GB2257967A

GB2257967A - A process for preparing a compost substrate

Info

Publication number: GB2257967A
Application number: GB9215024A
Authority: GB
Inventors: Ronald Christopher Wilson; Stephen Carleton
Original assignee: BRENCIS Ltd
Current assignee: BRENCIS Ltd
Priority date: 1991-07-24
Filing date: 1992-07-15
Publication date: 1993-01-27
Also published as: IE912604A1; BE1003215A6; GB9215024D0

Abstract

A compost substrate for use in the cultivation of mushrooms is prepared from a mixture of straw, poultry litter and water which is composted and then subjected to a peak heating cycle which comprises an equalising phase, a warm up phase, a pasteurizing phase, a conditioning phase and a cooling down phase. Air is passed through the composted mixture during all phases. The composted mixture is maintained at a temperature of approximately 58 DEG C during the pasteurizing phase and at a temperature of approximately 48 DEG C during the conditioning phase. The temperature of the composted mixture is reduced between the pasteurization phase and the conditioning phase in step changes of 5 DEG C per hour.

Description

The present invention relates to a process for preparing a compost substrate for use in the cultivation of mushrooms, and the invention also relates to the compost substrate produced according to the process.

Compost substrate for the cultivation of mushrooms is generally prepared from a mixture of straw, poultry litter, gypsum and water. The straw, poultry litter, gypsum and water are thoroughly mixed together to form a compost mixture which is then formed into a relatively large clamp for composting. Such clamps are generally relatively high, usually being of height of the order of three metres. The compost mixture is allowed to compost in the clamp for a period of seven to fourteen days. The clamp is then formed into a plurality of elongated rows for a further period of six to eight days. The rows, in general, are relatively high, commonly being up to three metres high.After the compost mixture has been composted in the clamps for seven to fourteen days and then in the rows for six to eight days, the mixture is sufficiently composted, and the composted mixture is then ready for subjecting to a peak heating cycle. The peak heating cycle is a relatively critical cycle. Unwanted and harmful organisms and bacteria are destroyed during the peak heating cycle. However, it is important that the peak heating cycle should not destroy all organisms and bacteria, in particular, those the absence of which would adversely affect the nutritional value of the compost substrate. Unfortunately, it has been found that in order to adequately destroy the harmful organisms, many of the desirable organisms and bacteria which contribute to the nutritional value of the compost substrate are, to some extent, adversely affected.

There is therefore a need for a process for preparing a compost substrate for use in the cultivation of mushrooms which minimises the risk of destruction to desirable organisms and bacteria during the peak heating cycle of the process.

The present invention is directed towards providing such a process, and a compost substrate prepared according to the process.

According to the invention, there is provided a process for preparing a compost substrate for use in the cultivation of mushrooms, the process comprising the steps of preparing a compost mixture by mixing straw, poultry litter and water, subjecting the compost mixture to a composting cycle for composting the compost mixture, placing the composted mixture in a peak heating tunnel, and subjecting the composted mixture to a peak heating cycle, the peak heating cycle comprising the steps of subjecting the composted mixture to a pasteurizing phase for a time period in the range of eight hours to fourteen hours and subsequently subjecting the pasteurized composted mixture to a conditioning phase for a period of at least eighty four hours air being passed through the composted mixture during the pasteurizing phase and the conditioning phase at a rate in the range of 150 cubic metres of air per hour per cubic metre of composted mixture to 200 cubic metres of air per hour per cubic metre of composted mixture, the temperature of the air being passed through the composted mixture during the pasteurizing phase being maintained in the range of 540C to 560C, and the oxygen content of the air during the pasteurizing phase being maintained in the range of 8% to 18% by volume of air, the temperature of the air being passed through the composted mixture during the conditioning phase being maintained in the range of 420C to 450C, and the oxygen content of the air during the conditioning phase being maintained in the range of 8% to 21% by volume of air, the temperature of the composted mixture being reduced gradually between the pasteurizing phase and the conditioning phase by gradually reducing the temperature of the air being passed through the composted mixture at the rate of 40C to 60C per hour. Preferably, the temperature of the air being passed through the composted mixture is reduced in steps at hourly intervals between the pasteurizing phase and the condition phase.

