Die Bohnenfarbe zeigt den Röstgrad.

Because German very often combines nouns into a single compound noun.

• Bohne = bean
• Farbe = color

Together, Bohnenfarbe means bean color.

This is completely normal in German. Where English often uses two words, German often prefers one compound word.

In German compound nouns, the last part determines the gender.

Here, the last part is Farbe, and die Farbe is feminine. So the whole compound is also feminine:

• die Farbe
• die Bohnenfarbe

That is why the sentence starts with Die Bohnenfarbe.

This is a very common feature of German compounds. The first noun often appears in a modified form, sometimes using a plural-like ending or a linking form.

Here:

• Bohne = bean
• Bohnen- = bean / beans as the first part of a compound

So Bohnenfarbe is the natural form, not Bohnefarbe.

You do not always need to think of it as a true plural in meaning; it is just the standard compound form here.

Because Röstgrad is the direct object of the verb zeigt.

The verb zeigen usually takes:

• a subject in the nominative
• a direct object in the accusative

In this sentence:

• Die Bohnenfarbe = subject, nominative
• den Röstgrad = direct object, accusative

Since Röstgrad is masculine, its article changes like this:

• nominative: der Röstgrad
• accusative: den Röstgrad

It is in the nominative case because it is the subject of the sentence — the thing doing the action.

The structure is:

• Die Bohnenfarbe = the bean color
• zeigt = shows
• den Röstgrad = the roast level

So the bean color is what shows something.

Zeigt is the 3rd person singular form of the verb zeigen, which means to show.

The infinitive is:

• zeigen = to show

Because the subject is singular (die Bohnenfarbe), the verb becomes:

• die Bohnenfarbe zeigt = the bean color shows

This is the normal present-tense form for he/she/it and singular nouns.

It is another compound noun:

• Röst- comes from rösten = to roast
• Grad = degree / level

So Röstgrad literally means roast degree or roast level.

In coffee contexts, this refers to how lightly or darkly the beans have been roasted.

Because German main clauses normally follow the verb-second rule.

That means the finite verb usually comes in the second position:

• Die Bohnenfarbe | zeigt | den Röstgrad

This is standard German word order for a simple statement: subject + verb + object

Yes, that is also possible.

• Die Bohnenfarbe = the bean color
• Die Farbe der Bohnen = the color of the beans

Both are grammatical. The compound Bohnenfarbe is more compact and very natural in German. German often prefers compounds where English might prefer an of phrase.

Because all nouns are capitalized in German.

So in this sentence:

• Bohnenfarbe is a noun
• Röstgrad is a noun

That is why they begin with capital letters, even in the middle of the sentence.

A rough pronunciation guide is:

• Bohnenfarbe ≈ BOH-nen-far-buh
• Röstgrad ≈ RURST-graht or RERST-graht depending on your accent guide

A few helpful notes:

• ö does not exist in standard English; it is somewhat like the vowel in British bird, but with rounded lips.
• rösten / Röst- has that same ö sound.
• grad ends with a t sound in standard pronunciation, even though it is spelled with d. This happens because final d is devoiced in German.

Most likely, yes. The word Röstgrad is especially common when talking about things that are roasted, and Bohnenfarbe strongly suggests coffee beans in many contexts.

So while the sentence is grammatically general, in real life it would very often be understood in a coffee context.