What kind of preparation is needed for apple juice to make a raspberry-pear couscous cake?
apple juice is a name of an ingredient; raspberry-pear couscous cake refers to title
SELECT T2.preparation FROM Recipe AS T1 INNER JOIN Quantity AS T2 ON T1.recipe_id = T2.recipe_id INNER JOIN Ingredient AS T3 ON T3.ingredient_id = T2.ingredient_id WHERE T1.title = 'Raspberry-Pear Couscous Cake' AND T3.name = 'apple juice'