We cultivate the spores on solid plate count agar medium in cake pans at
30-35 C. Plate count agar seems to work just fine with over 90% spores in
about a week. Then we scrape off the spores with 70% isopropyl alcohol.
That kills off most everything except the spores. Storage in 70% IPA at
2-8 C has been very good with only a one log reduction in ten years. The
scraped suspension is 10^10 to 10^11 CFU/mL (a thick moist, IPA paste).