Usually when wine tastes of vinegar it has been exposed to air for too long and has been attacked by a bacteria called Acetobacter.
Acetobacter reacts with oxygen and this reaction changes the taste of a wine to a vinegary flavour. In fact, this is how vinegar is made.
- Air could have got in during the brewing stage if there isn't a fully airtight seal.
- Also it is carried by fruit flies. These are tiny little flies that are present in most homes where there is fruit and vegetables and they carry acetobacter in their intestines and if they get into the wine and die and subsequently break down, this will cause the wine to taste of vinegar. 1-2 flies is all it would take to cause this reaction.
Be extra vigilant when removing the lid of your brewing vessel and try and keep covered with a clean cloth during any process to prevent anything getting in.
We would suggest you sterilise all your equipment thoroughly before using again to ensure the infection is not carried over to a new brew.