WO2025000017A1

WO2025000017A1 - System and method for producing nutritious food-grade powder

Info

Publication number: WO2025000017A1
Application number: PCT/AU2024/050637
Authority: WO
Inventors: Matthew KRONBORG
Original assignee: Grainstone Pty Ltd
Current assignee: Grainstone Pty Ltd
Priority date: 2023-06-30
Filing date: 2024-06-18
Publication date: 2025-01-02
Anticipated expiration: 2025-12-30

Abstract

The invention relates to methods and systems for producing food-grade powders. More particularly, the invention relates to a system and method for producing healthy food-grade powder from wet carbohydrate materials, particularly with nutritional composition such as brewers spent grain. In preferred forms, the invention provides a renewable-electric powered energy efficient system and methods that enable the recovery of certain traditional food waste streams into versatile powders providing substantial environmental benefit. However, it will be appreciated that the invention is not limited to these particular fields of use.

Description

SYSTEM AND METHOD FOR PRODUCING NUTRITIOUS FOODGRADE POWDER

Field

[0001] The invention relates to methods and systems for producing food-grade powders. More particularly, the invention relates to a system and method for producing food-grade powder from wet carbohydrate materials, particularly those with nutritional composition such as brewers spent grain. In preferred forms, the invention provides low carbon energy efficient systems and methods and enables the recovery of traditional food waste streams providing a substantial environmental benefit.

Background

[0002] Over 1.3 billion tonnes of food is wasted globally each year, around 40% of all food produced. This is a major global systemic inefficiency. Much of this is created in farming and processing upstream of the consumer. Food demand is expected to increase over 70% by 2050 due population growth and consumer mega trends.

[0003] Brewers spent grain is the main by-product of brewing. Each year over 300,000 wet tonnes of brewers spent grain is produced in Australia and over 40 million tonnes is produced globally. Most of this is made from the highest grade of barley. Historically, recovering brewers spent grain to food grade product has been seen as unviable due to complex interrelated challenges including food safety, finished product quality, sensory quality, nutritional quality and production cost - compounded by being a non-priority for brewers. Given this, brewers spent grain is traditionally either treated as a waste product or a used as low value by-product in animal feed or compost fertilizer.

[0004] Despite the fact that brewers spent grain is conventionally viewed as an acceptable system inefficiency, it typically contains a nutritional profile valuable to human health (including being a good source of protein, fibre, Niacin (b3), calcium, iron, magnesium, zinc). The starch fraction of whole grain barely is largely removed by the mashing and lautering of the brewing process, nutritionally concentrating brewers spent grain in favour of protein and fibre. The comparatively high percentage of good quality protein compared to regular plain flour is seen as particularly valuable for wide consumption by humans. Given this, and the objective to reshape the global food system towards one that is more efficient it is desirable to process brewers spent grain to form a basic product from which these nutritional elements can be recovered.

[0005] As discussed above, brewers spent grain is conventionally considered difficult to process. For example, typical methods to mill this grain are ineffective due to high amount of fibre and high mineral content, resulting in significant losses and potential damage to equipment. Milling via standard hammer mill, standard pin mill, Fitz mill or other typical impact grinding mill doesn’t reduce particle size sufficiently requiring major fraction to be lost to sieving for oversize particles. Further, the high mineral content of brewers spent grain causes abrasion on the impact faces over time resulting in high wear costs and the high fibre content can cause equipment blockage problems.

[0006] Further brewers spent grain has a high moisture content which must be removed. Typical methods to remove the water in brewers spent grain have multiple down sides, including but not limited to having large energy requirements for conventional evaporative drying, invariably using natural gas (or other fossil fuels) combusted in an on-site burner to heat the air, steam or other heat transfer fluid to dry the grain. Further, extended exposure to oxygen rich atmospheres provides an ideal environment for aerobic microbes to propagate. To expedite drying and minimise the growth of microbes, these processes are generally conducted at high temperature. However, excessively high temperatures have a deleterious effect on the grain, such as damaging the sensory quality (flavour, aroma, colour) and nutritional quality (including damaging proteins) of the dried grain. Conversely, whilst drying at lower temperatures may be desirable in order to maintain the nutritional profile, such low temperature processes can take a very extended duration, up to days which, as noted above, can lead to issues with microbial growth and inefficient asset utilisation.

[0007] There are also issues of scale up. The traditional grinding and drying equipment required to process and dry large volumes of brewers spent grain is extremely costly in terms of both capital and operating costs.

[0008] It is desirable to provide a method and/or system for conversion of brewers spent grain and other conventionally low-value carbohydrate sources with food-grade potential such as distillers spent grain, carrot pomace, apple pomace, peach pomace, pear pomace, citrus peel and pomace, soy okra, off- specification whole fruits and vegetables, wheat milling by-products, reduced- starch barley, to high value nutritional products. It is an object of the invention to address at least one shortcoming of the prior art and/or provide a useful alternative.

Summary of Invention

[0009] In one aspect of the invention there is provided a method for drying a wet plant based or plant derived biomass material, the method comprising: subjecting the wet biomass material to vacuum conditions whilst maintaining and/or heating the wet biomass material to a temperature of from about 35°C up to about 80°C, to produce water vapor and a dried biomass product; and removing the water vapor.

[00010] In an embodiment, the wet biomass material has an initial moisture content of about 50 wt% or greater. It one form the initial moisture content is from about 60 wt%, or from about 65 wt%, or from about 70 wt%. In one form, the initial moisture content may be up to about 95 wt%, or up to 90 wt%, or up to 85 wt%. By way of example, in one embodiment the initial moisture content is from about 60 to 95 wt%. In another embodiment, the initial moisture content is from about 65 to 90 wt%. In yet another embodiment, the initial moisture content is from about 70 to 85 wt%. In still another embodiment, the initial moisture content is from about 72 to 82 wt%.

