A few months ago I stumbled across a case full of bottles in my attic. I brought them down to the basement to clean them out and found about eight of them that still were full. I'm assuming they were the remnants of some homebrew my father brewed 20+ years ago. The attic is unheated and only has a couple of exhaust fans to let out hot air in summer, so the temperature probably fluctuates between 40 and 110 degrees Fahrenheit over the course of a year. These aren't ideal conditions for beer storage or yeast health. And I shuddered to think of what 20-25 years of those fluctuations did to that beer.
But of course I had to taste it. So, I put a bottle in the fridge for a few days and popped it open. The result: interesting. There was plenty of carbonation but no head to speak of. The beer was very clear, dark, tasted like perhaps it was originally an Irish red. Of course most of the yeast had fallen out of suspension, but they had obviously done a thorough job of digesting sugars, so the beer was very dry, not much flavor to it. Surprisingly, there were no off flavors like you would expect from dead yeast, improper storage, or all-around skunkiness. And while I wouldn't want to drink this on a regular basis, it's good to know that you can still drink old beer and not have to worry about getting sick. So now you know.