Originally Posted by Hermit
I was ridiculed for saying this before but it would explain why people 'suddenly' have a favorite batch they have been nursing along suddenly 'go bad' on them. A few bacteria doubling under hostile conditions might take a long time to reach a detectable threshold level but the last doubling could appear to be quite sudden.
OK but let's recognize that there are other things that cause beer stored for a long time to go bad:
1. Oxidation: Some of these reactions are slow. If the wort/beer is not in a reduced state when packaged and if oxygen is not excluded from the package then over time the beer may develop the (alas) familiar cardboard or other tastes.
2. Diacetyl: I keep beer for a long time because I brew large batches (and I do that so I'll have it around for a long time). Diacetyl forms after fermentation and lagering is, therefore, done over yeast so they can reabsorb it. Because I'm keeping the beer for a long time I lager in the package (kegs) and make sure there is plenty of yeast in there. Eventually the yeast die and are no longer able to remove diacetyl. Eventually (a year or more) the diacetyl starts to creep back up (the beers begin to taste caramel like). Don't really know the mechanism - is there still acetolactate in there converting to diacetyl with no viable yeast to pick it up?
3. Whatever happens to Weizen beer: This is probably the most extreme example. Weizen beer just can't be stored for more than a couple of months. I suspect the problem is oxidation by my Weizens are stored no differently that my lagers. I remember trying to explain (in my halting German) to a bunch of good Burghers who wanted to know if we had Weizen in the US. I said no because by the time it got over here it wasn't Weizen any more.
I have had infection in a keg (fortunately only one out of the 4 I typically fill) but it came up right away. The other problems (except 3) take more than a year in my experience.
In case you think that I am advising that boiling isn't necessary let me be clear that it is one of those things you can probably get away with omitting 99 times out of 100 but it isn't worth risking it.