[0010] In an embodiment, the dried biomass product has moisture content of up to about 15 wt%. In one form, the moisture content is up to 13 wt%, or in another form up to 12 wt%. Additionally or alternatively, the moisture content is at least 2 wt% or at least 5 wt%, or at least 8 wt%. In one form the moisture content is 5-15 wt%, preferably 5-13 wt%, and most preferably 8-12 wt%.

[0011] In an embodiment, the dried biomass product has a water activity of from about 0.3 up to 0.7. Preferably the water activity is from about 0.4 up to about 0.65. Most preferably the water activity is from about 0.5 up to about 0.63.

[0012] In an embodiment, the temperature is from about 50°C up to 65°C when the wet biomass has a moisture content 20 wt% or greater. [0013] In an embodiment, the temperature is from about 65 °C up to 80°C when the wet biomass has a moisture content below 20 wt%.

[0014] In an embodiment, the method includes determining the moisture content of the wet biomass material, and (i) maintaining and/or heating the wet biomass material to a temperature of from about 50°C up to 65°C when the wet biomass has a moisture content 20 wt% or greater; and/or (ii) maintaining and/or heating the wet biomass material to a temperature of from 65 °C up to 80°C when the wet biomass has a moisture content below 20 wt%.

[0015] In an embodiment, the step of subjecting the wet biomass material to vacuum conditions is carried out in a hermetically sealed chamber. In traditional high temperature dehydration processes, it is common to use natural gas (or other fossil fuel) via local combustion to directly heat the air, with most of that heat wasted via venting directly to the atmosphere. Advantageously, the use of a hermetically sealed system allows heat energy to be recovered from the water vapor phase and optionally reused in the system, thus improving overall energy efficiency of the system.

[0016] In one form of this embodiment, the method further comprises heating a wall of the hermetically sealed chamber to a wall temperature of from about 45°C up to about 130°C to maintain the temperature of, or to heat the wet biomass material. Preferably the wall temperature is from about 50°C up to about 100°C, and more preferably from about 50°C up to about 85°C.

[0017] In one form of the above embodiment, the step of determining the moisture content is conducted prior to the step of subjecting the wet biomass material to vacuum conditions. In additional or alternative forms of the above embodiment, the step of determining the moisture content is conducted during the step of subjecting the wet biomass material to vacuum conditions.

[0018] In an embodiment, the vacuum is from about 0.5 kPa up to about 15 kPa absolute pressure. In one form, the pressure is from about 1 kPa, preferably from about 2 kPa, more preferably from about 4 kPa and most preferably from about 6 kPa. Alternatively or additionally, the pressure is up to about 14 kPa, more preferably up to about 12 kPa, and most preferably up to about 10 kPa. An exemplary pressure range is from about 6 kPa up to about 10 kPa. [0019] As generally described above, the invention relates to a process for drying a wet plant based or plant derived biomass material. The wet plant based or plant derived biomass material includes any wet carbohydrate material, product or ingredient, any biomass feedstock or any high fibre feedstock. In one or more embodiments, the wet plant based or plant derived biomass material is a wet carbohydrate material and/or a wet fiber material, such as a high fiber material. In one or more forms, the wet biomass comprises at least 10 wt% carbohydrates. In one or more forms, the wet biomass comprises at least 40 wt% fibre as determined on a dry basis, and preferably at least 45 wt% fibre as determined on a dry basis. More preferably, the fibre is dietary fibre. In various embodiments, the wet biomass material is a tacky material / pomace material / sludge material / slurry material / cake / homogeneous mixture / fibrous material / viscous material.

[0020] In an embodiment, the wet biomass material is selected from the group consisting: of grain, brewers spent grain, distillers grains, barley, carrot pomace, apple pomace, pear pomace, lemon pomace, orange pomace, tomato pomace, soy okra, fruit matter, and vegetable matter.

[0021] In an embodiment, the method further comprises pre-treating the wet biomass material with a pulsed electric field prior to the step of subjecting the wet biomass material to vacuum conditions. This pre-treatment step may advantageously reduce microbial growth and/or open the cell structure and/or increase the surface area to marginally increase drying efficiency. In one form of this embodiment, the pulsed electric field pre-treatment is about 2.8 kV/cm with 3000 pulses of 20 ps pulse- width.

[0022] In an embodiment, the method further comprises the step of comminuting the dried biomass product to produce a dried biomass or food powder.

[0023] In an embodiment, the dried biomass and/or the dried biomass powder is food-grade.

[0024] In an embodiment, the method further comprises the step of pre-heating the wet biomass material to a temperature of between 50°C and 90°C prior to subjecting the wet biomass material to the vacuum. Preferably the temperature is sufficient to complete a pasteurization treatment of the wet biomass material. [0025] In an embodiment, the method further comprises the step of maintaining or heating the wet, drying, or dried biomass material to a temperature of greater than 62°C, and preferably over 70°C for a time sufficient to pasteurize the biomass material.

[0026] In an embodiment, the step of subjecting the wet biomass material to vacuum conditions is carried out for about 10 hours or less. Preferably, about 6 hours or less. Most preferably about 4 hours or less.

[0027] In an embodiment, the step of subjecting the wet biomass material to vacuum conditions further comprises agitating the wet biomass material. Preferably, via a heater agitation apparatus, such as a hollow blade or hollow disc agitator.

[0028] In another aspect of the invention, there is provided a system for producing, or when used to produce, a dried biomass product from a wet biomass material, the system comprising: a vacuum dryer configured to receive a wet biomass material, wherein the vacuum dryer is configured to subject that wet biomass material to vacuum conditions whilst maintaining and/or heating the wet biomass material at from about 35 °C up to about 80°C to produce water vapor and a dried biomass product; and an extraction system for removing the water vapor from the vacuum dryer.

[0029] In an embodiment, the system is configured to: maintain and/or heat the wet biomass material to a temperature between 50°C and 65°C when a moisture content of the wet biomass material is above 20 wt%; and/or maintain and/or heat the wet biomass material temperature is maintained between 65°C and 80°C when the moisture content of the wet biomass material is below 20 wt%.

