Most french fries are produced from frozen potatoes which have been blanched or at least air-dried industrially. Most chains that sell fresh cut fries use the Idaho Russet Burbank variety of potatoes. It has been the standard for french fries in the United States. The usual fat for making french fries is vegetable oil. In the past, beef suet was recommended as superior, with vegetable shortening as an alternative. In fact, McDonald's used a mixture of 93% beef tallow and 7% cottonseed oil until 1990, when they switched to vegetable oil with beef flavoring. Starting in the 1960s, more fast food restaurants have been using frozen french fries.