EP3569932B1 - Method for low-temperature cooking of food products - Google Patents

Description

The invention relates to a method for low-temperature cooking of food.

It is well known that food can be cooked at low temperatures, that is, at temperatures slightly above the target core temperature of the finished food. Such methods are very gentle on the food and result in a cooking product of very high quality in terms of sensory properties.

The disadvantage of low-temperature cooking, however, is that the finished food is not optimal in terms of food safety. Unlike foods that are seared, boiled or cooked in superheated steam at very high temperatures, low-temperature cooking may not completely kill off any germs. Certain important germs are killed from 49°C, but not all. In addition, a very long holding time is required for sufficient germ inactivation. Therefore, low-temperature cooked foods are not safe for risk groups (e.g. elderly or sick people and children). In addition, foods cooked at low temperatures often only have a short shelf life.

the EP 2 537 418 A1 discloses a method for cooking food in a cooking appliance without the cooking chamber temperature having to be very high. The cooking process can be divided into a food temperature control phase and a high-temperature phase. During the cooking process, a cooking chamber temperature should not exceed a limit temperature TLIM, which is at most 20° above the final temperature of the food to be cooked.

the DE 10 2013 218 785 A1 describes a method of cooking food that takes place at a relatively low temperature of, for example, 55°C to 65°C. A controller can use stored values or algorithms to calculate the required cooking time. After the cooking time has elapsed, the power can be reduced by at least 5% to 25%.

The object of the invention is to create a method for low-temperature cooking of food, with which the food can also be cooked in commercial applications (e.g. in restaurants, canteens and large catering establishments) in such a way that it is impeccable in terms of food safety , have a longer shelf life and still have a high sensory quality.

To solve this problem, a method according to claim 1 is provided according to the invention.

The method according to the invention combines two measures in order to obtain a foodstuff during low-temperature cooking that is impeccable from a food-technical point of view. On the one hand, a maximum duration of the cooking phase is specified. The cooking phase is particularly critical with regard to food safety, since the food passes through a critical temperature range during cooking, in which the majority of germ multiplication takes place. According to the invention, it is ensured that the cooking phase does not last longer than can be tolerated, taking food safety requirements into account. On the other hand, a pasteurization phase is provided according to the invention, with which any germs are reduced to such an extent that the food is safe even for risk groups and can be stored for a certain period of time. Here, use is made of the finding that a longer holding time, even at comparatively low temperatures, kills germs.

According to the invention, the control module calculates a minimum duration of the pasteurization phase. This minimum time may depend on the food being cooked and the core temperature of the finished food.

The parameters relevant to the cooking time, in particular the geometric shape that is used to calculate the temperature profile of the cooking process, can in particular be the diameter of the food and/or the size. These are, in particular, those parameters which, with regard to heat conduction, are relevant for when a specified core temperature is reached in the center of a specific food.

The possible geometric shapes can be classified into groups, with the detected geometric shape being classified into one of the groups. This reduces the effort involved in calculating the temperature profile of the cooking process. The geometric shape of the food can, for example, be assigned to the groups plate, cylinder or sphere, with the cross-section of the food to be cooked being taken into account here in particular. In the case of the thickness of the food, for example, the different groups can represent a distinction between small, medium and large.

According to the invention, the duration of the cooking phase is determined using the following formula: $$\mathrm{t}=\mathrm{a}\ast \ln \left(\mathrm{GT}-{\mathrm{T}}_0\right)\ast {\left(\mathrm{bx}\right)}^2$$

t:

Garzeit [Minuten]

a:

empirisch ermittelter Faktor der Garzeit pro Temperaturdifferenz und Fläche [s/(In(°C) ∗ cm²]
Dieser Faktor ist abhängig von der Temperaturdifferenz zwischen der Garraumtemperatur und der Soll-Kerntemperatur und dem Verhältnis aus Breite und Dicke (B/D) des zu garenden Nahrungsmittels. Dieser Faktor wird für die einzelnen Produktgruppen definiert.

GT:

Garraumtemperatur [°C]
In der Regel beträgt GT gleich der Soll-Kerntemperatur plus 2 °C. Diese Differenz zwischen der Garraumtemperatur und der Soll-Kerntemperatur kann dann höher gewählt werden, wenn andernfalls nicht innerhalb der vorgegebenen Maximaldauer die Soll-Kerntemperatur erreicht werden kann.

