Meaning of "seldom anything but"

Question

These old folks, you must know, were quite poor, and had to work pretty hard for a living. Old Philemon toiled diligently in his garden, while Baucis was always busy with her distaff, or making a little butter and cheese with their cow’s milk, or doing one thing and another about the cottage. Their food was seldom anything but bread, milk, and vegetables, with sometimes a portion of honey from their beehive, and now and then a bunch of grapes, that had ripened against the cottage-wall.

The above is from "The Miraculous Pitcher" by Nathaniel Hawthorne, derived from the Greek myth of Philemon and Baucis.

My question is that "seldom anything but" seems to be meant for "just only". It is a double negative form, I believe, and could it be replaced by 'nothing but'?

It is written in 1851, a long time ago, but is it a proper expression without any grammatical error?

I am not a native English speaker, so I've never come across with 'seldom anything but' kind of expression.

Answer 1

The sentence means that they rarely had anything else than bread, milk and vegetables, with sometimes some honey and sometimes also a bunch of grapes.

The word sequence "seldom anything but" can also be found in other 19th-century publications. Here is an example from Work and Leisure, the Englishwoman's Advertiser, Reporter and Gazette. Volume 8 (1883):

At one school, (...), this supper consisted of dry bread and water, with one glass to the tableful. Elsewhere, it was seldom anything but bread and cheese, or perhaps, rarely, a piece of cold pudding.