yasui guzai ga warui to ha kagiranai.

とは限らない is a very common grammar pattern meaning it is not necessarily the case that... or ...is not always true.

So here:

安い具材が悪いとは限らない。

means:

It is not necessarily true that cheap ingredients are bad.

A key nuance:

• It does not mean cheap ingredients are definitely good.
• It means you should not assume they are bad just because they are cheap.

In this pattern, と and は work together as part of a set expression.

• と marks the statement before it, almost like quoting an idea:
  • 安い具材が悪い = cheap ingredients are bad
• は highlights that whole statement as the thing being discussed
• 限らない literally comes from 限る, but in this pattern the whole phrase is idiomatic

So it is best to learn X とは限らない as one chunk:

• Xとは限らない = X is not necessarily true

You can understand the pieces, but if you translate them too literally, it becomes confusing. As a learner, it is usually more helpful to memorize the whole pattern.

Because inside the quoted statement 安い具材が悪い, 具材 is the grammatical subject of 悪い.

The sentence is built like this:

• 安い具材が悪い = cheap ingredients are bad
• 安い具材が悪いとは限らない = it is not necessarily true that cheap ingredients are bad

Using が here makes the inner statement sound like a straightforward claim.

If you used は instead:

安い具材は悪いとは限らない

that is also possible, but the nuance shifts a little. It sounds more like:

• As for cheap ingredients, they are not necessarily bad

The original with が sounds a bit more like rejecting the proposition cheap ingredients are bad.

Yes.

In Japanese, an い-adjective can directly modify a noun:

• 安い = cheap
• 具材 = ingredients / fillings
• 安い具材 = cheap ingredients

This works the same way as:

• 高い店 = expensive shop
• おいしい料理 = delicious food
• 新しい本 = new book

So 安い directly describes 具材.

Because the clause before と is in plain form.

In Japanese, when a statement is followed by と in patterns like this, the part before と is usually plain:

• 安い具材が悪い
• 安い具材が悪いとは限らない

Here 悪い is the plain non-past form of the adjective.

This does not mean the sentence is specifically about the present moment. In Japanese, the plain non-past form is often used for general statements, habitual facts, or broad judgments. So here it means something like:

• cheap ingredients are bad as a general claim

Then the speaker says that claim is not necessarily true.

They are similar, but not identical.

• 具材: ingredients or fillings that go into a dish, often the visible components of the finished food
• 材料: materials / ingredients in a very general sense
• 食材: food ingredients; often broader and a bit more formal

Examples:

• In soup, curry, or a rice ball, the chunks or fillings can be called 具材
• For cooking ingredients in general, 材料 is very common
• 食材 is often used in contexts like cooking, restaurants, or food sourcing

So 具材 gives a slightly more concrete feeling, like the ingredients used in the dish itself.

No.

This is a very important nuance.

安い具材が悪いとは限らない means:

• cheap ingredients are not necessarily bad

It does not mean:

• cheap ingredients are good
• cheap ingredients are always fine
• cheap ingredients are better

It only rejects a strong assumption.

English parallels:

• Not necessarily bad
• Not always bad
• You can't conclude they're bad just because they're cheap

So the speaker is being cautious and non-absolute.

Yes, that version is possible too.

The difference is mainly one of nuance:

• 安い具材が悪いとは限らない

  • focuses on the proposition cheap ingredients are bad
  • sounds like denying that specific claim

• 安い具材は悪いとは限らない

  • makes cheap ingredients the topic
  • sounds more like as for cheap ingredients, they are not necessarily bad

Both are natural, but the original with が fits especially well when the speaker is responding to a belief or stereotype.

Because the sentence is not simply saying cheap ingredients are not bad.

Compare:

• 安い具材は悪くない

  • cheap ingredients are not bad

• 安い具材が悪いとは限らない

  • it is not necessarily true that cheap ingredients are bad

The second one is softer and more careful. It leaves room for different cases:

• some cheap ingredients may be bad
• some may be fine
• you cannot make a blanket statement

So とは限らない is used when the speaker wants to avoid an absolute conclusion.

The spaces are only there to help learners read the sentence.

Normally, standard Japanese would be written without spaces:

安い具材が悪いとは限らない。

Textbooks, flashcards, and learning materials sometimes add spaces to make the structure easier to see, especially for beginners. But in real Japanese writing, you usually will not see those spaces.