T0:

Ausgangstemperatur [°C]
Hier kann aus Gründen der Vereinfachung stets von T₀ gleich 0 °C ausgegangen werden.

b:

empirisch ermittelter Faktor, der repräsentativ für die Formänderung des zu garenden Nahrungsmittels während des Garprozesses ist. Er ist abhängig von der Soll-Kerntemperatur und von der Produktkategorie, da sich manche Lebensmittel (insbesondere Fleischsorten) mehr verändern als andere. Dieser Faktor wird insbesondere bei im Ganzen gegartem Roastbeef benötigt, das auf eine Kerntemperatur größer 60 °C gegart werden soll.

x:

charakteristische Länge, also kürzeste Strecke zum Schwerpunkt des Produkts. Bei einem zylindrischen oder kugelförmigen Nahrungsmittel entspricht x der halben Dicke oder des halben Durchmessers; bei einem quaderförmigen Produkt entspricht x der Hälfte der Dicke.

There are:

t:

Cooking time [minutes]

a:

empirically determined factor of the cooking time per temperature difference and area [s/(In(°C) ∗ cm ² ]
This factor depends on the temperature difference between the cooking chamber temperature and the target core temperature and the ratio of width and thickness (B/D) of the food to be cooked. This factor is defined for the individual product groups.

GT:

Cooking chamber temperature [°C]
Typically, GT is equal to the target core temperature plus 2°C. This difference between the cooking chamber temperature and the target core temperature can then be selected to be higher if the target core temperature cannot otherwise be reached within the specified maximum period.

T0:

Initial temperature [°C]
For reasons of simplification, T ₀ can always be assumed to be 0 °C.

b:

empirically determined factor that is representative of the change in shape of the food to be cooked during the cooking process. It depends on the target core temperature and the product category, since some foods (particularly types of meat) change more than others. This factor is required in particular for whole roast beef that is to be cooked to a core temperature of more than 60 °C.

x:

characteristic length, i.e. the shortest distance to the center of gravity of the product. For a cylindrical or spherical food, x is half the thickness or half the diameter; for a parallelepipedal product, x is half the thickness.

The method according to the invention uses a maximum temperature during the cooking phase which is no higher than 90°C. The lower the maximum temperature during the cooking phase, the higher the quality of the cooked food. It is therefore advantageous that the maximum temperature is no more than 20 °C above the target core temperature. It is optimal that the maximum temperature during the cooking phase is no more than 2 °C above the target core temperature. It is always assumed here that the specified maximum duration of the cooking phase is maintained with the selected cooking chamber temperature, ie the target core temperature is reached before the specified maximum duration is reached.

According to an advantageous embodiment of the method according to the invention, the specified maximum duration is 4 hours. This value is advantageous in terms of food safety and is generally accepted.

According to an advantageous embodiment of the invention, the food is cooked in a steam atmosphere. On the one hand, this has the advantage that there is a high heat input into the food to be cooked. This allows the cooking phase to be kept as short as possible. On the other hand, a steam atmosphere has the advantage that the food does not dry out during the pasteurization phase.

According to the invention, it is provided that the parameter relevant to the cooking time is determined by means of a camera and an image evaluation module. This prevents operating errors. According to the invention, it can also be provided that the parameter relevant to the cooking time is queried using a user interface. This can be done either in addition to recording by means of a camera and image analysis module, for example if an automated assignment is not possible with the desired level of security, or exclusively if the effort for the camera and the image analysis module is to be avoided.

• Figur 1 schematisch ein Gargerät, das beim erfindungsgemäßen Verfahren verwendet wird;
• Figur 2 in einem schematischen Diagramm den Verlauf der Garraumtemperatur und der Kerntemperatur bei einem ersten Ausführungsbeispiel; und
• Figur 3 in einem schematischen Diagramm den Verlauf der Garraumtemperatur und der Kerntemperatur in einem zweiten Ausführungsbeispiel.

The invention is explained below using exemplary embodiments which are illustrated in the accompanying drawings. In these shows:

• figure 1 schematically a cooking appliance that is used in the method according to the invention;
• figure 2 in a schematic diagram the course of the cooking chamber temperature and the core temperature in a first exemplary embodiment; and
• figure 3 in a schematic diagram the course of the cooking chamber temperature and the core temperature in a second embodiment.

In figure 1 a cooking appliance 10 is shown schematically with which the method according to the invention can be carried out. This is a cooking appliance for professional use, especially for restaurants, canteens and large catering establishments.

The cooking appliance has a cooking space 12 in which food can be cooked. A food item 14 which is roast beef is shown here as an example.

In the cooking chamber 12, the food can be cooked in a cooking chamber atmosphere, which is characterized in particular by the temperature and the humidity. In order to set these parameters, the cooking appliance 10 has a heating device 16 and a steam generator 18 . These are controlled by a control device 20 .

The control device 20 also controls the drive motor 22 of a fan wheel 24 with which the circulation speed of the cooking chamber atmosphere in the cooking chamber 12 can be controlled.

