IMPROVEMENTS RELATING TO THE CULTIVATION OF MUSHROOMS

Abstract: In a process for cultivating mushrooms wherein a substrate (10, 20) of mushroom compost is pasteurised before adding mushroom spawn, at least one ventilation passage (14, 23) is formed in the core of the substrate before and/or after adding the spawn whereby air is free to circulate through the substrate to control the temperature of the substrate during the pasteurisation and/or spawn running processes.

Description: IMPROVEMENTS RELATING TO THE CULTIVATION OF MUSHROOMS This invention relates to the cultivation of edible fungus, such as Agaricus bisporus (mushrooms), under controlled conditions, and to the preparation of compost for use in the cultivation process. A problem which is common to all current mushroom cultivation processes is that of temperature control in the substrate. In particular, during the spawn running phase of the process and after the mushroom spawn have been growing in the compost for about 8 to 10 days, there is a thermophilic reaction within the compost that produces a surge of heat. Without temperature control, the resulting temperature within the compost can easily rise above tne thermal death point of the mushroom spawn. The problem is particularly acute during the hot summer months. Accordingly, most modern cultivation methods at present require sophisticated air conditioning equipment to control the air temperature, relative humidity and carbon dioxide content. In particular, in a multi-tier system where the compost/spawn mixture is retained in stacked pallets or on shelves, it is essential to maintain a flow of air between the superimposed layers. A single tier system in which the compost/spawn mixture is contained in plastic bags, sacks or trays at floor level does not require this forced air flow and produces good quality mushrooms without the need for expensive air conditioning equipment. However, the output per unit area of built floor space is not as high. Moreover, as the capacity of a bag increases, so does the risk of overheating at the centre of the bag. A somewhat similar problem exists in the composting phase -of the mushroom cultivation process. This is generally divided into two principal phases. During the first phase temperatures within the compost heap are generally in the range of 65-80 , while in the second phase the temperatures are generally within the range of 45-55°C. The first phase is a softening process in which water is added to the raw material, such as horse manure and straw, and the material is repeatedly turned, mixed and aerated over a period of days. After some days, the partially decomposed compost has sufficient cohesion that it can be formed into a compost heap which will have a temperature profile somewhat as shown in Fig. 1 of the accompanying drawings. This temperature profile is generally unsatisfactory since only a relatively small proportion 52 of the heap 55 is under the optimum conditions for decomposition. The outer layers 50, 51 of the heap are well aerated but too cool, the central zone 53 is warmer but is poorly aerated, and there is also a foul-s el 1ing anaerobic core 54. The second phase of the composting process is a pasteurising and conditioning process which is carried out under cover in a controlled environment either in the final beds or trays in which the mushrooms are cultivated, or in bulk tunnel systems. During this phase, the temperature is closely controlled and any remaining ammonia released during the first phase is converted by the thermoph lic microflora into protein as food for the mushrooms. Although the composting process does not have the problem of heat surges, it does have the problem of preventing environmental pollution due to the foul-smel1ing anaerobic core. Moreover, the temperature difference between the core of the compost and the outside layers is generally undesirable and requires considerable mixing and/or turning of the compost, thereby prolonging the composting process. Attempts have been made to force air upwardly through the core of the compost to achieve more uniform temperature distribution, but these have not been successful. According to the present invention, a compost or compost/spawn substrate in a process for cultivating a mushroom is formed with at least one ventilation passage for the flow of air through the substrate. The ventilation passage can be lined or unlined, and preferably extends in a generally vertical direction from top to bottom of the substrate. In this case, the substrate is supported above ground level and the ventilation passage acts as a chimney. The upward flow of air through the passage provides improved aeration and a more uniform temperature distribution through the core of the substrate. Moreover, where spawn has been added to pasteurised compost, the venting of the substrate reduces the risk of the substrate overheating during the spawn running phase of the process. Accordingly, a greater depth of compost can be used, and this provides an increased yield of mushrooms per unit area of floor space. In addition, for those species of mushroom requiring a layer of casing on top of the substrate, less casing is required compared to a system in which the same amount of compost is arranged in two or more tiers. Where the ventilation passage extends from the bottom to the top of the substrate, it may then continue upwards through the top layer of casing. Alternatively, to retain the maximum surface area of the casing for growing mushrooms, the continuation of the ventilation passage may extend below the surface of the casing in a transverse direction. In practice, an array of bins or bags each containing a substrate with a single ventilation passage could be provided. However, in a preferred embodiment, a compacted block of the compost or compost/spawn mixture is formed with an array of ventilation passages arranged, for example, in rows and columns. For example, a block measuring 1.0M x 1.5M x 0.5M (length x breadth x height) might have rows and columns of ventilation passages spaced apart by about 20cm. Such a block is preferably formed by positioning an array of tubular formers within a temporary.enclosure, lowering an apertured tray over the formers, filling the enclosure with the compost or compost/spawn mixture, compacting the fill, and thereafter removing the enclosure and relatively moving the tray and the formers to withdraw the formers from the compacted block. The invention will be further described, by