This is a message I got on another forum, I decided to post it here too so we have it:
"Not necessarily. If the majority of seed are sterile, you can often tell just by the way they behave. They don't fall individually, they stay clumped. Some seeds sink fairly quickly and some float until they become more saturated. I do a 24 hour pre-soak with sugar water and a bit of dish soap. After 24 hours with frequent agitation, the seeds containing embryos should be on the bottom. Sterilization will be more thorough because air in the seed will have been displaced and the sugar water should help stimulate any contaminants in their cystic stage to become active so they can be killed."