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The term frozen food refers to one of the chief means of food preservation, one that has been used for thousands of years in colder climates. The modern technique arrived with the invention of mechanical refrigeration in the 19th century. Some foods, such as ice cream, are made and eaten frozen, while others, including fruits, vegetables, and meats, are kept frozen until use. In 1924 Clarence Birdseye developed a method of rapidly freezing foods in small packages for retail sale. (See also food processing, “Freezing.”)