritis.

For this reason, salmonella infections are notifiable in Germany. Every case of illness, even suspected salmonellosis, must be reported by the treating physician to the responsible health authority. If salmonella is found in food during routine testing, the laboratories are required to report these findings to the food authorities. The latter are then usually required to withdraw the product from circulation.

Raw pistachios are not particularly tasty. They are therefore usually roasted before packaging and sale to consumers. Although pistachios can be shelled and then roasted, meaning only the kernels are roasted, the nuts are often roasted in their shells, meaning the kernels are still inside the shell. This process is also known as in-shell roasting, and the resulting product is referred to as an in-shell pistachio.

Such in-shell roasting is typically performed using hot gases. Typical roasting parameters for state-of-the-art in-shell roasting of pistachios with hot gases are a roasting time of 10 to 20 minutes and gas temperatures of approximately 140 to 180°C.

For a long time, professional roasters held the view that the thermal energy introduced into the pistachios during this roasting process was sufficient to reliably kill any salmonella present. This view initially seems plausible. The specialist literature cites temperatures of 70-72°C for a ten-minute exposure time as the prerequisite for killing salmonella, a process also known as pasteurization. However, it must first be made clear that the required killing temperature of 70°C must be reached inside the Salmonella, or more precisely, in its cell nucleus, in order to ensure reliable and reproducible killing.

As explained above, hot-air roasting of in-shell pistachios is typically carried out at considerably higher temperatures in order to develop the desired roasting aromas and achieve a crisper texture of the pistachio kernel, thus altering the kernel's cell structure accordingly. The fact that these massive temperature-induced changes occur in the kernel's cell structure seemed to further confirm the assumption that Salmonella colonization of pistachios cannot survive such a process alive, or at least not with the ability to reproduce. This view is supported by the fact that experience has shown that the degree of roasting, or rather the texture, of in-shell pistachios is quite uniform, which indicates a uniform heat effect of the roasting energy on the entire fruit, at least on the kernels.

Pistachios are unique as roasted nuts because, although they are roasted in their shells, the shells are partially open. The degree of this opening can vary greatly, from almost closed to the shell breaking in two. Unlike pistachios, most nuts are roasted in their shells, i.e., without the shell. Peanuts can be roasted whole, i.e., in their shells, as can certain types of almonds.

If shelled nuts are roasted, the killing of Salmonella during the roasting process is reproducible and thus verifiable, because the heat input into the exposed skin or, in the case of blanched nuts, into the exposed flesh of the nut kernel is unproblematic. If whole nuts are roasted in the shell, with the shell intact and closed, it can be assumed that Salmonella cannot be transmitted through the intact shell into the can penetrate the interior of the nut. In this case, the destruction of Salmonella bacteria on the surface of the shell during a roasting process can also be demonstrated reproducibly and thus validated.

The situation is different with in-shell pistachios. The problem with roasting in-shell pistachios is that, on the one hand, the partially opened shell does not provide a barrier to the growth of microbes on the kernel surface or the skin surrounding the kernel, and, on the other hand, the shell impedes heat transfer to the interior. A cushion of air forms inside the opened pistachio, which is difficult to move and acts as a heat insulator. To make matters worse, the roughness of the kernel and shell surfaces causes the formation of immobile boundary layers. These boundary layers of immobile air act as thermal insulators.

The pistachio is typically elongated. The shell consists of two halves. The pistachio opens by the halves separating along one narrow side. At the opposite narrow sides, the two shell halves remain connected, forming a kind of biological hinge. The further a given point is inside from the open narrow side and the closer this point is to the closed narrow side, ideally along the centerline in the longitudinal axis, the lower the likelihood that air will exchange with the environment at this point during the roasting process. Heat transfer in these areas occurs little or not at all through convection of heated air, but rather through heat conduction from the outside of the shell to the inside of the nut.

Heat conduction into the interior of the pistachio, into areas where little or no heated air penetrates through convection processes, can be adversely affected. The kernel usually lies loosely within the open shell and therefore inevitably has only a very small contact area with the shell. In unfavorable cases, this contact only exists at three points.

