You really need to include some grain bits in the sample, as that is where any remaining un-gelatinized starch will be. You cannot reach 100% conversion if you don't first achieve 100% gelatinization. If you don't sample the grain, as well as the wort, you won't know if you have remaining un-gelatinized starch.
Many brewers don't like to include grain in their iodine test sample, as they never seem to get starch free result if they include grain. But if including grain gives you a positive test for starch, then your mash isn't done converting, even if a grain free sample tests negative for starch. This is why I never recommend the starch test, and always recommend monitoring the SG. If you like the starch test, then go ahead and do it.
Brew on