It is particularly important that the rate of reduction of the air temperature should not exceed 60C per hour between the pasteurizing phase and the conditioning phase to minimise the destruction of desirable organisms and bacteria. Furthermore, if the rate of reduction of the air temperature is below 40C per hour between the pasteurizing phase and the conditioning phase, the time taken to reduce the air temperature to that of the conditioning phase is uneconomically long.

It has been found that by maintaining the rate of reduction within the limit of 40C to 60C per hour that desirable organisms and bacteria which may have been adversely affected during the pasteurizing phase are provided with an opportunity to recover and an economical process is provided. It has been found that optimum results are achieved when the rate of reduction of the air temperature is 50C per hour. In fact, it has been found that by step changing the temperature of the air at the rate of 50C per hour the recovery of the desirable organisms and bacteria is further improved.

In another embodiment of the invention, the composted mixture is maintained at a pasteurizing temperature in the range of 560C to 600C during the pasteurizing phase. Preferably, the composted mixture is maintained at a pasteurizing temperature in the range of 570C to 590C during the pasteurizing phase. Advantageously, the composted mixture is maintained at a temperature of approximately 580C during the pasteurizing phase.

In another embodiment of the invention, the composted mixture is maintained at a temperature in the range of 46.50C to 49.50C during the conditioning phase.

Preferably, the composted mixture is maintained at a temperature of approximately 480C during the conditioning phase.

It has been found that by maintaining the temperature of the composted mixture as close to 580C during the pasteurizing phase and as close to 480C during the conditioning phase destruction of desirable organisms and bacteria is minimised and their subsequent recovery is optimized.

In another embodiment of the invention, the temperature of the air being passed through the composted mixture is maintained at a temperature of approximately 550C during the pasteurizing phase. Preferably, the temperature of the air being passed through the composted mixture is maintained at a temperature of approximately 440C during the conditioning phase.

Advantageously, the oxygen content of the air being passed through the composted mixture is maintained in the range of 8% to 18% by volume of air during the conditioning phase.

In one embodiment of the invention, the time period of the pasteurizing phase is in the range of eight hours to twelve hours, and preferably, approximately ten hours.

In another embodiment of the invention, the time period of the conditioning phase is in the range of eightyfour hours to one hundred and thirty hours, and preferably, approximately ninety hours. It has been found that where the temperature of the composted mixture is maintained between 470C and 490C and preferably 480C during the conditioning phase for a period within the range of eighty-four hours to one hundred and thirty hours, particularly enhanced recovery of desirable microflora is achieved, and also good assimilation of ammonia is achieved. Where ammonia levels in the composted mixture are relatively high during the conditioning phase, the conditioning phase may be extended to improve the assimilation of ammonia. High levels of ammonia in the compost substrate inhibit mycelium growth.

In a further embodiment of the invention, the air is passed through the composted mixture during the pasteurizing phase at a rate of approximately 200 cubic metres of air per hour per cubic metre of composted mixture, and preferably, the air is passed through the composted mixture during the conditioning phase at a rate of 160 cubic metres of air per hour per cubic metre of composted mixture to 180 cubic metres of air per hour per cubic metre of composted mixture.

Preferably, the air is passed through the composted mixture during the conditioning phase at a rate of approximately 170 cubic metres of air per hour per cubic metre of composted mixture.

In a preferred embodiment of the invention, the composted mixture prior to being subjected to the pasteurizing phase is subjected to an equalising phase during which phase the temperature of the composted mixture is adjusted to an equalising temperature in the range of 450C to 470C. Advantageously, the equalising temperature of the composted mixture is adjusted to approximately 460C during the equalising phase.

In a preferred aspect of the invention, the composted mixture is subjected to a warm up phase between the equalising phase and the pasteurizing phase to raise the temperature of the composted mixture from the equalising temperature to the pasteurizing temperature, the temperature of the composted mixture being gradually raised during the warm up phase at a rate in the range of 10C to 1.40C per hour. Preferably, the temperature of the composted mixture during the warm up phase is raised at a rate of approximately 1.20C per hour.

