For a 1 quart mason jar

160ml rye kernels (about 150g dry weight)
130ml distilled water (u can use tap, I prefer distilled)
1/2 teaspoon calcium carbonate. This is basically chalk, although I buy it at the drugstore as powdered oyster shell, also in pill form. If I can only get pills I put them in a coffee grinder and it does a great job of powdering them. The calcium is a PH buffer to bring the acidity of the rye down to mushroom friendly levels.

Substitue birdseed for rye and it's a lot easier. Only reason for that is that it's easier to find organic birdseed than rye. I went to a health food store and bought rye and it wasn't organic... can you believe that? All birdseed I've ever come into contact with is organic. Very cheap too at el peto smarto...