How to pasteurize
The common method of pasteurization used in Zimbabwe is the hot water bath. Some use other methods: steam method and some are using chemicals (some detergents, others hydrogen peroxide). The easiest method is the hot water bath and is easy and less risk as compared to steam, which needs boilers, some have invented their own boiler as the proper boilers are expensive and these are death traps as they can explode at any time. The substrate should be able to retain moisture content of 70 percent at spawning.
Hot Water bath
The hot water bath method will be described as it is the easiest and cheapest and has been used for a long time in Zimbabwe.
Other methods are still research level although others may use them with success. Used oil drums are cheap and readily available countrywide. Fire wood is the main source of energy cheaply available to most people in Zimbabwe. The substrate is stashed into a drum, after which it is put on a stand and then fill the drum with water slightly above the substrate. it is heated until the water reaches a temperature of 70 degrees Celsius and the temperature is maintained for one and half hours.
And then the substrate is removed from the drum using a garden fork on to a clean surface, preferably a cleaned plastic sheet. It is let to cool to 25 degrees Celsius or less and to reach moisture content of 70 percent. Some may be frightened on how to measure temperature it can be done without a thermometer. If you can place your hand in the substrate and you can keep it in there without getting burn, then you can inoculate. The right moisture content can be tested by the “squeeze test.” If a lot of water leaks out of straw as squeezing, then it is certainly too wet. Just a few drops of water should be released with some pressure. The test is applied to all the substrates.
Personally I prefer heating water in the drum after which the water is poured over substrate stashed in a separate drum. Heat water to 75-80 degrees celcius, by the time you finish pouring water into the substrate the temperature will be down to an average of 70 degrees celcius, cover drum and keep at that trmperature that levels. After 1 hour pasteurization is complete.
The equipment required for steam pasteurization is a boiler. (refer to the our button mushroom manual for a simple drum boiler) substrate is prepared as above, the substrate is placed in a bunker with a lid, a 200 litre drum with removable lid or a pasterurisation room this all depends on scale of operation. The steam is piped in until the temperature reaches between 60?c and 70?c and the temperature is help there for 2 to 4 hours. The temperature can be controlled by removing and replacing the lid/or switching the steam on and off.
*Bags-most common and easy
*Shelves- like button mushrooms with the exception that oyster mushroom does not require casing soil.
Mixing and bagging
There has been no standard of bag size with almost each farmer using his/her own. Most farmers have been using bags large enough to hold between 20-25kg of prepared substrate. Some use bags that are 60-100 centimeters long and having a diameter of 25-40 centimeters, the challenge comes at lifting these bags to hang them or place them on shelves. I recommend a diameter of 25-30 centimeters and a length of 40-50 centimeters. Plastic tubing of the correct diameter can be bought from suppliers and cut to the required length. The ends can be tied with string or the plastic itself can be knotted. Holes are punched into the bags for aeration.
Some growers have tried to make their own spawn in an effort to reduce expenses. Those who want to start the mushroom growing business would master and improve on the growing techniques every time and leave spawn production to others because sometimes diversification may bring disappointment to the grower as there may be risks associated with crop failure, high levels of contamination and low yields. First layer of substrate is put into the bag (5-10 centimeters* layers of 5cm quicly colonises faster) and then sprinkle spawn. This is repeated until the bag is full. It is necessary to decide how many layers are to be used and then divide the full amount of spawn for the bag so that each layer receives the same amount of spawn.
*Note that the incubation period can be increased due to various factors 14days is the general standard.
spawn. The density of the packed, spawned substrate must be loose enough to allow air to penetrate but the pieces of waste material must be close enough to maintain contact so that the mycelium can spread from one piece to the other. After packing make holes in the bag for aeration with a nail or wire and bags are moved to the dark room for spawn run.
Spawn run is the period of time when the mycelium is colonizing the substrate. There has been a wide gap of days allowed for spawn run by growers in this Zimbabwe, with time ranging from two weeks to four weeks. Which is the right time? After inoculation, the bags are incubated for 12-21 or more days at a temperature of 25-27?c. Bags are put in a dark room and the carbon dioxide content, moisture level and humidity level within the closed bags will be maintained for the duration of spawn run without any intervention by the grower. At the end of spawn run the substrate will be compact and become white with mycelium. I advise use of sample bags (On bags packed have at least two bags that are transparent as this will allow you to monitor the colonization and it can also allow you to detect contamination at an early stage.
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