way of example only, with reference- o the accompanying drawings in which: Fig. 1 is a diagrammatic temperature profile of a prior art compost heap, Fig. 2 is a diagrammatic perspective of a compost stack embodying the invention for cultivating the Agaricus mushroom in individual bins, Fig. 3 is a diagrammatic side view of an alternative compost stack embodying the invention for cultivating the Agaricus mushroom, Fig. 4 is a diagrammatic top view of the stack shown in Fig. 2 but with the top layer of casing removed for clarity, Fig. 5 illustrates diagrammatically a process for producing the compost stack of Figs. 3 and 4, Fig. 6 illustrates diagrammatical ly a further step in the process of Fig. 5, Fig. 7 is a scrap section showing one alternative method of venting the top of the stack of Figs. 3 and 4, and Fig. 8 is a scrap section similar to Fig. 7 showing a further alternative method of venting. Referring first to Fig. 2, two generally cylindrical bins 10, 11 are positioned εide-by-side with additional bins (not shown) being provided as required to form an array consisting of rows and columns of bins. The bins are made of any suitable rigid, or semi-rigid material, preferably a metal such as steel, but might also consist of plastics materials which are sufficiently thin or which have been perforated or otherwise vented to allow the passage of heat. Each bin is filled with a mixture 12 of pasteurised compost and mushroom spawn. The compost is generally a mixture of animal excreta, such as horse manure or chicken droppings, and fibrous matter such as straw, particularly wheat straw. The spawn is generally cereal grain which has been sterilized and impregnated with selected inoculants made from spores, tissue or mycelium under aseptic laboratory conditions. A top layer of soil or peat casing 18, such as peat and chalk, is then added. The rigid or semi-rigid cylindrical wall 13 of the bin not only provides a greater volume but allows compression of the compost such that the weight of compost in each bin is higher than can be achieved with flexible bags or sacks. The increased weight produces a corresponding greater yield of mushrooms. For a single tier system, rigid or semi-rigid bins therefore retain more compost per unit area of floor space, without increasing 5 the amount of cas.ing 18 required. A funnel-shaped metal or plastic duct 14 is positioned over a central opening 15 in the base 16 of the bin before filling the bin with the compost/spawn mixture. The duct 10 14 is either fixed or removable, and provides a ventilation passage through the core of the compost. The base 16 is supported above the ground, optionally on legs 17, such ' that air can pass upwardly through the opening 15 into the duct. After forming the ventilation passage, the duct 14 15 can be left in place or removed. The spawn colonise the compost and after a number of days there is a thermophilic reaction which generates excess heat. The function of the ventilation passage formed by 20 the duct 14 is to convey some of this excess heat away from the central region of the bin, thereby preventing overheating of the mushroom spawn. As the temperature rises, cooler air is drawn by convection through the opening 15, and this air rises through the ventilation 25. passage and emerges at the other end at or above the top level of the casing 18. The duct 14 therefore acts as a chimney. Optionally, the top of each ventilation passage formed by 30 the duct 14 is closed with a removable closure member (not shown), the member being inserted or closed when the bin is filled, and only being removed or opened when cool ng is required. The member can therefore be used to control the compost temperature, not only to prevent overheating, but 5 also to retain the heat during certain periods of the crop, particularly during the cold winter months. Opening and closing could advantageously be controlled thermostatically using, for example, a bimetallic strip. A deflector (not shown) might also be located at the top of the ventilation passage such that the warm air emerging from the passage is deflected over the bed of casing 18 to assist the growing process. The system also lends itself to capillary watering. In this case, a trough of water (not shown) extends between adjacent rows or columns of bins and a capillary wick for each bin has one end immersed in the water in the trough and its other end feeding the casing material 18. With the above arrangement, assuming a 600mm diameter bin, no compost will be more than 150mm from a ventilated surface. Accordingly, the thermophilic generation of heat is less of a problem, and the risk of the compost temperature reaching the thermal death point of the spawn is substantially reduced. The slight taper of the bins allows them to be nested within one another for stacking and transportation when empty. The ducts 14, if retained, can also be nested within one another. The legs 17, if fitted, can be positioned to interlock for double or treble stacking. Each bin can be fitted with a removable lid or cover (not shown) with a hole aligned with the ventilation passage formed by duct 14. The lid or cover can be used to enhance the control of carbon dioxide at the relevant stages of the crop. Both the bin and the lid or cover can be cleaned and re- used . In general, the system maximises the output per square metre of floorspace for a single tier system, but can also be used in a multi-tier system. The system is ideally suited for a satellite production system where the bins are filled at a large central station and despatched to a number of smaller satellite stations where the mushrooms are grown. The use of bins has the further advantage of providing a comfortable picking height. In the alternative compost stack illustrated in Figs. 3 and 4, an array of -ventilation passages 23 are formed in a compacted generally rectangular block 20 of the compost/spawn mixture, the block being supported clear of the ground on a stillage 22. This ventilation arrangement can also be used during the composting phase of the mushroom growing process before the compost is planted with mushroom spawn. A typical sequence of operations for producing the compacted, ventilated, rectangular block 20 is illustrated in Figs. 5 and 6. A formwork 30 having an array of tubular formers 31 arranged in rows and columns is located at the filling point and secured to the floor 44. The stillage 22 consisting of a flat apertured tray 32 is positioned over the