Answer
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
When wine turns to vinegar by itself, without any deliberate treatment needed for it to be changed, it is permissible to eat, drink and handle it.
Answering your question, the Fatwa Center at Islam Q and A, states:
Is consuming vinegar halal?
Vinegar is a well-known basic foodstuff, made from wine of which the composition has changed so that it is no longer sweet but is acidic or sour.
Jabir (may Allah be pleased with him) reported that the Prophet (peace be upon him) said: “What a good food is vinegar.” (Muslim)
When wine turns to vinegar by itself, without any deliberate treatment needed for it to be changed, it is permissible to eat, drink and handle it, according to the consensus of the scholars, because of the hadeeth quoted above.
But if the wine has become vinegar because of deliberate treatment, by adding vinegar, onions, salt etc., or by any other process, in this case the scholars differ as to whether it is permissible.
The Shafi’i, Hanbali and some of the Maliki scholars say that it is not permissible to deliberately change wine to vinegar because then it is not pure. The evidence for this is the hadith of Anas ibn Malik (may Allah be pleased with him) who said: “The Messenger of Allah was asked whether wine could be changed to be used as vinegar. He said, ‘No.’” (Muslim)
Abu Talhah (may Allah be pleased with him) reported that the Prophet (PBUH) was asked about some orphans who had inherited some wine. He said, “Pour it away.” He was asked, “Could they not make it into vinegar?” He said, “No.” (Muslim)
Can we change wine to vinegar?
Why is it not permissible to change wine to vinegar? The reason for this is:
Allah has commanded us to avoid wine. Keeping it and treating it until it turns into vinegar means handling it and being involved with it by storing it and benefitting from it, and this is not permitted.
It is permitted for a Muslim to buy vinegar from someone who is selling it, unless he realizes or comes to know that it was produced by means of a deliberate process. ‘Umar (may Allah be pleased with him) said: “… There is nothing wrong with a man buying vinegar from the people of the Book, if they sell it, so long as he knows that they did not deliberately process it from wine.” (Al-Mughni, 8/330)
Almighty Allah knows best.
Source: Islam Q&A