Technical Field

The invention relates to food processing technology. More particularly, it is related to a method and a mixer for cooking a food product that comprises starch.

Background Art

Today mixers are widely used in the field of food processing for dissolving, emulsifying or dispersing powder and liquid ingredients into a liquid medium. A benefit of using mixers, such as high shear mixers, is that it is made possible to achieve a food product that is smooth, homogenous and with consistent quality. A wide range of products can be processed in mixers, such as sauces, mayonnaise and recombined milk.

A specific use of mixers involves starch processing, also referred to as starch cooking, starch preparation or starch gelatinization. If starch is used as a thickener in a food product, the starch processing is often one of the first steps in a food processing scheme. For instance, in case a low fat mayonnaise is to be produced, one of the first steps in the process may be to process the starch. If this step is performed in the high shear mixer, starch granules may be fed into the mixer and in the mixer, these are combined with water, heated and subjected to shear such that a smooth mixture of starch and water is formed, by swelling the starch so that a more viscous mixture is obtained.

After the mixture is formed, further ingredients may be added into the mixer such that also further processing steps in preparing the food product is performed in the mixer. Alternatively, after the starch is prepared in the mixer, this may be fed into a tank and transported to another piece of equipment performing the further steps in processing the food product.

Even though it is known to process starch in mixers, there is room for improvement. More particularly, by being able to more precisely control the starch processing, there will be less undercooked and overcooked starch granules, in turn resulting in less starch being needed for obtaining the desired product properties. Reducing food waste has in turn positive effects on both cost efficiency as well as environmental impact. Summary

It is an object of the invention to at least partly overcome one or more of the above-identified limitations of the prior art. In particular, it is an object to provide improved starch processing within the food industry, enabling a smaller amount of starch being required. Another object is to improve energy efficiency when using starch as an ingredient in a food product. Still another object is to provide improved quality of the food product made based on a mixture resulting from the starch processing.

According to a first aspect, it is provided a method for cooking a food product by using a mixer having a vessel at least partially surrounded by a heating jacket, and a steam injector arranged to inject steam into the vessel. The food product comprises starch and the method comprises: providing liquid into the vessel; providing starch into the vessel; mixing the liquid and the starch to form a mixture inside the vessel; heating the mixture for gelatinizing the starch by injecting steam at a first steam flow rate into the vessel during a first period of time until a first set point temperature is reached; heating the mixture for gelatinizing the starch further by feeding a heating medium through the heating jacket during a subsequent, second period of time until a second set point temperature is reached which is higher than the first set point temperature; and during the step of heating by feeding the heating medium through the heating jacket, reducing the injecting of steam at to a second steam flow rate, wherein in the second steam flow rate is 0 to 30% of the first steam flow rate.

Herein, “steam flow rate” should be understood as the mass (or amount) of steam that is injected per unit time. The temperature of the steam is higher than the temperature of the mixture. The steam flow rate is therefore directly related to the rate by which the temperature of the mixture increases, which could be measured e.g. in °C per minute. Thus, reducing the injecting of steam to a second steam flow rate that is 0 to 30% of the first steam flow rate means that the rate by which the mixture’s temperature increases due to steam injection is lower during the heating by feeding the heating medium through the heating jacket, as compared to when steam is injected at the first steam flow rate. Typically, the heating by feeding the heating medium through the heating jacket may comprise heating the mixture such that the rate by which the temperature of the mixture increases due to both jacket heating and steam heating is 0 to 30 % lower compared to the rate by which the temperature of the mixture increased during the heating by injecting steam at the first steam flow rate.

An advantage with heating the starch by using a two-stage approach is that a high quality product can be provided in an energy efficient manner and with low product losses. By rapidly increasing heat during the first stage by using the steam and thereafter, during the second stage, more slowly increasing the temperature by using the heating jacket, a risk of under-cooking as well as a risk of over-cooking starch granules can be lowered while still ensuring a relatively fast cooking time. As an effect of that less starch granules being non-optimally processed, a better yield can be achieved.

The first set point temperature may be within a range of 20-75 % of the second set point temperature. Alternatively, the first set point temperature may be within a range of 20-65 % of the second set point temperature. Alternatively, the first set point temperature may be within a range of 10-64 % of the second set point temperature. The first set point temperature may be within a range of 5-45 °C. The second set point temperature may be within a range of 50-70 °C.