In addition, the pistachio kernel is surrounded by a skin. Due to the drying processes and the different expansion rates of skin When the kernel is exposed to the pistachio, the flat bond between the skin and kernel separates, at least partially. Furthermore, the skin can tear, forming loose pieces of skin that become trapped in the cavity between the kernel and the shell. It can be assumed that in isolated cases, loose skin particles can become wedged between the pistachio kernel and the pistachio shell, resulting in only point-like contact at two or three points. This then results in very high heat transfer resistance from the kernel or shell into the skin particles at these points.

For roasting in-shell pistachios, current technology uses mesh belt roasters, in which the nuts to be roasted pass through a roasting chamber on a mesh belt. These mesh belt roasters are typically heated by burning natural gas or hydrogen in a burner, but are occasionally also operated with oil, particularly when gas is unavailable. The heating of the process air, which is directed onto the nuts in a cross-flow process, can occur directly through the burner or via heat exchangers. It is also expected that in the future, the air used to heat the roasted product will be heated using electrical resistance heaters. In this case, the infrared heat would act indirectly on the nuts via the hot air carrier medium.

For roasting pistachios with heated gases in mesh belt roasters, the roasted product is conveyed through the system on a mesh belt. The mesh belt is designed to prevent the nuts from falling through openings, but also to allow airflow perpendicular to the horizontal direction, usually in a vertical plane. This is a cross-flow process. The thickness of the layer on the mesh belt ranges from approximately 3 cm (corresponding to 3 to 4 layers of pistachios) to over 20 cm.

Typically, the airflow through the roaster is very large and turbulent; air volumes of 10,000 to 100,000 cubic meters per hour are the norm. To promote even roasting, mesh belt roasters can be divided into segments. In such cases, the direction of airflow through the roasted material is rotated by 180 degrees from section to section. In one segment, the heated air flows from top to bottom. In the following segment, the air in the opposite direction. This is intended to improve the heat transfer from the heated air into the roasted material. In terms of its flowability, the roasted material is therefore understood as a type of diode, i.e. as a mass through which, in discrete areas, flow is better in one direction than in the opposite direction. Reversing the flow direction is intended to compensate for this diode effect and make the roasting more homogeneous. In addition, there will be areas whose flow resistance is higher than the average value of the flow resistance of the roasted material layer. These points must be imagined as throttles. There will also be areas that have a lower flow resistance. The inventor assumes that the flow resistance of the roasted material layer can be described by a Gaussian distribution of the probability density. The inventor further assumes that the flow through these areas with different flow resistances follows the laws of parallel connection of resistances, meaning that the flow rate per area is inversely proportional to the flow resistance. This results in the areas with low flow resistance allowing significantly more heated gases to pass through, at the expense of the areas with high flow resistance. In reality, the flow of hot air through the roasted material is therefore significantly more uneven than assumed by the state of the art.

Also considered state-of-the-art are rotary kiln roasters with infrared heating of the roasted product through direct irradiation. The combination of this technology with the addition of water or steam for pasteurization is described, for example, in DE 10 2018 121 453 A1.

Manufacturers and users value the state-of-the-art mesh belt roasters for their very simple mechanical design and their high throughput. Mesh belt roasters are particularly easily scalable in terms of their operating principle and design, allowing them to be designed for very high throughput.

In industrial mass production, mesh belt roasters with capacities of up to 7,000 kilograms of in-shell pistachios per hour are used. With a unit weight of approximately 1.2 grams per pistachio, this means that such a roaster roasts over 4 million pistachios per hour. If we now assume, as a conservative estimate, a prevalence of 0.5% for the occurrence of Salmonella in the roasted material, this means that 20,000 contaminated pistachios are fed into such a roaster per hour. It follows that with regard to the destruction of Salmonella, the roasting process must be understood as a safety device that is exposed to a hazardous event for an extremely long time and extremely frequently. It follows that the process must run extremely uniformly and stably if the breakdown safety against the identified risk is to be guaranteed despite the high exposure intensity. In the inventor's opinion, this is precisely not the case with the state of the art. The recalls of roasted pistachios due to contamination with Salmonella confirm this view.

Salmonella detections in roasted pistachios during routine random sampling have now occurred with a frequency that refutes the above-mentioned assumption of reproducible pasteurization through state-of-the-art roasting processes. For example, in the USA, there have already been several recalls of pistachios that were roasted in the shell and found to be contaminated with salmonella.

