Whilst most of the world’s mushroom supply comes from commercial mushroom farms, growing mushrooms is not as simple as many people believe. In fact, mushroom growing is one of the most technologically advanced and sophisticated agricultural industries in the world. Commercial mushroom production costs are high and require extensive capital investment. Whether you grow on small scale as a hobby; or on a larger scale, modern mushroom production is highly mechanized, requiring detailed knowledge and a high level of management skill and commitment for success. This commitment is required from the start all the way through to cropping and marketing.
In South Africa the white button and brown mushrooms are mainly grown, both of these belonging to the genus Agaricus. Furthermore it is mainly a fresh market with only a small percentage of SA’s mushroom production being processed into canned product, sauces and other value added products. It seems that the South African consumer has clearly made the choice to eat fresh mushrooms rather than processed mushrooms.
Less than 5% of the mushroom market is taken up by so called exotic mushrooms, including Pleurotus spp (Oyster mushrooms) and Lentinula spp (Shiitake). Although these mushrooms seem on paper to be less complicated to grow, one should not be deceived in thinking that it is an easier option. Even though oysters grow on uncomposted cellulose material (no casing material is needed), and Shiitake on woody substrates containing lignin compounds, they still require the sophisticated technology to manufacture substrate and then climate controlled growing rooms.
The basic process of growing Agaricus Mushrooms is set out below
Mushrooms belong to the fungi kingdom, which are heterotrophic organisms which lack chlorophyll and consequently produce their own food from an organic material. In the commercial production of Agaricus bisporus this food-and energy source is provided by a highly complex substrate or compost. Selective compost for mushrooms is found at the end of a complex, controlled biological process involving micro-organisms. When well prepared, it is a living ecosystem that is suitable for the growth of mushrooms. To consistently prepare a high yielding compost is probably the most difficult part of the growing operation. In the South African industry most growers produce their own compost unlike in Europe for instance where mushroom companies specialize in making compost for resale or growing the mushrooms from compost purchased from a composter. Unfortunately in SA there is no compost readily available to purchase so mushroom farmers will have to make their own compost first.
The basic ingredients for preparing a synthetic compost are:
The quantities used depends on the chemical analysis of the ingredients in particular the nitrogen content of the chicken litter.
A typical formula is : 1 000 kg straw (moisture content 15%)
800 kg broiler chicken litter (moisture content 40%, nitrogen 4%)
85 kg gypsum
The process of changing these ingredients into a suitable medium for mushroom production takes place in distinct phases.
The purpose of this phase is to wet and mix the raw materials. Biological activity does not take place unless water and a supply of available nutrients is added. Straw bales are stacked outside and continuously sprayed with water (often the run-off water from the compost yard collected and aerated in a pit). After wetting for 5-6 days the bales are broken and part of the chicken litter (30-50%) is mixed through. The portion of chicken litter applied depends on the quality of the straw, the time of the year (in summer less is added in the beginning) and the nitrogen content of the chicken litter.
The initial wetting and mixing phase occurs over a period of 7 days.
After wetting and mixing the compost is formed into long narrow stacks or windrows (typically 1.8 - 2m wide and 2m high) either in the open or in a covered area. The stacks are mechanically turned with compost turners (usually every other day) and watered. At some point the balance of the chicken manure is added and mixed through. This process allows for micro-organisms to grow and reproduce. Their activities cause the temperature in the pile to rise. The centre of the stack should reach 70 - 80oC. Much of the nitrogen present is ammonified. Such a conventional phase I usually takes about 7 days.