The first period of time may be within a range of 20-50 % of the second period of time. Alternatively, the first period of time may be within a range of 30-50 % of the second period of time. The first period of time may be within a range of 2-10 min. Alternatively, the first period of time may be within a range of 2-8 min. The second period of time may be within a range of 10-30 min.

The heating during the first period of time may comprise increasing the temperature of the mixture by a first rate during the first period of time, and the heating during the second period of time may comprise increasing the temperature of the mixture by a second rate during the second period of time, wherein the second rate may be lower than the first rate.

The second rate may be less than 80 %, less than 60 % or less than 50 % of the first rate. The first rate of increasing the temperature may be within a range of 1-10 °C per minute. The second rate of increasing the temperature may be within a range of 1-5 °C per minute.

The method may further comprise cooling the mixture by decreasing the temperature of the mixture by a third rate during a third period of time, wherein the third rate of decreasing the temperature may be within a range of 1-8 °C per minute.

The method may further comprise subjecting the mixture to a first shear rate during the first period of time by injecting steam into the vessel at the first steam flow rate, and subjecting the mixture to a second shear rate during the second period of time by rotating an agitator and/or using the rotor-stator arrangement located inside the vessel, wherein the second shear rate may be lower than the first shear rate.

According to a second aspect, it is provided a mixer for cooking a food product, said mixer comprising a vessel at least partially surrounded by a heating jacket, a steam injector arranged to inject steam into the vessel, a processor unit and a memory unit that comprises software instructions which when executed by the processor unit cause the mixer to carry out the method according to the first aspect, including all embodiments thereof.

The mixer may further comprise an agitator and/or a rotor-stator arrangement inside the vessel, wherein the steam injector may be arranged to subject the starch to a first shear rate, and the agitator and/or the rotor-stator arrangement may be arranged to subject the starch to a second shear rate.

Still other objectives, features, aspects and advantages of the invention will appear from the following detailed description as well as from the drawings.

Brief Description of the Drawings

Embodiments of the invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which

Fig. 1 is a cross-sectional view of a mixer.

Fig. 2 is a graph illustrating temperature and shear versus time in a method for cooking a food product that comprises starch.

Fig. 3 is a flow chart illustrating a method for cooking a food product that comprises starch.

Detailed Description

With reference to Fig. 1 a mixer 100, such as a high shear mixer, is generally illustrated. The mixer comprises a vessel 102, often made of stainless steel, provided with a heating jacket 104. A liquid, such as water, W can be provided into the vessel 102 via a first inlet 102 and starch STA, e.g. in the form of starch granules or powder, can be provided via a second inlet 108. Even though illustrated that the first and second inlet 106, 108 are placed in a side wall of the vessel 102 in fig. 1, it is also possible to have these inlets placed in a bottom of the vessel 102. To provide for that the starch STA and the liquid W in the vessel 102 may be heated or cooled, a jacket inlet 110 and a jacket outlet 112 are connected to the heating jacket 104 such that a heating medium HM or a cooling medium CM can be fed through the heating jacket 104.

Once the starch STA and the liquid W are combined into a mixture MIX, this may be fed out from the vessel 102 via an outlet 114 in form of a food product FP. The food product FP may be a final food product or may be a food product that may be further processed to thereafter form a final food product that can be consumed by humans. In the latter case the mixture MIX, sometimes referred to as starch phase, may as indicated be transferred to another piece of equipment in which this is combined with other food ingredients and processed into a final food product. In the former case food ingredients may be added into the vessel 102 such that the mixture MIX in combination with the other food ingredients form the final food product inside the mixer 100.

Further, to provide for that the starch STA and the liquid W are heated efficiently when being processed into the mixture MIX, steam STE may be injected into the vessel 102 via one or several steam injectors 116a,b placed in the bottom of the vessel 102.

To provide for that the starch STA and the liquid W are heated efficiently via the heating jacket 104 during the processing, an agitator 118 may be provided. The agitator 118 serves the purpose of mixing the starch STA and liquid W thereby resulting in that different parts of mixture MIX are subjected to heat exerted from the heating jacket 104 such that even heat distribution can be provided, but also that the starch STA and liquid W are subjected to a shear. By being subjected to a shear, properties of starch STA are affected and as an effect, a more efficient mixing can be achieved.