In the inventor's opinion, the procedure according to the state of the art and the considerations and assumptions made so far do not sufficiently take into account that certain Salmonella strains successfully respond to thermal stress by producing protective proteins and being able to enter a dormant state. The transition of Salmonella into this more heat-resistant dormant state can be promoted by heating them gradually rather than suddenly, i.e. as quickly as possible. The slower the heating takes place, the more time the Salmonella has to successfully enter the dormant state. Furthermore, it is not taken into account that Salmonella in a dry environment can also withstand temperatures of 90 degrees Celsius and above for extended periods. According to the inventor, these little-noticed phenomena are one reason for the observed survival of Salmonella in conventional hot air roasters.

When treating pistachios, the following considerations apply:

A very large proportion of pistachios are treated with brine before roasting to intensify the flavor through the addition of salt. The water that transported the salt into the pistachios evaporates during the roasting process, and the finely crystallized salt remains in the roasted product. In large-scale applications, this is usually done using machines known as coaters. These are rotary tube conveyors into which the brine is sprayed via a probe. The conveying movement of the rotary tube creates both a linear movement component in the product parallel to the axis of rotation of the rotary tube and a rotation of the product flow. This rotation leads to the formation of a product roller, which can be imagined as a kind of permanent avalanche that stands still. The mixing effect of such rotary tubes can therefore be very good if the machine is long enough. In practice, experience has shown that the mixing of the brine is still not optimal. In a bag of 250 grams of pistachios, or roughly 200 pistachios, there are usually at least two or three that taste less salty than expected. This is a clear indication that the brine process is often less stable and reproducible than desired.

The prevailing view is that this addition of water or brine increases the thermal conductivity in the roasted product during the subsequent roasting process and thus promotes the destruction of Salmonella. This overlooks the fact that, under optimal conditions, Salmonella can double in number within 20 minutes on a given substrate if sufficient free water is available. The addition of brine provides free water in a relevant amount. Relevant in this context is the addition of free water that exceeds 25% of the residual moisture present in the kernels. which, according to the UNECE standard (standard of the United Nations Economic Commission for Europe), can be up to 6.5%. The water activity is at an Aw value of around 0.65.

Salmonella reacts to the provision of free water by spontaneously beginning to multiply until the available free water is consumed. The optimal temperature for such multiplication of Salmonella is between 35 and 43°C. However, Salmonella multiplication can be inadvertently promoted, particularly in the large-scale industrial roasting of pistachios, by the effects of waste heat from the actual roasting process. Since multiplication only stops above a pH value of 9, the addition of normal amounts of salt does not prevent the multiplication of Salmonella in pistachios as a result of the salting process.

The proliferation of Salmonella in the pistachios is further facilitated by the fact that an unheated intermediate bunker is typically installed at the inlet of a belt roaster. The purpose of this intermediate bunker is to convert the concentrated, point-like product discharge of the rotating coater into a linear discharge, which ensures uniform feeding of the mesh belt across its entire width. Such intermediate bunkers, especially unheated ones, are problematic because the theoretical average residence time of the moistened pistachios in the bunker is significant compared to the aforementioned 20-minute splitting time of Salmonella, thus greatly facilitating the spread of Salmonella contamination. Considering that, due to short-circuit effects, there are partial quantities in a vertical plane above the bunker outlet whose residence time is very short, it becomes clear that, to balance the flow balance, there must also be zones in the bunker where partial quantities remain for significantly longer periods, for example, in the corners. This means that in these delayed partial quantities, the salmonella contamination can increase dramatically.

The risk of uncontrolled proliferation of Salmonella in moistened pistachios is also particularly acute in transient operating conditions of the roasting plant. in which the occupancy of the plant does not remain constant, but increases or decreases. On the one hand, this can be due to machine malfunctions in the roaster, which result in moistened pistachios remaining in the storage bunker for significantly longer than during regular operation, in which the occupancy remains constant and which is referred to here as the steady state. But planned operational interruptions, such as a lunch break, also result in moistened pistachios remaining for a longer period before they are roasted. Transitional processes such as starting up the plant after a shutdown, for example the day after a weekend or an interruption in operations, or running the plant empty for a change of order, can lead to the residence time of moistened pistachios before roasting increasing significantly compared to the average values of normal, dynamic operation.