[0030] In an embodiment, the vacuum dryer further comprises: a hermetically sealed chamber for receiving the wet biomass material, and the system further comprises a water heating circuit in thermal communication with a wall of the hermetically sealed chamber; and wherein the water heating circuit is configured to maintain the wall of the hermetically sealed chamber at a wall temperature of from about 45°C up to about 130°C to maintain the temperature of and/or heat the wet biomass material. Preferably the wall temperature is from about 50°C up to about 100°C, and more preferably from about 50°C up to about 85°C. [0031] In an embodiment, the vacuum dryer further comprises an agitator configured to agitate the wet biomass material within the vacuum dryer. Preferably, the agitator is a heated agitator, such as a hollow blade or hollow disc agitator.

[0032] In an embodiment, the system further comprises a mill configured to comminute the dried biomass product to a dried biomass powder with an average particle size with a diameter of less than 500pm, more preferably less than 350 pm. Preferably, the mill is a modified hammer mill, or more preferably a modified air classifier mill.

[0033] In an embodiment, the system further comprises a pre-heating arrangement configured to heat the wet biomass material to a temperature of between 50°C and 90°C upstream of the vacuum dryer.

[0034] In an embodiment, the system is electrically powered, preferably using renewable energy such as solar or wind power as the energy source. That is, the system is not directly powered by combustible fuels such as natural gas, coal, and the like. This differs from traditional food drying processes and systems which typically use a natural gas or coal powered burner or boiler to generate a source of combustion gases or steam to provide heat to the process or system.

[0035] In a further aspect of the invention, there is provided a dried food powder produced according to the method of the first aspect of the invention and/or embodiments and/or forms thereof.

[0036] In an embodiment, the dried food powder has moisture content of up to about 15 wt%. In one form, the moisture content is up to 13 wt%, or in another form up to 12 wt%. Additionally or alternatively, the moisture content is at least 2 wt% or at least 5 wt%, or at least 8 wt%. In one form the moisture content is 5-15 wt%, preferably 5-13 wt%, and most preferably 8-12 wt%.

[0037] In an embodiment, the dried food product has a water activity of from about 0.3 up to 0.7. Preferably the water activity is from about 0.4 up to about 0.65. Most preferably the water activity is from about 0.5 up to about 0.63.

[0038] In an embodiment, the dried food powder comprises from about 15 up to about 30 wt% protein. [0039] In an embodiment, the dried food powder comprises from about 0.1 up to about 5 wt% ash.

[0040] In an embodiment, the dried food powder comprises from about 5 up to about 15 wt% fat.

[0041] In an embodiment, the dried food powder comprises from about 40 up to about 60 wt% dietary fibre.

[0042] In an embodiment, the dried biomass is a food-grade powder.

[0043] In yet another aspect of the invention, there is provided a mill comprising: a milling chamber having a rotor and a stator, wherein the rotor has a first contact surface and the stator has a second contact surface, the first contact surface being in opposition to the second contact surface for milling a material there between on relative rotation between the rotor and stator; and wherein the first contact surface and/or the second contact surface comprise a plurality of saw-tooth projections.

[0044] In an embodiment of the first aspect of the invention, the method uses the mill defined above to comminute the dried biomass to produce the dried biomass powder.

[0045] In an embodiment, saw tooth projections on the first contact surface project in a direction toward a direction of rotation of the rotor.

[0046] In an embodiment, saw tooth projections on the second contact surface project in a direction away from the direction of rotation of the rotor.

[0047] Reference to any prior art in the specification is not an acknowledgment or suggestion that this prior art forms part of the common general knowledge in any jurisdiction or that this prior art could reasonably be expected to be understood, regarded as relevant, and/or combined with other pieces of prior art by a skilled person in the art. [0048] As used herein, except where the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude further additives, components, integers or steps.

Brief Description of Drawings

[0049] Further aspects of the present invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example and with reference to the accompanying drawings.

[0050] Figure 1 is a flowchart of a method for drying a wet biomass material according to an embodiment of the invention;

[0051] Figure ! is a block diagram of an example system for producing food-grade powder from a wet biomass material according to another embodiment;

[0052] Figure 3 is a drawing of a jacketed storage tank with mechanised agitation auger;

[0053] Figure 4 is a schematic diagram of a vacuum subsystem of the system of Figure 2;

[0054] Figure 5 is a schematic diagram of a milling subsystem of the system of Figure 2;

[0055] Figure 6 shows a mill chamber of a modified air classifier mill;

[0056] Figures 7 shows alterations to the mill of Figure 6.

[0057] Figure 8 is a graph showing the particle distribution size of a dried milled biomass powder formed according to the method of the invention.

[0058] Figure 9 shows a stator of a modified hammer mill in accordance with one aspect of the invention.

[0059] Figure 10 shows a stator and rotor of a modified hammer mill in accordance with one aspect of the invention.

Description of Embodiments [0060] The present disclosure provides a method for drying wet plant based or plant derived biomass materials, such as brewers spent grain, under vacuum and at relatively lower temperatures. Drying at relatively lower temperatures and vacuum has various potential advantages. For example, given the system has a very high Coefficient of Performance (COP), the method does not require use of fossil fuel powered burners or boilers to generate a heated transfer medium to cost efficiently perform the drying operation. Accordingly, alternative heating methods such as using electricity from renewable sources and/or energy recovered from nearby processes can be harnessed, which is more energy efficient, have a better environmental impact, and leave a substantially smaller carbon footprint.

[0061] Furthermore, the use of lower temperatures minimises the likelihood of thermal damage to the wet biomass material, such as by cooking, burning, or toasting the biomass and thus maintains the nutrient profile and the desirable sensory characteristics of the wet biomass material in any dry biomass powder produced therefrom.

