Take a small sample (few drops) of you grain based mash after conversion.
Drop one drop of starch indicator into the grain sample
If the starch indicator remains brown, the starch in the grain converted fully to sugars
If the starch indicator turns blue/black, no or little conversion took place
The darker blue/black the indictor, the less conversion took place.
If no conversion took place - review your mashing procedure and temperatures, source of enzymes and conversion times.