As illustrated, it is further possible to have a rotor-stator arrangement 120 placed in the bottom of the vessel 102. This arrangement also serves the purpose of subjecting the starch STA and liquid Wto shear, resulting in that the mixing is made efficiently.

To control the operation of the mixer 100, a control unit 122 may be provided. Even though not illustrated, the control unit 122 may be communicatively connected to the different parts of the mixer 100 such that the operation of these parts can be made on individual basis, e.g. the control unit 122 can be arranged to control the steam injectors 116a, 116b, the flow of the media through the heating jacket 104 and the agitator 118 individually. The control unit 122 may comprise a processor unit 124 and a memory unit 126 that comprises software instructions which when executed by the processor unit 124 cause the mixer 100 to carry out the method described herein. Even though not illustrated, temperature sensors may be provided for continuously reporting a temperature of the mixture MIX to the control unit 122.

With reference to Fig. 2, to provide for the starch STA is gelatinized efficiently, that is, providing for that a level of undercooked starch is low and/or that a level of overcooked starch is low, it has been found that a two-stage heating approach is advantageous. In one example, in a first stage performed during a first period of time Ati, starting in an initial point of time t ₀ and extending to a first point of time ti , the steam STE can be injected into the mixture MIX. During this stage heating may be provided via the heating jacket 104 as well. This stage continues until a first set point temperature Ti is reached, i.e. until a temperature of the mixture MIX is increased from an initial temperature To to the first set point temperature Ti. An effect of injecting steam into the mixture MIX is that rapid heating can be achieved. As illustrated, the temperature of the vessel 102 can be increased at a first rate Qi. The first rate cu is the temperature increase per unit time, which could be measured as °C per minute. During this first stage, steam is injected at a first steam flow rate.

Once having reached the first set point temperature Ti and until a second set point temperature T2 is reached, during a second period of time At2, running from the first point of time ti to a second point of time t2, the temperature of the mixture MIX is increased by that the mixture MIX is heated via the heating jacket 104 either in isolation or in combination with that the steam STE is injected via the steam injector 116a, b at a much lower steam flow rate. Thus, during this second period of time At2, the steam STE is injected at a second steam flow rate that is lower than the first steam flow rate, such as 0 to 30% of the first steam flow rate. This means that the stem injection may, in one embodiment, be fully stopped during the second period of time At2. As an effect of lowering or cutting off steam inflow into the vessel 102, a second rate a ₂ , representing temperature increase rate during the second period of time At ₂ , is lower than the first rate Qi.

Each of the first and second set point temperatures Ti, T ₂ may be reached by using both steam and the heating jacket during both periods of time Ati , At2. However, the second rate 02 is lower than the first rate Qi. This is preferably accomplished by injecting steam STE at the second steam flow rate during the second period of time At2, with the second steam flow rate being 0 to 30% of the first steam flow rate which was used during the first period of time Ati.

By using first quicker heating, i.e. a first and higher heating rate cu, and thereafter a second slower heating, i.e. a second and lower heating rate 02, gelatinizing the starch STA can be improved both in terms of quality, i.e. reduced number of undercooked and/or overcooked starch granules, as well as energy efficiency.

During a third period of time At ₃ , running from the second point of time t2 to a third point of time t ₃ , the temperature can be kept at the second set point temperature T2. During this period of time, shear and agitation may be provided via the agitator 118 and/or the rotor-stator arrangement 120.

During a fourth period of time At4, running from the third point of time ts to a fourth point of time t ₄ , the temperature can be lowered at a third rate a ₃ from the second set point temperature T ₂ to a third set point temperature T ₃ . In this cooling phase, the cooling medium CM may be fed into the heating jacket 104. Even though not illustrated, it is also possible to cool down the mixture MIX by using an external device, such as a scraped surface heat exchanger (SSHE), a plate heat exchanger (PHE), or a tubular heat exchanger (THE). The mixture MIX may be fed to this external device and then fed back to the mixer 100 for further processing or the mixture MIX may be fed downstream to other pieces of equipment for further processing. An advantage of having the external device for cooling down the mixture MIX is that a risk of overheating the mixture MIX can be reduced, thereby reducing the risk of overcooking the starch STA, which may in the form of a starch phase or in a starch- thickened condiment sauce, e.g. marinade or barbecue sauce. By being able to reduce the amount of overcooked starch, i.e. by improving the yield of the starch, it is made possible to achieve a high viscous food product from a low amount of starch. In addition to delivering high quality product properties, the improved viscosity also has an effect of shelf life, i.e. the properties of the food product can be maintained for a longer period of time.