Preferably, air is passed through the composted mixture during the equalising phase and the warm up phase at a rate of 100 cubic metres of air per hour per cubic metre of composted mixture to 200 cubic metres of air per hour per cubic metre of composted mixture.

Advantageously, the temperature of the air being passed through the composted mixture during the warm up phase is raised at a rate in the range of 10C to 1.40C per hour during the warm up phase, and preferably, at the rate of approximately 1.20C per hour.

In a further embodiment of the invention, the composted mixture is subjected to a cooling down phase after the conditioning phase, the temperature of the composted mixture being adjusted to a final temperature lying in the range of 160C to 250C and the composted mixture being maintained at the final temperature for a time period in the range of eight to ten hours. Preferably, the temperature of the composted mixture is reduced at a rate in the range of 50C to 100C per hour during the cooling down phase, and advantageously, approximately SOC per hour.

In one embodiment of the invention, air is passed through the composted mixture during the cooling down phase at a rate substantially similar to the rate at which the air is passed through the composted mixture during the pasteurizing and conditioning phases.

Preferably, the temperature of the air being passed through the composted mixture during the cooling down phase is reduced at a rate in the range of 50C to 100C per hour until the temperature of the composted mixture reaches the final temperature, and preferably, at the rate of approximately 50C per hour.

In general, it is envisaged that the air being passed through the composted mixture will be recycled, and preferably, the oxygen content of the air being passed through the composted mixture will be maintained within predetermined limits by the addition of fresh air to the recycled air.

Preferably, the compost mixture comprises straw, poultry litter and water in the following range of proportions by weight of the compost mixture: straw 28% to 40%, poultry litter 15% to 30%, water 40% to 50%.

In a preferred embodiment of the invention, the compost mixture comprises straw, poultry litter and water in the following range of proportions by weight of the compost mixture: straw 30% to 36%, poultry litter 15% to 25%, water 45% to 50%.

Advantageously, the compost mixture comprises straw, poultry litter and water in the following approximate proportions by weight of the compost mixture: straw 35.5%, poultry litter 20%, water 44.5%.

In a further embodiment of the invention, the compost mixture on being mixed is formed into a clamp and composted for a period of at least seven days.

Preferably, the clamp is turned at least once during the composting period, advantageously, the clamp is turned at least twice during the composting period.

Preferably, water is periodically added to the clamp to maintain the water content of the mixture relatively constant during the composting period.

Advantageously, gypsum is added to the compost mixture in the clamp. Preferably, the gypsum constitutes in the range of 1% to 3% by weight of the compost mixture, and preferably, 2% by weight of the compost mixture.

Additionally, the invention comprises a compost substrate for use in the cultivation of mushrooms, the compost substrate being prepared according to the process of the invention In one embodiment of the invention, the compost substrate further comprises mushroom mycelium, preferably, the compost substrate is packed into bags, each bag containing in the range of 18 Kg to 22 Kg of compost substrate. Advantageously, the mushroom mycelium is added to the compost substrate as the compost substrate is being packed into the bags.

The invention will be more clearly understood from the following description of a preferred embodiment thereof, given by way of the following non-limiting example.

Example A compost substrate according to the invention is prepared using a process according to the invention which will be described below. The compost substrate is prepared using the following ingredients in the proportions set out below by weight of the compost mixture: straw 35.5%, poultry litter 18.15%, water 44.35%, and gypsum 2% approximately.

For convenience, the compost mixture is mixed in batches, each batch constituting approximately 138,000 Kg of compost mixture.

The compost mixture is prepared by thoroughly mixing the straw, poultry litter and water. To ensure good reaction between the poultry litter and the straw, the stalks of the straw are split prior to mixing to accelerate the composting process. Some of the water is added to the straw prior to mixing with the poultry litter. By moistening the straw, it has been found that the composting process is accelerated. The remainder of the water is then added to the mixture of straw and poultry litter. The straw, poultry litter and water are thoroughly mixed together to form the compost mixture.

