Gruel is a type of food consisting of some type of cereal—oat, wheat or rye flour, or rice—boiled in water or milk. It is a thinner version of porridge that may be more often drunk than eaten and may not need to be cooked. Historically, gruel has been a staple of the Western diet, especially for peasants. Gruel is often made from millet, hemp, barley or, in hard times, from chestnut flour or even the less bitter acorns of some oaks.