As illustrated in Fig. 2, the shear subjected to the mixture MIX is different during different periods of time. In the example illustrated, a first shear rate Pi, illustrated by dotted line, can be provided during the first period of time AU and a second shear rate p ₂ , being less than the first shear rate Pi, can be provided during the second, third and fourth period of time At ₂ , At ₃ , At ₄ . The first shear rate Pi may be at least 50% greater than the second shear rate p ₂ . By adjusting the flow rate of steam STE injected during the second period of time At ₂ , the shear rate can be affected. Further, the shear rate may also be affected by the rotor-stator arrangement 120 and/or the agitator 118. During the fourth period of time A , the shear rate may also be affected by the external device used for cooling the mixture MIX.

Even though the temperatures and periods of time may be different for different mixtures MIX, and in turn different food products, it has been found that the first set point temperature Ti may be within a range of 20-75 % of the second set point temperature T ₂ . Further, it has been found that the first set point temperature Ti can be within a range of 5-45 °C. The second set point temperature T ₂ may be within a range of 50-70 °C. Regarding the periods of times being used, the first period of time AU may be within a range of 20-50 % of the second period of time At ₂ . The first period of time AU may be within a range of 2-10 min. The second period of time may be within a range of 10-30 min. Regarding the first, second and third rates ai, a ₂ , a ₃ , these may also vary for different food products, but it has been found beneficial to have the second rate a ₂ is 80 % of the first rate Qi or lower. The first rate Qi of increasing the temperature may be within a range of 1-10 °C per minute. The second rate of increasing the temperature may be within a range of 1-5 °C per minute. These values applies for most starch types commonly used in food products.

In practical applications the rates Qi, 02, 03 may not always be as linear as illustrated in Fig. 2. Instead they may look more like one of the lines illustrated by dashed lines I and II.

By being able to control the heating, the shear rate and also the cooling as described above, it is made possible to achieve a high yield during starch processing, which may be 10% or less under-cooked starch granules, at least 80% properly cooked starch granules, and 10% or less over-cooked starch granules.

Fig. 3 is a flowchart illustrating a method 200 for cooking a food product which includes gelatinizing starch STA by using the mixer 100 illustrated in fig. 1. As illustrated, in a first step 202, the liquid W can be provided into the vessel 102 via the first inlet 106. In parallel, before or after, in a second step 204, the starch STA can be provided via the second inlet 108. After having received the liquid W and the starch STA, in a third step 206, the liquid W and the starch STA can be mixed into the mixture MIX. In a fourth step 208, the mixture MIX can be heated by the steam STE injected into the vessel 102. After being heated by the steam STE, in a fifth step 210, the mixture MIX can be heated by using the heating jacket 104. As described above, the steam STE may also be injected during the fifth step 210, but at a lower steam flow rate compared to the fourth step 208.

In line with the graph presented in Fig. 2, the fifth step 210 may be followed by a sixth step 212 in which the mixture MIX is cooled. The cooling may be provided by that the cooling medium is fed through the heating jacket 104, but it is also possible, as described above, to cool down the mixture MIX via the external device.

In parallel with the fourth step 208, the mixture MIX may be subjected to the first shear rate Pi in a seventh step 214. This first shear rate Pi may be formed by the steam STE injected via the steam injector 116a,b.

In parallel with the fifth step 210, while the mixture MIX is heated via the heating medium HM fed through the heating jacket 104, the mixture MIX may be subjected to a second shear rate P2 in an eighth step 216. The shear in this step may be generated by the agitator 118 and/or the rotor-stator arrangement 120. The shear may also be generated, in combination with the agitator 118 and/or the rotor-stator arrangement 120, by the steam STE injected via the steam injectors 116a, b, but the second steam flow rate used during this eighth step is lower than the first steam flow rate used during the seventh step 214. From the description above follows that, although various embodiments of the invention have been described and shown, the invention is not restricted thereto, but may also be embodied in other ways within the scope of the subject-matter defined in the following claims.