Depends what kind of cooking you're talking about and when you're doing the rinsing. If you mean when you're cooking your dinner and that you rinse it afterwards, that'll be starch. People do the same rinsing trick with sliced potatoes to stop them being all stodgy when you bake them. Or they'll rinse cooked pasta with some boiling water to get the stickyness off it, which is starch again.
In terms of making up cakes, I never bother weighing the stuff out.
Put your brown rice in the food processor or blender and grind the living shit out of it. It can take AGES in those two. A better option is a coffee grinder. Preferably one of those ones that has a cap you take off and then there's a pair of high speed blades you can poke with your finger. It may seem small, but it'll powder it in seconds. You can also pick the coffee grinder up and shake it to speed it up even more. I used to put jaw breaker candies in ours and grind them to dust, then lick it up.
Sieve it. You want fine particles, not big lumps. Don't go crazy though, it doesn't need to be like baking flour; which might help clump up your media.
I drench the vermiculite in boiling water, or boil it up in a pan (MUCH BETTER), then dump it into a sieve and let it drain. Do that before starting your rice grinding, so it has a good chance to drain. Cover the sieve with a big pan lid, foil or film so it doesn't have shit from the air falling on it as it drains, and so it doesn't completely dry out.
Remember that the vermiculite has come out of an extremely hot kiln and gone straight into reasonably clean bags. The kiln will have been around a thousand degrees and killed everything on the vermiculite, even things autoclaves, ethylene oxide or radiation won't kill. So it's super clean when it's in the bag. Once it comes out, you should try to treat it aseptically, hence hydrating it with boiling water and covering it to retain that level of cleanliness. I used to tape the bags closed again after I'd used them. And not just because I kept accidentally emptying them out.
If you boil the vermiculite in a big pot, all the super fine dust that would clump up your media will fall to the bottom, and you can scoop the big particles off from the top. Top tip! :idea:
Once you have your damp (but well drained) vermiculite and your flour, choose a big mixing bowl and give that a rinse with some boiling water too; don't bleach or chemically clean things that'll contact the media as chlorine is extremely good at slowing down or killing myeclium and it's not necessary when boiling water will work (you should also consider filtering the water you use to hydrate the vermiculite). Dump in the vermiculite and start spooning on the flour. Wear some new latex gloves or use a spoon that's been rinsed with boiling water to give it a really good stir or mix as you go. Once it's all coated and the flour has started falling to the bottom, it's done. Don't pile on loads or you'll make a sticky lump, or dry it out too much.
Filling more jars or cups with less material is better than a few with lots in it. That way, contaminations mean less. And the longer it takes to fully colonize the higher than chances of a contamination establishing are. Also, even with no contaminations present and ideal growth conditions, psilocybe mycelium will usually slow down or even stop once you start trying to grow it through large batches. It seems to instinctively get ready for fruiting around a certain network size.
Your jars or glasses should have been rinsed with boiling water and allowed to dry. Turn them upside down to let them dry so airborne shit won't fall into them. Don't use a towel or tissue paper since you'll be wiping germs and spores all over the inside. A kitchen towel is about the most germ ridden thing in your home, seriously. Other than you of coarse, the perfect germ incubator.
I'm terms of packing the mix, you can do away with that if your vermiculite is a small grain size as it'll pack it's self quite well, give them a bit of a wiggle and tap them on the surface to help it settle. If it still has large gaps in it, use the bottom of a glass (cleaned with boiling water) and place it on the surface. You will barely need to press down. If you push with anything more than gentle fingertip pressure, you're fucking it up. Imagine you're playing with an 18 year old virgin, about that much pressure. :P
Incubating before sterilizing not only hatches the contaminating spores into a more easily sterilized form, it causes the enzymes in the rice to begin breaking down some of the carbohydrates and reforming them into amino acids or proteins, creating a more nutritionally complex dinner for the mushrooms.
The minute the mix is done, spoon it out into the jars or glasses and immediately foil them over. Put them in your incubator (a plastic box that's been bleached or rinsed with boiling water), cover, let them sit somewhere warm for a day or two. Sterilize. Inoculate. Straight into the incubator. Cover. Keep them dark and warm. Never breath over them, never touch them without alcohol washed gloves on. Don't take them out and stare at them, breathing germs all over them. You should only be touching them if you can't see any colonization. Ignore and do not touch, more than once every week or two at most (and only if they seem to have stalled), until fully colonized.