[0062] Performing drying under vacuum advantageously provides a low oxygen environment, which can reduce the rate at which the wet biomass material oxidises during the drying process whilst also reducing the propagation of aerobic microbes.

[0063] Referring now to the drawings, Figure 1 is a flowchart generally representing a method for drying a wet biomass material 100 in accordance with one or more embodiments of the invention. The method 100 comprises providing a wet biomass material 102 to a hermetically sealed drying chamber, and drying 104 the biomass under vacuum at a temperature of from about 35 °C and up to 80°C to produce a dried biomass product.

[0064] The drying step 104 is carried out under vacuum, such as, for example, at an absolute pressure of between 0.5 kPa and 15 kPa. Drying under vacuum lowers the boiling point of water, entailing that moisture within the wet biomass material evaporates at a lower temperature. Performing drying under vacuum may also have the additional benefit of providing a low oxygen environment, which may reduce oxidation and hinder the propagation of aerobic microbes as discussed above.

[0065] By drying the wet biomass material in a vacuum, the method 100 can advantageously be carried out at a lower temperature than typical methods of the prior art. Lower temperatures can help reduce instances where the wet biomass material is burned, toasted or cooked during l l drying, and can result in more efficient and cost effective drying while still achieving the required moisture levels. Drying at lower temperatures may also have advantageous nutritional effects and may improve sensory characteristics of a food-grade powder produced from the dried biomass product as discussed above.

[0066] The method can be used to treat a wide variety of wet biomass material, a non-limiting list of which consists of: brewers spent grain, distillers grain, barley, apple pomace, pear pomace, lemon pomace, orange pomace, carrot pomace, tomato pomace, soy okra, fruit matter, vegetable matter, wheat milling by-products, and reduced- starch barley.

[0067] In some embodiments, during the drying step 102 the temperature of the wet biomass material may be maintained between 50°C and 65°C while a moisture content of the wet biomass material is above 20 wt%. Further, in some embodiments, once the moisture content falls below 20 wt% the temperature may be increased, or increase of itself due to reduced evaporation and moisture levels in the wet biomass material, to between 65°C and 80°C.

[0068] Advantageously, the increased temperature of above 62°C and especially between 65°C and 80°C, in addition to any associated drying effect, may have a pasteurising effect on the wet biomass material, and may destroy some harmful microbes within the wet biomass material.

[0069] The wet biomass material may have an initial moisture content of between 50 and 90 wt%. Once dried, the dried biomass product may have a relative moisture content of between 5 and 15 wt%. The dried biomass product may have a water activity between 0.3 and 0.7.

[0070] The method 100 comprises the step of comminuting 106 the dried biomass product to produce a food-grade powder. The step of comminuting 106 may comprise milling the dried biomass product to an average particle size with a diameter of less 500 pm and more preferably less than 350 pm. Preferably, at least 97% of particles have a diameter under 1,000 pm.

[0071] The method 100 can be used to produce, for example, apple flour, orange flour, soy okra flour, pear flour, lemon flour, carrot flour, lettuce flour, tomato flour which can be used to add novel sensory and wholefood nutritional profiles to food products.

[0072] The method 100 may comprise the step pre-processing the wet biomass material before drying the wet biomass material under vacuum. For example, pre-processing may comprise pre heating the wet biomass material to a feed temperature of between 50°C and 90°C before placing the wet biomass material under vacuum. Pre-heating the wet biomass material can reduce the energy requirements for drying the wet biomass material under vacuum and reduce the time that the wet biomass material is kept under the vacuum. The wet biomass material may also be received in a pre-heated form on being received from another process, e.g. residual heat may be preserved in the wet biomass material from another process, such as on receipt of the brewers spent grain from a distillery.

[0073] In one or more embodiments, pre-processing comprises mechanically dehydrating the wet biomass material. Mechanical dehydration typically refers to a process that includes mechanical pressing to force surface moisture from the wet biomass material. Mechanical dehydration can be performed with a belt press, a screw press or a centrifuge, for example. However, one issue with the use of mechanical dehydration is that the water extracted through this process may be rich in nutrients, such as soluble protein and minerals. As a result, mechanical dehydration may change the nutritional characteristics of the biomass material compared to drying alone. In other embodiments, the wet biomass material is received after being subjected to a mechanical dehydration process. This typically occurs to reduce the cost of transporting the wet biomass material to a facility for processing in accordance with the present invention.

[0074] In one or more embodiments, pre-processing comprises comminuting the wet carbohydrate material. Comminution can be achieved using methods known to those skilled in the art, such as by macerating the wet biomass material. Macerating whole or part fruit and vegetable matter down to a slurry may be achieved using a macerator type mill. In still further embodiments, depending on the type of wet biomass material, pre-processing may include destemming and/or de -pipping the wet biomass material to improve the sensory quality of any finished food-powder produced from the wet biomass material. Stems and pips may produce dark specs in light coloured food-powder and/or add undesirable flavour elements.

[0075] The invention will now be described in relation to a preferred embodiment as illustrated in Figures 2 to 5. Figure 2 is a process flow diagram illustrating a system 200 according to one embodiment of the invention for producing food-grade powder from wet biomass material 200 such as spent brewers grain. The system 200 can broadly be divided into three subsystems, namely pre-processing 202, vacuum drying 204 and comminuting 206. In the exemplified embodiment, wet biomass material in the form of brewers spent grain is fed into the preprocessing subsystem 202, before being dried under vacuum in the vacuum drying subsystem 204, and comminuted in comminuting subsystem 206. The skilled person will appreciate that in some embodiments pre-processing is not required, and wet biomass material is fed directly into the vacuum drying subsystem 204.

