COMPOST
13) Pasteurisation assumed to be at 56°C (white line), in reality it is only 54°C (red line).
Trichoderma can have enormous impact, but the
disease is pretty easy to detect, identify and manage.
mould can survive, Trichoderma almost certainly can too. I recommend activating the humidification during spawn run and in the pasteurisation tunnels to prevent the formation of dry patches. Most composters mix approximately 1% of phase II compost through phase I when filling the pasteurisation tunnels, but this practice is not without risk. Phase II compost often con- sists of what is left over of the compost after spawning. This is not always the best quality and may also contain dry patches which enter the pasteurisation and conditioning process for a second time. Any mould in these patches will not be destroyed because the conditions are far too dry. This presents a serious risk.
Dry bulb and wet bulb sensors Mushroom farms measure relative humidity in the growing rooms using two air sensors: a dry bulb and a wet bulb temperature sensor. The difference in temperature between the two sensors can easily be converted to the relative humidity. The same measuring principle is used in spawn run tunnels to measure the inlet air. The wet bulb temperature measurement measures the enthalpy of the air and indicates how much kJ of heat the air contains. This results in very stable control during mycelium growth. Wet bulb control is however rarely used in pasteurisation tunnels. It is not considered necessary because the RH is always high. However, this assumption is incorrect and greatly depends on the climate. The temperature measurements of the dry bulb and wet bulb can deviate considerably when the outside air is dry and a lot of fresh air is used. In this example, the inlet air temperature is measured and controlled based on the dry bulb sensor, but the wet bulb temperature is also
24 MUSHROOM BUSINESS
registered. The assumption is that pasteurisation is at 56°C, but in reality this is only 54°C according to the wet bulb temperature (photo 13). The inlet air temperature is also several degrees lower than assumed. It goes without saying that the pasteurisation process will be ineffective and any undesirable moulds will be activated during conditioning. The answer is clear to me. Regulate the air temperature using the wet bulb in the pasteurisation process too!
Pasteurisation phase Many people firmly believe that the pasteurisation phase kills competitor moulds, however, I must disappoint you. This explains my comments regarding dry patches that are mixed into the compost again. The purpose of pasteurisation at 60°C is not to kill competitor moulds but to weaken them. This gives beneficial moulds and bacteria an advantage and enables them to make the compost more selective. Some studies have revealed that Trichoderma was able to survive in compost that was steam treated in growing rooms at 60-65°C for 20 hours. We can also learn a lot from the following interesting example: One of my clients has a modern tunnel company with very good hygiene and only supplies phase II spawned compost in 20 kg blocks. These blocks are pressed in the spawning hall, wrapped in film, placed on the pallets and then delivered to mushroom growers. On arrival, the film is left intact until the day before casing. However, well before the blocks are opened, you can see signs of Trichoderma in ten of the blocks out of the 3000 filled at the farm (photo 14) which represents 0.3% of the total. The only explanation I have is a few lumps of compost in the pasteurisation tunnel that offer Trichoderma
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