Can't execute query

SELECT p.*,c.id as cid FROM products_tw as p, categories_tw c, products_category_tw as it WHERE (p.id = 'bean-noodles' || p.serial_no = 'bean-noodles') AND p.id = it.pid AND it.category=c.id AND p.available = '1' AND c.available = '1' AND it.category in (grains) GROUP by it.pid

MySQL Error: Unknown column 'grains' in 'where clause'

This script cannot continue, terminating.