The present invention relates to a method and system for freeze-drying batches of solid frozen protein rich food products in the industrial scale production of freeze-dried protein rich food, such as insects, shrimps, diced meat, in particular of red meat or poultry or diced tofu.

Freeze drying is a method of dehydration, the removal of water, by sublimation of solid frozen water, i.e. ice, under high vacuum into water vapour. Freeze-drying works by freezing a water containing material and then reducing the surrounding pressure to allow the frozen water in the material to sublimate directly from the solid phase to the gas phase. For water ice sublimation occurs at pressures below 6.1 mbar and temperatures below 0 °C. This drying method is known for its ability to sustain food quality during drying because of a minimum loss of flavour and aroma, negligible shrinkage and the absence of water, which minimizes the chance of microbial growth. Freeze drying is applied to increase the shelf life of insects. Non-treated dead insects, or defrosted insects will deteriorate quickly, and will go bad/ decay in a few hours. On the other hand, frozen insects are kept well in freezer, e.g. at -18°, for months.

The freeze drying technique is commonly used in the pharmaceutical industry and for the preservation of food. However, it is quite an expensive technique. Alternatives such as conventional air drying or vacuum drying, under low pressure and at a reduced temperature, are commonly preferred.

Freeze-drying requires adequate temperature of the product, ensuring a solid to gas transition and preventing a direct liquid-gas transition. In a first freezing phase of the product, the product is cooled below its triple point: the lowest temperature at which the solid and liquid phases can coexist. This ensures that sublimation rather than melting will occur in the following freeze-drying phase. In a subsequent freeze-drying phase, the pressure is lowered and enough heat is supplied to the product for the ice to sublime into vapour. The supply of too much heat should be prevented as this may result in product deterioration. In this initial drying phase, about 95% of the water in the material is commonly sublimated.

In a preferred subsequent secondary drying phase, unfrozen water molecules are removed, since the ice was removed in the primary drying phase. This part of the freeze-drying process is governed by the material's adsorption isotherms. In this phase, the temperature is raised higher than in the primary drying phase, and can even be above 0 °C, to break any physico-chemical interactions that have formed between the water molecules and the frozen material. Usually the pressure is also kept low in this stage to encourage desorption.

After the freeze-drying process is complete, the vacuum is usually broken with an inert gas, such as nitrogen, before the material is sealed in a packaging container.

At the end of the operation, the final residual water content in the product is commonly extremely low, around 1 % to 5%.

Insects that are used or envisaged for the industrial scale production of protein rich food naturally contain water. In addition thereto, water may be clinging to the insects as a result of a blanching or steaming process, generally up to 7% water, which is often a preferred way of killing the insects. This naturally present water, and possibly also the clinging water is to be removed in a freeze drying method system. It is noted that alternative methods of killing insects, such as by heating and/ or sterilization include irradiation, e.g. by infrared or gamma rays are also envisaged in the context of the present invention. After killing, it is common for the insects to be frozen to prevent product deterioration such as discoloration.

Despite the relatively high costs, freeze-drying is a preferred technique to dry frozen insects, as this technique optimizes the preservation of shape, colour, taste and proteins of insects.

Known systems for freeze-drying batches of frozen insects comprise:

- a drawer adapted to receive a batch of frozen insects to be freeze-dried,

- a vessel having a horizontal longitudinal axis, wherein at least one head end of the vessel is adapted to be opened, such that in an open position the vessel is able to receive the drawer, and which is adapted to be closed into a vacuum-tight closed position by a closure device,

- a vacuum pump in connection with the vessel, to reduce the gas pressure in the vessel and thereby allow frozen water in the batch of frozen insects to sublime into vapour, - a condenser in connection with the vacuum pump, the condenser comprising a chilled surface to collect the sublimed vapour on the surface by deposition into ice,

- a heat source provided in the vessel to supply the energy of sublimation to the frozen insects.

