Fermentace pokračuje natolik rychle, že bochník brzy vykyne.

This is a very common Czech pattern meaning so ... that or to such an extent that.

So:

• natolik rychle = so quickly
• že = that

Together:

• natolik rychle, že ... = so quickly that ...

A very close, often more common alternative is tak ... že:

• tak rychle, že ... = so quickly that ...

Natolik can sound a bit more formal or more emphatic than tak.

Because in Czech, a subordinate clause introduced by že is separated by a comma.

Here the sentence has two parts:

• Fermentace pokračuje natolik rychle
• že bochník brzy vykyne

The second part depends on the first, so Czech punctuation requires a comma before že.

This is standard Czech punctuation, not optional.

Pokračuje is the 3rd person singular present tense form of pokračovat = to continue.

Why this form?

• the subject is fermentace = fermentation
• fermentace is singular
• so the verb must also be singular

That gives:

• fermentace pokračuje = fermentation continues / is continuing

Because rychle is an adverb, and it modifies the verb pokračuje.

It answers the question:

• How does fermentation continue?
• Rychle = quickly

By contrast:

• rychlý / rychlá / rychlé are adjectives
• adjectives describe nouns, not verbs

So:

• rychlá fermentace = fast fermentation
  but
• fermentace pokračuje rychle = fermentation continues quickly

Because bochník is the subject of the verb vykyne.

In the clause:

• bochník brzy vykyne

the loaf is the thing that performs the action of rising. In Czech, the subject is normally in the nominative case.

So:

• bochník = nominative singular

This is a very important Czech point: perfective verbs use present-tense forms to express the future.

The verb here is vykynout / vykynout? Actually the form vykyne comes from vykynout / vykynout-type perfective verb meaning to rise fully. In normal usage, vykyne means:

• will rise
• will have risen in the right context

So even though the form looks present, its meaning is future because the verb is perfective.

Compare:

• kyne = is rising / rises regularly
• vykyne = will rise fully

This is mainly a difference of aspect.

• kynout = imperfective
  focuses on the process: to be rising, to rise as an ongoing action

• vykynout = perfective
  focuses on the result/completion: to rise fully, to finish rising

So in this sentence, vykyne fits well because the idea is a result:

• fermentation is proceeding so quickly
• that the loaf will soon have risen / will soon rise

If you used the imperfective verb, it would sound more like you are describing the process rather than the completed result.

Yes, absolutely.

• tak rychle, že ... = very common, neutral
• natolik rychle, že ... = also correct, slightly more formal or more emphatic

So both work:

• Fermentace pokračuje tak rychle, že bochník brzy vykyne.
• Fermentace pokračuje natolik rychle, že bochník brzy vykyne.

The meaning is very similar.

Bochník means a loaf, especially a whole loaf of bread.

It is a common bread-related noun. In this context, it refers to the shaped loaf of dough/bread that is rising.

So it is more specific than just bread:

• chléb = bread
• bochník chleba = a loaf of bread
• sometimes bochník alone is enough if the bread context is clear

Because brzy is an adverb meaning soon, and Czech word order is flexible.

Here:

• bochník brzy vykyne

is a natural, neutral order.

You could also hear:

• bochník vykyne brzy

but that can shift the emphasis slightly.

In the original sentence, putting brzy before the verb makes the timing feel smoothly connected to the result: the loaf will soon rise.

Yes, it is grammatical and understandable Czech.

That said, depending on context, native speakers might sometimes choose more specific wording in baking contexts, for example talking directly about:

• kynutí
• kvašení
• těsto kyne
• fermentace probíhá rychle

But Fermentace pokračuje natolik rychle, že bochník brzy vykyne is still a valid sentence. It sounds a bit technical or explanatory, which may be exactly what is intended.

Yes: it is a classic cause/degree → result structure.

Pattern:

• X happens to such a degree, that Y happens

In Czech:

• Fermentace pokračuje natolik rychle, že bochník brzy vykyne.

Breakdown:

• Fermentace pokračuje = the process is continuing
• natolik rychle = to such a degree / so quickly
• že = that
• bochník brzy vykyne = the loaf will soon rise

This pattern is very useful and common in Czech, especially with:

• tak ... že
• natolik ... že
• tolik ... že

So this sentence is a good model to learn from.