The compost mixture is subjected to a composting cycle to form a composted mixture and the composted mixture is then subjected to a peak heating cycle for pasteurization and treating of the composted mixture.

The composting cycle and the peak heating cycle will be described separately.

Compostinq cycle The compost mixture is formed into a clamp on a concrete base in the open air for partial composting.

The clamp is made up of a single batch of compost mixture, and accordingly, comprises approximately 138,000 Kg of compost mixture. The clamp is formed to a height of approximately 3 metres. The compost mixture is allowed to partly compost in the clamp for a period of seven to eleven days, during which time the clamp is turned two or three times for aeration at substantially equal intervals of time. The water content of the clamp is maintained substantially constant by periodically sprinkling water over the clamp. Needless to say, in warm dry weather, more water is required than in humid or cooler weather.

Indeed, in wet weather the addition of water to the clamp will generally not be required. The time period of seven to fourteen days during which time the compost mixture is partly composted in the clamp largely depends on the time of year, the weather and the quality of the ingredients. However, it is important that the compost mixture should be allowed to compost in the clamp until the colour, texture and moisture content of the partly composted mixture are correct.

This is determined by a visual inspection of the partly composted mixture in the clamp, the touch of the mixture and the smell.

After the compost mixture has been partly composted to the required degree in the clamp, the partly composted mixture is then formed into a plurality of elongated rows on a concrete base in the open air. Each row is approximately 2 metres high by 2 metres wide. The partly composted mixture is allowed to compost in the rows for a further period of six to eight days. During the six to eight day period the compost mixture is in the rows, the rows are turned two to three times.

Preferably, the rows are turned on the second, fourth and sixth day. Where the compost mixture is allowed to compost in the rows for only six days, the compost mixture is turned only twice on the second and fourth days. Whether the compost mixture is allowed to compost in the rows for six or eight days depends on the time of year, the quality of the ingredients and the weather. The compost mixture is allowed to compost in the rows until composting has been completed and a composted mixture is formed. This is determined by a visual inspection of the material in the rows, by touch and smell.

The PH of the compost mixture in the rows is reduced to between 8.2 and 8.3 by the addition of gypsum to the compost mixture as the compost mixture is being turned in the rows.

The water content of the compost mixture in the rows is maintained substantially constant by periodically sprinkling the rows with water.

Peak heat ins cycle On composting having been completed, the composted mixture is transferred from the rows and placed on the floor of an enclosed peak heating tunnel where the composted mixture is subjected to the following five phases: 1. an equalising phase, 2. a warm up phase, 3. a pasteurizing phase, 4. a conditioning phase, 5. a cooling down phase.

Such peak heating tunnels will be well known to those skilled in the art.

During the above five phases, the composted mixture remains undisturbed in the peak heating tunnel and is subjected to the phases sequentially, in the order 1 to 5 as set out above. During the peak heating cycle air is continuously passed through the composted mixture through a plurality of air inlets provided in the floor of the peak heating tunnel. The rate at which air is passed through the composted mixture during the equalising phase and the warm up phase is approximately 100 cubic metres of air per hour per cubic metre of composted mixture. The rate at which air is passed through the composted mixture during the pasteurizing phase and cooling down phase is approximately 200 cubic metres of air per hour per cubic metre of composted mixture.The rate at which air is passed through the composted mixture during the conditioning phase is approximately 170 cubic metres of air per hour per cubic metre of composted mixture. The air is continuously recycled during the peak heating cycle, and fresh air is added to the recycled air for maintaining the oxygen content of the air passing through the composted mixture within predetermined limits, as are discussed below. The fresh air also partly facilitates regulating the temperature of the air being passed through the composted mixture. During the equalising phase, the oxygen content of the air is maintained at 8% oxygen by volume of air or greater.

During the warm up phase, the pasteurizing phase and the conditioning phase, the oxygen content of the air is maintained within the range of 8% to 18% oxygen by volume of air. The oxygen content of the air is maintained at a maximum, namely, 21% oxygen by volume of air during the cooling down phase.

