Mushroom Straw: Selection, Storing, Mixing, Moisturizing Guide

An integral part of most substrates for growing oyster mushrooms is the straw of cereals (wheat, barley, rye, oats, rice, millet, etc.). Good results are obtained on stems, seed husks, and husks of various agricultural crops (rapeseed, sunflower, buckwheat, etc.).

During the growing season, plants become infected with various microorganisms (primary infection), including competitive oyster mushrooms. To prevent the development of competitive microflora, a number of rules must be observed.

mushroom straw

Selection of raw material for mushroom straw for mushroom growing

An integral part of most substrates for growing oyster mushrooms is the straw of cereals (wheat, barley, rye, oats, rice, millet, etc.). Good results are obtained on stems, seed husks and husks of various agricultural crops (rapeseed, sunflower, buckwheat, etc.). During the growing season, plants become infected with various microorganisms (primary infection), including competitive oyster mushrooms. To prevent the development of competitive microflora, a number of rules must be observed (using straw as an example):

Raw materials must be fresh, dry

It is better to collect straw immediately after threshing cereals. Straw must be harvested in dry weather. Moistened straw is an excellent substrate for the development of competitive microflora.

Raw materials must be clean, homogeneous in composition

Straw should not contain foreign impurities: earth, weeds, green parts of plants. Good quality straw is golden yellow in color with no signs of decay or mold.

Proper storage of raw materials

Raw materials must be stored under conditions that prevent moisture. Straw is often stored in stacks. If the straw in the rick is stacked correctly, then only the outer layer of straw gets wet, and the inner layers are kept dry. Straw, compressed into bales and laid under a shed or in a hangar, is the most preferred storage option.

Procurement of raw materials in the amount of annual demand

If raw materials are harvested for a year of work before the next season of harvesting, then it is possible to ensure sufficient stability of the characteristics of raw materials, provided that they are stored correctly. All this as a whole will improve the reliability of the mushroom farm.

It is known that freshly harvested straw inhibits the development of oyster mushroom mycelium in the first 3 months of storage. A certain supply of well-stored last year’s straw will help solve this temporary problem. A somewhat different situation arises when using sunflower husks. The husk obtained by threshing freshly harvested sunflower seeds is of excellent quality. However, if sunflower seeds have lain for half a year, and even in humid conditions, then the husk obtained from them causes a lot of problems due to the development of competitive microflora.

Quality control of raw materials

quality control of raw materials is carried out at the place of collection (visually, organoleptically), during its delivery and, finally, at the enterprise itself, where various analyzes are carried out: chemical (total nitrogen content, pH), physical (humidity of air-dry raw materials before storage ), microbiological (infection with competitive microorganisms), hygienic (the content of pesticides, heavy metals, radioactivity).

The ecological purity of raw materials is a necessary condition for obtaining environmentally friendly products – mushrooms. Mushroom mycelium has the ability to accumulate some heavy metals, especially zinc and cadmium. Certain types of raw materials may contain an increased amount of these elements, for example, waste from printing houses. Mushrooms grown on a substrate containing such components will no longer be environmentally friendly and may become hazardous to human health.

According to some reports, the use of pesticides in the cultivation of wheat had no effect on the quality and size of the oyster mushroom crop. Nevertheless, when choosing a place for harvesting raw materials, not only its environmental friendliness (contamination with heavy metals, radionuclides) is taken into account, but also the intensity of plant treatments with pesticides!

Storage of mushroom straw

Raw materials are stored in a dry, ventilated room with convenient access for transport, an unloading platform, mechanization of loading and unloading operations, and fire extinguishing equipment.

Equipment for mushroom straw storage room

Raw material warehouse equipment.

  1. Waste container. 
  2. Silo unloading auger. 
  3. Silo tower for wet dust from straw. 
  4. Exhaust axial fan with humidifier. 
  5. Bales of straw (15 kg, 25 kg, 100 kg, 200 kg). 
  6. Lift. 
  7. Roller conveyor. 
  8. Closed connecting gallery. 
  9. Substrate preparation workshop.

During the loading and setting of the bales, the room is maintained at a reduced pressure so that dust does not spread throughout the mushroom farm. Lifting devices are used for storage. Dust is captured by an exhaust axial fan, wetted with water and fed into the silo, then by auger into a closed garbage container.

Check the guide on  How to Clean and Store Mushrooms.