Over the last few years, the use of specially built bunkers with under floor ventilation and sometimes with an open or partly open top has become popular. This is to make the process more environmentally friendly by reducing the “smell pollution” dramatically. After the initial pre-wetting and mixing of the raw ingredients (5-6 days) the material is built into a loose flat pile and turned every other day for approximately another 7-10 days. At some point the balance of the chicken manure is added and mixed through. Temperatures in the pile are kept from exceeding 65oC in order to allow microbial activity. From there the material is filled into a bunker. Oxygen levels in the bunker are monitored to ensure that compost does not go anaerobic. The supply of air from below the pile results in the bulk of the compost reaching temperatures of more than 80oC. The wetted and mixed ingredients are usually taken out of these bunkers at 3-4 day intervals and put back (total of about 7 days). The move during this process ensures thorough mixing of the ingredients. At these high temperatures microbial activity ceases and chemical reactions take place leaving the compost with a dark-brown colour indicating caramelization and browning reactions have occurred. At this stage the compost should be pliable, the water content 72-75%, the smell of ammonia very strong and the pH in excess of 8.
Phase II is carried out under carefully controlled conditions mostly in bulk in specific designed tunnels with aerated floors. Phase II has two main purposes, firstly pasteurization (to free the compost from undesirable microbes and pests) and secondly conditioning (to become mushroom specific by getting clear of ammonia and free of readily available carbohydrates). Through proper manipulation of temperature and ventilation these two primary objectives are accomplished.
Initially the compost is allowed to settle so that it is more or less uniform throughout. This may take up to 10 hours and is called equalizing or leveling. Thereafter the the pasteurization (also referred to as the kill) phase occurs where the temperature is allowed to rise to 60oC (either by itself or by the introduction of steam). The temperature is held at this level for 8-10 hours. After pasteurization the temperature of the compost is reduced to 48oC for the conditioning process which usually is about 4 days. In total the phase II process usually lasts about 6 days. At the end of conditioning the compost must be stable and free from ammonia. It is then cooled to around 25oC by circulating filtered air through the material.
At this stage the compost should xhave a moisture content of 68-72%, nitrogen content of 2.3-2.4% and pH of around 7.3 and ready to be spawned.
Spawn (mushroom mycelium grown on sterilized grain), commercially available, is mixed into the compost at a rate of 8 litres per tonne (0.5% by weight). The spawned compost is filled into the final growing containers (bags, trays or shelves) for incubation or ‘spawn running’.
This part of the process takes place in purpose built tunnels, spawn running rooms or in the growing rooms. These rooms must be well insulated and equipped with air-handling systems to maintain temperature and relative humidity levels. The air that enters such units should be filtered in order to eliminate dust that carries large loads of bacteria and fungal spores that may cause disease. During this stage mushroom mycelium is growing from the sterilized grain into the compost. The end result is a compost completely colonized by mushroom mycelium.
Compost temperatures during spawn run should be maintained at 25oC by using filtered air. Compost temperatures normally reach a peak around the 9th day and it is advisable to have cooling facilities in the spawn running room. The humidity in this stage is kept high and the carbon dioxide concentration at 2% or higher. During the spawn run, which takes between 14 and 17 days, the mushroom mycelium colonizes the compost.
To grow mushrooms economically all year round there must be substantial investment into the growing rooms. Growing rooms must be well insulated and purpose built to ensure maximum yield and quality of mushrooms. It is necessary to control the temperature, maintain high relative humidity and supply adequate fresh air in the growing room. Air that enters a growing room should also be filtered. Good lighting is needed to assist harvesters later in the harvesting of the mushrooms.
There are three main types of growing room systems, these being the shelf system, tray system and lastly the more economical to start up, the bag system. These systems have different advantages and disadvantages and must be thoroughly researched prior to deciding which system to adopt.
To stimulate the mushroom mycelium to convert from the vegetative to the reproductive phase, a 4-5cm thick layer of a suitable material needs to be applied onto the surface of the fully colonized compost.
If spawn run was done in bulk the compost has to be filled into the growing containers, compacted and then covered with a casing layer. The casing layer protects the compost from drying out, and it provides a suitable micro climate for the pin head to develop. The casing layer serves as a water reservoir and therefore needs to have a high water holding capacity. It must have a neutral or alkaline pH of about 7.5 and a low conductivity. Usually the casing layer harbors bacteria that stimulate pinhead formation.
The most popular and effective material used these days, is a mixture of humified black peat and sugar beet lime (for adjusting the pH), imported from Europe. In South Africa no natural peat moss is available, only limited resources of topgenous (reed sedge) peat.
