Avia dicit ex una vite multos racemos colligi posse.

The sentence has:

• a main clause: Avia dicit = Grandmother says
• an indirect statement after dicit: ex una vite multos racemos colligi posse

A very literal breakdown is:

• Avia = grandmother
• dicit = says
• ex una vite = from one vine
• multos racemos = many clusters / bunches
• colligi = to be gathered
• posse = to be able

So Latin is literally saying something like:

Grandmother says many bunches to be able to be gathered from one vine.

That sounds awkward in English, but it is normal Latin indirect statement structure.

Because Latin commonly uses the accusative-and-infinitive construction for indirect statement.

In English, we say:

• She says that many bunches can be gathered.

In Latin, after a verb of saying, thinking, knowing, hearing, and so on, Latin often says:

• She says many bunches to be able to be gathered.

That is exactly what is happening here:

• dicit = she says
• multos racemos colligi posse = that many bunches can be gathered

So instead of a separate that-clause, Latin uses an infinitive construction.

This is one of the most important things to notice.

In the indirect statement after dicit, the subject of the infinitive is put in the accusative.

Here, multos racemos is the logical subject of colligi posse:

• many bunches can be gathered

Even though many bunches would be the subject in English, in Latin indirect statement it appears in the accusative:

• multos racemos

So this is not the direct object of dicit. It is the accusative subject of the infinitive phrase.

Because colligi is the present passive infinitive of colligere.

• colligere = to gather / to collect (active)
• colligi = to be gathered / to be collected (passive)

The meaning of the sentence requires the passive idea:

• many bunches can be gathered not
• many bunches can gather

So Latin uses colligi.

Posse means to be able or can.

It combines with another infinitive:

• colligi posse = to be able to be gathered
• more natural English: can be gathered

So:

• multos racemos colligi posse = that many bunches can be gathered

This is a very common Latin pattern:

• infinitive + posse = can + verb

For example:

• venire posse = to be able to come = can come
• videri posse = to be able to be seen = can be seen

Because ex takes the ablative case.

• ex = out of, from
• therefore the noun after it must be ablative

Here:

• vitis = vine
• ablative singular = vite

And una agrees with vite, so it is also ablative singular:

• ex una vite = from one vine

Vite is the ablative singular of vitis, vitis (feminine), meaning vine or grapevine.

This noun belongs to the third declension.

A learner might expect something like a first-declension ending because the English word vine feels similar to many Latin first-declension words, but vitis is actually third declension.

So:

• nominative singular: vitis
• ablative singular: vite

That is why the sentence has ex una vite.

Because adjectives must agree with the nouns they describe in gender, number, and case.

Here una describes vite:

• vite is feminine
• vite is singular
• vite is ablative

So the adjective must also be feminine singular ablative:

• una

Thus:

• ex una vite = from one vine

Racemos is the accusative plural of racemus.

It means clusters, bunches, especially of grapes.

Since the sentence also mentions a vine, the natural sense is:

• many bunches of grapes

Depending on context, English might translate racemos as:

• bunches
• clusters
• grape clusters
• bunches of grapes

Because it agrees with racemos.

• racemos is masculine accusative plural
• therefore multos must also be masculine accusative plural

So:

• multos racemos = many bunches

This agreement is separate from the reason the phrase is accusative.
The whole phrase is accusative because it is the subject of the infinitive in indirect statement; within that phrase, the adjective agrees with the noun.

Not exactly. This is where Latin and English grammar can feel tricky.

Because colligi is passive, multos racemos is the thing being gathered. In an ordinary finite passive sentence, it would be the grammatical subject:

• Multi racemi colligi possunt = Many bunches can be gathered

But in an indirect statement, the subject of the infinitive is put into the accusative:

• multos racemos colligi posse

So it is best understood as:

• the subject of the passive infinitive
• but in the accusative because of indirect statement

Not after dicit, if the writer wants standard indirect statement.

If you changed the sentence into a direct statement, you could say:

• Ex una vite multi racemi colligi possunt.
• Many bunches can be gathered from one vine.

There multi racemi is nominative because it is the subject of a normal finite verb.

But after dicit, Latin typically shifts to indirect statement:

• Avia dicit ex una vite multos racemos colligi posse.

So multi racemi becomes multos racemos.

Latin word order is more flexible because the endings show grammatical function.

English depends heavily on word order:

• Many bunches can be gathered from one vine.

Latin can move things around more freely:

• ex una vite multos racemos colligi posse
• multos racemos ex una vite colligi posse
• avia ex una vite multos racemos colligi posse dicit

These can all express basically the same idea, though the emphasis may shift slightly.

In your sentence, ex una vite comes early, which gives some prominence to the source: from one vine.

Dicit is present tense, third person singular:

• she says
• grandmother says

Because the main verb is present, the indirect statement is presented from that present point of view.

The infinitives themselves do not work exactly like English finite tenses, so it is usually best not to force them into a tense label too early. The important meaning here is simply:

• Grandmother says that many bunches can be gathered from one vine.

Its most common meaning is grandmother, and that is almost certainly the meaning here.

In some contexts avia can also function as an adjective meaning remote or out-of-the-way, but in this sentence it is clearly a noun:

• Avia dicit = Grandmother says

So a learner should read avia here as grandmother.

Here are the likely dictionary forms:

• avia, aviae = grandmother
• dico, dicere, dixi, dictum = say, tell
• ex = out of, from
• unus, una, unum = one
• vitis, vitis = vine
• multus, multa, multum = much, many
• racemus, racemi = bunch, cluster
• colligo, colligere, collegi, collectum = gather, collect
• possum, posse, potui = be able, can

Knowing these forms helps explain why the sentence looks the way it does.

A very literal version would be:

• Grandmother says many bunches from one vine to be able to be gathered.

That is not natural English, but it shows the Latin structure.

A natural English translation is:

• Grandmother says that many bunches can be gathered from one vine.

Or, if the context is clearly grapes:

• Grandmother says that many bunches of grapes can be gathered from one vine.