Quem cozinha em casa sabe que alho e cebola mudam tudo.

Here quem means whoever, anyone who, or the person who.

So Quem cozinha em casa sabe... means something like:

• Whoever cooks at home knows...
• Anyone who cooks at home knows...

In Portuguese, quem is very commonly used for general statements like this.

Because quem normally takes the verb in the 3rd person singular.

So even though the idea is general, Portuguese says:

• Quem cozinha... sabe...

not:

• Quem cozinham... sabem...

This is standard grammar. English often uses a plural idea like people who cook at home know, but Portuguese structures it differently.

Here it is the verb cozinhar in the 3rd person singular present:

• cozinhar = to cook
• cozinha = he/she cooks, you cook, one cooks

So:

• Quem cozinha em casa = Whoever cooks at home

As a noun, cozinha can also mean kitchen, but in that case the sentence structure would be different, usually with an article:

• a cozinha = the kitchen

Em casa is a fixed, very common expression meaning at home.

• em casa = at home

If you say na casa, that usually means in/at the house of someone or some specific house:

• Estou em casa. = I am at home.
• Estou na casa da minha mãe. = I am at my mother’s house.

So in this sentence, em casa means cooking at home, not just in some house.

Here que means that and introduces a new clause:

• sabe que alho e cebola mudam tudo
• knows that garlic and onion change everything

In Portuguese, que is very common after verbs like:

• achar que = to think that
• dizer que = to say that
• saber que = to know that

Unlike English, Portuguese often keeps que where English might sometimes omit that.

Portuguese often omits articles when talking about things in general, especially ingredients, foods, or concepts.

So:

• alho e cebola mudam tudo = garlic and onion change everything

This sounds natural as a general statement.

You could also hear:

• o alho e a cebola mudam tudo

That can also be correct, and it may sound a little more specific or stylistically more explicit. Both are possible, but the version without articles sounds very natural in a general, proverb-like sentence.

Because the subject is alho e cebola, which is a compound subject:

• alho
  • cebola = two things

So the verb must be plural:

• alho e cebola mudam tudo = garlic and onion change everything

Compare:

• O alho muda tudo. = Garlic changes everything.
• Alho e cebola mudam tudo. = Garlic and onion change everything.

Portuguese often leaves out subject pronouns when the verb form already shows who or what the subject is.

Here, mudam is a plural verb, and the subject alho e cebola is already stated, so no pronoun is needed.

Portuguese generally avoids unnecessary subject pronouns more than English does.

Yes. Tudo literally means everything.

In this sentence, though, mudam tudo is also a very natural, slightly emphatic way to say:

• they change everything
• they make all the difference
• they transform the result

So it is literal, but also idiomatic in tone.

Grammatically, that is possible, but it sounds old-fashioned or unnatural in modern English.

Better translations are:

• Anyone who cooks at home
• Whoever cooks at home
• People who cook at home

So quem often matches whoever or anyone who better than he who.

It is neutral and natural. It works well in everyday speech and writing.

Nothing in it is especially slangy, literary, or formal. It sounds like a common observation or a little piece of practical wisdom.

A learner often notices two things here:

• lh in alho
• the unstressed vowels in cebola

Alho has the sound lh, which is similar to the lli in million for many English speakers, though not exactly the same.

• alho ≈ AH-lyoo / AHL-yu depending on accent

Cebola in Brazil is usually pronounced roughly like:

• seh-BO-lah

with the stress on bo.

A rough full-sentence pronunciation guide could be:

• Keng ko-ZEE-nyah eng KAH-zah SAH-bee kee AHL-yoo ee seh-BO-lah MOO-dam TOO-doo

That is only approximate, but it can help at first.

Yes. A more direct version could be:

• Se você cozinha em casa, sabe que alho e cebola mudam tudo.
• If you cook at home, you know that garlic and onion change everything.

This is also natural, but it feels a bit more direct and conversational.

The original with quem sounds more general, almost like a saying or shared truth.

The sentence uses the present tense throughout:

• cozinha = cooks
• sabe = knows
• mudam = change

Portuguese often uses the present tense for general truths, habits, and things that are usually true, just like English does.

So this sentence is not about one specific cooking event. It is making a general statement.