The relatively low frequency of Salmonella detections in roasted pistachios compared to the quantity produced is a strong indication that the survival of Salmonella in the roasting process is related to unsteady plant conditions or transient processes, since these only affect a small fraction of the finished product.

It is therefore clear that Salmonella contamination of the interior of a pistachio cannot be reliably eliminated by conventional roasting methods. In particular, Salmonella that has colonized skin particles that have detached from the kernel during or before the roasting process are, in individual cases, so protected from heat transfer by convection or conduction that they have a realistic chance of survival relevant to potential contamination.

In the inventor's opinion, and contrary to the accepted state of the art, the addition of brine does not improve the killing reliability, but rather creates another problem. While it is true that added water or brine can improve heat conduction or heat transfer, it cannot be guaranteed that the inside of a pistachio will be completely wetted by the brine, meaning that the The entire inside of the shell, the entire skin, whether loosely wedged in the shell or attached to the kernel, and all other exposed areas of the kernel. The aforementioned uneven salting demonstrates this. The current state of the art overlooks the fact that the evaporation energy absorbed by the added liquid during the roasting process is relevant to the heat capacity of the pistachios' shell and kernel. This unintentionally introduces highly effective evaporative cooling into the process, which also has an uneven effect. This significantly impairs the reproducibility of the heating process and significantly increases the chance of survival of bacterial colonization.

To reliably eliminate Salmonella from in-shell pistachios, it could be considered to add a separate process step prior to roasting pistachios, allowing for the reliable destruction of Salmonella through a separate pasteurization process. However, due to the problem of the open shell, pistachios cannot be pasteurized with sufficient safety using processes known for pasteurizing nuts and nut products, or at least not with a reasonable level of effort.

The following basic procedures are known for the separate pasteurization of nuts:

It is known to heat nuts or nut kernels inside a spiral-shaped stainless steel tube conveyor through which an electric current flows. This is an electrical resistance heating system. Such systems are manufactured, for example, by Revtech Process Systems. The systems are open at the inlet and outlet, so that atmospheric pressure is generally present inside. Heat transfer from the heated tube conveyor to the treated nut occurs through thermal conduction, so that the problems described above using the example of hot air roasting can be transferred via the thermal conduction conditions inside the pistachio. The addition of water or steam in certain sections of the tube does not fundamentally change this. The same considerations apply here that were made in connection with the addition of brine. In the case of pistachios, the situation is further complicated by Another factor is that the contact surfaces between the shell and the pipe wall are predominantly point-shaped, making heat transfer difficult. These systems are very well suited for pasteurizing nut kernels, but not for pasteurizing pistachios.

Also known are systems that use wet steam as a heat transfer medium. To lower the boiling point of the wet steam and thus prevent undesirable changes in the nuts, some designs of these systems create a vacuum. Therefore, the treatment chambers in these cases must be pressure-resistant, which significantly increases the cost of these systems. These system concepts also offer the option of alternately drawing a vacuum and then refilling the vacuum with wet steam. These long-wave pulsations of the chamber pressure can positively influence the penetration of the material being treated. Pasteurization processes using such methods typically last several hours, and for large chambers, up to a day or longer. Such machines are offered by the companies Napasol and H2OExpress. It seems possible that such systems could also kill salmonella in pistachios with a high degree of reliability, especially if the process time is significantly extended and the degree of evacuation is significantly increased. Furthermore, the number of cycles between evacuation and steaming can, of course, be increased. However, such processes are too expensive for the large-scale industrial pasteurization of in-shell pistachios. Further complicating the problem is the fact that in-shell pistachios have a lower density than nut kernels, so the utilization of the vacuum chamber in terms of mass throughput is correspondingly low.

The use of microwaves for food pasteurization is also considered state-of-the-art. However, these are rarely used in the large-scale processing of nuts, seeds, and nut kernels due to the high investment volume relative to the processing capacity and the inherent radiation protection concerns.

