There are many ways of making vinegar. Two common examples of vinegar are wine vinegar and balsamic vinegar.
Wine vinegar is made from alcoholic wine through a process of removing sulfur dioxide from the wine thus enabling acid bacteria to turn the wine into alcohol after a number of months. Balsamic vinegar is made from boiling down grape juice until two-thirds evaporates and turns into a concentrate and then fermenting the concentrate over a number of years. These two processes introduce potential problems. Is the wine in wine vinegar a problem? Is the boiling of grape juice in balsamic vinegar a problem?
Vinegar made from wine is considered both tahir and halal to drink, as long as it turns into vinegar. The process of wine turning into vinegar is called inqilab (change) in Islamic jurisprudence. Ayatollah Sistani, in A Code of Practice for Muslims in the West, is asked the following question: “There is this vinegar that is made from wine, in the sense that it was wine and then, through a manufacturing process, changed into vinegar. Therefore, the label on the bottle reads: “wine vinegar” as opposed to the vinegar made from barley or other items…[can this vinegar be consumed]?” He answers: If the name “vinegar” can be applied in the view of common people upon that product, as has been assumed in the question, the same rule governing vinegar would apply to it. [That is, it is pure as well as permissible.]” Ayatollah Khamenei, via Imam Khomeini’s Tawdih al-Masa’il states that “alcohol which turns into vinegar by itself or through mixing with another substance, e.g. salt or vinegar, becomes tahir” and permissible to consume.
Boiling grape juice is part of the process of making balsamic vinegar. This is not problematic since two-thirds of the grape juice evaporates and the juice turns into a concentrate. Ayatollah Sistani states in Islamic Laws that if grape juice “ferments by itself, or when heated, it becomes haraam. However, if it boils so much that only 1/3 part of it is left, it becomes halal.” In ruling 204, he does state that if the remainder ferments and is considered grape juice then it would be haraam (per obligatory precaution.) But, when making balsamic vinegar, the remainder is not commonly considered grape juice, rather it becomes a concentrate or syrup. Therefore does not fall under the scope of this precaution. Ayatollah Khamenei, once again via Imam Khomeini’s Tawdih al-Masa’il has a similar ruling. He states: “Grape juice that is boiled is not considered najis, but is prohibited to consume until two-thirds evaporates.” This means that if two-thirds evaporates it is permissible to consume. The verdict continues: “if it is established that it becomes intoxicating than it is prohibited and najis and will only become tahir and halal if it turns into vinegar.” Hence, since two-thirds of the grape juice that boils in the process of making balsamic vinegar evaporates and the remainder is considered a concentrate it is permissible to consume.
Therefore, there is no Islamic problem in consuming either wine vinegar or balsamic vinegar.