Beer hazes can be divided into microbial (i.e. caused by bacteria or yeast) and non-microbial. There are also various types of non-microbial hazes, but the most common is that caused by protein-polyphenol complexes and I will focus on that in this article.
Protein-polyphenol complexes are a major component of trub, hot break, cold break, chill haze and some permanent hazes. They are formed when haze forming proteins bind with haze forming polyphenols (tanninogens). When these complexes form particles large enough to precipitate they cause a haze. At first these particles are less soluble at lower temperatures so reversible chill hazes can appear when beer is cooled.
Predominantly they originate from the malt but a number of factors at various stages of the brewing process can contribute to their existence. This goes to the very start of the brewing process, as the correct mineral composition of brewing liquor is important to prevent their formation. Calcium levels in brewing liquor should be greater than100mg/l and the residual alkalinity as carbonate should be less than 50mg/l. Calcium has the effect of lowering the pH of the mash, and carbonate will keep the pH high. You should aim for a mash pH of around 5.2 to 5.4. If the pH is too high more polyphenols will be extracted from the malt and the beer is more likely to be hazy. The most common way of removing carbonate is to add food grade acid to the Hot Liquor Tank, and calcium salts can be added by mixing them in with the grist. The choice of acids and salts used will affect the chloride/sulphate ratio of the beer which will have some effect on the flavour.
The protein component of hazes will come from the malt and if the total nitrogen content is over 1.65% haze is more likely to form. Protein content can be lowered by using a proportion of low protein adjuncts, such as sugar or rice, to make up some of the extract. It is also possible to get malt from barley varieties that have been bred to remove the haze forming polyphenol proanthocyanidin. The use of “ProAnt” free malt will reduce the formation of haze in beer.
Over sparging of the mash will cause more polyphenols to be extracted into the wort. The more the mash is sparged the more it will lose its buffering capacity and the pH will start to rise. To prevent high levels of tannins being extracted stop sparging when the gravity of the last runnings has dropped to 1.005.
During the boil the hot break will form as proteins coagulate, which can be removed as trub with the hops. Copper finings, a polysaccharide derived from seaweed, should be added towards the end of the boil to aid cold break formation and the subsequent removal of more protein-polyphenol complexes. The addition rate for copper finings should be optimised as over or under addition will give poor fining action. Ideally the addition rate is optimised for each batch of malt.
Polyphenols from hops will be extracted during the boil and can contribute to haze, particularly in highly hopped beers.
Protease enzymes can be added to the fermenter to break down haze forming proteins. This also has the benefit of making the beer gluten free! Auxiliary finings, polysaccharide or silicate based, can also be added to the fermenter or conditioning tank and will also help with protein removal. They can even be added to the cask, but should not be added at the same time as isinglass finings or they will bind to each other!
Other processing aids available to brewers can also help reduce haze. Silica hydrogel or xerogel will also help remove haze forming proteins, and PVPP can be used to remove haze forming polyphenols. These products are available in a mix containing both of them, which is usually added prior to filtration, though they can be used without filtration and left to settle in a tank. Rather counter intuitively tannins can also be added to beer to help clarify it. Adding an excess of polyphenols in the form of tannic acid means more protein-polyphenol complexes are formed and can be removed in the brewery.
The fact that more haze forming particles come out of suspension at lower temperatures can be used to our advantage. Cold conditioning prior to filtration, at a temperature of 0ºC or lower, will maximise the amount of haze particles removed and make a clearer and more stable beer.
This post comes from a talk I gave at the SIBA conference that I then wrote up for their magazine.