Verbal nouns instead of verbs

Question

Could someone offer some guidance for using verbal nouns? In particular, those of the form “zu(m/r) or beim/bei der [the infinitive of the verb in noun form].” When should I replace verbs with these constructions? What affect does choosing the verb instead of the verbal nouns (and vice versa) have on the reader? Does usage change throughout the registers? Any other notes would be welcome.

Here's an example from Quora:

"Ist Blockfett ungesund zum Essen?"

Why is it "zum Essen" rather than "zu essen"?

Answer 1

Dieses Zeug ist kaum zu essen.

This is a predicative phrase on the verb essen. The whole phrase kaum zu essen is used as it was an adjective. English does not have this option, you have to use a real adjective instead. German has this option, too:

Dieses Zeug ist kaum essbar.

This stuff is barely edible.

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Dieses Zeug ist kaum zum Essen (geeignet).

This stuff is barely (suited) for eating.

This in contrary is a predicative phrase on the Partizip II of the verb eignen. Participles can be used as adjectives in their nature, no further transformation required. The item zum Essen is only a supplement to that adjective phrase kaum geeignet.

Answer 2

A pseudo-German sentence from a dubious site - that's not quite the right way when trying to learn German. Translated into English, the sentence reads:

*Is block grease ( = a lubricating grease; DIN 51818, Klasse 6) unhealthy for lunch/dinner?

See how absurd that is? And how ungrammatical? Thus your question "Why is it 'zum Essen' rather than 'zu essen'?" comes to nothing because the starting point, that pseudo-German sentence, does not and cannot exist. If ever, someone might ask: Schadet Blockfett der Gesundheit, wenn man es isst?, but I doubt that anyone would ever want to aks that.