FAQ: For Stage one of micropropagation, surface sterilization, how do I know what disinfectants and concentrations will be effective without damaging my material?
How to sterilize your plant material will depend on the type of propagule you have as well as its characteristics (size, durability, maturity). There are common practices for plant tissue sterilization (see George 1996) with minimum exposure times varying with the disinfectant. Orchids present a special case, with their very tiny seed requiring a gentler touch. However, it may also be possible to sterilize their immature seed pods instead.
Orchid seeds can vary widely in their need/tolerance of bleaching. The bleaching process in orchids both sterilizes the seed and breaks the dormancy, and the dormancy break can be both physical and chemical. Some orchid seeds will only tolerate a few minutes of bleach, some seem to need an hour or more before anything "happens". We don't do much green pod propagation (the seed pod sterilization technique mentioned) because our main focus is figuring out how to reconstitute orchid populations from seeds in a seed bank so those seeds, theoretically, will have matured and gone into dormancy.
A 10% bleach concentration (and that's a 10% concentration of commercial bleach, which is already at about an 8-12% concentration depending on brand) seems to be the standard for surface sterilization across seeds and somatic tissue, but my experience with somatic tissue sterilization is extremely limited. It appears that the time exposed to bleach is what is varied, not the concentration of the bleach. The standard clorox type bleach is typically used, but at least for orchids, some people use hydrogen peroxide to sterilize/break dormancy.