Commonly multiple shallow drawers are provided above one another in the vessel. A disadvantage of such known freeze-drying systems is the relatively low yield: it takes relatively long to dry a relatively small amount of insects. As an example, it has been experienced that drying an amount of 200g of insects in a system for freeze-drying with multiple shallow drawers takes 36 hours.

It is an aim of the present invention to increase the yield of food products that is freeze-dried in a system for freeze-drying batches of solid frozen protein rich food products in the industrial scale production of freeze-dried protein rich food, such as insects, shrimps, diced meat, in particular of red meat or poultry or diced tofu.

According to the present invention, the drawer is embodied as an elongated canister having over at least a majority of its length a canister wall that is open at a part of its circumference in cross-section to define a bottom and an opening at the top, and in that the vessel and the canister are adapted so that the canister is held in the vessel with its longitudinal axis horizontally with the opening upwards.

In embodiments, the vessel is essentially cylindrical and the bottom of the canister is rounded. Preferably, the circumference of the canister in cross-section is semi-circular.

In embodiments, the opening at the top of the canister is provided with a porous cover, e.g. a mesh or gauze, or is embodied as a perforated zone.

According to the present invention, at least one head end of the vessel is adapted to be opened. In the open position, the vessel is able to receive the canister with its longitudinal axis horizontally and with the opening upwards. The head end is adapted to be closed by a closure device into a vacuum-tight closed position such that a vacuum can be established to perform freeze-drying. During freeze-drying, the vessel holds the canister with its

longitudinal axis horizontally and with the opening upwards. In embodiments, the closure device can be a closure plate, adapted to be connected to the head end of the vessel. In an alternative embodiment, the closure device is embodied as a door formed at the head end of the vessel. The volume of a batch of solid frozen protein rich food products to be freeze-dried in such a canister is significantly larger than compared to common shallow drawers. As a result, the costs of freeze-drying of a fixed amount of product in a system according to the invention when compared to the conventional shallow drawers is significantly reduced. Possible dimensions of a canister are 40 +/- 5 cm in diameter, and the length may vary between 60 - 200 cm, advantageously 100 +/- 20 cm. In embodiments, a vessel having dimensions adapted to receive 5-10 shallow drawers may freeze dry a batch of 200-300 g of frozen food products, in particular insects. The same vessel being adapted to receive a canister according to the invention, may freeze dry a batch of 4-5 kg of frozen food products, in particular insects.

According to the present invention the canister is provided with a mechanical mixer comprising at least one mobile blade and a transmission assembly, and a mixer drive motor is provided that connects to the transmission assembly of the canister when received in the vessel, so that operation of the mixer drive motor causes the mobile blade to move and entrain therewith a portion of the batch of frozen food products to increase exposure thereof. An advantageous effect of mixing the batch of frozen food products to be freeze-dried in the canister is that the energy supply of the radiant heat source is distributed more

homogenously over the batch of frozen food products, resulting in a more uniform temperature throughout the entire batch, thus optimizing the freeze-drying process in that it reduces the risk of local undried and wet products and/ or thaw out and optionally deteriorated products. This may attribute to shorten the duration of a successful freeze- drying process. A further effect of mixing the batch of products is that the removal of sublimed water is assisted, as the sublimation surface increases during mixing. This may also attribute to shorten the duration of the freeze-drying process. As an example, it has been experienced that drying a batch of 200-300 g of frozen insects in a system with shallow drawers takes about 36 hours. The same vessel receiving a canister according to the invention with a batch of 4-5 kg of frozen insects and with a mechanical mixer will dry the batch in 20-24 hours. With the system and/ or method of the present invention, the frozen insects are dried to an extent that 2-5%, preferably 2-2,5% water remains in or on the insects. A possible disadvantage of mixing is the risk of damaging the insects, in particular the shape of the insects as it is prone to breaking during the mixing process. The canister of the present invention is held horizontally in the vessel. The effect of a horizontal canister, when compared to a vertical or tilted canister provided with a mechanical mixer, is that it diminishes the risk of breakage.

