The original folding fruit knife (aka melon tester) was made of silver and mother-of-pearl in the late 1700s in England. While silver is relatively soft, it is resistant to citric acid and does not rust. The stainless-steel fruit knife became popular in the 1930s. They were standard issue for sanitarians and are still one of the most useful tools when conducting food inspections.
These specialty knives are made with long, skinny, spear blades (4.5 in. blade). They are used to get a sample from deep inside the product such as fruit, vegetables, and meat. The inspectors can then examine the smell, texture, and color of the product.
The knife pictured above was issued in 1965 and is typical of most melon testers. The melon testers were given as advertising products, imprinted with the company logo. This knife was made by Colonial Cutlery in Providence, Rhode Island, which was founded in 1926 and is the leading manufacturer of switchblades and utility knives.