formwork 30 and lowered toward the floor with the tubular formers 31 being slidably received in the respective apertures 33. The tray rests on feet 43. An external rectangular form 34 is then positioned around the outside of the tray 32 to act as temporary shuttering, and the resulting assembly is loose filled with either compost or a spawn/compost mixture 35 to the required volume/weight. A compression plate 36 with the same profile as the apertured tray 32 is then placed on top of the loose filling 35 and pressed downwards to the required level shown by the dashed line 'A' (Fig. 6). The fibrous nature of the compost 35 provides sufficient cohesion that the pressure exerted by the plate 36 binds the compacted compost into a cohesive block. The compression plate 36 and the external form 34 are then removed, and the apertured tray 32 carrying the compacted block 20 is lifted clear of the tubular formers 31, for example using a fork lift truck. The compacted block 20 is thus formed with an array of ventilation passages 23 extending from top to bottom of the block. Advantageously, the apertures 33 protrude above the surface of the tray 32 and have a flared configuration. This not only smooths the flow of air into the ventilation passages 23, but also resists slippage of the block 20 during transit. When using the described ventilation arrangement in the spawn running phase of the mushroom cultivation process, the ventilated block 20 of compost/spawn mixture may then be wrapped in lastic film wrapping or netting to eliminate minor spillages during subsequent transport of the block. Advantageously, the flexible wrapping extends above the top surface of the block to provide flexible retaining walls for a subsequent layer of soil or peat casing. When using the described ventilation arrangement in the composting phase of the mushroom cultivation process, the ventilated block 20 initially consists of unpasteurised, partially decomposed compost. This is left for several days in a controlled environment to complete the pasteurising and conditioning of the compost before planting the mushroom spawn. The original block 20 is preferably broken up before adding the spawn. The process of Figs. 5 and 6 can then be repeated to produce a new compacted, ventilated block 20 of compost/spawn mixture for the spawn running phase of the process. Alternatively, the compost/spawn mixture can be used in the embodiment of Fig. 2 , At the mushroom cultivation site, netting 39 may be secured over the top surface of the block before adding a layer of casing 24. The netting 39 prevents the casing falling down the vent holes 23, and can also be used to reclaim the casing at the end of the crop. At the same time the top ends of the vent holes .23 are vented to the atmosphere either directly through the layer of casing 24 or in a transverse direction beneath the surface of the layer of casing. In the former arrangement, each vent hole 23 is provided with an individual chimney pot 41 (Fig. 8) . In the preferred alternative arrangement, either plastic - channels 25 (Figs. 3 and 4) are laid across the top of each column or row of vent holes before applying the layer of casing 24, or the top surface of the ventilated compost block 20 is provided with channels 42 transversing the respective rows or columns of vent holes 23 (Fig. 7). The channels 42 could be formed, for example, during compression of the block 20 by forming the underside of the pressure plate 36 with ribs having the profi e of the channels 42. Advantageously, in the former case, a capillary wick 46 (Fig. 3) extends along the top of each channel 25 to provide a continuous water supply for the casing material 24 without wetting the compost/spawn mixture 35, each capillary wick having one end immersed in a reservoir of water. After the mushroom spawn has been growing in the compost for about 8 to 10 days, the temperature in the core of the substrate rises due to a thermophilic reaction. However, this surge in temperature is controlled by cooler air -being drawn by convection into the ventilation passages 23 as shown by the arrows in Fig. 3. Accordingly, the risk of the temperature in the core of the substrate exceeding the thermal death point of the spawn is reduced. The chimney pot 41, channel 25 or channel 42, may incorporate a valve or similar blocking device (not shown) for selectively controlling the flow of air along the ventilation passage. This can provide additional control of the temperature within the block 20. When using the described ventilation arrangement during the spawn running phase of the mushroom cultivation process, the presence of the ventilating passages 23 prevents overheating in the core of the block 20 so that a significantly greater depth of compost/spawn mixture can be used compared to a system without ventilation. This increases the yield of mushrooms per unit area of floor space and reduces the amount of casing 24 required per ton of compost. It therefore leads to increased production and substantial savings in the crop producers' costs. The total number of passages 23, the precise cross-section of each passage, and the spacing between the passages is selected to ensure adequate ventilation with minimum loss of compost/spawn mixture. In general, I have found that the distance between the ventilated surfaces should not exceed about 20cms. When using the described vent lation arrangement during the composting phase of the mushroom cultivation process, the presence of the ventilating passages 23 provides better aeration and a more uniform distribution of temperature throughout the block compared to that shown in Fig. 1. A much higher proportion of the compost is therefore at the optimum condition for decomposition. This can significantly reduce the time and amount of machinery required for composting, in particular by eliminating the ' mechanical handling of separate trays in a multi-tier shelf system. It can also overcome the environmental problems associated with foul-sme l ng anaerobic cores. The compost that is used in the above process will already have undergone the first stage of the composting process in which the mixture of dung, such as horse manure, and fibrous matter, such as wheat straw, is partially decomposed by wetting a stack and then turning and aerating -the stack at regular intervals over a period of days. A survey of present composting techniques will be found in the article by J.W. Sinden in The Mushroom Journal Aug. 1989 No. 200 pp 242-46.

