What causes cloudy beer?

What causes cloudy beer?

There are numerous causes, from particles in suspension (like yeast), to uncoagulated proteins (chill haze).

How do you prevent it?

A couple of things help. One is time- in general, the longer the beer sits, the clearer it is. So, patience often helps. Another thing that helps is careful racking- leaving all the trub behind when racking to the bottling bucket. One common cause of cloudy beer is chill haze- that's when protein particles are obvious when the beer is cold. This can be prevented by getting a good "cold break" when chilling the wort, as well as using kettle finings like whirlfloc in the boil. The key to a good cold break is getting the wort from boiling to under 70 degrees in under 20 minutes or so. Then, great big globs of coagulated protein fall out of the beer. I'll see if I can find a picture- it's good for the beer, but looks really gross! Also, a good strong boil and a good "hot break" hellp.

Well, I am not an expert, but I know of a few things you can do to make your beer clearer.

1. Use a wort chiller to get a good cold break. This will coagulate proteins and cause them to sink to the bottom and out of solution.
2. Aging your beer for the appropriate length - allows more particles to settle out of solution (among many other advantages).
3. Using a secondary, in theory, helps make clearer beer (this is debatable).
4. Lagering your secondary or cold conditioning your bottles - this will help the yeast flocculate to the bottom and clear up the beer.

I am sure some of the experts can give you more ideas.

EDIT:
Yooper beat me to the punch.

This is what I've done the past couple of batches and have had very clear beer. I give my beers and extra week in primary after fermentation is done. Then I add gelatin, based on a thread posted here, I put the whole carboy in the fridge for a few days and let it cold crash. When I keg at this point. I'm leaving as much of the sediment behind as possible. After about a week for carbonation, my beer is crystal clear.

The best ways I know to produce clear beer are:
1. Use a highly flocculant yeast like WLP002
2. Brew English beers (see 1 above) which should be drunk at temperatures in the upper 50's. This is not cold enough to produce chill haze.

-a.

Besides what's listed above, refrigerating your bottles for a week or more before opening helps a lot, even chill haze is noticeable reduced or mostly eliminated by this.