In most cases, the complete destruction of a Salmonella colonization of a food is not possible without exposing it to excessive energy input to destroy or at least noticeably reduce its enjoyment value. According to the current state of the discussion, for pragmatic reasons, a kill rate of 10Exp4, which is a reduction by a factor of 10,000, colloquially referred to as "10g4", or 10Exp5, which is a reduction by a factor of 100,000, colloquially referred to as "10g5", is considered sufficiently safe. In the USA, the pasteurization of almond kernels with a safety factor of 10g5 is legally required. Pasteurization of pistachios is legally required there with a safety factor of 10g4. By setting lower legal requirements for pistachios, the American legislature accepts the fact that pistachios should be pasteurized and that this is more difficult to achieve than the pasteurization of nut kernels. An improvement in pasteurization compared to the state of the art is therefore fundamentally desirable.

Based on the above-assumed contamination of 20,000 Salmonella-infected pistachios per hour in a conventional roaster, a reduction rate of 10g4 would theoretically mean that at least 2 contaminated nuts would pass through the process alive. This is a theoretical model calculation to clarify the relationships. The inventor is aware that the prevalence, i.e. the rate at which Salmonella is found before or after a process step, theoretically says nothing about the infectivity of a Salmonella colonization, because the concentration of Salmonella contamination in the food also plays a very large role in the severity of the disease course of a Salmonella infection. Healthy people can survive an infection with a small amount of Salmonella without problems, sometimes even unnoticed. Older and sick people are at a much higher risk. Ideally, reducing the concentration of a given Salmonella contamination is more important than reducing the number of Salmonella nests. On the other hand, food contaminated with salmonella is generally withdrawn from circulation by German food authorities, regardless of the level of contamination. From both ethical and economic points of view, any improvement in the pasteurization of pistachios compared to the state of the art is highly desirable.

The present invention therefore aims to develop a reliable, cost-effective process for the treatment, including roasting, of in-shell pistachios in industrial mass production that significantly reduces the survival rate of Salmonella, or even completely eliminates it. Furthermore, a robust method for validating the successful killing of Salmonella should be provided that allows the identification and elimination of the influence of random factors.

This object is initially achieved by a method for treating in-shell pistachios with the features of patent claim 1. Advantageous developments of such a method are specified in claims 2 to 11. A solution to the further object is provided by a method for checking the kill rate of a method for treating in-shell pistachios for salmonella control, as defined in claim 12. A possible development of such a method is specified in claim 13.

According to the invention, a method for treating in-shell pistachios, i.e., pistachios containing a kernel enclosed in a shell, generally comprises the following steps: a. Wetting the pistachios with water, which can be conventional water or water with a proportion of table salt, i.e., a brine. b. Heating the wetted pistachios for pasteurization and/or roasting.

According to the invention, one or more of the following steps are carried out: I. The pistachios are treated with ultrasound during wetting with water, in particular brine, and/or afterward.

II. The heating of the wetted pistachios comprises a step of heating the pistachios in a flat, preferably single-layered, spread-out bed by irradiation with short-wave infrared radiation with a wavelength of X< 1.4 /m, in particular with a wavelength X of 1.2 /m <X< 1.4 /m.

III. Heating involves shock heating of the pistachios using hot air at a temperature of 300-600°C for a period of 10 to 60 seconds.

The inventor discovered in experiments that even pistachios immersed in water or brine trap air bubbles between the shell and kernel. The inventor further discovered in experiments that the volume of trapped air can be significantly reduced by the action of ultrasound. Reducing the volume of trapped air reduces the variance of subsequent process steps, making them more consistent and manageable. This allows for complete wetting of the kernel of the pistachios and also the surrounding shell and skin with the liquid, i.e., the pure water or brine. This leads to improved thermal conductivity due to the liquid. This effect then offsets and exceeds the evaporative cooling that occurs during subsequent heating and evaporation of the liquid.

