How to pasteurize substrate with Lime bath treatment
Prepare a solution using calcium hydroxide Ca(OH)2) and water at a ratio of 1% lime to water. Submerge the substrate completely in the lime solution for 12-24 hours. After soaking, drain the substrate and inoculate immediately.
Say Hello to my little friend: Hydrated Lime
If Tony Montana had a pasteurization technique, this would be it. Mounds of white powder, submerging things with bricks, chopping things into little pieces! It’s also a very simple method to pull off for the first-time grower that eliminates the need to heat water and burn fuel. Instead of pasteurizing with heat, we are using a chemical process to kill off the competing organisms. The goal is essentially to dump enough Hydrated Lime into a cold-water mixture and soak our substrate overnight. We can then drain and inoculate immediately with a more resilient mushroom species like the Oyster mushroom. It’s a great way to utilize agricultural waste products to grow some extra food.
Is it safe to work with hydrated lime?
Yes, it is safe for humans to work with hydrated lime. The high pH level of hydrated lime mean sit will act as an irritant if it gets on our skin, but we can take simple precautions to stay safe. I prefer working with this alkaline solution over the risk of open flame and heat in the realm of safety. We eliminate the risk of fires and burns and can walk away from the operation while its soaking to work on other things. The waste-water from the lime mixture can pose an issue for plant life, but we can easily neutralize the pH level to make It safe and beneficial for the garden.
What are the benefits of lime bath pasteurization?
The benefits of using lime to pasteurize include efficiency, ease of use, and minimal equipment. You will not need a propane burner or sterile environment. We just need to be patient and achieve the proper pH level. Using lime is a good option if you don’t want to babysit a boiling stock pot or smell-up your apartment with boiled substrate. It is also been calculated to be more energy and cost efficient that using heat to pasteurize.
- Low-Tech & Minimal Equipment
- Cost Efficient
- Easy
- Energy Efficient
- No sterile environment required
What are the limitations of using the lime bath pasteurization method?
Lime bath pasteurization requires at least 12-24 hours to be effective. Where you gain energy efficiency, you lose in time. For the home growers, this probably is not a concern but this method might not scale as well when you start to pasteurize large quantities of substrate at a commercial level. You are also left to deal with the acidic mixture once the pasteurization. It will require a little extra work to make it safe for your garden, so we don’t kill your petunias.
- Scalability
- Time
- Caustic Waste by-product
- Energy inefficient
What mushroom substrates can I pasteurize with lime?
Lime pasteurization works best with non-supplemented agricultural waste or pelletized hardwoods. There are lots of agricultural waste products we can experiment with that normally get thrown out as garbage. Many of these we can find for free and use to grow some mushrooms!
- Straw
- Sawdust (un-supplemented)
- Hardwood pellets
- Wood chips
- Corn cobs
It is important to note that the substrate will retain a high pH value even a few days after it is removed from the mixture and drained. Because of this, we need to use a resilient and hearty species such as the Oyster, Shiitake or Reishi mushroom, that will survive the alkaline substrate.
Which hydrated lime can I use to pasteurize mushroom Substrate?
Use a Hydrated Lime mixture with a magnesium content of less than 5%. We need a high-calcium mix intended for chemical and industrial applications. You can find these online and at local home improvement stores.
Don’t Use Gardening Lime!
Avoid lime mixtures intended for gardening that contain Dolomitic Lime or Calcium Carbonate Lime. Use more concentrated hydrated lime mixtures intended for construction that contain Hydrated Lime.
Use Higher pH concentration and lower magnesium mixtures
We need to choose an appropriate lime product that will have a high enough pH value to kill the organisms in the substrate. Normally, the gardening mixtures will not produce a potent enough mixture for pasteurization and are loaded with magnesium.
Step-by-Step Guide: How to pasteurize mushroom substrate with Lime
Materials:
- Soaking Container
- Hydrated Lime
- pH Testing Strips
- Hand and Eye protection
- Weights
- Mesh bag
- Muriatic Acid
- Water
I would not consider the pH strips a necessity but can be helpful with your first attempt at achieving the necessary pH level. Also, if you are trying to re-use the water in the garden, it might be good to test that you have neutralized the alkaline before dumping it.
For the Soaking Container, we can use drums, plastic container, large stock pots, etc. This is where we will soak the substrate in the Hydrated Lime mixture, so it has to be large enough to accommodate the substrate bulk.
Mesh Bag like used in construction or gardening. This is to contain the substrate and make it easier to work with in the lime mixture. You can find these at home improvement stores or online. An old pillow case would also work.
For the Weights, we can use rocks, bricks, anything heavy that we can use to submerge the substrate into the Hydrated Lime mixture.
Step 1: Preparing your Substrate
- If using straw, chop into smaller pieces. While not necessary, this will aid mycelium colonization speed. Stuff all the substrate in the mesh bag so that we can weight it down into the lime mixture later. This will also make it easier to drain.
Step 2: Preparing the Lime Bath Mixture
- Add enough water in your soaking container just so the substrate can be fully submerged.
- Add the Lime to water and mix. We are trying to achieve a 1% mixture of Lime in the water to achieve the appropriate pH balance. This equates to about 6 grams of Lime per 1 Gallon of water or 2g of hydrated lime per 1 liter of water.
- Test with pH Strips. We are looking to get a range between 12-13.
Step 3: Soaking the Substrate
- Place the substrate into the soaking vessel and make sure all the substrate material is completely submerged. Because straw has the tendency to float in water, we will need to make sure it stays submerged.
- Soak the substrate in the lime bath for at last 12-24 hours.
Step 4: Draining the Substrate
- Lay out the substrate on a strainer or hang bag to drain most the liquid. We are trying to achieve a good “Field Capacity”. This basically means we have the correct amount of moisture for our mushrooms to grow. If you can squeeze the substrate with your hands and only 1-2 drops of liquid come out, then this is considered a good Field Capacity. You can either drain longer or add water as needed to achieve this.
Step 5: Inoculation
- After your substrate has been soaked and properly drained, you are ready to proceed with your spawn inoculation of choice. The substrate will maintain a higher pH level at first, but should drop in the next 3 days. It’s best to inoculate immediately with a mushroom species that can tolerate the pH level.
How to dispose of the lime bath waste water
When pasteurizing with lime, you are left with waste water that shouldn’t be just dumped in the garden. Because of the alkaline level of this waste water mixture, we should be mindful of how we dispose of it. This caustic mixture will kill plants and should not be introduced into any watershed.
To mitigate the negative effects of the lime water, we can neutralize the pH value by either diluting with more water or adding muriatic acid (HCL). This neutralized mixture can be distributed back into your garden and will actually provide some nutrition.
Conclusions on Using the Lime Bath Pasteurization Method
Pasteurizing substrate using a lime bath method is an efficient and effective way to prepare for mushroom cultivation. This technique leverages the high pH of hydrated lime to eliminate competing organisms, providing a low-tech, cost-effective, and energy-efficient alternative to traditional heat pasteurization. While it has its limitations, such as longer processing time and handling caustic waste, the benefits far outweigh these challenges for many home growers. By following the step-by-step guide, you can easily implement this method and enjoy a fruitful harvest of resilient mushrooms like Oyster, Shiitake, or Reishi. Remember to take necessary safety precautions and properly neutralize the waste water to protect your garden and the environment. Happy growing!