Excerpt from the Course
SPAWNING
Spawning is the procedure where spawn is added to the prepared compost. The following things are most important:
*Grains of spawn should be separated from each other as thoroughly as possible as the spawn is spread over the surface of the compost.
*Spawn should be mixed evenly through the compost.
*Conditions should be kept as sterile as possible (Wear clean clothing and footwear, wash your hands before carrying out spawning, tools should be sterilized in detail, formalin or some other antiseptic which will not damage the mushroom).
In many larger and sophisticated mushroom farms, the practice is to mix spawn throughout the compost thoroughly using machinery. The older system involves spreading the spawn over the surface and mixing it in with forks.
Do not add spawn to compost while the temperature of the compost is above 30 degrees centigrade. (34 degrees will kill the mycelium). If there is any ammonia present in the compost (i.e.: through composting being incomplete), the mycelium is likely to not grow at all.
Normally 6 to 10 litres of grain spawn should be used for every tonne of compost.
The optimum temperature for the mycelium to grow is 25 degrees centigrade. Three or four days following spawning, a cottony growth should appear around the grain, and depending on conditions, the mycelium should have thoroughly grown through the compost after about 2 weeks.
Once the mycelium has grown to this point it will generate increased heat in the compost. It is important that the temperature be held down, and this is normally done by ventilation or by a cooling system.
In summary:
Spawn – consists of living mushroom mycelium growing on sterilised wheat or sorghum grain. This is sown onto the compost.
Spores – these are equivalent to the reproductive ‘seeds’ of mushrooms (technically are not seeds). They are produced when the mushroom breaks the veil and the gills are exposed, thereby releasing the minute dust-like spores.
Spawn production
Spawn of Agaricus bisporus is produced by growing the mycelium of the mushroom on sterilized cereal grains under sterile, laboratory conditions.
Virtually any type of grain can be used, though rye and millet are most commonly used in commercial situations.
Spawn suppliers often claim millet is better because it produces more inoculating points per unit weight than larger grains. Another argument is sometimes put that larger grains such as rye, provide greater food reserves for the mycelium than the smaller grains such as millet.
TYPICAL METHOD OF PRODUCING RYE GRAIN SPAWN
1. Grain is boiled in water (Use hard type grain so it doesn’t burst in boiling). Moisture content of the grain will be increased by 10 – 40% at this stage.
2. Drain off excess water and mix with 2% gypsum (by weight) and 0.2% calcium carbonate (by weight). This both adjusts pH and reduces the tendency for grains to stick together.
3. Grain is then placed into containers and sterilized in an autoclave (i.e.: steam sterilized under pressure ‑an autoclave is a device similar to a steam cooker). Treat for 1.5hrs at 121 degrees centigrade and at 15 p.s.i. Grain is then allowed to cool.
4. Spawn which has been grown on a special (different) substrate is then added to a container of prepared grain. This provides a “master culture”. The master culture is grown at 25 degrees C. for 11 to 14 days. Over this period, the spawn is shaken in its container at least twice to ensure thorough mixing. The containers used might be glass or polypropylene jars, or perhaps autoclavable bags.
5. Samples of inoculated grain is then taken from the master culture and added to containers of prepared spawn to produce larger numbers of “secondary cultures”.
Varieties
Numerous hybrids and varieties of Agaricus spawn are available from spawn suppliers. These are generally known by numbers rather than names (such as are used for varieties of green plants).
A range of commercially successful hybrid strains were developed in both Holland and Taiwan in the early 1980’s.
Dutch hybrids released in 1981 were called U1 and U3. These have since been given names U1 being called “Horronda” and U3 being called “Horwitu”. These two were the result of breeding aimed at combining the desirable characteristics of the off white and the pure white spawn types.
The off white produce better size and weight than pure white. The pure white produce a smooth, more attractive, white cap. These varieties have been very successful in the western world producing high quality and high levels of production.
Susan Stephenson