[0076] In the exemplified embodiment, pre-processing subsystem 202 includes a bin lifter/tipper 310 for loading the wet biomass material, such as unfermented fresh brewer’s spent grain, into a vibrating hopper 312. In most embodiments the grain will be hot (typically at about 60-80 °C) or treated in a way to preserve their food-grade quality. In most embodiments the grains will have a moisture content of 60-90%. In this embodiment, the wet biomass material is loaded into hopper 312 e.g., via a tipper truck, manual shovel, screw auger, pneumatic pump, or the like. Hopper 312 temporarily acts as a buffer before the wet biomass material is transferred to main jacketed holding tank 314.

[0077] The wet biomass material may be transferred from hopper 312 to main jacketed holding tank 314 by conveyancing means including a screwless lifting auger (not shown) such as a u- shaped screwless lifting auger. In the illustrated embodiment, the wet biomass material is passed through a metal detector 316 during transfer from hopper 312 to jacketed holding tank 314 to detect the presence of magnetic metal objects in the wet biomass material for food safety and to reduce risk of damage to machinery.

[0078] Referring now to Figure 3, an example of the jacketed holding tank 314 is shown. Jacketed holding tank 314 is thermally insulated to minimize energy loss since the wet biomass material can be pre-heated or pre-cooled. In this embodiment, the wet biomass material is fed into the pre-processing subsystem 202 at a temperature of between 60°C and 80°C. Jacketed holding tank 314 is configured to maintain the temperature of, or otherwise heat the wet biomass material to a temperature of at least 63°C, preferably at least 70°C, but less than 80°C. Jacketed holding tank 314 can be heated using recycled heat energy from another process in the system, e.g. from vacuum drying subsystem 204. Advantageously by maintaining the temperature of the wet biomass material, heat captured in the wet biomass material while undergoing other processes can be conserved and utilized in drying the wet biomass material under vacuum, which can reduce the time required to dry the wet biomass material and increase the energy efficiency of the process. In one or more embodiments, jacketed holding tank 314 further comprises cooling means, such as a refrigeration circuit, to permit the wet biomass material to be cooled, such as to a temperature of 15°C or less, for example, to keep the wet biomass material from spoiling if held in the holding tank 314 for an extended period of time, such as overnight. Lower temperatures may be achieved using glycol as an energy transfer medium in thermal communication with an electric refrigeration system. A heat exchange system can also be used to cool the wet biomass material or dried biomass product, e.g., by using a low temperature stream from another subsystem or process.

[0079] Jacketed holding tank 314 comprises a stirrer in the form of an auger 318 to agitate the wet biomass material and to free any bridging in the wet biomass material. Additionally, the auger 318 can provide a lifting function to lift the wet biomass material within the holding tank 314 as well as a forcing function to force the wet biomass material down and out of the holding tank. The holding tank 314 comprises a valve 320 forming an outlet of the holding tank 314. The valve may be manually operated or automatically controlled.

[0080] In some embodiments, the pre-processing subsystem comprises a wet mill such as a colloid mill (not shown). Wet milling can be used to increase the surface area of any solid biomass structure to be dried, which may reduce overall drying time and reduce overall energy requirements. In some embodiments the wet biomass material is fed directly from the wet mill into vacuum drying subsystem 204.

[0081] In various embodiments, pre-processing subsystem 202 further comprises a mechanical dehydrator such as a belt press, a screw press, or a centrifuge, for example. However, water extracted through mechanical dehydration may be rich in nutrients, such as soluble protein and minerals. As a result, mechanical dehydration may change the nutritional characteristics of the wet biomass material compared to drying alone. This nutrient rich water may be recovered.

[0082] In the exemplified embodiment, the wet biomass material is transferred from preprocessing subsystem 202 to vacuum drying subsystem 204 by means of screwless auger 410. One type of vacuum dryer that is suitable for the current application is a water source vacuum dryer 412 an example of which is shown in Figure 4. Preferably, the dryer is an electric powered water-source vacuum disc dryer, rather than utilising steam boilers and natural gas. A vacuum disc dryer is an indirect-contact dryer under high vacuum internal conditions to considerably reduce water boiling point. The dryer consists of a jacketed hermetically sealed cylindrical drying chamber and a rotor fitted with hollow discs. Typically, a heat medium, such as hot water, hot thermal oil, or steam flows both inside the jacket and hollow discs to form heat transfer surface.

[0083] The technical advantages of using a water-source vacuum disc dryer in the method of the invention include: (1) low temperature drying since the vacuum pressure can reach as low as about 1000 Pa., and the corresponding boiling point of water at this pressure is about 45 °C. Under these conditions, the evaporation rate can reach 6-8 kg water/hr/m² when heating walls of the disc dryer to 80 °C using hot water; (2) low energy consumption with the average heat consumption to evaporate 1 kg water being about 600 kcal due to the high vacuum, and (3) almost zero fugitive emissions since the drying process is conducted in a hermetically sealed system and the evaporated water vapour is trapped by an air-liquid separator and tubular condenser to prevent emission, and when utilising renewable electricity as power source the dryer can also be operated with essentially zero carbon emissions; and (4) the ability to operate in batch, semi-batch, or continuous operation.

[0084] Referring to Figure 4, vacuum dryer 412 comprises a drying chamber 414 for receiving and drying the wet biomass material and produce a dry biomass product. The vacuum dryer comprises water heating circuit 416 including a heating jacket for heating walls of the drying chamber 414. The walls of the chamber 414 are heated to a temperature of from about 45°C up to about 130°C to heat or otherwise maintain the temperature of the wet biomass material inside drying chamber 414 at a temperature of from about 35 °C up to about 80 °C.

