Is Balsamic Vinegar Halal?
Question

I live in XXX and I am aware of what happens in ketchup and mayonnaise factories, and how vinegar is made here. You should be aware of reality and not issue fatwas without knowledge. Throughout Europe, they first make wine, then when it has become wine, they treat it and turn it into vinegar. 
For that reason, the food authorities compel them to write the name precisely: Weinessig (wine vinegar) or Brandtweinessig (brandy vinegar) or Weingeistessig (wine spirit vinegar) or Weintraubenessig (grape vinegar) or Apfelweinessig (cider vinegar). 
All of these things are made of wine first, then after that they treat it and turn it into vinegar, so that the taste will be better. Here in our country, they prefer to make it with the best taste. … What they put in ketchup and mayonnaise is called Brandtweinessig (brandy vinegar) in German. 
Moreover, in Italy, balsamic vinegar is as expensive as wine, because they make it from aged wine so that it is aged and expensive, and its taste is good, then after that they turn it into vinegar. That is not right at all. 
In Germany, [Muslim] people have started to eat what is forbidden to eat, and you have no excuse before Allah, after I have explained the matter to you in this message. Ask about what happens in factories and how vinegar is made in Europe, and after that issue fatwas to the people. Is this the religion of Muhammad (blessings and peace of Allah be upon him)? O Allah, I have conveyed the message, so bear witness.
Praise be to Allah.Ruling on wine turned into vinegar 
If wine turns into vinegar by itself, without any treatment, then there is no difference of scholarly opinion concerning the fact that it is permissible to use this vinegar that has developed from wine. The same applies if it is turned into vinegar by moving it from the sun to the shade, or vice versa, according to the majority of jurists.
It is proven that the Prophet (blessings and peace of Allah be upon him) ate vinegar, and he praised it and spoke highly of it, as 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.”
With regard to treating wine so that it becomes vinegar , by adding vinegar, onions or salt into it, or putting it on the fire for the purpose of turning it into vinegar, such treatments are haram according to the more correct scholarly view. This is the view of the Shafi'is and Hanbalis, and is mentioned in one report from Malik.
“The Hanafis say – and this is the more correct view according to the Malikis – that it is permissible to turn wine into vinegar, and it is permissible to eat and drink that vinegar, because the Prophet (blessings and peace of Allah be upon him) said: “What a good condiment vinegar is” in general terms, without differentiating between vinegar that is produced by subjecting it to a deliberate process and vinegar that results from a natural process.
That is also because subjecting wine to a deliberate process to turn it into vinegar removes the evil characteristics [of wine] whilst leaving the good characteristics, because it contains some characteristics that are beneficial for medicinal and nutritional purposes, and other purposes. If the corrupt element which dictates the prohibition of wine is removed, it becomes halal, just as in the case when it turns into vinegar by itself.
That is because subjecting wine to a deliberate process to turn it into vinegar is rectifying its character, therefore it becomes permissible, by analogy with the permissibility of tanning animal hides.” (Al-Mawsu‘ah al-Fiqhiyyah, 19/260, see also: al-Fiqh al-Islami wa Adillatuhu, 4/2629)
The evidence for the prohibition on subjecting wine to a deliberate process to turn it into vinegar is the report narrated by Ahmad (12189) and Abu Dawud (3675) from Anas ibn Malik, according to which Abu Talhah asked the Prophet (blessings and peace of Allah be upon him) about some orphans who had inherited some wine, and he said, “Pour it away.” Abu Talhah said: Can we not turn it into vinegar? He said: “No.”
The hadith was classed as sahih by al-Albani in Sahih Abi Dawud.
An-Nawawi (may Allah have mercy on him) said: 
“… According to the scholarly views concerning wine that turns into vinegar by itself and subjecting wine to a deliberate process to turn it into vinegar, if it turns into vinegar by itself, then it becomes pure (tahir), according to the majority of scholars. al-Qadi ‘Abd al-Wahhab al-Maliki narrated that there was consensus on that; others narrated from Sahnun al-Maliki that it does not become pure.
But if it turns into vinegar as the result of adding something to it, then our view is that it does not become pure. This was the view of Ahmad and the majority.
Abu Hanifah, al-Awza'i and al-Layth said: It does become pure.
Three reports were narrated from Malik. That which is most soundly narrated from him says that subjecting wine to a deliberate process to turn it into vinegar is haram, but if it turns into vinegar by itself, it becomes pure. The second view is that it is haram and does not become pure. The third view is that it is halal and does become pure.” (al-Majmu‘, 2/596)
Shaykh Muhammad al-Mukhtar ash-Shinqiti said in Sharh Zad al-Mustaqni‘: 
“The majority of scholars are of the view that if wine turns into vinegar by itself, it becomes halal and pure, because the Prophet (blessings and peace of Allah be upon him) said, as is narrated in the sahih hadith: “What a good condiment vinegar is.” And vinegar cannot become vinegar until after it has been wine. This is what is meant, if it turns into vinegar by itself. The evidence that it is halal if it turns into vinegar by itself is the hadith of Abu Talhah (may Allah be pleased with him), when he asked the Prophet (blessings and peace of Allah be upon him) about wine that belonged to some orphans, and the Prophet (blessings and peace of Allah be upon him) instructed him to pour the wine away. If it had been permissible to turn the wine into vinegar [through a deliberate process], the Prophet (blessings and peace of Allah be upon him) would not have instructed him to pour it away. This indicates that it is not permissible for the owner of the wine to deliberately turn it into vinegar himself, but if it turns into vinegar by itself, then it is permissible and it is pure in that case.” 
Ruling on wine turned into vinegar by means of some deliberate process
If the wine turns into vinegar by means of some deliberate process, does the wine become pure and is it permissible to use the vinegar that has been produced by means of that haram process?
There is a difference of scholarly opinion concerning that; the soundest of the views are two views:

That it becomes pure, and the vinegar becomes permissible thereby, if a large amount of it does not cause intoxication.
That it becomes pure and the vinegar is halal, if it was turned into vinegar by someone who believes that wine is permissible. So vinegar that is produced by the People of the Book is permissible.

Shaykh Ibn ‘Uthamin (may Allah have mercy on him) said: 
“In the phrase “if it turns into vinegar [as the result of a deliberate process],” the pronoun refers to the wine, and what is meant is that something is deliberately added to it that will remove its intoxicating effects, such as nabidh and so on, or it is subjected to a process that takes away its intoxicating effect.
The well-known view in our madhhab is that if it is subjected to a deliberate process to turn it into vinegar, it does not become pure, even if its intoxicating effect is removed.
They quoted as evidence the fact that the removal of the intoxicating effect is achieved by doing something haram, so that does not change the ruling, because that process is not permissible, based on the report narrated by Anas according to which the Prophet (blessings and peace of Allah be upon him) was asked about turning wine into vinegar, and he said no to that. Moreover, this is a process that is not enjoined by Allah and His Messenger, so it is wrong and is to be rejected, and it changes nothing. The Prophet (blessings and peace of Allah be upon him) said: “Whoever does something that is not part of this matter of ours, it will be rejected.”
Some of the scholars said that it does become pure and permissible thereby, even though the action is haram.
They explained that by saying that the reason why it is impure is that it causes intoxication, but the intoxicating effect has been removed, so it becomes halal.
Others said that if it was turned into vinegar by one who believes that wine is permissible, such as the People of the Book, the Jews and Christians, it is permissible and has become pure. But if it is turned into vinegar by someone for whom it is not permissible, then it is haram and impure. This is the view that is most likely to be correct.
Based on that, the vinegar that comes from the Jews and Christians is halal and pure, because they did that on the basis of their belief that it is permissible, hence they are not to be prevented from drinking wine.” (Ash-Sharh al-Mumti‘, 1/432)
Based on that, the vinegar that is produced by the Christians in Europe and elsewhere by treating wine is permissible to consume.
Religion is about giving sincere advice
The one who wants to offer advice should be gentle and pay attention to the situation of those whom he is addressing, for there is no kindness in a matter but it beautifies it, and it is not absent from a matter but it makes it ugly.
Knowledge is broad in scope; perhaps a person may know one thing but be unaware of others.
The issue of making vinegar from wine is an old and well-known issue concerning which most of the fuqaha have given rulings. There is nothing new about that!
The scholars have differed concerning it, as noted above. You may find someone who issues fatwas stating that vinegar is permissible in all cases, and someone else who issues fatwas stating that it is haram in all cases, and another who differentiates and says that vinegar made by a kitabi [a Jew or Christian] is permissible whereas that produced by a Muslim is not.
And Allah knows best.