In further experiments, the inventor also discovered that the comparatively light shell of pistachios can be penetrated by short-wave infrared radiation (IR radiation) with a wavelength X < 1.4 /m, in particular a wavelength X of 1.2 /m < A < 1.4 /m, which therefore penetrates to the kernel, where it is absorbed by the kernel itself or by the kernel membrane. In this way, the interior of the pistachio can be reliably heated, particularly if the pistachios are distributed within the effective field of corresponding IR radiation during the exposure time in such a way that they do not lie on top of one another, thus preventing any fruit from being shaded. Finally, the inventor has also determined in experiments that the pasteurization effect of a known infrared rotary kiln machine is largely based on heat conduction within the product being treated. Adding water, which wets the surface of the product being treated, promotes heat conduction within the product roller. Furthermore, the inventor has determined in experiments that the improvement in heat conduction from one piece to another in the product roller by adding water, particularly with spherical products, is based on the fact that added water significantly increases the point contact area by several orders of magnitude due to capillary effects. It is this increase in the contact area, i.e., the conduction cross-section, that significantly improves heat conduction. Commonly claimed effects such as the influence of water vapor, which forms when added water evaporates, or the assumption that adding water significantly reduces heat transfer resistance, are significantly less significant than previously assumed when the product being treated has a spherical shape. As already described above, due to the uneven penetration of water into the fruit, the addition of water to pistachios does not result in a reproducible improvement in heat conduction in such a way that the entire fruit is sufficiently warmed throughout.

With respect to the known infrared rotary kiln processes, the IR radiation within the product roller does not affect the product being treated due to the shadowing provided by the topmost product layer. The inventor has determined in experiments that, at practical tube lengths and process durations, the probability of a single pistachio remaining in the product is not sufficiently high to allow sufficient radiation to penetrate through the shell into the interior of the fruit to reliably kill salmonella.

Furthermore, the inventor was able to determine in experiments that, contrary to popular belief, pistachios can be exposed to significantly hotter air for a short time without being damaged, especially when this superheated air is extremely turbulent and acts in a very strong airflow. Under suitable conditions, pistachios can be exposed to hotter air for a period of 15 to 60 minutes. Seconds at air temperatures of 300 to 600°C. This type of treatment is particularly suitable for fluidized bed applications. Due to the high temperature difference between the heat transfer medium and the material being treated, as well as significant turbulence, the likelihood of Salmonella successfully transitioning into a more heat-resistant dormant state can be significantly reduced.

Only one of the proposed specific treatment steps can be undertaken. However, two or all of the steps can also be combined to further improve the reduction of Salmonella load. In the inventor's opinion, due to the complexity of bacterial colonization of pistachios, it may be particularly advantageous to achieve the elimination of Salmonella contamination not through a single one of the measures proposed above, but rather to achieve a synergistic interaction by utilizing two or more of the approaches mentioned. This can further help ensure food safety within the typically required range of Iog4 or Iog5.

Furthermore, the water, especially the brine, can be preheated to a temperature above 60°C, preferably between 75 and 98°C, before being applied to the pistachios. This can be done partially or completely using waste heat from a downstream roasting process, for example, using an air-source heat pump or a heat exchanger. Bringing the liquid used to coat the pistachios to such a temperature already ensures that a temperature level at which salmonella preferentially spreads and multiplies is exceeded. In particular, initial effects of killing germs can already be achieved.

Advantageously, the pistachios moistened with water, in particular with brine, are then kept at a temperature of above 60°C, in particular above 65°C, preferably 70-90°C, after wetting and until subsequent heating. Such warming of the brine- or water-coated pistachios at temperatures above 60°C, in particular 65°C, preferably between 70 and 90°C, during the subsequent treatment until heating, i.e., in particular in a mixing device, on transport equipment, and in the holding bunker, i.e., maintaining the temperature from the beginning of the addition of water or brine until, in particular, the start of the roasting process, ensures that a temperature that promotes the proliferation of salmonella is not maintained during the further treatment process. Here, too, the heat required for warming can be obtained partially or even entirely by utilizing waste heat from a downstream roasting process, for example, using an air-source heat pump or a heat exchanger.

During the wetting process, the pistachios can also be heated with short-wave IR radiation with a wavelength of X < 1.4 /m and an energy input of preferably 0.1 to 0.2 kWh per kg of treated product, in particular to a temperature above 60°C, especially above 65°C, preferably between 70 and 90°C. This can be done, for example, in a rotary kiln. This measure also serves to create an environment unfavorable for Salmonella proliferation.

