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.
Other Forms of Haze
Other non-biological forms of haze can develop from raw materials or processing conditions. These are not common and can be difficult to diagnose.
Polysaccharide hazes
These hazes are caused by polysaccharides, which are carbohydrates whose molecules consist of multiple sugar units bonded together. Examples include β-glucan and pentosans, which are derived from barley cell walls that have been incompletely modified during the malting and mashing processes.
These hazes can also be a factor when brewing with unmalted grains, e.g. unmalted wheat, which is part of the standard grist in a Belgian Wheat beer. To prevent these hazes from forming when using undermodified malts or unmalted grains, the brewer needs to ensure the β-glucan and pentosans are sufficiently broken down during the mashing process. This can be achieved by including a lower temperature mash stand (e.g. 45 ºC) or by the addition of exogenous enzymes, such as β-glucanase.
Exogenous β-glucanase is an enzyme that breaks down β-glucans and is derived from bacterial and fungal sources.
Mannan hazes
These are derived from yeast cell walls, caused by poor yeast management or aggressive handling, for example, centrifugation. Mannan is found in yeast and not cereals; they are a useful marker in haze identification. However with mannan haze (and most other hazes), collecting sufficient haze material to do a proper analysis is difficult and requires high g-force centrifugation.
Starch hazes
A starch haze (α-glucan haze) can occur from the incomplete breakdown during mashing.
α-Glucan can cause so-called invisible hazes that are detected only by a haze meter.
Non-polysaccharide hazes
This diverse group of hazes are caused by processing aids, additives or poor brewing practices. Let us explore the more common causes:
- Oxalic acid – this is present in malt and has a high affinity for calcium, leading to the formation of oxalate crystals that can cause haze in the final beer. To ensure that this does not occur, the brewer needs to add sufficient calcium during mashing and/or wort boiling so that all the oxalic acid is precipitated out in the brewhouse and removed in the spent grain or trub.
- Collapsed foam – this can occur if the bright beer tank (BBT) or Final Product Tank (FPT) is purged, for example, to correct high oxygen levels or low CO2 levels. The foam collapses, leaving a solid residue in the beer. These can often be seen in the BBT/FPT outlet sight glass as flakes.
- Filter materials – both powders and particles from the support material can make their way into the BBT/FPT. Sheet material is visible as small fibres in poured beer. In the case of a hazy BBT/FPT, the best course of action is to re-filter the beer, although this practice may be negative for both foam and flavour stability.
- Propylene glycol alginate or PGA – this is a foam stabiliser that we covered in the Beer Foam lesson. PGA has been known to form a haze after heat treatment through pasteurisation and can bind protein if overcharged, causing ‘bits’ and haze.
- Other process aids – these include such things as silica gels, which can form silicate hazes, as well as packaging chain lubricant from conveyors entering bottles or cans. These will form hazes and cause flavour taints too.
- Freezing point – this depends on the alcohol content. If beer is physically frozen after filtration, for example in a bright beer tank or a bottle, a permanent haze will result. These hazes consist of β-glucans, oxalate, dextrin, and proteins.
- Metals – these are found concentrated in beer haze and together with oxygen, they catalyse the formation of permanent haze from chill haze. Iron is a common culprit and is often derived from the brewing plant equipment or from the water supply. In older brewhouses, copper can be leached from the vessels.
- Dead bacteria – these are considered non-biological particles and originate from malt. They can pass through the filter, resulting in beer haze. This is an often overlooked area when troubleshooting colloidal instability.