Lesson 4 - Beer Haze
In this lesson we will discuss beer haze. This will include defining the biological and non-biological (protein-polyphenol) haze types and their formation. We will also identify other hazes that can occur in beer. We will consider the influence of raw materials and discuss processing. To end the lesson, we look at how haze is measured and how we can use accelerated shelf-life testing to predict colloidal stability.
Brewing Materials
As we have seen, malt and hops contain the proteins and polyphenols of chill haze, as well as the polysaccharides β-glucan, α-glucan and pentosans. Let us take a look at how we can influence wort and beer processing to minimise the risk of haze in a packaged beer.
Water
Brewing water should be low in haze forming catalysts such as iron and copper. These catalyse oxidation and polymerisation of polyphenols. Water should not be high in alkalinity nor have a high pH that would favour polyphenol extraction during the sparging process. Water should contain sufficient calcium to precipitate oxalic acid from the malt as calcium oxalate.
Malt
Proanthocyanidins, the haze active dimers and trimers of flavanols, were introduced under haze formation as major components in protein-polyphenol complexes. Proanthocyanidin-free barley varieties have been bred for the purpose of creating a colloidally stable product through the removal of one of the haze components. However, they have not been widely adopted by brewers because they create other issues such as lower extract recovery, higher soluble nitrogen and darker worts.
Malt low in total nitrogen is lower in haze protein and can be selected to reduce haze complexes in beer. Care must be taken to provide sufficient nitrogenous material for yeast nutrition and foam. A rule of thumb is that levels of total nitrogen should be > 10 mg/L/°Plato wort original extract, although this consideration is more relevant for regions producing lower nitrogen malt and using starch adjuncts.
β-glucan levels in malt should be < 200 mg/L and the malt should be well modified to produce a low β-glucan, clarity stable product.
Hops
Hops contain polyphenols that are polymerised and precipitated in the boil. Those that survive the boil polymerise further in the presence of oxygen and metals, forming haze complexes with proteins.
Some hop extracts do not contain any polyphenols. Brewing with proanthocyanidin-free malt and polyphenol free hop extract will produce a beer with excellent colloidal stability.
High use of isomerised or reduced isomerised hop products downstream in the process can lead to hazes; however, these should be able to be removed in the filtration process and are only a problem in unfiltered beer. Dry hopped beers tend to become hazy from the hop polyphenol interactions with polypeptides.
Adjuncts
Liquid adjuncts dilute protein in the wort and improve colloidal stability. Solid adjuncts containing wheat will increase the chances of a hazy product. This is because wheat contains higher protein levels, allowing more protein-polyphenols complexes to form and be removed from the beer. Wheat also provides pentosans.
In selecting raw materials for a beer, we need to be careful. Proteins are needed for foam and possibly the mouthfeel, whereas polyphenols at higher levels add astringency to beer. Liquid adjuncts are deliberately used for certain beer styles to lighten the taste. Wheat can be used both for flavour and head retention.
With this in mind, let us look at some of the practices in wort and beer processing that reduce the risk of hazy beer.