The system for freeze-drying of the invention comprises a vacuum pump in connection with the vessel, to reduce the ambient gas pressure in the vessel, and thereby allow frozen water to sublime into vapour. The vacuum speeds up the sublimation, making it useful as a drying process. The vacuum is preferably less than 1000 Pa, more preferably less than 20 Pa. In embodiments, the vacuum is maintained at the same level during primary and secondary drying. Optionally, the vacuum is released gradually at the end of the freeze-drying process.

The system for freeze-drying of the invention comprises a condenser in connection with the vacuum pump, the condenser comprising a chilled surface to collect the sublimed vapour on the surface by deposition into ice. The condenser can be embodied as a condenser chamber and/ or condenser plate(s), providing a surface for the water vapour to re-solidify on. The condenser plays no role in keeping the product frozen, rather, it prevents water vapour from reaching the vacuum pump, which could degrade the pumps performance. Condenser temperatures are typically -40°C to -80 °C. Advantageously, the capacity of the capacitor, i.e. the amount of ice that can be collected, matches the amount of water present in or on the food products to be freeze-dried. Advantageously, after freeze-drying, the condenser is cleared of ice that has been collected by the condenser, prior to a subsequent freeze-drying process. Possibly, the condenser is also at an elevated temperature.

As indicated above, freeze-drying requires adequate temperature control. Product deterioration as a result of thawing out at higher temperatures may result in discoloration for particular insects, which is undesired. Furthermore, as the invention is directed to industrial scale production, the optimization of the yield is also desired. Hence, an optimum uniform temperature throughout the entire batch should be aimed for.

According to the present invention, a heat source is provided in the vessel to supply the energy of sublimation to the frozen insects. The heat is brought mainly by conduction or radiation; the convection effect is negligible, due to the low air density. The heat source is preferably a radiant heat source, wherein radiation is e.g. infrared radiation or microwave radiation. In the art, conduction heat sources are known, e.g. providing heat to the walls of the vessel. However, this type of heating has an increased risk of thawing out products. In embodiments, the heat source is provided in an upper part of the vessel, above the position of the canister, to supply the energy of sublimation to the frozen insects.

Advantageously, one or more temperature sensors are provided in vessel, or preferably in the canister, which are in communication with the radiant heat source to provide an input signal based on the actual temperatures. During primary drying, the product temperature is kept below the triple point, in particular below 2°C, preferably between -5 and 0°C, to prevent the ice from melting into water. To keep the product temperature constant, the capacity of the heat source decreases over time as the amount of ice that is to be sublimed decreases. During optional secondary drying, at the end of the freeze-drying process, the temperature of the insects may be allowed to increase up to 10-20°C, while maintaining the vacuum. This is effected by increasing the capacity of the heat source.

In embodiments, the system further comprises a control unit to control the mixer drive motor and thereby the operation, e.g. rotation speed of the mixer, during freeze drying. For example, the applied rotation speed is dependent on the type of insect that is to be freeze dried.

The control unit may comprise an associated computer with a memory in which the rotation speed or a rotation speed profile for different types of food products that are to be freeze- dried is stored. A rotation speed profile enables the control unit to vary the rotation speed of the mixer during freeze-drying. For example, the initial rotation speed may be higher for food products that were frozen with clinging water than for food products with only water that is naturally present therein. The increased rotation speed may assist in the removal of the frozen clinging ice, and because the freeze-dried food products are less prone to breakage just after the freezing step this may be advantageous. It is also conceivable that the rotation speed is allowed to decrease during freeze-drying, as over time and upon increasing temperature the freeze-dried food products are more susceptible to break. Hence, in embodiments the type of insect and the presence of clinging water/ ice is put into the control unit, and on this basis the rotation speed of the mixer drive motor is controlled.