The casing layer has to be applied as evenly as possible on a level and compact surface. The mushroom beds should be watered as soon as the casing is applied. Frequent waterings should be given up to about 2 days before mushrooms are initiated (pinning). The amount of water depends entirely on the nature and structure of the casing soil. The aim is to raise the moisture level to field capacity and to prevent water from running through into the compost.
During the pre-pinning the compost temperature is maintained at the same level as during the spawn running (25-27oC) with a high CO2 level (2 – 3%) and relative humidity (90 – 95%).
Once the mycelium has reached the surface of the casing (9-11 days after casing), the crop is induced to fruit. This is done by reducing the air temperature to 16-18oC over 3-5 days and also reducing the carbon dioxide concentration in the air to about 0.8-1% by generous ventilation. This temperature ‘shock’ combined with the lower CO2 leads to pin formation. At this stage the humidity can be lowered to about 87-90%, a constant supply of fresh air to keep the CO2 below 2% and an air temperature of about 18oC will encourage pin outgrow and usually takes between 5-9 days. Higher CO2 levels and higher temperatures lead to less pins developing and lower CO2 levels and temperatures will lead to more pins developing.
Fruiting occurs in breaks or flushes beginning about 17 days after casing and continues at weekly intervals. Generally three breaks are picked and then the crop is removed to make room for a next crop. Between breaks the beds should also be watered. To reduce discolouration, chlorine can be applied with the water at a rate of 90-120ml/100litres.
In South Africa mushrooms are picked by hand and therefore it is a hugely labour intensive exercise employing many people in the areas around the farms.
Button mushrooms are picked when the cap reaches maximum size and before the veil opens. They are individually picked with an upward, twisting pull. The lower part of the stem is cut off with a sharp knife and the mushrooms are graded as they are picked and placed directly into the marketing containers. The brown mushrooms are harvested as closed buttons and sold as Portabelinnis or they are harvested as big open mushrooms sold as Portabellos.
It is of utmost importance that mushrooms should be handled with extreme care as they are bruised easily. After harvesting they should be cooled as soon as possible, transported in cooled trucks and displayed on refrigerated shelves. The most suitable temperature in a cold room is 2-4oC with a high relative humidity.
At the end of a mushroom crop the growing room and its contents should be sterilized with live steam. The compost temperature should be held at 70oC for 8-12 hours. This eliminates pest and diseases that might have appeared during the growing cycle and also kills mushroom spores and living mycelium that may transmit virus disease. The spent compost should be removed from the farm as soon as possible as it poses a source for pests and diseases. Spent mushroom compost is much sought after as a valuable weed free fertilizer for gardens and in most cases sold to landscapers to be put back into the earth.
It is very difficult to estimate the total cost of setting up a mushroom-growing facility. Many factors need to be considered, such as cost and availability of raw materials, the market size and proximity, the composting process (the extent of mechanization, composting in ricks or bulk tunnels, aerated floors, blending lines etc.), the growing system (bags, trays or shelves), labour cost, size of the facility etc. A rule of thumb that the larger commercial mushroom farmers work by is R2 million per ton of mushrooms that you want to grow per week. This investment can be broken down as: R1 million for the composting and Phase II sections and R1million for the growing rooms. This excludes the costs for a packhouse, distribution fleets and staff buildings such as change rooms and toilets.
Mushroom growing is a scientific operation which requires meticulous record keeping to achieve consistent results. Records and data sheets should be kept on each compost, from the time of pre-wetting until it is finally removed from the growing room as spent compost at the end of the crop. Such data should include the composition of the compost, analysis of the raw materials and the compost at various stages, growing parameters, performance of each batch of compost in terms of quality of mushrooms, size and yield.
For those interested in mushroom farming, it is important to do your homework before investing in land or a production facility.
Useful websites include
Agaricus spawn is supplied by
Sylvan Africa (Pty) Ltd Tel: +27.12.665.2210 Fax: +27.12.665.2212