I have a cider (kit) sitting in a pressure barrel. It's been there for 2.5 months now. I've had the odd glass along the way, but I'm trying my hardest to leave it alone. The thing I've noticed is that it's quite sour. This might just be the apples, but I'm concerned it might be infected. Can I open the top to see if there is an infection - i.e. will the CO2 protect it - or will this completely destroy it? Are there any other clear signs of telling if it's infected?