Depending on the time of year, the temperature of the composted mixture, when initially placed in the peak heating tunnel, ranges from 300C to 570C. The compost mixture is first subjected to the equalising phase during which the temperature of the composted mixture is adjusted to an equalising temperature of approximately 460C. This is achieved by setting the temperature of the air being passed through the composted mixture at an appropriate level, and the equalising phase continues until the temperature of the composted mixture has been adjusted to approximately 460C.

On completion of the equalising phase, the composted mixture is immediately subjected to the warm up phase which raises the temperature of the compost mixture to the pasteurizing temperature of approximately 580C.

During the warm up phase the temperature of the composted mixture is raised at a rate of approximately 1.20C per hour. This is achieved by increasing the temperature of the air being passed through the composted mixture at the rate of 1.20C per hour. The warm up phase continues until the temperature of the composted mixture has been raised to the pasteurizing temperature of approximately 580C. At that stage, the warm up phase is completed, and the peak heating cycle moves into the pasteurizing phase.

During the pasteurizing phase, the temperature of the composted mixture is maintained relatively constant at the pasteurizing temperature of approximately 580C.

This is achieved by maintaining the temperature of the air being passed through the composted mixture during the pasteurizing phase at approximately 550C. The pasteurizing phase continues for approximately ten hours. On completion of the pasteurizing phase, the temperature of the pasteurized composted mixture is reduced gradually to a temperature of approximately 480C, at which stage the conditioning phase commences.

The temperature of the composted mixture is gradually reduced at the rate of approximately 50C per hour.

This is achieved by reducing the temperature of the air passing through the composted mixture in step changes of 5 at one hourly intervals. In other words, the temperature of the air is reduced in steps of 50C once per hour until the composted mixture is at a temperature of approximately 480C. At that stage, the conditioning phase commences.

The conditioning phase lasts for approximately ninety hours. During the conditioning phase, the temperature of the composted mixture is maintained at approximately 480C by maintaining the temperature of the air being passed through the composted mixture at a temperature of approximately 440C.

At the end of the conditioning phase, the composted mixture is subjected to a cooling down phase during which the temperature of the composted mixture is gradually reduced to a final temperature to lie within the range of 180C to 250C inclusive, depending on the time of year. In the summer, the final temperature to which the composted mixture is reduced is approximately 180C, while in the winter the final temperature of the composted mixture is approximately 250C. The temperature of the composted mixture is reduced during the cooling down phase at a rate of approximately 50C per hour. This is achieved by reducing the temperature of the air being passed through the composted mixture in step changes at the rate of 50C per hour. On the temperature being reduced to the final temperature, the composted mixture is maintained at this temperature for approximately eight to ten hours, at which stage the compost substrate is formed. The compost substrate is then removed from the peak heating tunnel to a bagging plant. Mushroom mycelium is mixed with the compost substrate, which is then packed in bags. Ideally, each bag contains approximately 20 Kg of compost substrate.

Claims

1. A process for preparing a compost substrate for use in the cultivation of mushrooms, the process comprising the steps of preparing a compost mixture by mixing straw, poultry litter and water, subjecting the compost mixture to a composting cycle for composting the compost mixture, placing the composted mixture in a peak heating tunnel, and subjecting the composted mixture to a peak heating cycle, the peak heating cycle comprising the steps of subjecting the composted mixture to a pasteurizing phase for a time period in the range of eight hours to fourteen hours and subsequently subjecting the pasteurized composted mixture to a conditioning phase for a period of at least eighty-four hours, air being passed through the composted mixture during the pasteurizing phase and the conditioning phase at a rate in the range of 150 cubic metres of air per hour per cubic metre of composted mixture to 200 cubic metres of air per hour per cubic metre of composted mixture, the temperature of the air being passed through the composted mixture during the pasteurizing phase being maintained in the range of 540C to 560C, and the oxygen content of the air during the pasteurizing phase being maintained in the range of 8% to 18% by volume of air, the temperature of the air being passed through the composted mixture during the conditioning phase being maintained in the range of 420C to 450C, and the oxygen content of the air during the conditioning phase being maintained in the range of 8% to 21% by volume of air, the temperature of the composted mixture being reduced gradually between the pasteurizing phase and the conditioning phase by gradually reducing the temperature of the air being passed through the composted mixture at the rate of 40C to 60C per hour.

