Tannins are organic compounds found in the husks’ grains. Excessive tannins are almost always considered to be a flaw in beers and are interpreted as a harsh astringent bitterness or a mouth drying sensation. Excessive tannins are typically caused by too high of a mash pH or excessive temperatures during mash out or sparging. Tannin extraction is dramatically increased when mashing or sparge water temperatures exceed 170° F. Please also note that as the lautering and sparge process comes to a finish, the pH of a mash is increasing, which compounds the potential for tannin extraction. In addition to the off flavors created by tannins, they can also be significant contributors to chill haze in a beer. Hops release tannins into beer, but the hop tannins are not considered to be significant contributors off flavors or chill haze.
Ways of removing excess tannins from beer including cold crashing, or cold conditioning the beer at approximately 34° F for two or more weeks. That should cause some of the excess tannins and proteins to precipitate out of the beer onto the bottom of the fermenter or conditioning vessel. You may also use a beer a beer fining agent such as gelatin or isinglass to help clear the tannins.
Chill haze is the cloudy or hazy appearance that a chilled beer gets when it is too high in residual proteins or tannins. For the most part, haze and turbidity are highly undesirable unless you are brewing a beer such as an American wheat, hefeweizen, or Belgian wit, where the style calls for a certain amount of haze. It is easier to try and avoid chill haze as opposed to trying to remove it from a beer.
Best practices for avoiding chill haze include properly controlling your mash out, sparging, lautering, and recirculation temperatures. Tannin extraction becomes a real issue when you exceed a temperature of 170° F in your mash tun, so always do your best to keep your sparge temp near 168° F for proper sugar extraction, but do not exceed it or else you will risk stripping too much tannin from the grain.
A consistent rolling boil and hot break are also important when it comes to reducing excess proteins. During the boil and hot break, proteins will merge together, becoming very dense and dropping out to the bottom of the kettle where they can be separated and not transferred to the fermenter. Perhaps one of the best and easiest ways to help avoid chill haze is to use an inexpensive fining such as whirlfloc. Whirlfloc is my personal favorite haze clearing fining; it is a blend of Irish moss and purified carrageenan. The Irish moss and carrageenan bind with the proteins and aid in precipitation. I will typically use one tablet per 5 to 15 gallons and add it at the last 15 minutes of the boil.
If you find yourself in the situation where when chilled your beer has haze and you have not yet bottled it, you can try one of the following methods to help clear chill haze. Extend your conditioning time and cold crash your beer to 34° F for a couple of weeks. This will aid in precipitation and help move suspended yeast and protein to the bottom of the vessel so that you can rack or transfer the clarified beer off the top of it. As a last ditch effort, you can use a beer clarifier such as gelatin. The gelatin should bind to the excess proteins, and drop some of the haze out of your beer.