A friend of my family gave us an unopened bottle of Bollinger champagne from 1979. It is a vintage champagne. Is it safe to drink? As far as I understand, the worst that could happen to alcohol is that it turns into vinegar. However, we opened it and it does not take like vinegar. It lost all the fizz, and tastes a bit like cheap wine + sweet (desert) wine. But we are not sure it is safe to drink. Any advice?
Simple answer is yes! The more complex answer is that it might not taste all that great but I've had some aged sparkling wines that were 10+ years old and were quite nice. But having lost it's carbonation does not make it bad, it will taste just like you described, cheap old wine.
Definitely, I wanted to expand on why you should try it. Some quick points:
Vintage champagne, whilst not to everyone’s tastes, is usually only created when harvests are at their best. Furthermore the grapes must be aged in a bottle for longer (a minimum of three times longer if memory serves) before release. This should be at least 18 months so the flavour develops. Finally the taste develops in the bottle, just some reasons but it wasn’t designed to be drank in 1979.
As others have said a lot of people don’t often realise that vintage champagne is flat, the carbonation doesn’t last forever. The taste you are experiencing sounds right though and it is safe as long as it’s been sealed for it’s life etc.
Hope that makes sense, hope it tastes nice!