Breakdown of Если добавить в бульон маленькие фрикадельки и сельдерей, суп становится сытнее.
Questions & Answers about Если добавить в бульон маленькие фрикадельки и сельдерей, суп становится сытнее.
Russian often uses an impersonal infinitive in general statements, especially in recipes and instructions.
So Если добавить... means something like:
- if you add...
- if one adds...
- if we add...
The person doing the action is left unspecified because it is not important.
Добавить is perfective, so it presents the action as a completed addition that produces a result.
Here the idea is:
- first, the ingredients get added
- then, as a result, the soup becomes more filling
That is why добавить fits well.
If you used добавлять, it would sound more like an ongoing, repeated, or habitual process of adding, which is less natural in this sentence.