Question: What are the names of the characteristics of the product 'sesame' that have the characteristic type code 'Grade'?
SQL: SELECT t3.characteristic_name FROM products AS t1 JOIN product_characteristics AS t2 ON t1.product_id  =  t2.product_id JOIN CHARACTERISTICS AS t3 ON t2.characteristic_id  =  t3.characteristic_id WHERE t1.product_name  =  "sesame" AND t3.characteristic_type_code  =  "Grade"