nagaku yake ba, yakikagen ga yoku naru to ha kagiranai.

長い is an i-adjective meaning long. When an i-adjective modifies a verb, it changes to its -く form.

• 長い = long
• 長く焼く = to cook/grill for a long time

So 長く is acting like for a long time / longer here, modifying 焼けば.

焼けば is the ば conditional form of 焼く.

• dictionary form: 焼く = to grill, bake, roast, cook
• conditional: 焼けば = if you grill/cook it, if it is cooked/grilled

So:

• 長く焼けば = if you cook it longer / if you grill it for a longer time

The subject is not stated explicitly, which is very normal in Japanese.

For a godan verb like 焼く, the ば form is made by changing the final u-sound to the corresponding e-sound and adding ば.

• 焼く
• 焼け
• 焼けば

This pattern is very common:

• 書く → 書けば
• 読む → 読めば
• 待つ → 待てば

The ば conditional often sounds a little more general, logical, or rule-like than some other conditionals.

Here, 長く焼けば、焼き加減が良くなるとは限らない has the feeling of:

• If you cook it longer, that does not automatically mean the result will be better
• Cooking it longer does not necessarily improve the doneness

It sounds like a general statement or caution, not just a one-time situation.

All three can relate to conditions, but the nuance changes.

• 長く焼けば
  more general/logical: if you cook it longer
• 長く焼いたら
  more situational: if/when you cook it longer
• 長く焼いても
  means even if you cook it longer

In English, this sentence is often translated a bit like even if you cook it longer, it won’t necessarily..., so learners may expect ても. But Japanese often uses ば for this kind of general principle. The sentence is saying that a longer cooking time does not automatically guarantee a better result.

焼き加減 means the degree of cooking, how done something is, or the state of the cooking/grilling.

It is made from:

• 焼き = cooking/grilling/roasting
• 加減 = degree, condition, adjustment

So 焼き加減 is something like:

• doneness
• how well it’s cooked
• the cooking result

For example, with meat, this could be like rare, medium, well-done, etc.

In 焼き加減が良くなる, 焼き加減 is the thing that becomes good/better, so it takes が.

• 焼き加減が良くなる
• the doneness becomes better

This is very common with なる:

• 天気が良くなる = the weather gets better
• 成績が良くなる = grades improve
• 焼き加減が良くなる = the doneness improves

Because the sentence is using the verb なる (to become).

The adjective 良い changes to its adverbial form 良く before なる:

• 良い = good
• 良くなる = become good / improve / get better

So:

• 焼き加減が良くなる = the doneness improves

You cannot say 焼き加減が良いなる.

とは限らない means it is not necessarily the case that... or it is not always true that...

It is a very common pattern used to soften or limit a statement.

So:

• 焼き加減が良くなるとは限らない = it does not necessarily mean that the doneness will improve = the doneness will not always get better

This pattern is useful when Japanese wants to avoid making an absolute claim.

Examples:

• 高い物が良いとは限らない。
  Expensive things are not necessarily good.
• 日本人だから敬語が完璧とは限らない。
  Just because someone is Japanese does not necessarily mean their honorific speech is perfect.

The と marks the preceding clause as the content being evaluated.

In other words, the part before とは限らない is the proposition:

• 焼き加減が良くなる
• the doneness gets better

Then とは限らない says:

• it is not necessarily true that [that proposition]

So the structure is:

• [statement] + とは限らない
• it is not necessarily true that [statement]

The は adds contrast/emphasis, giving the nuance of not always / not necessarily.

The sentence is not saying:

• Cooking longer never helps

It is saying:

• Cooking longer does not necessarily improve the result
• A longer cooking time is not a guarantee of better doneness

So the speaker is warning against a simple assumption: longer cooking time = better result
That assumption is what とは限らない is rejecting.

Yes. Japanese often leaves out things that are understood from context.

In 長く焼けば, the thing being cooked is not stated. It could be:

• meat
• fish
• bread
• pizza
• anything that can be 焼く-ed

English often needs an object like it, but Japanese does not.

So the sentence naturally means something like:

• If you cook it longer, the doneness does not necessarily improve.

Literally, 長く means for a long time. But depending on context, English may translate it as longer.

So this sentence could be understood as:

• if you cook it for a long time
• if you cook it longer

The reason longer works well in translation is that the sentence is comparing the idea of more cooking time with better doneness.

It breaks down like this:

• 長く焼けば
  if you cook it longer
• 焼き加減が良くなる
  the doneness gets better
• とは限らない
  is not necessarily true

So the whole sentence is:

• If you cook it longer, it does not necessarily mean the doneness will improve.

Or more naturally:

• Cooking it longer won’t necessarily make it come out better.

Yes. It is natural and grammatically standard.

It sounds like something you might hear in:

• cooking advice
• instructions
• general explanations
• cautionary statements

The pattern Xば、Yとは限らない is especially common when someone wants to say:

• just because X happens, you cannot assume Y

So this sentence has a very natural explanatory tone.