Wetting the pistachios with water or brine can be done in a conventional and known manner in a rotary kiln. However, it can also advantageously be done by immersion, particularly in a flooded raw material conveyor. If necessary, excess brine must be removed after such an immersion process, which can be achieved, for example, on screen conveyors by shaking or using centrifuges. An ultrasonic treatment advantageous according to this invention can be combined with both the known rotary kiln process and the immersion process proposed here.

The pistachios can be heated by means of short-wave infrared radiation, in particular before a roasting process carried out by further heating, wherein the short-wave infrared radiation is then preferably introduced with an energy quantity of 0.15-0.3 kWh/kg, preferably 0.185-0.22 kWh/kg, related to the mass of the pistachios. If necessary, one or more Several turning operations can be performed during the heating process. Ideally, however, the pistachios should be distributed so that the layer thickness is one pistachio height, so that no fruit overlaps and shadows each other.

Pistachios can also be roasted using infrared radiation. However, they can also be roasted using an additional or alternative heat treatment in a mesh belt roaster. If the pistachios are roasted using hot air in a mesh belt roaster, it is advantageous to apply a possible shock heating of the pistachios using hot air at a temperature of 300-600°C for a period of 10 to 60 seconds during roasting in the mesh belt roaster.

Shock heating of the pistachios for 10 to 60 seconds in very hot air at an exposure temperature of 300-600°C can preferably be carried out with very turbulent air, in particular, but not exclusively, in a fluidized bed reactor.

During roasting in a mesh belt roaster, the pistachios can be turned by turning elements installed in the mesh belt roaster, which can particularly be ploughshare-shaped turning elements, to compensate for uneven airflow. The ploughshare-shaped turning elements should be designed and arranged in such a way that 50% of the layer thickness remains undisturbed at the point of exposure, thus preventing any break-throughs for the hot air and maintaining a constant pre-pressure in the ventilation system. The number, penetration depth, and arrangement of the turning elements are advantageously staggered so that the pistachios are completely turned at least once in a single pass.

During the heating of the pistachios, steam, particularly in the form of saturated steam, superheated steam or hot steam, can advantageously be introduced, e.g. via steam injection into a process chamber. Another aspect of the invention is an improvement in the inoculation of reference material with a bacterial suspension for challenge tests to validate the kill rate of a process.

The validation of the kill rate of a process for nuts and nut kernels is usually carried out according to the state of the art as follows, through so-called challenge tests:

Preparation/cultivation of a representative but non-pathogenic strain of Salmonella for inoculation, adjusted to achieve a suitable microbial concentration of approximately 10 ⁶ CFU/g on the product. Then, inoculation of a product sample, e.g., a quantity of approximately 2 kg, with a microbial suspension at a suitable microbial concentration by wetting or immersion. The inoculated sample is then passed through the process to be evaluated in such a way that it can subsequently be clearly identified and separated. The separated sample is examined for the extent of any surviving microbial contamination.

This state-of-the-art procedure suffers from the same methodological weakness with regard to potential transfer to in-shell pistachios as brine salting: namely, the penetration of the liquid into the opened shell cannot occur in a reproducible manner, so it cannot be ensured that the entire interior of the fruit has been inoculated during the product sample. This does not ensure that the challenge test simulates the worst-case scenario.

To minimize this problem, the wetting of the interior of the pistachio can also be improved by using ultrasound. An alternative possibility for achieving a very significant improvement is achieved by immersing the pistachios in the inoculation solution in a suitable, pressure-resistant container and then applying negative pressure to the interior of the container and then bringing it back to normal pressure. For immersion in the inoculation solution, the pistachios can conveniently be immersed using a grid. The pistachios are then particularly below the surface of the liquid level. The container is closed, and, as mentioned, a vacuum is applied. This causes the trapped air bubbles to expand and therefore protrude from the shells. The effect can be enhanced by repeating this treatment several times, if necessary with a rearrangement or mixing of the pistachios between each treatment. Ideally, the vacuum container is transparent so that it can be observed whether bubbles are released or whether the inoculation has been successfully completed.

