Is it permissible to eat vinegar?

Firstly:

The basic principle concerning foods is that they are halal, except that which the evidence indicates is haram. Allah, may He be exalted, says (interpretation of the meaning):

{There is not upon those who believe and do righteousness [any] blame concerning what they have eaten [in the past] if they [now] fear Allah and believe and do righteous deeds} [al-Ma’idah 5:93]

{It is He who created for you all of that which is on the earth} [al-Baqarah 2:29]

{Say, “I do not find within that which was revealed to me [anything] forbidden to one who would eat it unless it be a dead animal or blood spilled out or the flesh of swine – for indeed, it is impure – or it be [that slaughtered in] disobedience, dedicated to other than Allah”} [al-An‘am 6:145].

Secondly:

It is proven that the Prophet (blessings and peace of Allah be upon him) ate vinegar, and even praised and commended it. Muslim (2052) narrated from Jabir ibn ‘Abdillah (may Allah be pleased with him) that the Prophet (blessings and peace of Allah be upon him) asked his family for condiments and they said: We do not have anything but vinegar. He called for it and he started eating it, saying: “What a good condiment vinegar is, what a good condiment vinegar is.”

The word translated here as condiment refers to that which is eaten with bread.

An-Nawawi (may Allah have mercy on him) said in Sharh Hadith Muslim:

This hadith points to the virtue of vinegar, that it may be called a condiment and that it is very good. End quote.

It says in al-Mawsu‘ah al-Fiqhiyyah (19/262): There is no difference of opinion among the fuqaha’ regarding the fact that it is permissible to eat and drink vinegar, whether it is made from grapes or anything else. There is also no difference of opinion regarding the fact that it is permissible to eat vinegar made from wine that has turned into vinegar by itself, without being treated in any way, because the Prophet (blessings and peace of Allah be upon him) said, “What a good condiment vinegar is.” End quote.

And Allah knows best.