Мякиш плотный, оттого что при автолизе клейковина осталась слабой.

In Russian, the verb to be is usually omitted in the present tense.

So:

• Мякиш плотный = The crumb is dense
• literally: Crumb dense

This is completely normal in Russian.
If you wanted past or future, then a form of быть would appear:

• Мякиш был плотным = The crumb was dense
• Мякиш будет плотным = The crumb will be dense

Мякиш means the soft inside part of bread, usually called the crumb in baking English.

That is different from:

• корка = crust
• хлеб = bread in general

So in a baking context, мякиш плотный means the bread’s interior has a dense texture.

Because it agrees with мякиш, which is a masculine singular noun.

• мякиш = masculine singular
• therefore плотный = masculine singular adjective

Russian adjectives must agree with the noun in:

• gender
• number
• case

Here мякиш is the subject, so the adjective is in the matching form:

• masculine singular nominative: плотный

Оттого что means because, from the fact that, or due to the fact that.

In this sentence, it introduces the reason:

• Мякиш плотный, оттого что...
  = The crumb is dense because...

It is very close in meaning to потому что. In many cases they are interchangeable.

A rough nuance:

• потому что = the most common neutral because
• оттого что = a bit more literary or explanatory, sometimes with the feel of that’s because...

So this sentence could also be written with потому что without much change in meaning.

Because при requires the prepositional case, and автолиз changes to автолизе in that case.

• dictionary form: автолиз
• after при: при автолизе

Here при means something like:

• during
• in the course of
• under conditions of

So при автолизе means during autolyse or in the autolyse stage/process.

Клейковина means gluten.

It is a feminine noun, which matters for verb agreement later in the sentence:

• клейковина = feminine singular
• so the past-tense verb is осталась (feminine singular)

In baking Russian, клейковина is the normal technical word for gluten.

Because the subject is клейковина, and Russian past-tense verbs agree with the subject in gender and number.

• клейковина = feminine singular
• so: осталась

Compare:

• клейковина осталась = the gluten remained
• мякиш остался = the crumb remained
• ингредиенты остались = the ingredients remained

So the feminine ending -ась / -а here comes from the feminine subject.

This is a very common learner question.

After verbs like быть, стать, оказаться, остаться, Russian often uses the instrumental case for the noun or adjective that describes the resulting or continuing state.

So:

• слабой = instrumental feminine singular
• it agrees with клейковина

That is why you get:

• клейковина осталась слабой = the gluten remained weak

This instrumental after остаться is very natural.

You may sometimes encounter nominative in similar structures in Russian, but with остаться the instrumental is especially common and standard.

Form breakdown:

• dictionary form: слабая
• instrumental feminine singular: слабой

The verb остаться is perfective, while оставаться is its imperfective partner.

Here:

• осталась suggests a completed result: the gluten ended up remaining weak / turned out to have remained weak
• it fits well with a finished baking process being described

Compare:

• клейковина оставалась слабой = the gluten was remaining weak / stayed weak over a period of time
• клейковина осталась слабой = the gluten remained weak as the final result

In practical translation, English may still just use remained, but the Russian aspect helps show whether the speaker is describing a process or a result.

A useful breakdown is:

• Мякиш плотный = The crumb is dense
• оттого что = because
• при автолизе = during autolyse
• клейковина осталась слабой = the gluten remained weak

So the structure is:

• main statement
  • reason clause

More literally:

• The crumb is dense because during autolyse the gluten remained weak.

This is a very normal Russian pattern: statement first, reason after it.

Because оттого что introduces a subordinate clause of reason.

Russian uses a comma before subordinate clauses much more consistently than English does.

So:

• Мякиш плотный, оттого что при автолизе клейковина осталась слабой.

The comma marks the boundary between:

• the main clause: Мякиш плотный
• the subordinate clause: оттого что при автолизе клейковина осталась слабой

Yes. Russian word order is flexible, though different orders can change emphasis.

The original sentence is natural and straightforward:

• Мякиш плотный, оттого что при автолизе клейковина осталась слабой.

Possible variations:

• Мякиш плотный, потому что при автолизе клейковина осталась слабой.
• При автолизе клейковина осталась слабой, поэтому мякиш плотный.

These all express nearly the same basic idea, but the emphasis shifts:

• original = starts with the result
• reordered version = starts with the cause

So yes, the order can change, but the original is perfectly normal.