Claims

Claims 1 . A method for treating in-shell pistachios, i.e. pistachios containing a kernel enclosed in a shell, comprising the following steps: a. Wetting the pistachios with water, in particular with a brine, b. Heating the wetted pistachios for a pasteurization and/or for a roasting process, wherein the pistachios are treated with ultrasound during the wetting with water, in particular the brine, and/or subsequently thereto and/or wherein the heating of the wetted pistachios comprises a step of heating the pistachios in a flat, preferably single-layered, spread-out bed by irradiation with short-wave infrared radiation with a wavelength of X< 1.4 /m, in particular with a wavelength X of 1.2 /m < X < 1.4 /m, and/or wherein the heating comprises a shock-like heating of the pistachios by means of hot air with a temperature of 300-600°C for a period of 10 to 60 seconds. 2. Process according to claim 1, characterized in that the water, in particular the brine, is preheated to a temperature above 60°C, preferably 75-98°C, before being applied to the pistachio. 3. Process according to claim 2, characterized in that the pistachios moistened with water, in particular with brine, are kept at a temperature of above 60°C, in particular above 65°C, preferably of 70-90°C, after wetting and until subsequent heating. 4. Method according to one of the preceding claims, characterized in that the pistachios are heated during wetting with short-wave IR radiation with a wavelength of X< 1 .4 /m and preferably with an energy input of 0.1 to 0.2 kWh per kg of treated material, in particular to a temperature of above 60°C, in particular above 65°C, preferably of 70-90°C. 5. Method according to one of the preceding claims, characterized in that the wetting of the pistachios with water, in particular brine, takes place by a dipping process, in particular in a flooded raw conveyor. 6. Process according to claim 5, characterized in that after the immersion process, excess brine is separated, in particular by shaking on one or more sieve conveyors or by centrifuging. 7. Method according to one of the preceding claims, characterized in that the pistachios are heated by means of short-wave infrared radiation before a roasting process carried out by further heating, the short-wave infrared radiation being introduced with an energy quantity of 0.15-0.3 kWh/kg, preferably 0.185-0.22 kWh/kg, related to the mass of the pistachios. 8. A method according to claim 7, characterized in that the pistachios are turned in one or more turning operations during heating with the short-wave infrared radiation. 9. Method according to one of the preceding claims, characterized in that roasting of the pistachios takes place by introduction of hot air and in a mesh belt roaster, wherein a possible shock heating of the pistachios by means of hot air at a temperature of 300-600°C for a period of 10 to 60 seconds takes place during roasting in the mesh belt roaster. 10. The method according to claim 9, characterized in that during roasting in the mesh belt roaster, the pistachios are turned by turning elements introduced into the mesh belt roaster, in particular ploughshare-like turning elements of this type, in order to compensate for irregularities in the air flow. 1 1. Method according to one of the preceding claims, characterized in that steam, in particular in the form of saturated steam, superheated steam or hot steam, is introduced during the heating of the pistachios. 12. A method for testing the kill rate of a method for treating in-shell pistachios, i.e. pistachios containing a kernel enclosed in a shell, for killing Salmonella, in particular a method for treating in-shell pistachios according to one of the preceding claims, comprising the following steps: i. preparing and/or culturing a representative, but non-pathogenic strain of Salmonella for inoculating a test batch of in-shell pistachios, ii. selecting an amount of Salmonella to achieve a suitable germ concentration of approximately 10 ⁶ CFU/g in the test batch and introducing this into a germ suspension, iii. inoculating the test batch with a germ suspension at the suitable germ concentration by wetting or immersion, iv. Carrying out the method for treating in-shell pistachios on the test batch in such a way that the pistachios of the test batch can be clearly identified and separated after undergoing the treatment, v. Examining the separated treated test batch for the extent of any surviving contamination, characterized in that the pistachios inoculated with the germ suspension are subjected to an ultrasound treatment and/or that the pistachios inoculated with the germ suspension are immersed in the inoculation solution in a pressure-resistant vessel and held below the surface of the liquid level and the vessel is then closed, wherein a negative pressure is applied in the interior of the vessel and after a holding time the interior of the vessel is brought back to normal pressure. 13. The method according to claim 12, characterized in that the application of a negative pressure and bringing it to normal pressure is carried out repeatedly in stages, optionally with a rearrangement or mixing of the pistachios between the treatment stages.