Poriluk i celer dodajem na početku, jer tada juha ima bolji okus.

Because Croatian usually does not need a subject pronoun when the verb already shows who is doing the action.

• dodajem = I add
• The ending -em tells you it is 1st person singular

So Ja dodajem is possible, but ja is normally omitted unless you want extra emphasis, contrast, or clarity.

For example:

• Dodajem poriluk. = I add leek.
• Ja dodajem poriluk, a ti mrkvu. = I add leek, and you add carrots.

They are direct objects, but for these nouns the accusative singular looks the same as the nominative singular.

In this sentence:

• poriluk i celer = the things being added, so they are direct objects
• masculine inanimate nouns often have:
  • nominative singular = accusative singular

So:

• poriluk (nom.) / poriluk (acc.)
• celer (nom.) / celer (acc.)

That is why the form does not visibly change.

This is different from masculine animate nouns, where accusative usually looks different:

• vidim čovjeka = I see a man

But with inanimate nouns:

• dodajem celer = I add celery

Dodajem is the imperfective verb, and it fits well here because the sentence describes a habitual action or a general cooking practice.

• dodavati / dodajem = imperfective, ongoing/repeated/habitual
• dodati / dodam = perfective, one completed addition

So this sentence means something like:

• I add leek and celery at the beginning...
  as a usual method or rule.

If you used dodam, it would sound more like a single completed action in a specific context, and in many situations present-tense perfective verbs in Croatian have a future-like sense.

So for recipe habits or general instructions, dodajem is very natural.

Na početku means at the beginning.

Here:

• na
  • locative can express position in time or place
• početku is the locative singular of početak

So:

• početak = beginning
• na početku = at the beginning

In this sentence, it means at the beginning of the cooking process or right at the start.

A learner may wonder why it is not u početku. The two are not the same:

• na početku = at the beginning, right at the start
• u početku = in the beginning, initially

For cooking, na početku is the natural choice.

Because jer introduces a subordinate clause meaning because, and in standard Croatian it is separated by a comma.

So the structure is:

• main clause: Poriluk i celer dodajem na početku
• subordinate clause: jer tada juha ima bolji okus

This comma is normal and expected in written Croatian.

Both jer and zato što can mean because.

In many everyday sentences, they are interchangeable:

• ...jer tada juha ima bolji okus.
• ...zato što tada juha ima bolji okus.

But jer is often shorter and very common in neutral speech and writing.

A rough comparison:

• jer = because
• zato što = because / for the reason that

In this sentence, jer is perfectly natural.

Here tada means then or at that time.

So:

• jer tada juha ima bolji okus
  = because then the soup tastes better

Tada and onda can often both mean then, but there is a slight difference in feel:

• tada often sounds a bit more tied to a specific moment or time
• onda is very common in conversation and can also mean then / in that case / so

In this sentence, tada works very well because it refers to the timing: adding the vegetables early gives the soup a better flavor.

Because juha is the subject of the second clause, not the object.

In:

• juha ima bolji okus

the soup is the thing that has the better flavor, so juha is nominative singular.

Compare:

• Juha ima dobar okus. = The soup has a good taste.
• Jedem juhu. = I am eating soup.

In the second example, juhu is accusative because it is the object.

Because bolji okus is the direct object of ima.

• ima = has
• What does the soup have?
  bolji okus = a better taste/flavor

Now, a detail that often confuses learners:

• okus is masculine singular inanimate
• its accusative singular looks the same as its nominative singular

So although okus is the object, it does not visibly change.

The adjective bolji agrees with okus, and for masculine inanimate singular, nominative and accusative are also the same in form.

So:

• dobar okus / bolji okus
  look the same whether nominative or accusative

Yes. It literally means has a better taste/flavor, and it is natural Croatian.

Croatian often uses imati okus:

• Juha ima dobar okus. = The soup has a good taste.
• Ovo ima čudan okus. = This has a strange taste.

In natural English, you might often translate it more idiomatically as:

• the soup tastes better

So the Croatian is normal, even if English would sometimes phrase it differently.

Sometimes, but okus is usually the safer and more standard choice for taste/flavor in this context.

Very roughly:

• okus = taste, flavor
• ukus can also mean taste, but it often means taste in the sense of style or aesthetic taste

In food contexts, okus is generally the most straightforward word.

So:

• Juha ima bolji okus. = very natural

Croatian word order is more flexible than English word order. The sentence begins with Poriluk i celer to put focus on the ingredients being discussed.

So:

• Poriluk i celer dodajem na početku.
• Dodajem poriluk i celer na početku.

Both are possible.

The version with Poriluk i celer first feels like:

• As for leek and celery, I add them at the beginning.

This kind of fronting is very common in Croatian.

Yes. Croatian often leaves that kind of context unstated if it is obvious.

So in a cooking sentence:

• na početku naturally means at the beginning of the cooking process, at the start of making the soup, or something similar.

You could make it more explicit if needed:

• na početku kuhanja = at the beginning of cooking
• na početku pripreme = at the beginning of the preparation

But in the original sentence, that extra wording is not necessary.

Yes. In a sentence like this, Croatian usually names the ingredients by their basic noun forms, without needing to specify whether they are whole, chopped, sliced, and so on.

So:

• poriluk i celer dodajem...
  simply means I add leek and celery...

If you wanted to specify the form, you could say:

• nasjeckani poriluk i celer = chopped leek and celery
• korijen celera = celery root
• stabljiku celera = a celery stalk

But the plain nouns are completely normal in recipe-style language.

Most likely a general habit or a usual cooking method.

That comes mainly from:

• the imperfective verb dodajem
• the general explanatory clause jer tada juha ima bolji okus

So the feeling is:

• I add leek and celery at the beginning, because the soup tastes better that way.

It sounds like someone explaining how they usually cook, not just describing one specific moment.