How to pasteurize mushroom substrate with steam?
To pasteurize mushroom substrate with steam, place the substrate in a heat-resistant container and steam it at 160-180°F (70-82°C) for 1-2 hours. Ensure the container is covered to maintain the temperature and prevent contamination. After steaming, let the substrate cool down in a clean environment before inoculating with mushroom spores.
Is Steaming Effective for Pasteurizing Small Batches of Mushroom Substrate?
No. While steaming is effective, it is probably best suited for a medium to large scale grower. It requires more equipment, time and energy to accomplish. If you are considering a pasteurization method you can use with a small batch in your kitchen, steaming is probably not your solution. While steaming does have its advantages, these don’t become as apparent until you are working with larger quantities of substrate.
What are the benefits of Steam Pasteurization?
1. Less Environmental Waste
There are generally fewer waste by-products with steaming. When using the Hot Water method, you are left with an acidic water mixture to dispose of. Chemical treatment methods also leave you with water mixtures that can be harmful to other organisms.
2. Higher Mushroom Yields
Because the substrate is not fully submerged in a water mixture, it does not leach out the valuable sugars. By steaming, we retain more nutrients for the substrate that ultimately produce higher fruit yields.
3. Scalability
While not best suited for small scale batches, steaming allows you to effectively pasteurize a large amount of substrate at a time. As long as you have the room and equipment, this method can be effectively scaled up to fit your goals.
What are some Cons of Steam Pasteurization?
1. Time
Getting the desired temperatures for pasteurization usually takes longer than other methods. It also takes longer to cool your substrate with this method. With more time, comes more room for contamination and errors made by cultivator. Any process that requires more attention and baby-sitting creates more opportunity for error.
2. Inconsistency
Using steam can be difficult to consistently heat all of your substrate. Hot pockets may form in some areas if the steam is not distributed evenly. This can over heat the substrate and effectively kill the good microbes. This can be overcome with the right equipment and knowledge, but adds risks of partially sterilizing the substrate.
3. Poor Energy Efficiency
Because it takes longer to pasteurize, you will be running your heating element longer. This means for fuel or electricity, depending on your setup. This creates higher energy costs and environmental footprint.
4. More Equipment
Setting up a system to steam substrate can be done in a variety of ways, but generally requires more equipment and setup than other methods. The equipment needed generally can’t be gathered from most people’s existing household items.
When should I use the steaming method to pasteurize mushroom substrate?
Using steam pasteurization might make the most sense if you are working with a large quantity of substrate. This might be a reasonable option if you looking to reduce the amount of waste material produced during the pasteurization process or you already have the necessary equipment on hand.
One specific use case where steaming your substrate might make the most sense is if you have an organic certified food farm. In some countries, there may be stricter rules in which you can be considered an organic grower. This might eliminate the possibility of using such chemical treatments like hydrogen peroxide or lime. Additionally, if you are using the Hot Water method, you are left with a waste by-product of very acidic water. Anywhere you are dumping this acidic waste water would make it difficult if not impossible to grow other food crops.
How to make a steam pasteurization setup
Because the method of creating steam is fairly simple, this lends itself to many types of steaming chambers. Essentially, we are just heating water to make steam, bringing the temperature in our chamber within the range of 140F-170F for about 1-2 hours.
When creating a setup for pasteurizing with steam, it’s probably best to separate the operation into two parts. The boiling chamber and the steam chamber. We might introduce more room for error if we attempt to steam the substrate in the same vessel, we are boiling water. We could run the risk of flooding the substrate with water, or overheating the substrate.
The Boiling Chamber
This is the place where we will boil water to create steam. We can use something like a large stock pot to boil water and somehow channel the steam to the steaming chamber with some kind of piping system. One option might be to install some ball valves in the stock pot and attach a stainless-steel hose to channel to steam into our steaming chamber. We should use not use any kind of plastic piping for this purpose as it will melt.
We also need a way to replenish water to the boiling chamber and we generate steam. If you are running this boiling chamber for long periods of time, we need to make sure the pot doesn’t run dry. This can be done by either manually adding water with a hose, or we can setup a ball valve with a float attached, much like a toilet float valve. This way, we can hook up our hose and it will add water automatically whenever our levels are too low.
The most basic way we can heat the water in the boiling chamber is with a propane burner underneath the pot. If we are trying to use a more automated system, we can rig up an electric heating element to our stock pot and set it to a digital thermometer. If the temperature drops to a certain degree, the heating element will run and heat the water to the desired temperature.
The Steaming Chamber
The steaming chamber will have the piped steam entering into the bottom of the chamber so it can fill the vessel. We will need to create some space at the bottom of the steaming chamber where the substrate is placed, because there will be some initial moisture that drains collects. By creating a “stand-off” or “false bottom”, we can make sure our substrate doesn’t get submerged in water. Its also a good idea to create a valve in the bottom of the steaming chamber that will allow us to drain this water.
Some examples of steaming chambers created from re-purposed items…
- Old refrigerators (good insulation)
- 55-gallon steel drums
- Stainless Steel drums used for brewing or cheese making
- Shipping Containers (large scale)
Insulation to increase efficiency
When constructing both the boiling and steaming chambers, we need a way to boost our thermal efficiency. This can be done relatively cheaply with insulation. A common material used is closed-cell aluminum foil sleeping mats made for camping. You can cover both chambers in this material to help insulate the substrate and reduce your energy costs.
When considering efficiency in our setup, we need to also make sure there is a good seal at the lid of our steaming chamber. This can be achieved by creating a silicon gasket on the lid, so we can place some pressure or weight on the lid and get an air-tight seal.
Additional Safety Considerations of Creating a Steaming Setup
Any time we are using heat and pressure, we need to consider safety. We are not trying to create a pressure cooker, so we need to also consider a way for excess steam to escape if the pressure becomes too great. Aside from the safety aspect, the higher pressure will also overheat our substrate, which is bad because it kills our beneficial microbes.
Pressure control valve?
How to Steam Pasteurize Mushroom Substrate
Step 1: Hydrating the Substrate
Because pasteurizing mostly involves non-hydrated materials, we need to first reach a hydration level of about 75%. We need to incorporate enough water into our substrate so that when we squeeze a handful of material, we should get a couple drops of water.
Step 2: The Steaming Process
Similar to the Hot Water pasteurization method, we need to get the steaming chamber to a temperature range of 140-170F. Once we have achieved this range, we need to let the substrate stay at this temperature between 1-2 hours.
Step 3: The Cooling Process
Before we can inoculate the pasteurized substrate, we need to allow it to cool down to a temperature that won’t kill the spawn. This can be done by letting the chamber sit over-night so cool down.
Conclusions
The steaming method might not be the most energy or time efficient choice for pasteurization but does produce a quality pasteurized substrate and can be scaled as your growing increases. It might be a good option given constraints that exclude other pasteurization methods. It is also a strong candidate if you have some space and existing equipment.