Antes de cocinar, hay que pelar las patatas y rallar un poco de queso.

Hay que is an impersonal expression of obligation. It means something like:

• one must
• you have to
• it’s necessary to

So hay que pelar las patatas y rallar un poco de queso means that this is what needs to be done, without saying exactly who does it.

A very useful contrast is:

• hay que + infinitive = it is necessary to... / one must...
• tener que + infinitive = to have to... for a specific person

For example:

• Hay que estudiar. = You have to study / One must study.
• Tengo que estudiar. = I have to study.

They are in the infinitive because they come after hay que.

In Spanish, after expressions like hay que, you normally use an infinitive:

• hay que pelar
• hay que rallar
• hay que cocinar

This is similar to English to peel, to grate, to cook, although Spanish does not use to here.

So:

• hay que pelar = it is necessary to peel
• hay que rallar = it is necessary to grate

Antes de + infinitive means before doing something.

So:

• antes de cocinar = before cooking

This is a very common structure in Spanish:

• antes de salir = before leaving
• antes de comer = before eating
• antes de dormir = before sleeping

Spanish uses de before the infinitive in this pattern, so it is:

• antes de cocinar not
• antes cocinar

Good question. Both can mean before, but they are used differently.

1. Antes de + infinitive

Use this when you are talking generally, or when the subject is the same or not stated.

• Antes de cocinar, hay que pelar las patatas.

2. Antes de que + subjunctive

Use this when there is a new or explicit subject after before.

• Antes de que cocines, lava las manos.
  = Before you cook, wash your hands.

So in your sentence, antes de cocinar is the natural choice because it is a general instruction, not a clause with a new subject.

In Spanish, articles are often used more than in English, especially with nouns referring to things in a general or practical sense.

So pelar las patatas is the normal way to say peel the potatoes in a recipe or instruction.

Even when English might just say peel potatoes, Spanish often prefers the article:

• lava las manos = wash your hands
• abre la puerta = open the door
• corta las cebollas = cut the onions

Here, las patatas refers to the potatoes involved in the cooking process.

Because un poco is a quantity expression, and in Spanish quantity expressions are usually followed by de.

So:

• un poco de queso = a little bit of cheese
• un kilo de patatas = a kilo of potatoes
• un vaso de agua = a glass of water

You need the de after un poco.

Because queso here is being used as an uncountable substance: not a specific cheese, but some cheese.

Spanish often leaves out the article after quantity expressions:

• un poco de queso
• mucha agua
• poco pan

If you said un poco del queso, that would mean a little of the cheese — a specific cheese already known in the conversation.

So:

• un poco de queso = some cheese / a little cheese
• un poco del queso = a little of the cheese

Because this sentence is in Spanish from Spain.

In Spain, patatas is the usual word for potatoes.
In many Latin American countries, people often say papas instead.

So both can be correct depending on the variety of Spanish:

• Spain: patatas
• much of Latin America: papas

Since you are learning Spanish (Spain), patatas is exactly what you would expect.

Because one hay que can govern more than one infinitive.

So:

• hay que pelar las patatas y rallar un poco de queso

means:

• you have to peel the potatoes and grate a little cheese

Spanish does not need to repeat hay que before the second verb unless you want extra emphasis or clarity.

Both are possible:

• Hay que pelar las patatas y rallar un poco de queso.
• Hay que pelar las patatas y hay que rallar un poco de queso.

The first one is more natural here.

This is a very common confusion.

• rallar = to grate
  Example: rallar queso = to grate cheese

• rayar = to scratch, to draw a line on, or sometimes informally to annoy / obsess

So in a cooking sentence, it must be rallar.

Even though they may sound similar in many accents, the meanings are different.

Because Spanish often leaves out the subject when it is unnecessary, and in this case the main structure is already impersonal: hay que.

The sentence is not about I, you, or we specifically. It is just giving a general instruction:

• Antes de cocinar, hay que...

That sounds natural in recipes, instructions, and general advice.

English often uses you in this kind of sentence, but Spanish does not need to:

• Before cooking, you have to peel the potatoes...
• Antes de cocinar, hay que pelar las patatas...

It is very natural to put a comma there because Antes de cocinar is an introductory phrase.

So:

• Antes de cocinar, hay que pelar las patatas...

is standard and clear.

In some short sentences, punctuation can vary, but with an introductory phrase like this, the comma is normally a good idea. It helps separate the time expression from the main clause.