beans
菽 centers on beans as a plant or crop. It is a specific character for beans, not a general food term.
菽 combines the plant radical 艹 with 叔, which likely provides the sound. The character specifically denotes beans or legumes.
The plant top 艹 over 叔 suggests a crop: picture a bean plant with pods hanging down, the 叔 part resembling a hand picking the beans.
For シュク, imagine a shook bag of dried beans rattling: shook -> シュク, and the beans spill out under the plant top.