Substrate sterilization before adding psilocybe spores
STEP 5. Day 2. Grain substrate sterilization
What is sterilization?
Sterilization — heat treatment that deactivates all forms of microorganisms in substrate, such as bacteria and mold spores. It is carried out at temperatures above +100°C (212°F) for a certain period of time.
You can buy ready for inoculation sterile grain for mushroom spawn, so that skip next steps and move on Inoculation section. Such option can save your time greatly and money for expensive pressure cooker, jars and lids accessories. It's a great option if you just want to try mushroom cultivation with ease.
Shroomok's choice on Amazon:
All you need to prepare for grain sterilization
1️⃣ Pressure Cooker, Autoclave or Pressure Multicooker.
Shroomok's Choice on Amazon:
Pressure Canner and Cooker - 23 Qt - $128.63
Steam Autoclave Sterilizer - 8.5 Qt - $179.90
3️⃣ Prepared Spawn Jars or Spawn Bags with inoculation port and air filter. Check step Jars and Bags for Mushroom Spawn
4️⃣ Vermiculite or Vermiculite/Perlite 50/50.
Shroomok's Choice on Amazon:
Vermiculite 8 qt. - $16.10
Organic Vermiculite 8 qt. - $17.95
Premium Perlite 8 qt. - $12.89
Organic Perlite 8 qt. - $15.89
5️⃣ Aluminium Foil.
Preparation for grain substrate sterilization
1️⃣ Add 5-10 mm of vermiculite on the bottom of each jar (just to cover the bottom). In case there will too much moisture in the substrate, this vermiculite will help and compensate. It will absorb the excess moisture when you shake the jar with substrate.
2️⃣ Fill the jars with the prepared substrate, but no more than 2/3 or 3/4 of the jar. In the future you'll need to shake the content of the jars without opening them. If you fill the jar to the top, you will not be able to shake the substrate.
3️⃣ Close the jars tightly with the prepared lid (with inoculation port and filter). During sterilization lids on the jars may loosen under the influence of temperature. This applies to both metal and polypropylene lids. Make sure they are tightly closed before sterilization.
4️⃣ Wrap the lids of the jars with foil tightly. So that water will not seep through the patch on the lid during sterilization.
Grain substrate sterilization for mushroom spawn
1️⃣ On the bottom of the pressure cooker (or multicooker) put a cloth napkin. The jars and the bottom will not touch each other and less banging in the multicooker. This more concerned to glass jars, so that they do not break during sterilization.
Let us remind you, if the jar cracks or breaks during sterilization, you can't use it for further inoculation!
2️⃣ Fill the multicooker (or pressure cooker) with water. The level of water should reach half of the jars or a little bit more. Just keep in mind that the water will boil and if you pour more water, the lids will be filled with water. We can't let it happen!
3️⃣ Put the jars in pressure cooker (autoclave or multicooker). We put only 3 jars of 500 ml or 2 jars of 720 ml to it. Polypropylene jars can float because of their lightness. To prevent them from turning over, you can put a ceramic plate on top and close the lid of multicooker (pressure cooker).
4️⃣ Set the temperature +121°C or 250°F or 15 psi for Pressure Cooker and Autoclave.
Sterilization time depends on the type of grain:
⏰ Wheat, oats, barley, rye - 1 hour 30 minutes
⏰ Millet and brown rice - 1 hour and 20 minutes
⏰ Corn, popcorn, sorghum - 2 hours
🔴 Pay attention! The sterilization temperature should be higher than +100°C or 212°F! It gives more chances to destroy all the viable spore cells of molds, bacteria and their endospores that still alive in the grain.
🔴 Keep in mind polypropylene jars withstand temperatures up to +140°C or 285°F. Glass jars +160°C or 320°F and above.
5️⃣ When sterilization is complete leave the substrate cool slowly. Don't open the PC/multicooker and don't take the jars out immediately after sterilization is complete.
⛔️ First, you can suffer yourself with the steam.
⛔️ Secondly, if you open the PC/Autoclave/Multicooker the glass jars can break because of the difference in pressure and temperature. Broken jars go straight to the trash. Polypropylene jars you can take out immediately, but it would be better to let them cool down a little without a sharp temperature changer. At least for the first 2-3 hours after sterilization is complete.
⛔️ Third point - due to sharp temperature changes cold not sterile air come through air filter and can provoke contamination in future.
6️⃣ When you take the sterile substrate out of the pressure cooker, leave it to chill at room temperature.
Do NOT remove the foil! Mild condensation can appear in jars as they chill - don't worry, it's okay.
7️⃣ Then you can load the next batch for sterilization and so on with all jars with substrate.
✅ Does it possible to sterilize substrate without a pressure cooker (PC)? You can sterilize substrate in the oven. But PC/Autoclave is preferred because sterilization under pressure gives higher temperature in the substrate. Some mushroom growers sterilize jars with substrate just in a saucepan on the stove. This option is suitable for sterilizing secondary substrates (hay, coconut peat soil etc). Grain substrate requires higher sterilization temperatures to deal with contaminants. Therefore, in most cases, sterilization without a pressure cooker/multicooker leads to substrate contamination and all work done before will go to waste.
✅ Make sure that the lids on the jars are tightly closed before and after sterilization. It can happen that metal lids come loose and need to be tightened. If the lid is open at all (this happens with polypropylene lids), then the substrate must either be discarded or sterilized again.
✅ Ready non-sterilized substrate in jars can be stored in the refrigerator for 1-2 days. But it is better to sterilize fresh substrate. In 12 hours we sterilize about 6 liters of substrate.
✅ Some growers sterilize the jars twice. If you have doubts, you can repeat sterilization or increase the sterilization time. In my practice, 1 time and 2 times sterilization did not affect the final result. Details are in Growing experiments. Moreover, even 1 hour of sterilization (for wheat and oats) is enough if the grain was soaked and antibiotic (or peroxide) was used.
When all jars have cooled down to room temperature, it's time to move on — STEP 6. Day 2. Inoculation ▶️