Grinding of mushroom straw

Grain straw and stems of various agricultural crops must be crushed. Straw is crushed in various kinds of straw cutters, roughage choppers, plant material choppers, hammer crushers.

At the same time, various fractions of straw are obtained: 50-100 mm, 30-50 mm; 20-30 mm, 10-20 mm. The smaller the fraction, the denser and more uniformly the substrate block can be formed, and less effort is needed to form it.

The straw must not only be cut into pieces but also flattened, which is achieved using hammer crushers. The straw treated in this way is better moistened since the outer wax layer of the straw is damaged.

Uncrushed or coarsely chopped straw is poorly compacted, because of this, air cavities are created in the bags, where, during the period of fruit formation, the rudiments of fungi form and die if the film is not cut. Weak compaction of the substrate (less than 0.35-0.40 kg / l) leads to a significant decrease in the volume of the block after the incubation period or the 1st wave of fruiting. The film lags behind the substrate over the entire volume of the block. In such a situation, it is necessary either to remove the entire film or to make a new molding of the substrate, ensuring good tension of the film over the substrate block.

Thus, the degree of grinding of plant material affects the density of the substrate, the course of fruiting, the quality of mushrooms, as well as the yield of the crop from one container. Too small particles (less than 3 mm) create difficulties with gas exchange since over consolidation is possible during the formation of the block.

To create an optimal structure, the fine fraction is mixed with large particles (10-30 lamas). During grinding, a lot of dust is formed, consisting of the smallest particles of the substrate and spores of microorganisms. To prevent the spread of dust, the room where grinding is carried out is isolated from the external environment and from other rooms of the farm.

It is desirable to maintain a reduced pressure in this room, due to the operation of the exhaust fan, which collects dust in the silo device.

An easier option is to use a tarpaulin that limits the spread of dust. Very convenient grinders with a pneumatic conveyor that feeds the crushed meal directly into the heat treatment device.

General requirements

Room requirementSeparate, closed, adjacent to the preparatory workshop. Exhaust ventilation, dust is collected in a wet silo. The pressure is reduced. The room is dry, with a smooth finish.
EquipmentChopper. Exhaust fan with wet silo.
SafetyFire-fighting equipment.
TerritoryMaintained clean.

Various ways to moisten mushroom straw raw materials

Sprinkling2-4 days in a flat pile with occasional tedding
Cold soaking water1-3 days in baths (alkalinization of water with lime speeds up the process).
Soaking in the mountains water1-4 hours in bathtubs and faucets.

Mixing mushroom straw

If the substrate consists of several components or mineral and nutrient additives are used, then there is a need for uniform mixing. Mineral and nutritional supplements are subjected to the same heat treatment as the substrate. If the components are added after heat treatment of the substrate, they are pasteurized separately.

Various mechanisms are used for mixing: mixers, concrete mixers, feeders. In systems with mixing (mixers-steamers), a uniform distribution of all components is obtained. In systems without mixing (containers, tunnels), the components are mixed prior to loading or stacked in layers during loading.

Components used in small quantities (mineral, nutritional supplements) are conveniently added during inoculation along with mycelium, but they must be thermally pretreated.

In the technological chain, the mixing operation is as follows:

Straw pasteurization

chopped straw is soaked for 9-3 days.

  • after draining the water, the straw is mixed with 10% gypsum and 3% feather flour. Thoroughly mixed in a screw mixer;
  • pasteurize substrate at +60 °C for 24 hours under aerobic conditions.

Xerothermic treatment of straw

  • chopped straw is thoroughly mixed with 10% legume hay in a screw mixer and loaded into the tunnel;
  • steam dry substrate at 100 °C -1.5 hours;
  • moisten the substrate with drinking water in a screw mixer, adding the calculated amount of water.

Hydrothermal treatment

  • straw chopped is loaded into a container;
  • pour water with 0.5-1.0% lime;
  • treated at a water temperature of 60-70c (2-12 hours);
  • the water is drained, cooled, and mixed with seed mycelium and nutritional supplements (thermally treated separately).

Moisturizing Mushroom Straw

Humidification of the substrate should provide the necessary supply of moisture for the entire period of cultivation (usually 2-3 waves of fruiting). For a substrate packed in a polyethylene film with perforation occupying no more than 5% of the entire surface, the optimum humidity is 65-70%.

