Dejamos de esperar cuando termina la fermentación final.

Because the full structure is dejar de + infinitive, and that means to stop doing something.

So:

• dejamos = we leave / we let
• dejamos de esperar = we stop waiting

The little word de changes the meaning a lot.

Compare:

• Dejamos la mesa. = We leave the table.
• Dejamos de esperar. = We stop waiting.

Spanish often leaves out subject pronouns because the verb ending already shows who the subject is.

Here, dejamos ends in -amos, which tells you the subject is we.

So both are possible:

• Dejamos de esperar...
• Nosotros dejamos de esperar...

The version without nosotros is more natural unless you want emphasis or contrast.

For example:

• Nosotros dejamos de esperar, pero ellos siguen esperando.
  = We stop waiting, but they keep waiting.

After dejar de, Spanish uses the infinitive.

So the correct pattern is:

• dejar de + infinitive
• dejar de esperar
• dejar de comer
• dejar de hablar

Not:

• dejar de esperando ❌

This is just the normal grammar of that expression.

Be careful: dejar + gerund is a different thing and is generally not used this way. In this sentence, dejar de + infinitive is the fixed structure you need.

Because the subject of that verb is la fermentación final, which is singular.

• la fermentación final = singular
• so the verb is termina = it ends

If the subject were plural, the verb would be plural too:

• Cuando terminan las fermentaciones... = When the fermentations end...

So termina agrees with la fermentación final.

This is a very common question.

Both forms can be possible in Spanish, but they mean slightly different things depending on context.

In your sentence, cuando termina uses the indicative, which fits a general rule, habitual action, or process description:

• Dejamos de esperar cuando termina la fermentación final.
  = We stop waiting when the final fermentation ends.
  This sounds like a general statement or description of what happens.

If you are talking about a specific future event, Spanish often uses the subjunctive after cuando:

• Dejaremos de esperar cuando termine la fermentación final.
  = We will stop waiting when the final fermentation ends.

So, very simply:

• cuando termina = habitual / general / descriptive
• cuando termine = future, not yet completed

Grammatically, it is in the present:

• dejamos
• termina

But in Spanish, the present tense is often used for:

• general truths
• routines
• instructions
• process descriptions

So this sentence can sound like a general explanation of a procedure, for example in baking or fermentation.

If you want to make the future meaning clearer, Spanish often changes both parts:

• Dejaremos de esperar cuando termine la fermentación final.

That sounds more clearly like a future event.

Yes, esperar can mean either:

• to wait
• to hope

But here it clearly means to wait, because of the context:

• Dejamos de esperar cuando termina...
  = We stop waiting when it ends.

That idea matches wait, not hope.

A very common pattern for hope is:

• esperar que...
• Espero que salga bien. = I hope it goes well.

So in this sentence, esperar = to wait.

Because in Spanish, adjectives often come after the noun, especially when they are descriptive or classifying.

So:

• fermentación final = final fermentation

This is the normal order.

Putting final before the noun would sound unusual here:

• final fermentación ❌

Also, in technical or process-related language, Spanish often keeps the adjective after the noun:

• masa madre activa
• temperatura ambiente
• fermentación final

Spanish often uses the definite article (el, la, los, las) more often than English does.

Here, la fermentación final refers to a specific stage or process, so the article sounds natural.

• termina la fermentación final = the final fermentation ends

In English, you might sometimes omit the in certain technical contexts, but Spanish usually keeps it here.

You might hear alternatives in some contexts, but dejar de + infinitive is the standard and most natural way to say stop doing something.

So:

• dejamos de esperar = natural
• paramos de esperar = much less standard for this meaning

A more natural alternative might be:

• dejamos de esperar
• ya no esperamos = we no longer wait

But dejar de + infinitive is the best match for stop waiting.

The given order is very natural:

• Dejamos de esperar cuando termina la fermentación final.

But Spanish does allow some flexibility. For example:

• Cuando termina la fermentación final, dejamos de esperar.

This means the same thing, but it puts more focus on the time clause first.

So both are correct:

• Dejamos de esperar cuando termina la fermentación final.
• Cuando termina la fermentación final, dejamos de esperar.

The original version is simply a straightforward, neutral order.