A spawn substrate is a highly nutritious material used in the beginning of a cultivation cycle. These substrates are commonly inoculated and grown to full colonization in a sterile environment due to the increased susceptibility of nutritious material to contamination. Some spawn substrates are fruited by themselves (see brown rice flour cake) while others are combined with a bulk substrate and/or casing layer before fruiting to increase output or properly induce fruiting.
Cake spawn vs loose grain substrate
A cake spawn is often created with some combination of either brown rice flour or wild bird seed flour and vermiculite. It is referred to as a "cake" due to the way that mycelium growth turns it into a single solid piece of substrate. Cakes cannot be easily separated and need to be physically crumbled in order to combine with a casing layer or bulk substrate. Cake spawn are commonly fruited by themselves and perform well for species which do not require a casing layer.
A loose grain substrate is prepared by soaking hard-shelled seeds in hot water for a period of time and is never combined with vermiculite (as the seeds themselves can hold the necessary amount of water. A fully colonized grain substrate can be shaken loose while inside the jar in which it colonized. This is very beneficial since grain substrates are most often combined with a bulk substrate or casing layer. Grain spawn is rarely fruited by itself.
Common Grain Types
- Rye berries are also known as rye grain. Rye berries are the most commonly used loose grain substrate due to their relative low price and the ease of which they can be broken apart after full colonization. Rye berries can be found at most organic food stores. Take care to avoid fungicide treated rye grain.
- Brown Rice, most popular for its use in the brown rice flour cakes of the PF Tek, is most commonly used in its powdered form. Brown rice flour can be found at most grocery stores and brown rice itself can easily be ground to a powder.
- Wild Bird Seed is commonly abbreviated "WBS" and is often a mixture of several different types of seeds and can be used as either a loose grain or as a cake substrate. When it is dry, it can be powdered to create a flour commonly abbreviated as "WBSF".
- Popcorn Seed is another common substrate which can be used in its uncooked form in a fashion similar to rye berries.