Fermentace a kynutí jsou důležité.

Because the subject is plural: Fermentace a kynutí = fermentation and leavening/proofing.
When two things are joined by a (and), Czech normally treats them as plural, so the verb být (to be) must also be plural:

• je = is
• jsou = are

So:

• Fermentace je důležitá. = Fermentation is important.
• Kynutí je důležité. = Leavening/Proofing is important.
• Fermentace a kynutí jsou důležité. = Fermentation and leavening/proofing are important.

The adjective has to agree with the subject.

Here the subject is a combination of:

• fermentace — feminine singular
• kynutí — neuter singular

Together, they form a plural subject. With this kind of mixed non-masculine-animate subject, Czech uses the plural form důležité.

So the sentence is:

• Fermentace a kynutí jsou důležité.

If you describe just one noun, the form changes:

• Fermentace je důležitá. — feminine singular
• Kynutí je důležité. — neuter singular

They are in the nominative case, because they are the subject of the sentence.

You can tell because they are the things that are important.

• Fermentace = subject
• kynutí = subject
• jsou = verb
• důležité = predicate adjective

So this is a very typical nominative + být + adjective structure.

Kynutí comes from the verb kynout, which means to rise, especially dough.

Depending on context, kynutí can mean:

• rising
• proofing
• leavening

In baking, it usually refers to dough rising. So if the sentence is about bread, baking, or food processes, kynutí is probably best understood as proofing or rising.

It is a normal Czech word, and it is clearly understandable. It is also an international-style word, similar to English fermentation.

Czechs use it in scientific, culinary, health, and everyday contexts, for example:

• mléčné kvašení = lactic fermentation
• fermentace těsta = dough fermentation

So yes, fermentace is perfectly natural Czech.

A rough English-friendly guide is:

• Fermentace ≈ fer-men-TA-tseh
• a = ah
• kynutí ≈ KIH-noo-tee
  
  • y is not exactly English i, but for a beginner this approximation is fine
• jsou ≈ ysoh or s-oh with a light j-sound at the start
• důležité ≈ doo-leh-zhi-tay

A few important pronunciation notes:

• ů is a long ú sound
• é and í are long vowels
• ž sounds like the s in measure

So důležité has three noticeable long vowels/syllables: dů-le-ži-té.

Yes, they matter a lot. In Czech, accent marks are part of the spelling and usually affect pronunciation.

In this sentence:

• kynutí has a long í
• důležité has ů and é

If you leave them out, Czech readers will often still understand you from context, but it is considered incorrect spelling, and sometimes missing accents can change meaning or make a word look wrong or unnatural.

So it is best to write:

• kynutí, not kynuti
• důležité, not dulezite

Because Czech has no articles like English the and a/an.

So:

• Fermentace a kynutí jsou důležité.

can mean:

• Fermentation and leavening are important
• The fermentation and the leavening are important

Which exact meaning is intended depends on context.

This is very normal in Czech, and English speakers often need time to get used to it.

Yes. Czech word order is more flexible than English word order.

The neutral, straightforward version is:

• Fermentace a kynutí jsou důležité.

But other orders are possible for emphasis, for example:

• Důležité jsou fermentace a kynutí.
  = What is important is fermentation and leavening.

The basic meaning stays similar, but the focus changes. Czech word order often reflects emphasis, topic, and new information rather than strict grammatical necessity.

In a sentence like this, yes.
a is the normal Czech word for and.

So:

• fermentace a kynutí = fermentation and leavening

Do not confuse it with English a/an. Czech a never means an article.

The dictionary form is důležitý.

That is the masculine singular base form you would usually find in a dictionary. From that base, the adjective changes according to gender and number:

• důležitý — masculine singular
• důležitá — feminine singular
• důležité — neuter singular, and also a plural form in contexts like this one

So in this sentence, důležité is just the correctly inflected form of důležitý.

In standard Czech, no.
Because there are two coordinated subjects, the verb should be plural:

• Fermentace a kynutí jsou důležité.

Using je would sound ungrammatical in normal standard usage.

You can say each part separately:

• Fermentace je důležitá. = Fermentation is important.
• Kynutí je důležité. = Leavening/Proofing is important.

These are useful because they show how the adjective changes:

• with fermentace → důležitá
• with kynutí → důležité

Then when you combine them, the verb becomes plural:

• Fermentace a kynutí jsou důležité.