Wild Bird Seed (WBS) consists primarily of white millet. It is often a combination of white & red millet - with a small percentage of sunflower seeds and sometimes tiny amounts of crushed corn. Some expensive brands are coated with a fungicide. For use as spawn material, treated WBS is not advisable.
You can find untreated WBS in 5 -10 & 20 pound bags, at low prices at most large chain grocery stores, or chain type pet supply stores. For instance, PetsMart has 40 pound bags for around $8.
Simply place whatever quantity you intend to use in a plastic pot, tub or bucket. Bear in mind, dry seed will expand about 20 to 25% - after it absorbs its capacity of water. Add tap water & soak the seed overnight. A 8 to 12 hour soak is fine. Seed soaked longer will begin to ferment. But, is still usable after soaking 24 to 36 hours.
There is no need to remove any floating husks, or sunflower seeds. These add lignin ( a good thing) & do not harbor any more possible contams than does the millet. It is all going to get thoroughly sterilized - anyway.
Once soaked, simply rinse the seed very thoroughly in a colander, or strainer. Then allow it to drain - WELL. As in 30 or more minutes. If it is drips - one drop. It is not drained - WELL.
Load pint or quart jars ¾ full, apply internal filter disk, material, polyfil or whatever method you use allow gas exchange through a ¼ or 3/8 inch hole in the lid. Screw lid on tight & back it off ¼ turn. Place a double layer of paper coffee filters over the lid & jar top, held down by a thick rubber band. Place the jars in the PC.
PC at 15 pounds for a full 60 minutes. 90 minutes is better, if you have the time. Allow the PC pressure to drop to zero & let it cool a bit. Open while still hot & remove jars. The paper coffee filters will dry almost instantly, when the PC is opened. Tighten lids (if necessary), shake jars to insure there are no clumps of seed inside. Place jars inside the oven on a rack, to cool, overnight. External coffee filters simply add another layer of protection to the jars content.
Once cooled to room temperature, store in a clean cardboard box - until used. Using them sooner than later is preferable. Note: This method was done in an All American PC. Some brands with a weighted pressure system require more internal water & it may be advisable to also cover the coffee filters with tin foil- while PC'ing, so no excess boiling water gains entry into the jars. Simply remove the tinfoil when you remove the jars from the PC.