Edit (2024-08-19): Experienced heavy contamination. Likely the bran, but I also used micropore tape over the holes and I think this was the largest error.
It’s bucket day! And it’s time to get down and dirty with bucket prep, planning the substrate mix quantities, prepping it and seeing what it yields. I have a 16qt pressure cooker and so 12 half pint jars fit perfect in it. This is my first go at this small setup, so I’m documenting to see what happens!
Recipe
Recipe makes one 2.5 quart bucket. Multiply as needed for more buckets. All the details on how I came up with this are listed below.
Baby Bucket Details:
Mix:
- 1 half pint jar of grain spawn (1 cup)
- 7 cups of sawdust
- 2 cups of bran (baked at 2 hrs at 200F)
Hardwood Hydration to Make Sawdust:
- 4 cups water heated to 175F
- 3 cups hardwood pellets
Why Half Pint Jars?
First, my goals are not for mass production. I have a simple goal of having a small, active, mushroom garden. Everything I buy is to this means, including a smaller pressure cooker (16 qt) and small tent (2x2x4). I like the size of the 2.5 qt buckets, fitting nicely on the shelves in my tent and per recipe, the half pint jars workout nicely with a 1:1 ratio of 1 jar to 1 bucket. This makes it easy for me to experiment with a variety of mushrooms per batch, with up to 13 half pint jars fitting in my pressure cooker.
Pasteurization, Not Sterilization
I’ve decided I want to use a supplemented hardwood mix. According to various sources:
5 pound block = 5 cups hardwood pellets, 1.4 liters water, 1 1/4 cups bran (wheat or oat). This would need to be sterilized in a pressure cooker. (source)
Following this ratio, that would leave me with about 80% hardwood and 20% bran. I’m messing with the idea of pasteurizing the bran instead of sterilization. The idea is to take advantage of the microbial balance by *not* sterilizing:
Pasteurization is favored in mushroom cultivation for its ability to maintain a microbial balance that supports healthy mycelium growth. (source)
Sterilization, on the other hand, involves heating the substrate … to completely eliminate all living organisms within the substrate, both harmful and beneficial. (source)
Grain Spawn and Substrate Ratios
Now, for how much grain spawn to add to the bucket. It is suggested to use 5% – 10% grain spawn to substrate. So some math:
1 jar grain spawn (1 pint) = 2 cups
1 bucket (2.5 quart) = 10 cups
10% of the bucket = 1 cup or 1 half pint jar.
That leaves 9 cups, to be divided 80/20 for substrate
80% of 9 cups is approximately 7 cups hardwood20% of 9 cups is approximately 2 cups bran
Final:
1/2 pint jar of grain spawn
7 cups of sawdust2 cups of bran
Hydration for Hardwood Pellets
Now, breaking down how to create those 7 cups of sawdust and 2 cups of bran. I’m going to do a “lazy pasteurization” of the hardwood, since it’s less likely to contaminate. I have an electric kettle with a capacity of 1.7L that I will heat water in to 175F (green tea option) that should fall within the recommended 65C-85C range.
It’s recommended to use a 3 parts water to 2 parts hard wood pellet ratio for a 5 parts yield. The math of getting the sawdust for using my kettle:
3 of 5 is roughly 60%
2 of 5 is roughly 40%
60% of 7 cups is approximately 4 cups water
40% of 7 cups is approximately 3 cups hardwood pellets
This should yield 7 cups of sawdust, the amount needed for one bucket. Happily, my math with this formula matches the ratio I have in my notes from last batch: “1 kettle (4 cups) to 3 scoops of HWP”!
Finally for the bran, I plan to bake 2 cups of bran in a large pan at 200F for 2 hours. After the hardwood cools, I play to mix in the bran and begin filling the bucket with a mix of substrate and grain spawn.