2. A process as claimed in Claim 1 in which the temperature of the air being passed through the composted mixture is reduced in steps at hourly intervals between the pasteurizing phase and the condition phase.

3. A process as claimed in Claim 1 or 2 in which the composted mixture is maintained at a pasteurizing temperature in the range of 560C to 600C during the pasteurizing phase.

4. A process as claimed in Claim 3 in which the composted mixture is maintained at a pasteurizing temperature in the range of 570C to 590C during the pasteurizing phase.

5. A process as claimed in Claim 4 in which the composted mixture is maintained at a temperature of approximately 580C during the pasteurizing phase.

6. A process as claimed in any preceding claim in which the composted mixture is maintained at a temperature in the range of 46.50C to 49.50Cduring the conditioning phase.

7. A process as claimed in Claim 6 in which the composted mixture is maintained at a temperature of approximately 480C during the conditioning phase.

8. A process as claimed in any preceding claim in which the temperature of the air being passed through the composted mixture is maintained at a temperature of approximately 550C during the pasteurizing phase.

9. A process as claimed in any preceding claim in which the temperature of the air being passed through the composted mixture is maintained at a temperature of approximately 440C during the conditioning phase.

10. A process as claimed in any preceding claim in which the oxygen content of the air being passed through the composted mixture is maintained in the range of 8% to 18% by volume of air during the conditioning phase.

11. A process as claimed in any preceding claim in which the temperature of the air being passed through the composted mixture between the pasteurizing phase and the conditioning phase is reduced at the rate of approximately 50C per hour.

12. A process as claimed in any preceding claim in which the time period of the pasteurizing phase is in the range of eight hours to twelve hours.

13. A process as claimed in Claim 12 in which the time period of the pasteurizing phase is approximately ten hours.

14. A process as claimed in any preceding claim in which the time period of the conditioning phase is in the range of eighty-four hours to one hundred and thirty hours.

15. A process as claimed in Claim 16 in which the time period of the conditioning phase is approximately ninety hours.

16. A process as claimed in any preceding claim in which the air is passed through-the composted mixture during the pasteurizing phase at a rate of 200 cubic metres of air per hour per cubic metre of composted mixture.

17. A process as claimed in any preceding claim in which the air is passed through the composted mixture during the conditioning phase at a rate of 160 cubic metres of air per hour per cubic metre of composted mixture to 180 cubic metres of air per hour per cubic metre of composted mixture.

18. A process as claimed in Claim 17 in which the air is passed through the composted mixture during the conditioning phase at a rate of approximately 170 cubic metres of air per hour per cubic metre of composted mixture.

19. A process as claimed in any preceding claim in which the composted mixture prior to being subjected to the pasteurizing phase is subjected to an equalising phase during which phase the temperature of the composted mixture is adjusted to an equalising temperature in the range of 450C to 470C.

20. A process as claimed in Claim 19 in which the equalising temperature of the composted mixture is adjusted to approximately 460C during the equalising phase.

21. A process as claimed in Claim 19 or 20 in which the composted mixture is subjected to a warm up phase between the equalising phase and the pasteurizing phase to raise the temperature of the composted mixture from the equalising temperature to the pasteurizing temperature, the temperature of the composted mixture being gradually raised during the warm up phase at a rate in the range of 10C to 1.40C per hour.

22. A process as claimed in Claim 21 in which the temperature of the composted mixture during the warm up phase is raised at a rate of approximately 1.20C per hour.

23. A process as claimed in Claim 21 or 22 in which air is passed through the composted mixture during the equalising phase and the warm up phase at a rate in the range of 100 cubic metres of air per hour per cubic metre of composted mixture to 200 cubic metres of air per hour per cubic metre of composted mixture.

