The main difference between whole grain and PF style jars is that whole grain remains loose, and can be shaken, thus spreading the mycelium points and colonizing faster.
PF Jars are solid and cannot be shaken; however PF cakes can be used as spawn. If birthed and crumbled or grated they can become inoculation points for a bulk substrate and as such the cakes would be known as spawn. Ideally when using something as spawn it should not be consolidated. as soon as colonization reaches 100% you should use your spawn. When using cakes as cakes you allow them at least a week to consolidate before birthing.
The PF-tek substrate can be sufficiently sterilized even without a pressure cooker. While whole grain virtually requires a pressure cooker to sterilize effectively. It is possible to steam sterilize grain spawn like the PF tek but it needs 8 hours of steaming. With a pressure cooker/sterilizer/autoclave at 15psi it only takes 90-120 minutes for a quart jar and upwards of 3 hours for bags.
Grain can be inoculated with with a syringe, agar wedges of grain to grain transfer, while the PF-jars are limited to a syringe. To ensure clean spawn, the use of agar is essential.
Bulk Spawn Use:
This bulk substrate is typically 1-10 times the volume of the spawn grain and significantly increases yield per given volume of spawn. PF cakes are primarily a fruiting substrate but can be used as spawn for a bulk substrate, however they are not as effective as grain spawn.
How can I tell if my spawn is fully colonized?
Once all the grains are visibly covered with white mycelium, then the jar can be considered done. You can leave it to colonize a few more days to go sure.
What's the best way to prepare grain spawn?
The 3 most important aspects of grain preparation are to achieve an uniform, correct water content, to kill all contaminants and to get a shakeable substrate.
Choose a tek best suited for your choice of grain and follow it to a T.
Which kind of grain can I use?
You can use almost any grain as long ass' it's in it's whole form.
In general you want about 30% colonization before your first shake.
Grain to grain is a simple method of expanding grain spawn, it is done by using a colonized jar of grains and pouring that one jar into more jars of sterilized uninoculated jars of grain, refer to the teks for more details.