La tostada se quemó por un lado.

In Spain, la tostada usually means a slice of toasted bread / toast, especially the kind you might eat for breakfast.

So in this sentence, la tostada is most naturally understood as the piece of toast.

A learner from the US might think of a tostada as the Mexican dish with a crispy tortilla, but that is not the usual meaning here.

Spanish often uses the definite article more than English does.

Here, la tostada refers to the specific piece of toast being talked about. Even if English might just say Toast burned on one side, Spanish commonly prefers La tostada...

Also, tostada is a feminine singular noun, so it takes la.

Here, se shows that the toast got burned / burned itself, rather than someone actively burning something else.

Compare:

• Quemó la tostada = He/She burned the toast
• La tostada se quemó = The toast got burned / The toast burned

This use of se is very common in Spanish for things that happen by themselves, or when the focus is on the result rather than on who caused it.

It looks reflexive, but in practice it is better to think of it here as a middle / intransitive use rather than a true reflexive.

The toast is not literally burning itself on purpose. Instead, Spanish uses quemarse to mean to get burned.

So:

• quemar = to burn something
• quemarse = to get burned / to burn

That pattern is very common:

• romper = to break something
• romperse = to break
• abrir = to open something
• abrirse = to open

Quemó is the preterite, which presents the event as a completed action.

So La tostada se quemó means the burning happened and is viewed as a finished event.

If you said La tostada se quemaba, that would usually suggest:

• an ongoing past action,
• background description,
• or something habitual in the past.

Examples:

• La tostada se quemó por un lado. = It ended up burnt on one side.
• La tostada se quemaba mientras hablábamos. = The toast was burning while we were talking.

The accent shows both stress and meaning.

• quemó = he/she/it burned or got burned (preterite)
• quemo = not the correct written form for that meaning
• quemo without an accent would not be standard Spanish here

So the accent marks the correct past-tense form.

Here, por un lado means on one side.

In this sentence it means that only one side of the toast burned, not both sides.

So the phrase adds the detail that the burning was limited to one side.

This is just the most natural idiomatic expression in Spanish.

With physical meaning, por un lado often means something like:

• on one side
• along one side
• from one side

In this sentence, it is the normal way to express that only one side was affected.

You may also hear other phrases in other contexts, such as:

• de un lado
• por una parte
• de un solo lado

But for toast burning on one side, por un lado sounds very natural.

Yes, many Spanish speakers would understand it, and in some varieties it may sound natural. But por un lado is a very standard, idiomatic way to say it.

In Spain Spanish, La tostada se quemó por un lado sounds completely normal.

Yes, in this sentence lado is literal and physical: one face/side of the toast.

But in other contexts por un lado can also be figurative, meaning on the one hand.

For example:

• Por un lado, es barato; por otro, no es muy bueno. = On the one hand, it’s cheap; on the other, it isn’t very good.

That is not the meaning here. Here it is just the actual side of the toast.

It could be.

Both are possible:

• La tostada se quemó por un lado
• Se quemó la tostada por un lado

The version with La tostada first sounds a bit more neutral if the toast is the topic.

The version starting with Se quemó can sound a bit more like what happened was... the toast burned on one side.

Spanish word order is flexible, and the difference is usually about focus and flow, not basic meaning.

Yes, very often it does.

Using se quemó often gives the feeling that it happened, rather than strongly blaming a person for doing it.

That makes it similar to English it got burnt or it burned rather than someone burned it.

If you want to clearly mention the person who caused it, Spanish would normally use quemar without se:

• Juan quemó la tostada por un lado.

Yes, very common.

You can use quemarse for food that burns too much:

• Se quemó el pan.
• Se quemó la pizza.
• Se quemaron las galletas.

It is a very natural verb in kitchen contexts.

You would change the noun and verb to plural:

• Las tostadas se quemaron por un lado.

Changes:

• la → las
• tostada → tostadas
• quemó → quemaron

Yes, but the meaning changes slightly.

• La tostada se quemó por un lado. = The toast / slice of toast burned on one side.
• El pan se quemó por un lado. = The bread burned on one side.

La tostada usually refers to the prepared slice of toast.
El pan is more general: bread as a food item or loaf/piece of bread.

It is pronounced roughly keh-MOH.

A few useful points:

• qu before e sounds like a hard k
• the u in que is silent
• the stress falls on the last syllable because of the written accent: que-MÓ

So:

• quemó → keh-MOH