The Transformation of Wine to Vinegar

Assuming you are referring to vinegar that does not carry certification from a recognized scholarly body, please note the following:

While the Shāfiʿī school stipulates strict conditions for the transformation of an intoxicant into vinegar, namely, that no foreign substance may be added during the process, the Ḥanafī school does not impose this restriction and would therefore regard the resulting vinegar as pure.

Furthermore, scholars mention that determining whether this transformation has taken place depends on the liquid’s acidity. Once the acidity becomes predominant, the alcohol content decreases proportionately, and the liquid is then regarded as vinegar.

As a practical guideline, one may check the acidity percentage stated on the bottle. Once it reaches approximately 4%–5% acetic acid, the residual alcohol content is reduced to a level that has no intoxicating capacity, and the liquid is no longer regarded as an alcoholic beverage.

That said, a person is not obliged to investigate or verify all of the above in every instance. If a product is presented to us with no reasonable cause for doubt or suspicion, we may rely on its apparent state and regard it as pure.

The above discussion relates to naturally produced vinegar and not synthetic vinegar. Synthetic vinegar does not undergo a fermentation process and contains no intoxicating substance. It is therefore regarded as pure and permissible without any further consideration.

الله تعالى أعلم

And Allah knows best