Reposting a comment I penned on FUSSYlittleBLOG as to why “chunks” appear at the bottom of some beers, and why it’s NOT an indication of the beer going bad.
That crap you see at the bottom of a bottle of beer? That’s yeast and a slurry of proteins that have fallen out of suspension in the beer. Why is this a good thing? It’s preferential, first and foremost, but it’s also supposed to be there in the beers you find it in.
That crud indicates that the beer is unfiltered. No microscreening to make your beer crystal clear. The brewer made a decision to bottle you a beer straight-up the way the recipe was intended. Some brewers, even craft brewers like Dogfish Head, filter their beer, and that’s perfectly fine. But others do not. It could be based on style (wheat beers should have the particulate stirred up and poured over the head of your glass-poured beer – you’re missing out if you ignore this step), based on availability of equipment, or on brewer’s preference.
You also have the amazing bottle-conditioned beers, which are not carbonated prior to bottling. This is how I produce my homebrew, for what it’s worth. Before bottling, a small amount of sugar is added into the beer. The yeast still suspended in the beer “wake up” and go to town eating this sugar in the capped bottle, producing a negligible amount of alcohol but also carbon dioxide. Because the bottle’s sealed, the gas has nowhere to go, so it gets infused in the liquid, thus carbonating the beer. And while the yeast are working, they produce some additional esters that are then introduced into the beer.
Regardless the reason, the sediment is not an indication of anything bad. It’s there because it’s supposed to be. Plus, in that crud you will find a ton of flavor and healthy vitamins and minerals. The yeast is loaded with B vitamins, by the way. If it’s not to your liking, just be careful when pouring and stop once you see a particulate trail as you pour (likely at the last fluid ounce). Otherwise, enjoy!