Mushroom production
3. Hygiene procedures
Department of Primary Industries and Fisheries.
Mushrooms are the edible fleshy fruiting bodies of certain
fungi, which may be gathered wild or grown under cultivation. The most commonly
cultivated mushroom species is Agaricus bisporus, although many other
species are now gaining recognition in Australia due to the widespread
consumption of Asian cuisine.
Cultivated mushrooms are usually grown in the dark in climate-controlled rooms. The fungal inoculum or "spawn" is added to a pasteurised substrate in growing containers or beds. After the fungal strands (mycelia) have spread through the compost, a layer of peat or soil (the "casing") is added. The fruiting bodies begin appearing about 6 weeks after spawning and continue appearing in flushes about 7-10 days apart for the next 6-8 weeks. The first three flushes are the most productive. The cap and a small section of connected stem are usually harvested before the caps are fully expanded.
Pest management programs, particularly for diseases are made more difficult by the fact that the mushroom is itself a fungus. Strict adherence to hygiene programs at all stages of production will greatly reduce potential problems. Although the following procedures may appear excessive and shortcuts tempting, not maintaining high levels of hygiene will often result in production problems with a corresponding loss in yield.
Production stages
Buildings and farm layout
Farm design
It is much easier to maintain hygiene practices in a farm designed for mushroom growing than in one that has been modified from some previous purpose. When designing the farm layout, areas where pests and disease organisms would normally occur can be classified as 'dirty' (for example where the compost is produced). Movement between these and the 'clean' areas (eg the mushroom growing rooms) should be restricted.
Storage areas
Classify the storage areas as above. Do not allow used equipment to be placed in areas for storing growing or harvesting equipment unless it has been sterilised.
Growing areas
Ideally, after being established, the growing areas should be sealed at all but one entrance. Strict quarantine should be enforced with footbaths supplied at all entrances and the opening of doors kept to a minimum. If the growing areas are rooms off a cental corridor, keep the corridor clean at all times. Disinfect it regularly and ideally maintain a slightly higher air pressure in the corridor to prevent disease spores from leaving the growing rooms. All buildings should be thoroughly cleaned and routine disinfections carried out. All machinery and equipment should be thoroughly cleaned after each use.
Growing containers and media
A range of growing containers are suitable for mushroom production, ensure that they are free of contaminants before use.
The standard growing media is a partially-decomposed organic compost. This compost will have a range of micro-organisms contributing to the decomposition process, some of which will be detrimental to mushroom production. The growing media is therefore pasteurised (referred to as "peak heating") before the spawn is added. It should be noted that pasteurisation (a process commonly used on milk) is not the same as sterilisation. After peak heating, the compost should be used for growing as soon as possible to minimise possible re-contamination.
Care must be taken when preparing the spawn as this is an important production stage and contamination could result in heavy crop losses. The spawn production area should be quarantined with limited staff access. Any personnel who are required to enter should wear clean or protective clothing (overalls, plastic overshoes etc.).
Harvesting
Harvest progressively from the younger to the older areas. Pickers and equipment should be allocated areas or rooms and be restricted to these areas only. Provide the pickers with overalls that are washed daily. Equipment (knives, trays etc) should be disinfected after use.
Post harvest
The growing area should be thoroughly treated before the used compost is removed. Raising the temperature within the room (71oC for 12 hours or 60oC for 48 hours), known as "cooking out" is usually the easiest method. If the area is not suited to prolonged heat, apply both an insecticide and a fungicide to minimise remaining pests and diseases. If the area is sealable, a fumigant or sterilant could be considered. Remove the spent media and transfer it off the farm site to minimise disease risk.
All growing containers should be suitably disposed of after the production cycle or sterilised if being reused. If dipping equipment in a sterilising solution, change the solution regularly. Hose and scrub out the entire growing area once the spent media has been removed and disposed of. Disinfect the floor and walls of the growing area before using it for the next crop.
General hygiene
Visitors should be kept to a minimum, and the areas they can access restricted. These precautionary measures will particularly apply to people such as sales representatives that may have been into recent contact with other mushroom production areas.
Plan activities on the farm so to minimise cross-contamination. For example, the setting-up of new crops should not be taking place while old crops are being removed. As many pests can become airborne, the direction of the prevailing winds should be taken into account when planning (ie clean areas should not be situated down-wind from possible sites of contamination).
Ideally, there should be two tea-room areas for staff - one in each of the clean and dirty farm areas. Staff should also be restricted from entering any "clean" areas if they have been working in the dirty areas. In many cases, contamination within the growing areas can be traced to staff movements.
Further information
Other notes in the Mushroom Production series are:
The Australian Mushroom Growers Association regulates
the mushroom growing industry. They can be contacted at Locked Bag 3, 2 Forbes
St, Windsor, NSW, 2756. Ph (02) 4577 6877 or Fax (02) 4577 5830.
Information contained in this publication is provided as general advice only. For application to specific circumstances, professional advice should be sought. The Department of Primary Industries and Fisheries, Queensland has taken all reasonable steps to ensure the information in this publication is accurate at the time of publication. Readers should ensure that they make appropriate inquiries to determine whether new information is available on the particular subject matter.
Last updated 04 February 2004
