I'll shove a bit about starch haze here, even though it is unlikely to come under the banner of a persistent haze. Starch haze is caused by unconverted starch being carried across from the mash. The major way that this can happen is if a ridiculously short mash time is being employed, or by mashing-in with water so hot that the enzymes get knackered. Alternatively, a recipe employing an excessive amount of cereal adjunct may leave undegraded starch in the wort due to the pale malt possibly having insufficient enzymic activity to convert it all. Cereal adjuncts are also high in protein. I would think that it is impossible to persistently cock up a mash in this way, so this should not be an issue.

Ingredient Quality

The importance of ingredient quality should not be overlooked. A simple recipe employing good quality ingredients should be used for your "best practice" reference brew. Good, named, brewing-grade, low-protein primary malt, something like Maris Otter, will eliminate the possibility of excessive protein being supplied by poor-quality malt. Cereal adjuncts should be avoided or kept to a sensibly low level because cereals are high in protein, and also some starch may remain undegraded by the primary malt enzymes, which will also cause a haze.

Beer pH

If you happened to read the bits about charges and isoelectric points earlier in this section, it will be apparent that flocculation and clarification processes are affected by pH. The pH of the beer falls during fermentation from around pH5 at the end of the boil to pH4 or below at the end of fermentation, perhaps as low as pH3.7. The pH lowers slightly during maturation also. In fact it is unlikely that pH will be a problem and should only be considered as a possibility under panic or last-resort conditions. Assuming that you have the capability to measure beer pH, if it has not dropped to around pH4, then the beer has not passed through the isolelectric points of the various processes. This is most likely to be a water treatment issue, and indicates that some investigation into improving water quality is in order. Dealing with water treatment will simultaneously deal with beer pH issues. Degas the beer before measuring its pH.

Malt Extract and Beer Kits

A worrying myth that is propagated in home brewing is that malt extract and beer kits have been boiled during manufacture and are therefore free from protein-related hazes. Malt extract has not been boiled in the conventional sense. The temperature of the malt extraction process hardly exceeds mash temperature and any, so called, boiling is done at low temperature under vacuum during the evaporation process. It is not a "good rolling boil" and is not hot enough to denature much protein. Consequently, malt extract is full of haze-forming proteins. The same with beer kits. Some of the expensive 3kg beer kits, those that require no added sugar, have (allegedly) been boiled for a period to reduce their haze potential, but the cheaper beer kits, those that require a kilogramme of sugar, have not. Indeed, the cheaper beer kits can use cheaper feed-grade barley that is even richer in protein than brewing-grade barley. It is true that the malt extract used in beer kits would probably be mashed in a temperature-stepped fashion, with a protein rest at around 50°C, which will degrade some of the protein, and perhaps protein-degrading enzymes are added at manufacture too, but the good rolling boil will be missing. Cheap beer kits still have very high haze potential. The added sugar for these kits dilutes the haze potential of the finished beer substantially, and gives it reasonable clarity, at room temperature at least.

This would not be an issue if it were not for the frequent suggestion in online brewing forums to substitute malt extract for the sugar used in these cheaper kits to apparently enhance their quality. What is happening here is that one is adding unboiled protein-rich malt extract to an unboiled protein-rich beer kit and the haze potential suddenly becomes enormous. The haze-dilution effect that the sugar afforded has been lost. This is of no consequence in a dark beer, such as a stout or porter, because the haze cannot be tasted and the procedure will, in fact, enhance the quality of such beers, but a pale beer, if all the sugar has been replaced with malt extract, will haze at the drop of a hat.

There is no real answer to this dilemma, except to replace only part of the sugar with malt extract, perhaps replacing up to 60% of the sugar with malt extract. However, malt extract is disproportionately expensive compared to beer kits, and it is probably just as cost effective to use a 3kg beer kit in the first place. Indeed, a cheap beer kit using 40% sugar can not be expected to produce a quality beer, so moving up to a 3kg kit will make a significant stride forward in quality and will not be much more expensive than adding malt extract to a cheaper kit anyway. Most home-brew shops supply "Beer Kit Enhancer" (That says it all.), which is a blend of sugar and malt extract.

Malt Extract Beers

The myth that malt extract has been boiled at manufacture leads to some malt extract recipes calling (erroneously) for short boil times, often fifteen or thirty minutes. This is particularly common in recipes from American sources. Good quality malt extract is similar to an ex-mash-tun wort and should be treated in the same way as a fully mashed beer; boiled at close to full volume for at least sixty minutes, but preferably for ninety minutes; the use of copper finings and so on.