The prominent Muslim scholar, Sheikh Yusuf Al-Qaradawi, on this issue has said: “Muslim scholars unanimously agree that if wine turns into vinegar by itself, it is lawful. However, if it turns into vinegar with the aid of a chemical substance or by adding something, such as salt, bread or onion, to it, scholars hold different views regarding it. Although some scholars say that it is pure and lawful because it has been changed from its original state, others say that it is still impure and, thus, it is must be avoided.
In his book, Al-Majmu`, Imam An-Nawawi states: ‘If wine changes into vinegar by itself, it becomes pure according to the majority of scholars. However, if the change is a result of putting something in it, I say that it is still impure. Ahmad and most scholars also hold this view. Abu Hanifah, Al-Awza`i and Al-Layth consider it pure.’
Malik has reported three hadiths on this, the most authentic one is that treating wine is prohibited. But once it is carried out, wine becomes pure. In the books of the Maliki jurists, it is stated that it is permissible to treat wine so that it becomes vinegar.
What I see is that if wine changes into vinegar, it becomes pure and lawful as it has changed from its original state and this requires a new ruling as is the case with all other converted impurities regardless of whether this occurs naturally or by human interference. Wine itself is a pure substance as it was made from grapes. After becoming an intoxicant, it becomes prohibited. Once it changes and lacks the intoxicating characteristic, it regains its original ruling.
The view of the Hanafi scholars and those who follow them in this respect seems to be strong. They say that treating wine is similar to its natural change into vinegar as both involve the removal of the reason of prohibition, which is intoxication, as well as the attainment of its benefit of nourishment and medicinal purposes.
In addition, the reason for declaring it impure (i.e., intoxication) no longer stands. It is well known that a ruling is attached to its reason in terms of existence or otherwise.
In his book, Sharh Mushkil Al-Aathar, Imam At-Tahawi states: ‘Since treatment is a process of reformation, it is permitted as is the case for tanning impure leather. It is stated in an authentic hadith: ‘When animal leather is tanned, it becomes pure.’ This applies to the case in hand, i.e., vinegar, and it includes all its types.”
By and large, it’s clear from the above-mentioned statements and quotations that so long as vinegar originates from wine directly, without the aid of any additives, it is lawful according to the unanimous view of scholars. As for the vinegar that originates from wine through human interference, it’s somehow controversial among scholars, as you can see.