[0085] The operating temperature of vacuum dryer 412 can be controlled based on the moisture content of the incoming wet biomass material and/or based on the moisture content of the wet biomass material during the drying process and/or based the mechanical properties of the vacuum pump and/or based on the mechanical properties of the heat pump. In this way, the drying process can be controlled to optimise energy efficiency. Further, as the wet biomass material is dried and the moisture content is decreased it is beneficial to increase the heat supplied to vacuum dryer 412 to maintain the drying effect. By way of example, for when the moisture content of the wet biomass material is about 20 wt%, the temperature of the wet biomass material is ideally maintained at a temperature of from about 50 °C up to about 65 °C. However, as the wet biomass material dries, additional thermal energy is useful to maintain the drying effect. In some embodiments the temperature of the wet biomass material inside the chamber may be maintained at, or rise of its own accord to, between 65°C and 80°C when the moisture content of the wet biomass material is less than 20%. Higher moisture content in the wet biomass material may have an evaporative cooling effect on the temperature of the wet biomass material during the drying process. Accordingly, as the moisture levels decrease, the temperature of the wet biomass material may increase due to decrease in the evaporative cooling rate. This increasing temperature is advantageous since it also has a pasteurising effect on the wet biomass material when above about 62°C. Under vacuum conditions, heat transfer only effectively happens via physical contact. Heat radiation is very small because there is low/no air as a useful heat medium. The precondition of heat transfer is temperature difference. The bigger the temperature difference (between heating surface and feedstock), the higher rate of heat transfer.

[0086] Water source heat pump heating circuit 416 may comprise water heat exchanger 418 for heating water within water heating circuit 416. Water heating circuit 416 comprises cooling tower 420 for cooling water within the water heating circuit. Both hot and cold water from water heating circuit 416 can be used in other systems, such as heating or cooling jacketed holding tank 314.

[0087] Vacuum dryer 412 comprises vacuum circuit 422 for creating a vacuum inside vacuum drying chamber 414. Vacuum circuit 422 is configured create a vacuum of between 0.5 kPa and 15 kPa absolute pressure. During operation, the evaporation of water vapor can considerably offset the vacuum, typically the vacuum inside the drying chamber typically ranges from -0.09 to -0.095 Mpa (measured by relative vacuum gauge). As discussed above, when performing drying inside a relative vacuum, the boiling point of water is reduced, resulting in the water evaporating at a lower temperature such as between 40°C and 60°C, at a vacuum of between 0.5kPa and 15kPa absolute pressure. Note, when water is in different feedstock materials, especially material containing a percentage of oil, the actual boiling point can be higher than the theoretical boiling point of water. This is referred to as the equilibrium boiling point. Drying tests with a range of different wet biomass materials indicate that water starts to evaporate rapidly under at about 50-55 °C.

[0088] Vacuum circuit 422 is also configured to extract water vapour liberated from the wet biomass material inside drying chamber 414. Vacuum circuit 422 comprises a vacuum filter 424 for filtering the air extracted from the drying chamber 414. Water vapour extracted from the drying chamber is passed to condenser 426 where liquid water is recovered.

[0089] The drying process is conducted in a hermetically sealed system and water vapour is recovered via air- liquid separator and tubular condenser 426 to prevent emission. When utilising renewable electricity as power source the dryer may operate at near zero carbon emissions.

[0090] Vacuum dryer 412 can be operated in either a batch, semi batch, or continuous mode. However, the inventors have found that batch operation is generally more efficient.

[0091] Drying commences when wet biomass material is fed into the dryer via rotary valve or screw pump. Through the rotation of a central rotor (not shown), wet biomass material is mixed and pushed through the drying chamber 141 by agitator paddles (not shown). Fixed scraper bars may optionally be installed between the agitator paddles to prevent wet biomass material from sticking to the paddles or between the discs. The evaporated moisture is extracted via the vacuum pump and recovered by tubular condenser.

[0092] In most embodiments this dryer will operate on a batch basis. When the dryer reaches its design fill limit it will seal shut and begin a drying cycle. In a vacuum drying system, the drying time mainly depends on heating surface, drying temperature, and vacuum degree. Pre-heating the wet biomass material can considerably shorten the drying time as it is quicker for the wet biomass material to reach boiling temperature, which relates to the convergence of the internal air pressure and the temperature of the wet biomass material. In this system the drying temperature is typically from about 50 °C up to about 80 °C.

[0093] The drying process proceeds initially at a substantially constant rate, where for example, the wet biomass material is dried from a moisture content of 80 wt% to about 20 wt% under vacuum conditions in which the water in the wet material has a boiling point of about 55 °C. In this drying regime, evaporation of the water is occurs rapidly at a substantially constant rate. This rapid evaporation absorbs heat energy and thus a constant input of thermal energy is required to maintain the temperature of the wet biomass material. Once the moisture content of the wet biomass material falls to about 20 wt%, less moisture is produced and as such, the rate of evaporative cooling is lower. This causes accumulation of heat energy in the wet biomass material, which causes its temperature to increase, e.g., from about 55 °C to 65-70 °C. The increase in temperature is useful to facilitate further drying and to pasteurise the biomass material.

[0094] In this regard, the process may also comprise a ‘kill step’, such as thermal pasteurisation. The ‘kill step’ is to provide a 4-5 log reduction in microbial load to improve food safety. Where required, the ‘kill step’ may be included in the pre-treatment phase, e.g., by pre-heating the wet biomass product prior to the vacuum dryer, in the vacuum dryer, or downstream of the vacuum dryer.

[0095] In this example a heat exchange heat pump utilising a single screw compressor was used, with R134a, a commercially available refrigerant. Other refrigerants, such as R245fa may be used. R245fa is a more environmentally friendly option that may be preferred depending on the engineering design of the heat exchange heat pump.

[0100] To reduce energy loss, the vacuum dryer is thermally insulated. A wide variety of different forms on insulation may be used. However, in this example the vacuum dryer is covered with an 80mm thick layer of insulation material which in turn is covered by 2mm thick SUS304 plate. Ancillary piping can be similarly insulated.

[0101] Vapor from the vacuum dryer can be recovered via a condenser (such a tubular condenser) as hot water. This hot water can then be recycled to a water heater/steam boiler or adjacent process for heat recovery. The water heating circuit 416 may, for example, be connected to the condenser 426 to extract energy from the condensation process. Accordingly, some of the energy used to heat the drying chamber can be recovered from the vapor further improving the overall energy efficiency of the system.

