La costilla está bien asada.

Because estar is used here to describe the current state or condition of the food: it is cooked a certain way right now.

• La costilla está bien asada = the rib is nicely/well roasted
• Ser would sound odd here because it is not talking about an essential characteristic of the rib

In Spanish, cookedness, temperature, and similar food conditions usually take estar:

• Está caliente = it’s hot
• Está fría = it’s cold
• Está cruda = it’s undercooked/raw
• Está quemada = it’s burnt

Because asada agrees with costilla, which is a feminine singular noun.

• la costilla → feminine singular
• so the adjective/participle must also be feminine singular: asada

Compare:

• La costilla está asada
• El pollo está asado
• Las costillas están asadas
• Los filetes están asados

This kind of agreement is very important in Spanish.

Here bien means well in the sense of properly or nicely.

So bien asada suggests the rib is roasted/grilled to a good degree. Depending on context, it can imply:

• properly cooked
• nicely roasted
• well done
• thoroughly cooked

It does not mean good as an adjective. It is an adverb modifying asada.

It is originally the past participle of asar (to roast, grill), but in this sentence it functions like an adjective describing the rib’s condition.

So grammatically, you can think of it as:

• from the verb asar
• used adjectivally after estar

This is very common in Spanish:

• Está cerrado = it is closed
• Está roto = it is broken
• Está cocido = it is cooked
• Está asada = it is roasted/grilled

Spanish often uses the definite article el/la/los/las more often than English does.

So la costilla can mean:

• the rib
• or, in context, this rib / the rib we’re talking about

In food contexts, Spanish commonly includes the article where English might not always do so naturally.

For example:

• La sopa está fría
• El pescado está delicioso
• La carne está tierna

Yes. Costilla can refer both to:

• a rib in the body
• a rib as a cut of meat / food item

In a sentence like La costilla está bien asada, the food meaning is the natural one.

Also note that in real-life restaurant or cooking contexts, people often use the plural:

• Las costillas están bien asadas = the ribs are well roasted/grilled

It can mean roast, grill, or sometimes broil, depending on context.

So asada does not map to just one English word in every situation. For meat, it often suggests cooking over heat in a way that browns the outside.

That means bien asada could be translated as:

• well roasted
• nicely grilled
• well cooked

The best English choice depends on how the dish is actually prepared.

No, that would not be natural standard Spanish here.

You need estar because the sentence describes the rib’s cooked state:

• correct: La costilla está bien asada

Also, es bien asada sounds wrong because it treats bien asada as if it were a permanent defining quality rather than a current result of cooking.

The normal and natural order is bien asada.

• La costilla está bien asada = natural
• La costilla está asada bien = awkward or unnatural in most contexts

In Spanish, adverbs like bien often go before the participle/adjective they modify in this kind of expression.

You would change the article, verb, and participle to agree with the plural noun:

• Las costillas están bien asadas

Breakdown:

• la → las
• está → están
• asada → asadas

That agreement pattern is one of the key things to notice in Spanish.