I crushed up a bunch of walnut hulls, soaked them in water and poured the slurry into a qt jar. Within 6 months I had a thick mold growth on top of the slurry, dumped everything out.
For my next batch I mixed the same water hull slurry and added a cup of denatured alcohol. Been about ten years since I mixed up my stain, no mold, no stink and very usable. I wipe it on grainy slurry and all, let it soak in and wipe off the chunks and sand like slurry, stains really well, used it on some arrow shafts last week.