Why are fried potatoes called "pommes frites", and not "pommes de terre frites"?

Question

"Pomme" in French is apple, but "pomme de terre" is potato.

1. Why is the "de terre" part of the term not included, when talking about French fries?
2. Has it been like this since French fries were "invented" or was it called "pommes de terre frites" at first, but then shortened for convenience?

Answer 1

I never say pommes frites and rarely pommes de terre frites. As @RogerVadim commented, frites is by far the most usual name.

In any case, when I read pommes frites on a menu, I know they are made of potatoes as fried apples would likely be called beignets de pomme.

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Here are my answers to your questions:

1. Because pommes de terre is too long to write on a menu while frites alone is less "classy". Another well known dish cooked with potatoes is pommes dauphine. Both of them are actually exceptions. In most if not all other potato based dish names, pomme de terre is kept, even if the name is long, like pommes de terre en robe des champs.

2. Pommes de terre frites came first.

Answer 2

It is a fact that "de terre" is included more often than not. The reason for not including it is that some people find the full term too long, especially on menus.

The answer to your second question is to be read in the ngram shown above. The shortening started a little later, in the early 20th century, or, to be more precise, in the late 19th century.