The properties of the mixer are preferably adjusted to optimize mixing of a batch of food products. In particular the type and orientation and number of mobile blades can be set, resulting in a minimum of breaking of the food products, a reduction in the freeze-drying time and a minimum of damaged food products. In embodiments, the system for freeze-drying batches of food products comprises multiple mixers, wherein the type of mixer that is provided in the system for freeze-drying is dependent on the type of insect to be freeze-dried. For example, the mechanical mixer in a canister can be replaced. It is also conceivable that multiple canisters are provided, with distinct mechanical mixers, such that the type of mixer in the system for freeze-drying can be changed upon replacement of a canister.

In embodiments, the mechanical mixer is a rotatable mixer having a longitudinal axle to which mobile blades are connected. Alternatively, the rotatable mixer comprises one or more helical blades. It is conceivable that the mobile blade of the mixer extends in the longitudinal direction, in which case one mobile blade may suffice to result in optimum mixing of the batch of food products.

It is also conceivable that multiple mobile blades, e.g. 2-6 extend essentially adjacent each other in the longitudinal direction. In the radial direction, towards the wall of the canister, in embodiments only one mobile blade is provided. Preferably, 4-6 mobile blades are provided in the radial direction.

In embodiments, the mobile blades are embodied as elongated paddles connected to the longitudinal axle via distance keepers. The elongated paddles have a longitudinal axis. Embodiments are conceivable wherein the longitudinal axis of the paddles extends perpendicular to the longitudinal axle, or in line with the longitudinal axle, or at an angle there between. The type of mixer and mobile blades is insect-dependent. In a preferred embodiment, the four paddles are provided in radial direction, each having a longitudinal axis extending with an angle between -15° and 15° to the longitudinal axle.

Advantageously, an interspace is present between the at least one mobile blade and the canister wall to prevent the food products to break.

The invention also relates to an assembly for freeze-drying batches of solid frozen protein rich food products in the industrial scale production of freeze-dried protein rich food, such as insects, shrimps, diced meat, in particular of red meat or poultry or diced tofu, the assembly comprising:

- a freezer to freeze the food products into batches of frozen food products; - a system for freeze-drying batches of frozen food products as described above and according to claim 1.

The freezer preferably freezes the food products to -15 to -20°C. For a batch of 4,5 kg of insects with clinging water, this may take 12 hours. It is possible to keep batches of food products frozen for months, prior to freeze-drying according to the invention.

The present invention also relates to a method for freeze-drying batches of solid frozen protein rich food products in the industrial scale production of freeze-dried protein rich food, such as insects, shrimps, diced meat, in particular of red meat or poultry or diced tofu, wherein use is made of a system according to claim 1 , comprising the steps of:

- clearing the condenser of ice,

providing a batch of frozen food products into the canister,

- arranging the canister in the vessel,

- closing the closure device of the vessel vacuum-tight,

- essentially simultaneously:

o generating a vacuum in the vessel,

o supplying heat to the frozen food products,

o moving the mobile blade of the mixer to entrain therewith a portion of the batch of insects.

Clearing the condenser of ice after freeze-drying a batch of frozen insects may take e.g. 1 hour. The generation of a vacuum takes about 0,5 hour. Advantageously the vacuum is only applied after the condenser is cleared of ice, and after the condenser has collected vapour present in the system. This way, the possible contamination of the pump by water is prevented. The overall time to freeze-dry a batch of 4-15 kg of frozen insects (amount depending on the type of insect) in a canister according to the invention takes e.g. 15-30 hours (depending on the type of insect). For example, a canister may receive a batch of 6kg of frozen grasshoppers, and the same canister may receive a batch of 15kg frozen buffalos. The weight of a batch of insects may be reduced by 25 - 75% upon freeze-drying, generally to 1/3 of the weight before drying.

