More crusty; having a thicker, harder, or more prominent crust than something else, or more grumpy and irritable (informal usage).
From crusty (adjective meaning 'having a crust' or 'irritable') plus the comparative suffix -er meaning 'more.' It's the comparative form.
French baguettes are actually supposed to get crustier the next day as moisture continues to escape—that's why day-old bread can have an even more satisfying crunch than fresh bread, though the interior gets drier too.
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