Claims: CLAIMS 1. A process for cultivating mushrooms wherein a mixture of organic and fibrous matter is composted and planted with mushroom spawn, characterised in that at least one ventilation passage is formed through a stack of the compost to control the temperature within the stack. 2. A process according to claim 1 in which the ventilation passage is formed during preparation of the compost and before planting the mushroom spawn. 3. A process according to claim 1 in which the ventilation passage is formed during or after the planting of the mushroom spawn. 4. A process according to any one of the claims 1-3 in which the passage extends upwardly in a generally vertical direction through the stack, and the stack is supported above ground level. 5. A process according to claim 4 in which the ventilation passage is formed by compacting the compost about a former, and then withdrawing the former. 6. A process according to claim 4 or claim 5 in which an array of the ventilation passages is formed in the stack, each passage being aligned with a respective aperture in a base member supporting the stack. 7. A process according to claim 6 in which the base support member is generally flat and each aperture protrudes above the surface of the support member. 8. A process according to claim 8 in which the size of the aperture progressively decreases in an upward 'd rection. 9. A process according to any one of the claims 6-8 in which the ventilated stack is formed by inserting a plurality of formers through the respective apertures in the support member, enclosing the formers in a temporary enclosure, filling the enclosure with compost or with a mixture of compost and spawn, compacting the fill, and thereafter removing the enclosure and withdrawing the formers from the compacted fill. 10. A process according to any one of the preceding claims wherein a layer of soil or peat casing material is added to the stack. 11. A process according to claim 10 in which the side walls of the stack are wrapped in a flexible wrapping, the wrapping extending above the top surface of the stack to provide flexible side walls for retaining the layer of casing. 12. A process according to claim 10 or claim 11 wherein the or each -ventilation passage further extends upwardly through the layer of casing. 13. A process according to claim 10 or claim 11 wherein the or each ventilation passage includes a first portion extending from the bottom of the substrate to the top, and a second portion extending from the top of the first portion, the second portion being transverse to the first portion. 14. A process according to claim 13 in which the second portion of the passage is covered by the layer of casing. 15. A process according to claim 14 in which the second portion of the passage is formed by a length of material impervious to water, and in which a corresponding length of water absorbent material extends above the passage for watering the layer of casing by capillary action. 16. A process according to claim 4 in which the stack is contained in a container, and the ventilation passage is aligned with an opening in a base of the container. 17. A process according to claim 16 in which the ventilation passage is formed by a hollow tubular duct. 18. A process according to claim 17 in which the tubular duct tapers toward the top of . the passage. 19. A process according to any one of the preceding claims wherein the temperature within the stack is further controlled by selectively blocking the flow of air through the passage. 20. A compost stack for use in cultivating mushrooms, the . compost comprising a. partially decomposed mixture of organic and fibrous matter, characterised in that the stack includes at least one ventilation passage for the flow of air through the stack. 21. A compost stack according to claim 20 wherein the compost is planted with mushroom spawn. 22. A compost stack according to claim 21 further comprising a top layer of soil or peat casing, the ventilation passage extending through or beneath the said layer. 23. A mushroom when produced by a process according to any one of the claims 1-19.

Inventors: BARTON MICHAEL, BARTON, MICHAEL
Applicants: BARTON MICHAEL, BARTON, MICHAEL
Application year: 1991
Main classification: A01G1
IPC codes: A01G1