[0096] In an embodiment, the interior wall of the drying chamber is formed from mirror polished metal. However, the skilled person will appreciate that the interior wall of the drying chamber may be formed from other materials or coated. By way of example, in embodiments where the wet biomass material is sticky, such as with very high sugar content, the wet biomass material may stick to the inner surfaces of the drying chamber, to overcome this the inner heating surface walls can be coated in Teflon or ceramic. A coating such as this can also prevent corrosion. [0097] In the present embodiment, metal agitator paddles are attached to a central rotor which slowly rotates during the drying process. In some embodiments fixed agitator bars are installed to help dislodge wet biomass material from the rotating agitator paddles. In some embodiments the agitator paddles further comprise a silicone or polymer scraper attached to the end thereof. The polymer scrapers are useful for moving the dried product during the unloading phase of batch operation.

[0098] The Coefficient of Performance (COP) is a ratio of useful heating or cooling to work (energy). This ratio is useful to provide an indication of the energy efficiency of a process and an indication of operating costs. In the context of the process of the invention, the COP primarily depends on water source temperature and compressor performance. In summer, the COP is may be higher than winter because water source typically starts at a higher temperature. In the exemplified system, the water source can recover heat from the evaporated water vapor (via tubular condenser), vacuum pump and air-cooling tower. The air-cooling tower effectively becomes an air heating tower when the ambient temperature is higher than 25 °C. As a result, the COP of this system is not a fixed number but can reach 3.0 or even higher which is indicative of a highly energy efficient process.

[0102] Referring again to Figure 2, the dried biomass product produced by the vacuum drying subsystem 204 is be transferred to the comminuting subsystem by means of a pneumatic conveyor 510. The pneumatic conveyor 510 feeds the dried biomass product into a modified air classifying mill / modified hammer mill 512. The skilled person will appreciate that a modified hammer mill which will subsequently be described may also be used.

[0103] The inventors trialed traditional mills including standard pin mills, unmodified hammer mills, fritz mills, stone mills and other grinding mills. However, these mills were unable to achieve the particle size reduction of the modified air classifier mill for an equivalent energy input. The modified hammer mill illustrated in Figure 10 usefully provides result similar to that obtained with the modified air classifier mill but with larger average particle size which may better suit some food stuff applications.

[0104] An air classifying mill typically comprises a screw feeder, grinding chamber, cyclone, bag filter and control cabinet. Typically, the air classifier mill can accept a raw dry material maximum particle size of 10mm, in some embodiments it may accept a particle size up to 20mm, in some embodiments it may accept a particles size less than 30mm. The mill is principally powered by electric motors. Under the effect of strong cutting, shearing and impacting between the high-speed cutters and inner gear ring, the raw material is immediately pulverized into fine particles. Because of negative pressure and air flow in the milling chamber, pulverized particles enter into an air classifier where the qualified powder is separated out while bigger granules remain in the grinder chamber for regrinding. Milled powder flows into the cyclone and bag filter for collection and the air is exhausted by the draft fan. Most of the powder is collected in the cyclone, in some case up to 2%, 4%, 6%, 8%, 10% of the dried biomass powder may be sucked through to the bag filter (typically 3-5%). The bag filter includes a pulse dust collection box. This mechanism uses occasional jets of air and/or vibration to slough off particulate that then falls under gravity to the bottom of the bag filter chamber where it can be recovered via a release valve and returned to the main wet biomass material or disposed of. The product particle size can be adjusted from approximately 40-300 mesh by adjusting the speed of the classifier. The faster the speed of the classifier the finer the particle size but conversely the smaller the kg/hr capacity. The milling motor is constant speed so the feed rate needs to be reduced commensurately for smaller particle size to reduce excess torque overload on the milling motor.

[0105] The mill is configured to comminute the dried biomass product to an average particle size of less than 500pm and more preferably less than 350pm and where preferably, at least 97% of particles have a diameter under 1,000 pm. After milling the dried biomass product is separated out in either a cyclone stage or a bag filter 514.

[0106] Referring to Figure 5 the air classifier mill / modified hammer mill 512 comprises a milling chamber 516 for milling the dried biomass product into smaller particles. As the product is milled, the dried biomass product with appropriate particles size is transferred from the milling chamber 516 to the cyclone 518 where oversized particles are separated from ideally sized particles based on weight. Milled particles are captured in bag filter 520 or processed through to sieving 522.

[0107] As shown in Figures 6 and 7, the milling chamber 516 comprises a grinder 610 that further comprises a grinder rotor 612 and a grinder stator 614. The skilled person will appreciate that a modified hammer mill may also be used as described herein. [0108] In the embodiment illustrated in Figure 7 opposing surfaces of the grinder rotor 612 and the grinder stator 614 define saw tooth projections 616 for increasing sheer forces applied to the dried biomass product as it is being milled, and thus enhances the milling process.

[0109] The saw tooth projections 616 on the rotor project in a direction toward a direction of rotation of the rotor. The saw tooth projections 616 on the stator project in a direction opposing the direction of rotation of the rotor.

[0110] Figures 9 and 10 shows a stator of a modified hammer mill which has likewise been modified to include saw tooth projections similar to the modified air classifier mill discussed above.

