Learn Spanish (Latin America): La cocina huele a café.

Without the preposition, oler is an active verb meaning to physically sniff something (like when you smell a flower). By adding a, it acts as a linking verb that describes the scent something gives off, which is why huele a café means the kitchen itself emits the scent of coffee.

Why do we use the preposition a here instead of translating 'of' or 'like' directly?

In Spanish, sensory verbs that connect a subject to a noun describing its quality act as pseudo-copulative (linking) verbs and require the preposition a. You will see this exact same pattern with other sensory verbs like saber a (to taste like) and sonar a (to sound like).

Why doesn't huele start with an O like its infinitive oler?

Oler is an O-to-UE stem-changing verb. However, Spanish spelling rules forbid words from starting with the vowel combination ue. To solve this, a silent h is added to the front whenever the stem changes, giving us forms like huele and huelo.

Why is there no article before café in this sentence?

We leave out the definite article because we are talking about the general, uncountable essence of coffee. If you said huele al café, it would sound like the kitchen smells of a specific, previously mentioned batch of coffee rather than just having a general coffee scent.