Тесто начали складывать каждый час.

Russian often uses a 3rd person plural past verb with no stated subject to mean some unspecified people did it.

So начали here means something like they started, where they is indefinite: the bakers, the workers, people in general, etc.

This is called an indefinite-personal construction. English may translate it as:

• They started folding the dough every hour.
• or, more passively, The dough started being folded every hour.

But in Russian, the verb is still grammatically plural active.

Тесто is the direct object, so it is in the accusative case.

However, for inanimate neuter singular nouns, the accusative form is identical to the nominative. So:

• nominative: тесто
• accusative: тесто

That is why the form does not visibly change.

After phase verbs like начать / начинать (to begin / start), Russian normally uses the imperfective infinitive.

So:

• начали складывать = correct
• начали сложить = not normal Russian

The reason is that начать already expresses the beginning of the action. The infinitive that follows usually names the action as a process, so the imperfective is used.

Also, каждый час suggests repetition, which fits the imperfective very well.

Каждый час is an accusative expression of repeated time, meaning every hour.

Russian often uses the accusative without a preposition for this kind of idea:

• каждый день = every day
• каждую неделю = every week
• каждый час = every hour

Here:

• час is masculine singular
• каждый agrees with it in gender, number, and case

Because час is inanimate, the masculine accusative singular looks like the nominative, so the phrase appears unchanged.

It is grammatically active, not passive.

The hidden subject is an unspecified they:

• [They] started folding the dough every hour.

Even if English might sometimes translate this with a passive-like idea, the Russian structure itself is not passive.

Russian word order is flexible. Putting тесто first makes it the topic — the thing already being talked about.

So the sentence can feel like:

• As for the dough, they started folding it every hour.

Other word orders are also possible:

• Начали складывать тесто каждый час.
• Каждый час начали складывать тесто.

The basic meaning stays the same, but the emphasis changes.

Normally it means once every hour, or at hourly intervals.

So the idea is repeated action:

• they folded it
• then an hour later, folded it again
• and so on

It does not usually mean they were folding it continuously for the entire hour.

No. In English, that would wrongly make the dough the doer of the action.

In the Russian sentence, тесто is the object, not the subject. The implied subject is an unspecified they.

So the structure is really:

• [They] started folding the dough every hour.

Начали is the past tense plural form of начать, which is a perfective verb.

It marks the moment when the action began.

So the pattern is:

• начали = marked beginning, past, perfective
• складывать = the action itself, imperfective process

Together, начали складывать means started folding.