Many idioms are older than refrigerator technology. Butter is meant to be served at room temperature. A vessel called a butter crock preserves butter at room te

Many idioms are older than refrigerator technology. Butter is meant to be served at room temperature. A vessel called a butter crock preserves butter at room temperature by using a thin layer of water to create an airtight seal around an overturned cup of butter: http://i.imgur.com/oiNjjaW.png http://i.imgur.com/oiNjjaW.png