Wir rösten nach und stoppen vor dem zweiten Crack.

That is normal in German. In the present tense, the wir form of most verbs is the same as the infinitive.

For rösten:

• ich röste
• du röstest
• er/sie/es röstet
• wir rösten

So Wir rösten ... is a correctly conjugated finite verb form, even though it looks identical to the dictionary form.

German also uses the simple present where English might use either we roast or we are roasting.

Because the verb is nachrösten, which is a separable verb.

In a main clause, the conjugated part goes in second position, and the prefix moves to the end of the clause:

• Wir rösten nach.

In your sentence, that first clause is then followed by another coordinated clause:

• Wir rösten nach und stoppen vor dem zweiten Crack.

So nach is not a separate adverb here in the ordinary sense; it is the separated prefix of nachrösten.

You can see the full verb stay together in other structures:

• infinitive: nachrösten
• subordinate clause: ..., weil wir nachrösten
• perfect tense: Wir haben nachgeröstet.

Not really in a word-for-word way.

The prefix nach- often gives a sense like:

• further
• additionally
• afterward
• for a bit longer

So nachrösten means something like continue roasting, roast a bit more, or roast further.

This is a good example of why separable-prefix verbs should be learned as whole vocabulary items, not always translated piece by piece.

German often leaves out the repeated subject when two verbs share the same subject and are linked with und.

So this is natural:

• Wir rösten nach und stoppen vor dem zweiten Crack.

You could also say:

• Wir rösten nach und wir stoppen vor dem zweiten Crack.

That is grammatically correct, but it sounds more repetitive and would usually only be used for emphasis or contrast.

Because vor takes the dative case here.

The noun is der Crack in this context, so in the dative singular it becomes dem Crack.

Then the adjective zweite also has to match that form:

• nominative: der zweite Crack
• dative after vor: dem zweiten Crack

So:

• vor dem zweiten Crack = before the second crack

That ending comes from adjective inflection.

In dem zweiten Crack:

• dem already marks dative masculine singular
• so the adjective takes the weak ending -en

That is why you get:

• dem zweiten Crack

This is part of a very common pattern in German:

• mit dem heißen Kaffee
• nach dem langen Tag
• vor dem zweiten Crack

Yes. In coffee-roasting language, der Crack is a common technical term borrowed from English.

It refers to the audible cracking phase during roasting, as in first crack and second crack.

A few things to notice:

• It is capitalized in German because all nouns are capitalized.
• It is usually treated as masculine: der Crack
• In specialist language, English loanwords like this are very common.

So here Crack is not unusual at all for the topic.

Stoppen is standard German and very common, especially in technical, procedural, or everyday contexts.

So wir stoppen vor dem zweiten Crack sounds natural.

Depending on context, German could also use other verbs:

• aufhören = stop doing something
• beenden = end/finish something
• abbrechen = break off/cancel

But stoppen works well when describing a process that is deliberately halted at a certain point.

Because rösten is the normal verb for roasting things like:

• coffee beans
• nuts
• seeds
• sometimes bread or similar items

Braten is more often used for:

• frying
• roasting meat
• cooking food in fat or in a pan/oven

So in a coffee context, rösten is the correct and idiomatic choice.