During fermentation straw must decompose to release the nutrients required by the mushroom mycelium without causing the compost to lose too much structure. In tunnels this structure is necessary for sufficient aeration during the cook out process and mycelium growth.
In the growing rooms good compost structure prevents compost being over compacted in the shelves or trays so that water can be more evenly distributed over the entire compost layer This structure also guarantees sufficient gas exchange between the compost and the room air so the metabolic products can be removed and oxygen can reach the mycelium.
Good compost structure is obtained by shortening the fermentation period. The disadvantage is that the straw is less well decomposed Another way to create more structure in the compost is to mix well-fermented compost with less fermented material 10-15% is often just enough to get the right structure. The advantage of this method is that the majority of the compost is well decomposed so the mushroom mycelium can extract maximum nutrient value.
Con Hermans, AdVisie ‘The mushroom cultivation advisors'