Turbidity is haziness or cloudiness in beer or wort. It is caused by the suspension of particulate matter in the fluid. In order to remove the turbidity of wort in the mash or lauter tun, it is recommended that you recirculate the wort over the grain bed, which will act as a particle filter. Recirculation is a great method of clearing the wort prior to sending it to the boil kettle.
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.
Diacetyl is a naturally occurring compound formed during fermentation and has a perceived butter or butterscotch like flavor that is undesirable in most beers. It is important to note that other ingredients used in beer production, such as caramelized grains, may impart a somewhat similar flavor, and the two should not be confused.
Although Diacetyl is tolerated or even expected in some beer styles, recent research has shown that at very high levels and under the right conditions, it can be toxic. The good news is that diacetyl is typically only present at very low levels in beer and can be greatly minimized if certain protocols are followed.
One way to help reduce diacetyl in your beer is to clean and sanitize equipment properly because certain undesirable bacterias produce diacetyl. Another way to reduce the diacetyl in your beer is to pitch a sufficient quantity of healthy yeast and conduct a full fermentation and conditioning cycle prior to cold crashing or kegging your beer.
Yeast is responsible for creating and removing diacetyl at different stages of the fermentation process. Yeast creates diacetyl early in the fermentation process and breaks it down towards the end. If you did not pitch enough healthy yeast to complete the fermentation, placed your yeast in stasis, or destroyed your yeast before the end of fermentation, then you may end up with higher then desired levels of diacetyl.
If you happen to be fermenting a lager, a process known as a diacetyl rest (which requires a fermentation temperature increase) may also be helpful in reducing diacetyl in your beer.