This is how we make grown substrate
Horse and poultry manure, straw and gypsum form the basis for a natural nutrient medium on which millions of kilos of mushrooms grow. Through fermentation, pasteurisation and mycelial growth, we process these residual flows into high-quality grown substrate.
570,000 tonnes of raw materials processed per year
Residual flows from around 850 stables and 120 poultry farms
Good for weekly production of 3,500,000 kilos of mushrooms
This is how circular agriculture works
Walkro connects different links in the agricultural chain. What is a residual flow for one is a valuable raw material for another. This is how we close the cycle. Every day again.
Controlled processes, constant quality
Every week we process agricultural raw materials into high-quality grown substrate for mushroom cultivation. What starts with manure, straw and gypsum, through fermentation, pasteurisation and growing, becomes the nutrient medium on which millions of kilos of mushrooms grow. This is how we supply thousands of tonnes of substrate to growers all over Europe every week.
Phase 1 - Fermentation
In the first stage, we mix raw materials into a base mixture. Bacteria start a natural fermentation process in which sugars and other easily absorbable nutrients are broken down. At the same time, the wax layer around the straw breaks down, releasing nutrients. This creates a selective nutrient medium: ideal for the mushroom, but less suitable for competing organisms.
Bacterial activity raises the temperature to around 80°C. This heat occurs completely naturally, without mechanical heating. As bacteria need oxygen, we continuously aerate the substrate. The combination of nitrogen and high temperatures creates ammonia, which helps to further break down the straw particles.
Whereas this process used to take place outdoors, we now carry it out entirely indoors in closed tunnels. With sensors, fans and computer-controlled systems, we precisely control air, temperature and humidity. This is how we keep the process stable and the substrate quality constant.
The released air is cleaned in air scrubbers. The resulting process water is reused in the process. In this way, we create a stable and high-quality basis for the next steps in the process.
Phase 2 - Pasteurisation
Fermentation is followed by the sweating out or pasteurisation process. In this phase, we further prepare the substrate for the mushroom. We kill harmful organisms and break down the ammonia present, further increasing the selectivity of the substrate.
After the tunnels are filled, we let the substrate settle for 10 to 18 hours. Then the temperature rises to about 58°C due to activity of microorganisms. We maintain this temperature for eight hours so that harmful organisms are killed off under the influence of time, temperature and ammonia.
Then we lower the temperature to 43-48°C. In this temperature range, other micro-organisms convert the ammonia harmful to the mushroom into nutritious nitrogen.
The entire process takes five to six days and takes place in closed tunnels with slatted floors, through which the substrate is continuously aerated. With sensors, fans and filtered outside air, we precisely control temperature and air supply.
Phase 3 - Continuous growth
Phase 3, the growing-through process, is the final step in substrate preparation. The transition from phase 2 to phase 3 is the most critical moment in the process. After phase 2, the substrate is free of harmful organisms. Therefore, when we take it out of the tunnels to graft it, the production environment must be completely sterile.
At this stage, we inoculate the substrate with mushroom mycelium. This mycelium is pre-grown on sterilised cereal grains. These grains form the first food source for the mycelium and are also called spawn. Specialised companies supply this spawn to Walkro.
After inoculation, we store the substrate again in tunnels. At a temperature of about 25-26°C, the mycelium grows from the grains through the substrate and colonises the entire mixture.
After 15-18 days, we stop the grow-through process and load the substrate for transport to the customer. During this loading, we add a nitrogen-rich supplementary nutrient, often soya-based. This additional nutrient increases the final mushroom yield.
In some cases, the substrate grows further up to stage 4.
Phase 4 - Ingrowth and budding
In phase 4, the mycelium continues to grow and the mushroom begins to bud. We deliver this pre-fructified substrate in crates to mushroom growers. After delivery, the product is immediately ready for use.
Biological substrate
Walkro also produces substrate based on 100% organic raw materials. We produce this substrate via a specific production process and it is available in various forms, such as bulk, packages and phase-4 substrate in trays.
For this product, Walkro has SKAL and Bio Suisse certification.
Parcels and transport
In Belgium, Walkro has a modern facility where substrate is packed in 20 kg packages. From here, we supply our products to mushroom growers worldwide.
Together with partner DTO, we handle the loading, cooling and transport of the containers. Thanks to a patented loading method and continuous monitoring during transport, the quality of the substrate remains optimal.