The present invention also relates to a method for freeze-drying batches of solid frozen protein rich food products in the industrial scale production of freeze-dried protein rich food, such as insects, shrimps, diced meat, in particular of red meat or poultry or diced tofu, comprising the steps of: - optionally killing the food products, e.g. by heating, freezing or sterilization, e.g. by a water-assisted process such as steaming or blanching as a result of which water is added to the food products,

- freezing the food products,

- batching the frozen food products,

performing the freeze-drying method of claim 10.

It is also conceivable that the food products such as insects are frozen to kill, e.g. by shock- freezing, then possibly stored for hours, days or even up to months, and thereafter blanched prior to freeze-drying.

Known killing techniques for insects include blanching and steaming, which methods result in added clinging water to the insects, generally up to 7% water. Alternative methods of killing insects, not resulting in additional clinging water, include heating and/ or sterilization by radiation, e.g. by infrared or gamma rays. In embodiments, freezing is performed by a separate freezer unit. Alternatively, the step of freezing may be performed in a freeze-drying system.

The invention is further explained in relation to the drawings, in which:

Fig. 1 is a schematical representation of a system for freeze-drying insects according to the present invention;

Fig. 2 is a perspective view of a system for freeze-drying according to the present invention; Fig. 3 is a phase diagram of water;

Fig. 4 is a graphic representation of vacuum, product temperature, capacity heat source and rotation speed of the mixer.

In figs. 1 and 2 a system 1 for freeze-drying batches of frozen insects for industrial scale production of freeze-dried protein rich food according to the present invention is

represented. In fig. 1 the representation is highly schematically, and in fig. 2 a perspective view of a practical embodiment is shown.

The system 1 of fig. 2 comprises four canisters 2, one of which is shown schematically in cross section in fig. 1. The canisters 2 in the shown embodiment have an essentially cylindrical shape with a horizontal longitudinal axis 2c, having a cylinder wall 2a that is open at an upper part 2b of its circumference. The canisters 2 are adapted to receive a batch of frozen insects to be freeze-dried, e.g. 3-15 kg of frozen insects in each canister, the amount being dependent on the type of insect. In figs. 1 and 2, it is visible that the canisters 2 have been received and held by a vessel 3. The vessel of the shown embodiment is a cylindrical vessel. A head end 3b of the vessel 3 is adapted to be closed by a transparent closure plate 6, visible in the right-hand three of the four vessels of fig. 2. In an open position of the vessel 3, as visible in the most left-hand vessel 2 of fig. 2, the vessel 3 is able to receive the canister, as visible in the left-hand vessel of fig. 2. In the three right-hand vessels 2 of fig. 2, the vessels 3 are closed into a vacuum-tight closed position. In the shown embodiments, an elongated rotatable mixer 4 is provided in the canister 2. In the embodiment of fig. 1 , four mobile blades 4a are visible that are rotatable by a mixer drive motor 5 with a rotation speed to mix the insects to be freeze-dried, which mixer has a longitudinal axle 4c here coinciding with the longitudinal axis 2c of the canister 2, and here also with the longitudinal axis 3c of the vessel.

In the embodiment of fig. 2, an alternative type of mixer 40 is visible, comprising a longitudinal axle 40c to which mobile blades 40a are connected which are embodied as elongated paddles, connected to the longitudinal axle via distance keepers 40b. The elongated paddles have a longitudinal axis 40d extending with an angle a of about 10-30° to the longitudinal axle.

In the shown embodiment, a control unit 10 is provided to control the rotation speed of the mixer drive motor 5 and thereby the rotation speed of the mixer 4 during freeze drying.

Advantageously, the control unit 10 comprises a memory 12 in which the rotation speed or a rotation speed profile for different types of insects that are to be freeze-dried is stored. An exemplary rotation speed profile is visible in fig. 4, in which it is visible in the rigid line that the rotation speed is relatively high at the start of the process, and then constant over the remaining time of the freeze-drying process. For example, the rotation speed is 130 revolutions per hour at the start, decreasing during 60 minutes to 60 revolutions per hour, for the remainder of the freeze-drying process.