[0111] After milling the product is transferred via direct gravity or pneumatic conveyor to the inlet of the vibrating sieve. This machine uses an electric motor attached to a weight to continuously vibrate the sieves contained within. In some embodiments an ultrasonic vibrating sieve may be used - this typically converts 220v 50hz, or 1 lOv 60hz electrical energy into 38KHZ high frequency electric energy powered vibration. In most embodiments there will be one inlet flowing from overhead onto the first sieve screen. Particles of the right size will flow through this screen whilst oversize particles will be ejected via an adjustable gate side-door. In some embodiments the sieve mesh size will be 40 mesh, in some embodiments the mesh sieve size will be 50 mesh, in some embodiments the mesh sieve size will be 60 mesh, in some embodiments the mesh sieve size will be 70 mesh, in some embodiments the mesh sieve size will be 80 mesh. The retained particles will be high fibre, the adjustments ejecting oversize product at this point can be used with earlier controls on the milling, to modulate the protein and fibre ratio in the wet biomass material compared to the dried biomass product. These can help to support a more consistent output, higher protein finished powder product, to account for seasonal variation and brewery variation in protein levels batch to batch. Fines powder from the bag filter can also be blended back into the inlet of the sieve with the vibration of the sieving helping to support homogenous mixing. The powder that flows through the sieve to is the main dried and powdered biomass product.

[0112] The dried and powdered biomass product is vacuum pneumatically conveyed to the bagging machine. In some embodiments it is passed through a metal detector and machine learning optical inspector enroute. In some embodiments a high fibre fraction is recovered for bagging and also passes through this product quality control unit. In some embodiments the high fibre fraction is stored in a buffer silo to keep batches separate.

[0113] The bagged products are automatically sealed, dated, optionally boxed and robotically palletised. The pallets are then racked for storage and distribution. In some embodiments the bags are 250g- 1kg consumer retail packages, in some embodiments the bags are 12- 12.5kg sacks, in some embodiments they are 25kg sacks. In some embodiments the bags are 2500kg, 500kg, 750kg or 1,000kg bulk bags.

[0114] In some embodiments the entire process can be mechanised and automated to substantially reduce the labour requirements, reduce risk to workers, improve food safety outcomes and improve food monitoring quality.

[0115] An analysis of the properties of food-grade powder produced using the example system above is set out in Table 1 below and the resultant particle size distribution is shown in Figure 8 where the Y-axis represents fraction as a percentage and the X-axis represents diameter in microns. The D50 particle size was 51.3 microns and the D90 particle size was 158 microns.

Table 1: Analysis of dried and milled brewer’s spent grain

[0116] It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.

Claims

1. A method for drying a wet biomass material, the method comprising: subjecting the wet biomass material to vacuum conditions whilst maintaining and/or heating the wet biomass material to a temperature of from about 35°C up to about 80°C, to produce water vapor and a dried biomass product; and removing the water vapor.

2. The method of claim 1, wherein the wet biomass material has an initial moisture content of from about 60 wt%.

3. The method of claims 1 or 2, wherein the dried biomass product has moisture content of up to about 15 wt%.

4. The method of any one of the preceding claims, wherein the temperature is from about 50°C up to 65°C when the wet biomass has a moisture content about 20 wt% or greater.

5. The method of any one of the preceding claims, wherein the temperature is from about 65 °C up to 80°C when the wet biomass has a moisture content below about 20 wt%.

6. The method of any one of the preceding claims, wherein the vacuum is from about 0.5 kPa up to about 15 kPa absolute pressure.

7. The method of any one of the preceding claims, wherein the wet biomass material is selected from the group consisting: of grain, brewers spent grain, distillers grains, barley, carrot pomace, apple pomace, pear pomace, lemon pomace, orange pomace, tomato pomace, soy okra, fruit matter, and vegetable matter.

8. The method of any one of the preceding claims, further comprising the step of comminuting the dried biomass product to produce a food-grade powder.

9. The method as claimed in claim 1 further comprising the step of pre-heating the wet biomass material to a temperature of between 50°C and 90°C prior to subjecting the wet biomass material to the vacuum.

10. A system for producing, or when used to produce, a dried biomass product from a wet biomass material, the system comprising: a vacuum dryer configured to receive a wet biomass material, wherein the vacuum dryer is configured to subject that wet biomass material to vacuum conditions whilst maintaining and/or heating the wet biomass material at from about 35 °C up to about 80°C to produce water vapor and a dried biomass product; and an extraction system for removing the water vapor from the vacuum dryer.

11. The system of claim 10 wherein the system is configured to: maintain and/or heat the wet biomass material to a temperature between 50°C and 65°C when a moisture content of the wet biomass material is above 20 wt%; and/or maintain and/or heat the wet biomass material temperature is maintained between 65°C and 80°C when the moisture content of the wet biomass material is below 20 wt%.

12. The system of claim 10 or 11, wherein the vacuum dryer further comprises: a drying chamber for receiving the wet biomass material, and the system further comprises a water heating circuit in thermal communication with a wall of the drying chamber; and wherein the water heating circuit is configured to maintain the wall of the drying chamber at temperature of from about 45 °C up to about 130°C to maintain the temperature of and/or heat the wet biomass material.

13. The system of any one of claims 10 to 12, further comprising a mill configured to comminute the dried biomass product to a dried biomass powder with an average particle size with a diameter of less than 500 pm.

14. The system of any one of claims 10 to 13, further comprising a pre-heating arrangement configured to heat the wet biomass material to a temperature of between 50°C and 90°C upstream of the vacuum dryer.

15. A dried food powder produced according to the method of claim 8.

16. The dried food powder of claim 15, wherein the dried food powder has a moisture of up to 15 wt%.

17. The dried food powder of claim 15 or 16, wherein the dried food powder comprises from about 15 up to about 30 wt% protein.

18. The dried food powder of any one of claims 15 to 17, wherein the dried food powder comprises from about 0.1 up to about 5 wt% ash.

19. A mill comprising: a milling chamber having a rotor and a stator, wherein the rotor has a first contact surface and the stator has a second contact surface, the first contact surface being in opposition to the second contact surface for milling a material therebetween on relative rotation between the rotor and stator; and wherein the first contact surface and/or the second contact surface comprise a plurality of saw-tooth projections.

20. The mill as claimed in claim 19 wherein: saw tooth projections on the first contact surface project in a direction toward a direction of rotation of the rotor; and/or wherein saw tooth projections on the second contact surface project in a direction away from the direction of rotation of the rotor.