Water absorption of various types of plant materials is significantly different. Plant substrates that do not have a wax coating are easily wetted with water and quickly moistened (sawdust). Substrates with a waxy or fatty layer are slowly moistened and require prolonged soaking in water (cotton lint, straw). Straw chopped is moistened on the grounds, watered and periodically mixed for 1-3 days. Cotton linters are shed with water in layers during loading into a container before heat treatment.

The acceleration of the moistening process is facilitated by an increase in the temperature of the water and mixing of the substrate. In the case of xerothermic treatment, when dry chaff is treated with steam, subsequent wetting with water is much faster, since steam removes part of the wax shell and contributes to the swelling of the straw. Straw is usually mixed with the calculated amount of water in a screw mixer. The humidification process takes no more than 30 minutes.

Vacuum is used in some modern devices for straw moistening. This removes air bubbles from the straw and very quickly saturates the plant fibers with water. The moisturizing process is reduced to 10-15 minutes. Straw moisture reaches 75-78%. The alkaline environment contributes to the good wetting of straw. For example, the addition of lime shifts the pH of the medium to 7.5-8.5 and facilitates wetting.

Very often, obtaining a high yield of oyster mushrooms is limited by a lack of water in the substrate. Each kilogram of mushrooms removes 900 g of water from the substrate (the water content in mushrooms is about 90%) and the same amount is lost with transpiration evaporation from the surface of the fruiting bodies. When the moisture content of the substrate drops below 40%, the transport of nutrients from the mycelium to the fruiting bodies is inhibited. The substrate block in this state can form the rudiments of fruiting bodies, but their further development will be impossible.

A substrate covered with a polyethylene film and completely overgrown with mycelium is very difficult to re-moisten, therefore, during the initial moistening, it is necessary to saturate the substrate with water as much as possible, but in such a way that there is no free water. Areas of the substrate containing excess free water are colonized either by anaerobic bacteria or competitive molds. In this case, the block becomes spotty or striped, depending on the distribution of waterlogged zones. It is also necessary to take into account the formation of biological water during respiration (up to 20% of the dry mass of the substrate). In high, cylindrical bags, waterlogging is especially evident in the lower zones, where water accumulates under the influence of gravitational forces.

If you work on the 1st wave of fruiting, then the moisture content of the substrate can be formed at the level of 65-68%, if on 2-3 waves – at the level of 70-72%, of course, if the moisture capacity of the substrate allows it. In all cases, free water (flowing out when the substrate is squeezed in the hand) should be at a minimum level. The substrate in the polyethylene container must retain a small residual moisture capacity in order to absorb excess, free “biological water”.

Flushing mushroom straw

Substrate washing is used to remove contaminants or mycelial growth inhibitors.

For example, sunflower husks often contain small particles of threshed kernels. Without washing in the husk substrate during overgrowing, the temperature rises strongly (more than 30 ° C) and, as a result, various competitive molds (mucor, Trichoderma) develop.

A similar situation occurs on cotton linters, which contain a lot of dust fractions. Washing the tows from dust makes it possible to grow oyster mushrooms on such a substrate even without heat treatment.

Freshly harvested straw contains inhibitors of oyster mushroom mycelium growth, which are destroyed only after 3-4 months of storage. When straw is soaked in water, the inhibitors are washed out, and the mushroom yield increases (Table 3). Without soaking on straw, microflora antagonistic to oyster mushroom (competitive molds) often develops. This is due to the fact that during soaking, soluble forms of sugars go into solution and are removed with water.

Effect of straw soaking on the yield of oyster mushroom
(yield in % of the wet weight of the substrate)

TreatmentFresh strawStraw 6 months
Hydration + Soak**10.115.5

* Watering the straw on the site 2-3 days

** Soaking for 48-60 hours in water.

In France, they use long-term soaking of chopped straw for 60 hours in tanks with the substrate completely submerged underwater. After the water drains, the straw has a moisture content of 72-75%.

The temperature inside the substrate during the incubation period is one of the most important factors that must be controlled. When the temperature rises above 30 ° C, competitive molds and fungi (Trichoderma, mucor, dung beetles) rapidly develop in the substrate. When soaking, the substrate loses readily available nutrients, it is depleted due to the most “dangerous” nutrient fraction. On the soaked substrate, the temperature increase in the first days of incubation (thermogenesis) is much less pronounced, especially in large blocks weighing more than 15 kg.

In the USA, France, Italy, a combined version is used: moistening and washing. The crushed straw is moistened on the sites for 2-3 days and then soaked in water for a day, completely immersing the straw under a layer of water.