A vacuum pump 15 is provided, in connection with the vessel 3, to reduce the gas pressure in the vessel 3, and thus in the open-topped canister 2, and thereby allow frozen water to sublime into vapour. In the shown embodiment, the control unit 10 is also adapted to control the vacuum pump 15. In fig. 4, and exemplary vacuum profile is shown in a dashed line. Vacuum is created in the first 30 minutes of the process, and maintained at a constant level of 10 Pa in this example. A vacuum of 10-50 Pa is conceivable. As visible in the phase diagram in fig. 3, sublimation from frozen water ("solid") to vapour ("gas") takes place at temperatures below 273, 2K, i.e. 0°C, and below 0,006atm, i.e. below 610Pa. As the insects are frozen when provided in the canister 2 and in the freeze-drying system 1 , sublimation will occur once the pressure is lowered sufficiently.

The evacuated air from the vessel 3 leaves the vacuum pump to a condenser 16 in connection with the vacuum pump 15, the condenser comprising a chilled surface 16a to collect the sublimed vapour on the surface by deposition into ice. For example, at the start of the freeze-drying process, the condenser temperature is -60°C, which is lowered due to the deposition of condensed ice during freeze drying to a temperature of -70°C to -75°C. This depends on the type of condenser.

In the shown embodiment, the vacuum pump is positioned downstream of the condenser, to prevent water vapour/ ice to enter the vacuum pump. In addition, in the present

embodiment, a filter 17 is provided between the condenser 16 and the vacuum pump 15.

For example, a filter or sieve having openings of 0,2-0,5 mm is provided. Such a filter prevents particles to reach and contaminate the vacuum pump, e.g. the oil of the vacuum pump. Particles may e.g. comprise hairs, parts of skin or wing. With the mixer according to the invention, advantageously more of such particles are transported away from the batch of insects by the vacuum pump, resulting in a more clean batch of insects, without being contaminated by such particles.

Furthermore, a heat source 13 is provided in an upper part 3a of the vessel 3, above the position of the canister 2, to supply the energy of sublimation to the frozen insects. To adequately control the supply of energy, in the shown embodiment a temperature sensor 14 is provided in the canister 2, to measure the temperature of the batch of insects. As according to the invention the insects are mixed in the canister 2, the temperature of a batch may adequately be measured at any location in the canister 2. In fig. 4, an exemplary temperature profile of the product temperature is shown by the dotted line. Upon arrival in the freeze-drying system, the products are frozen to a temperature of -18°C, which gradually increases during primary freeze drying, but never exceeds 0°C. In the secondary drying step, i.e. here the last 2-3 hours of the freeze-drying process, the temperature increases to room temperature, i.e. about 20°C.

The heat source 13 is advantageously controlled on the basis of the temperature sensor 14. As shown by the dash-dotted line, it is conceivably that the data of the temperature sensor are provided to the control unit 10. In addition thereto, or instead thereof, it is conceivable that the heat source is not only controlled on the basis of the temperature sensor 14, but that the heat source 13 is controlled by the control unit 10, e.g. on the basis of the type of insects, the degree of vacuum, and/ or the rotation speed of the mixer. For example, a heat program is stored in the memory 12, on the basis of which the heat source is controlled.

An exemplary power profile of the heat source 13 is shown by the dash-dotted line. The heat source 13 is only activated after the vacuum is established, at a relatively high level. Halfway the primary freeze-drying step, the power of the heat source 13 is allowed to decrease gradually, until at the end of the primary freeze-drying step the heat source 13 is no longer active. Advantageously, the power of the heat source 13 is controlled to maintain the product temperature at a constant level, e.g. -2°C. During the start of the secondary freeze- drying step the heat source is activated, but not as intensive as during the first freeze-drying step.