24. A process as claimed in Claim 23 in which the temperature of the air being passed through the composted mixture during the warm up phase is raised at a rate in the range of 10C to 1.40C per hour during the warm up phase.

25. A process as claimed in Claim 24 in which the temperature of the air being passed through the composted mixture during the warm up phase is raised at a rate of approximately 1.20C per hour.

26. A process as claimed in any preceding claim in which the composted mixture is subjected to a cooling down phase after the conditioning phase, the temperature of the composted mixture being adjusted to a final temperature lying in the range of 160C to 250C and the composted mixture being maintained at the final temperature for a time period in the range of eight to ten hours.

27. A process as claimed in Claim 26 in which the temperature of the composted mixture is reduced at a rate in the range of 50C to 100C per hour during the cooling down phase.

28. A process as claimed in Claim 28 in which the temperature of the composted mixture is reduced at a rate of approximately 50C per hour during the cooling down phase.

29. A process as claimed in any of Claims 26 to 28 in which air is passed through the composted mixture during the cooling down phase at a rate in the range of 100 cubic metres of air per hour per cubic metre of composted mixture to 200 cubic metres of air per hour per cubic metre of composted mixture.

30. A process as claimed in Claim 29 in which the temperature of the air being passed through the composted mixture during the cooling down phase is reduced at a rate in the range of 50C to 100C per hour until the temperature of the composted mixture reaches the final temperature.

31. A process as claimed Claim 30 in which the temperature of the air during the cooling down phase is reduced at a rate of approximately 50C per hour until the temperature of the composted mixture reaches the final temperature.

32. A process as claimed in any preceding claim in which the air being passed through the composted mixture is recycled.

33. A process as claimed in Claim 32 in which the oxygen content of the air being passed through the composted mixture is maintained within predetermined limits by the addition of fresh air to the recycled air.

34. A process as claimed in any preceding claim in which the compost mixture comprises straw, poultry litter and water in the following range of proportions by weight of the compost mixture: straw 28% to 40%, poultry litter 15% to 30%, water 40% to 50%.

35. A process as claimed in Claim 34 in which the compost mixture comprises straw, poultry litter and water in the following range of proportions by weight of the compost mixture: straw 30% to 36%, poultry litter 15% to 25%, water 45% to 50%.

36. A process as claimed in Claim 35 in which the compost mixture comprises straw, poultry litter and water in the following approximate proportions by weight of the compost mixture: straw 35.5%, poultry litter 20%, water 44.5%.

37. A process as claimed in any of Claims 34 to 36 in which the compost mixture on being mixed is formed into a clamp and composted for a period of at least seven days.

38. A process as claimed in Claim 37 in which the clamp is turned at least once during the composting period.

39. A process as claimed in Claim 38 in which the clamp is turned at least twice during the composting period.

40. A process as claimed in any of Claims 37 to 39 in which water is periodically added to the clamp to maintain the water content of the mixture relatively constant during the composting period.

41. A process as claimed in any of Claims 37 to 40 in which gypsum is added to the compost mixture in the clamp.

42. A process as claimed in Claim 41 in which the gypsum constitutes in the range of 1% to 3% by weight of the compost mixture.

43. A process as claimed in Claim 42 in which the gypsum constitutes 2% by weight of the compost mixture.

44. A process for preparing a compost substrate for use in the cultivation of mushrooms, the method being substantially as described herein with reference to the accompanying example.

45. A compost substrate for use in the cultivation of mushrooms, the compost substrate being prepared according to the process of any preceding claim.

46. A compost substrate as claimed in Claim 45 in which the compost substrate further comprises mushroom mycelium.

47. A compost substrate as claimed in Claim 45 or 46 in which the compost substrate is packed into bags, each bag containing in the range of 18 Kg to 22 Kg of compost substrate.

48. A compost substrate as claimed in Claim 47 in which the mushroom mycelium is added to the compost substrate as the compost substrate is being packed into the bags.

49. A compost substrate substantially as described herein with reference to the accompanying example.