I wonder what an ‘infirm diet’ was?
I know what an "infirm diet" was when I was a youngster. It was anything soft that would glide down the throat. Would those infirm people have good teeth or no teeth to speak of?
A favourite to give children was hot milk poured over pieces of bread, with maybe a teaspoon of rum and a sprinkle of sugar to make the food palatable. It was known as pappe/pap. I've seen my mother have this too when she had a cold and a sore throat. I've heard "gruel" was given to invalids too.
"pap (plural paps)
(uncountable) Food in the form of a soft paste, often a porridge, especially as given to very young children.
Pap can be made from bread boiled in milk or water.
Origins unclear. Related to Middle Low German pappe, Dutch pap, Old French papa/pape, Latin pappa, Bulgarian папам (papam, “to eat”) and Serbo-Croatian папати/papati (“to eat”), among others. The relationships between these words are difficult to reconstruct. An (independent?) origin in imitative baby-talk, leading to constant reformation and renewal, is the best explanation in view of German Pappe (“pap, mush, porridge for children; sticky, mushy substance, paste, glue”), which fails to show the effects of the High German sound shift (no shifted form appears to be attested, making borrowing from Low German an unsatisfying explanation).