The cooking appliance 10 also has a device 26 for detecting at least one parameter of the foodstuff that is relevant to the cooking time. This is a camera. The camera 26 is connected to the control device 20 . A control module 28 is integrated into the control device 20, which can calculate a temperature profile of a cooking process on the basis of the parameter relevant to the cooking time.

The cooking appliance 10 also has a user interface 30, for example a touch-sensitive screen, with which an operator can select a cooking process or also directly enter parameters relevant to the cooking time.

It is assumed below that the piece of roast beef 14 is placed in the cooking chamber 12 and is to be cooked there in a low-temperature cooking process.

When the roast beef 14 is introduced into the cooking space, the size and shape of the piece of meat are recorded. Based on this, the control module calculates the temperature profile with which the piece of roast beef 14 should be cooked best.

It is assumed that a target core temperature of 57 °C should be reached. The control module calculates, for example using the formula given above, that at a cooking chamber temperature of 59° C., the desired target core temperature is reached with a cooking phase that ends at time t ₁ , the cooking phase lasting 3.5 hours. This duration is below a predetermined maximum duration, which is stored in the control device 20 as 4 hours.

In the diagram, the course of the cooking chamber temperature is shown with the solid line and the course of the core temperature in the roast beef 14 with the dashed line.

When the cooking phase is complete, a pasteurization phase starts, during which the core temperature remains essentially unchanged, since the cooking chamber temperature is lowered to the target core temperature on average. The pasteurization phase serves to reduce the contamination with any germs that may be present. The duration of the pasteurization phase can be calculated using the P-value method, for example.

When the precalculated pasteurization time has elapsed (here at time t ₂ ), a user is notified that the food is now fully cooked.

In figure 3 an exemplary embodiment is shown in which the control module 28 recognizes that when using a cooking chamber temperature which is only slightly above the target core temperature, the cooking phase would exceed the stored maximum duration. This can be due in particular to the fact that the roast beef 14 has too large a diameter. For this reason, a cooking chamber temperature that is 10 °C higher than in in is selected for the cooking phase figure 2 shown embodiment. This ensures that the core temperature of the roast beef 14 has reached the desired value of 57° C. at a point in time t ₁ , which is a maximum of 4 hours after the start of the cooking process. The cooking phase is followed by a pasteurization phase, during which the cooking chamber temperature is lowered to 57 °C so that the core temperature no longer increases, or at most only increases insignificantly.

Again, the operator is notified as soon as the pasteurization phase is complete.

Claims (6)

1. A method of low-temperature cooking of food by means of the following steps:

   - introducing the food to be cooked into a cooking chamber, wherein the food is detected and wherein cooking time-relevant parameters, in particular a geometric shape of the food, are detected by means of a camera and an image evaluation module or are queried by means of an operator interface;

   - calculating, by a control module, a temperature profile of a cooking process including a cooking phase and a pasteurization phase on the basis of the geometric shape, wherein a predefined maximum duration of the cooking phase is observed, which is a maximum of four hours, and wherein the cooking chamber temperature is lowered on average to the target core temperature during the pasteurization phase;

   - determining the duration of the cooking phase using the following formula: $$\mathrm{t}=\mathrm{a}*\ln \left(\mathrm{GT}-{\mathrm{T}}_0\right)*{\left(\mathrm{bx}\right)}^2$$

   

   where a is an empirically determined factor of cooking time per temperature difference and surface area, GT is the cooking chamber temperature, T₀ is an initial temperature, b is an empirically determined factor that is representative of a change in shape of the food to be cooked during the cooking process, and x is a characteristic length of the food;

   - calculating, by the control module, a minimum duration of the pasteurization phase as a function of the food to be cooked and of the core temperature of the ready-cooked food;

   - cooking the food using the calculated temperature profile;

   - informing an operator that the cooking process has been completed.
2. The method according to claim 1, characterized in that the geometric shape detected is a diameter and/or the size of the food.
3. The method according to claim 2, characterized in that possible geometric shapes are arranged in groups and in that the geometric shape detected is classified into one of the groups.
4. The method according to any of the preceding claims, characterized in that the maximum temperature during the cooking phase is not higher than 90°C.
5. The method according to claim 4, characterized in that the maximum temperature during the cooking phase is selected to be no higher than 20°C above the target core temperature so as not to exceed the maximum duration of the cooking phase.
6. The method according to claim 5, characterized in that the maximum temperature during the cooking phase is selected to be no higher than 3°C, and in particular no higher than 2°C, above the target core temperature if the resulting duration of the cooking phase does not exceed the predefined maximum duration thereof.

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