Cultivate Oyster Mushrooms | Hot water Pasteurization

There is a lot to say about cultivating a crop of your own mushrooms. “Firstly it’s NOT like growing beans, but surely much more rewarding.” The first time I saw the pinning mushrooms developing into fruit, is one of my fondest memories. For those out there that might want to take this up as a hobby, I have compiled some guidelines.

The Oyster mushroom family, Shiitake, Reishi and the Lions mane mushrooms are all part of a group of fungi called Saprophytes. In Nature Saprophytes will break down dead wood into humus and minerals. Typically mushrooms favor the type of wood / tree that they will inhabit. Shiitake loves the Oak tree stumps and Oyster mushrooms prefer poplar tree wood, being much softer than for instance Iron Wood or Black Wood trees. Generally speaking, avoid all aromatic woods, the rule of thumb is to use broad leaved trees that retains their bark well.

1: Choose the Type of mushroom and the substrate (food source for the mushroom) favored by the mushroom.

• It is important to find a substrate (the medium we use as food for the mushrooms) that is easily available to you. Having to travel far to collect your substrate will increase production cost.
• Wheat straw is one of the better substrates to use for Oyster mushroom cultivation. Use clean, uncontaminated chopped straw only. Do not chip too fine, 4-10cm pieces is perfect.
• Poplar leaves, banana fronds, coffee grounds, cotton seed meal can be added sparingly. Many other farm waste/recyclable materials can be used to supplement your substrate.

2: Choose the Production Method

• For those that use wheat straw as the main substrate, the pasteurization process can be used to prepare the substrate for the mushroom. Pasteurization does not sterilize the substrate but will remove the unwanted contaminants and retain the beneficial bacteria. This process is the easier and faster of the two but will consume more water.
• For those using wood chips and shavings as the main substrate, I recommend either autoclaving the prepared substrate bags or by steaming the prepared substrate bags for 5 – 6 hours. Prepare the wood chip / shaving and supplement mix to a moisture level of 55%, tightly pack the substrate into your bags and fold over the top 10cm of the bags. Use a rubber band to keep the bag closed.

A |  Pasteurization – STRAW – The tools needed for this process is a 210 liter steel drum (a large oil drum), a meshed basket to hold the substrate, a high pressure gas regulator and burner as well as access to water. Preheat the water in the steel drum to 65°C. Next lower your meshed basket with straw into the warm water. Place a weight on top of the straw to avoid it from floating up. Keep the temperature steady and leave the straw to soak in the water for 1 and a half hours. Now remove the meshed basket from the water or drain the water from the drum. The meshed basket with straw will be heavy; you may need an extra hand to pick it out of the drum. The straw needs to rest for some hours until it cools enough to receive the mushroom culture.

B | Steam sterilization – WOOD – Premix and bag your substrate. Prepare your steaming container. You can fit quite a couple of small substrate bags into a 210 liter steel drum. Pack the bags into your wire meshed basket. Allow some space under the basket for the water you will use to steam the bags. The boiling water underneath must not touch the bags. Fill the drum with water – the bottom 10 – 15 cm. You will come to know the exact amount of water to use after you have done the procedure a couple of times. Avoid running out of water while steaming as this may damage the plastic bags. Cover the drum with a couple of old blankets and some tarp. Use a rope to make a tight tie around the top of the drum over the covering to keep most of the steam in. It could take about 30 minutes to heat up the water before the steam will appear. I often have the top covering popping up like a mushroom when the steam is pumping. From this time I steam the bags for 4 to 5 hours – the average for a 9 kilogram gas bottle. Once completed, turn of the gas and leave the bags in the drum until cool. This may take up to 24 hours.

A | After Pasteurization – Once your substrate has reached a temperature below 25°C you are ready for inoculations. Carefully break up the seed spawn into individual kernels. Cut open the top corner of the spawn bag with sterile scissors. The easiest way to do the inoculation is by layering your straw and spawn seeds like a sandwich. Add straw in to the bottom of the bag then a bit of seed spawn then again some straw. Proceed until the bag is filled and can be tied closed. Puncture some holes into the sides of your bag to allow airation. Place the inoculated bags in a dark room for 10 – 14 days for the spawn run. You may lay the bags on their sides to avoid the water content to gravitate to the bottom of the bags. Avoid water collecting in the base of the bags. Maintain the temperature throughout at 18ºC.

B | After Steam Sterilization – Once your bagged substrate have reached a temperature below 25ºC you are ready for inoculations. I do this procedure in front of a laminar flow hood in a clean room. If you do not have access to this equipment, you may want to sterilize your space well before inoculation. I use a pre sterilized spoon to transfer seed spawn from one bag to the other. Use a 10% spawn ratio for inoculation. For every 1kg of substrate I will add 100g of grain spawn. TIP: Avoid having all the seed spawn in the top of the bag, work the seed down the inside of the bags by rubbing the bags, the better the seed dispersion at this time, the faster the spawn run will be. Use some filter material in the top of the bags and tape them closed (We use colored tape to separate different batches). The fungus must be able to breathe, so make sure you do not tie the filter in too tight. You can place the bags in a dark incubation room and maintain the temperature at 18ºC. Oyster mushrooms may take a little longer to complete the spawn run when using wood. Wait for the entire substrate to have been covered – the contents will now appear white.

4: Pinning and Maturing your mushrooms

Oyster mushrooms need fresh air, light and some cold days (12ºC – 16ºC) to initiate pinning. This is achieved by placing the mushroom bags in a well-ventilated grow space and piercing the plastic bags (make a X cut). The bigger your substrate bags, the more holes you can make in the plastic. Give your bags 12 hours of light per day to produce well-formed mushrooms. You will first notice minute little knots starting to develop where the bags were punctured. The knots will grow into baby mushrooms and within five days have matured to adults. Oyster mushrooms will produce well in temperatures ranging between 16ºC – 20ºC. Harvest the mushrooms before the cap have curled up. Store your oyster mushrooms refrigerated at 4ºC.