Если добавить немного муки, соус будет гуще.

In this sentence, если добавить немного муки is an impersonal way to say if you add a little flour or if one adds a little flour.

Russian often uses the infinitive this way when:

• the subject is general or unimportant,
• the sentence sounds like a recipe, instruction, or general observation.

So если добавить немного муки means something like:

• if you add a little flour
• if some flour is added

It avoids saying exactly who does the action.

A more personal version would be:

• Если ты добавишь немного муки, соус будет гуще.
• Если вы добавите немного муки, соус будет гуще.

Those are more direct. The original sounds more neutral and recipe-like.

Добавить is perfective because it refers to a single completed action: adding some flour, and then seeing the result.

The logic is:

• first, the flour gets added,
• then, the sauce becomes thicker.

Perfective is very natural here because the sentence describes the result of one completed step.

If you used добавлять, the meaning would change. Если добавлять... suggests repeated, habitual, or ongoing adding, something more like:

• if you keep adding flour
• if you add flour in general / repeatedly

So in a simple cause-and-result sentence, добавить is the normal choice.

Because немного requires the following noun to be in the genitive case.

So:

• мука = nominative singular
• муки = genitive singular

After words like:

• немного = a little
• много = much/a lot
• мало = little/not much

Russian normally uses the genitive.

So:

• немного муки = a little flour
• много воды = a lot of water
• мало соли = little salt

This is especially common with substances and uncountable nouns.

Both, really.

Grammatically, муки is genitive because it follows немного.

But semantically, it also has a partitive sense: not flour in general, but some amount of flour. English does something similar with a little flour.

This is very common with mass nouns in Russian:

• немного сахара = a little sugar
• немного масла = a little butter
• немного молока = a little milk

So yes, the genitive here fits both the grammar and the meaning of some/a little of.

Because гуще means thicker, not just thick.

The sentence is about a change in degree:

• after adding flour, the sauce will be thicker than before

If you said соус будет густой, that would mean:

• the sauce will be thick

That describes a quality, but not necessarily a comparison with its previous state.

So:

• густой = thick
• гуще = thicker

The comparative is the natural choice because the sentence describes a result of adding something.

Гуще is the comparative form of густой.

So:

• густой = thick
• гуще = thicker

This is one of the short comparative forms that Russian often uses in predicates:

• чай крепче = the tea is stronger
• вода холоднее = the water is colder
• соус гуще = the sauce is thicker

The formation is not always fully predictable from the adjective, so learners often just memorize common comparatives as vocabulary items.

In this case, the stem changes a little, so гуще is best learned directly as the comparative of густой.

Because the result is in the future.

The sentence means that after the condition is fulfilled, the sauce will be thicker. So Russian uses the future form of быть:

• будет = will be

That gives:

• соус будет гуще = the sauce will be thicker

In present-tense Russian, быть is usually omitted:

• соус гуще = the sauce is thicker

But in the future, you normally need будет.

Yes, absolutely.

Соус станет гуще means the sauce will become thicker, and it is very natural here.

Compare:

• соус будет гуще = the sauce will be thicker
• соус станет гуще = the sauce will become thicker

The difference is small:

• будет гуще focuses a bit more on the resulting state,
• станет гуще focuses a bit more on the change.

In a cooking context, both are good.

Yes. In the first clause, the subject is intentionally left unspecified.

Russian often does this in general statements, instructions, and recipes. The implied meaning is something like:

• if you add
• if one adds
• if flour is added

English usually wants a subject, but Russian can leave it out more easily, especially with infinitives.

That is why the sentence sounds natural even though nobody is explicitly named as doing the adding.

Yes.

You can also say:

• Соус будет гуще, если добавить немного муки.

This means the same thing. Russian word order is fairly flexible, and both versions are natural.

The difference is mostly about emphasis:

• Если добавить немного муки, соус будет гуще.
  starts with the condition
• Соус будет гуще, если добавить немного муки.
  starts with the result

Both are correct.

Because Russian uses a comma to separate the if-clause from the main clause.

Here the structure is:

• Если добавить немного муки = subordinate clause
• соус будет гуще = main clause

Russian punctuation requires a comma between them:

• Если добавить немного муки, соус будет гуще.

This is true whether the если clause comes first or second:

• Если добавить немного муки, соус будет гуще.
• Соус будет гуще, если добавить немного муки.

Sometimes, depending on context, yes.

In many practical contexts like cooking, если can feel close to English if or when:

• If you add a little flour, the sauce will be thicker
• When you add a little flour, the sauce will be thicker

But the core meaning of если is still if. It presents the action as a condition.

In a recipe or general instruction, English sometimes uses if where the real sense is almost whenever:

• If you add flour, the sauce gets thicker

So if is the basic translation, but in context it can sound very close to when.