I was told/read that as a rough guide a keg will give you about 4-6 months, plastic bottles about a year and glass 2+ years. I donât know how accurate that is but itâs the guidelines I was given. Spoilage is mainly down to oxygen reacting with a product, the longer you can keep oxygen out the longer it will last. Like cheese in your fridge, leave it unwrapped and it goes off quicker than if you wrap it cling film. Plastic does allow oxygen through slowly hence why a plastic bottle will still spoil. A well sealed glass bottle technically should not allow any oxygen so thereâs no reason it shouldnât keep a very long time. Apparently!! That is providing thereâs nothing else wrong with it from when it was bottled. Iâd have to join the majority and say sup it and see.