Lesson 4 - Beer Haze

Mashing and mash separation

A pH on the lower side of the accepted range of 5.2-5.4 will encourage polyphenol precipitation. When using less modified malts or adjuncts with high nitrogen a low temperature rest of 45-55°C may be employed. This allows for proteolysis, which will have the effect of degrading haze protein. There is a school of thought that little, if any, proteolysis occurs during mashing, with a much more significant factor being protein precipitation. Indeed, more protein leaves the solution in sweet wort production than in boiling.

Gentle handling, and avoiding shear when handling mash, is a good practice to avoid polyphenol and β-glucan extraction. Excessive lauter raking and over sparging also contribute to polyphenol extraction, as does high sparge temperature above 78 °C.

Wort boiling and wort separation

During boiling wort, protein is coagulated and subsequently separated out with the trub, along with protein-polyphenol complexes that have formed. A good rolling boil will favour this. Kettle finings, comprising negatively charged carrageenan, bind to positively charged haze forming proteins and precipitate these out during wort separation in the whirlpool.

Oxygen control is an important consideration in wort processing and subsequent beer processing, resulting in improved beer flavour stability. However, a reduction of oxygen during beer processing results in less polyphenol oxidation and lower amounts of subsequent polymerisation and precipitation. Aeration during wort cooling assists in polyphenol oxidation and later precipitation into cold trub, which is then removed from the cone of the fermenter.

Calcium, at the level of greater than 80 mg/L, needs to be present in wort to ensure precipitation of oxalate during subsequent processing. The role of calcium in water was discussed earlier.

Fermentation and maturation

The subsequent rapid cooling of boiled wort produces some cold break, which precipitates more haze precursors. During fermentation, as the pH drops, some protein and protein-polyphenol complexes precipitate out, and some colloidal molecules bind to the yeast cell walls – being removed with the yeast harvest.

The majority of chill proofing happens in maturation, or cold stabilisation, often in conjunction with added stabilising process aids. During this cold period, which can lasts from days to weeks, further polymerisation of chill haze complexes occurs. Temperature, rather than time, is the most important factor, and research has found that a period of 2-3 days at -2 °C is sufficient for cold stabilisation. The intended actual temperature reached depends on the refrigeration plant installed as well as the beer alcohol needed to avoid freezing. High gravity brewing, with higher alcohol content allows for lower maturation cooling temperatures, resulting in more colloidally stable beers.

A word of caution should be issued about adding recovered beer at this point. Recovered beer can contain haze precursors (as well as foam-negative components), and the effects need to be carefully monitored.

Filtration, bright beer and packaging

At filtration, the key is to maintain the temperature as it was in the maturation vessel. Chill haze can easily dissolve with temperature pickup and undo the days of chillproofing time. Oxygen pickup needs to be kept at a minimum at this point as there is no yeast to take it up; it will oxidise and polymerise polyphenols, which encourages permanent haze formation. Ingress of metals at this point is to be avoided; they too, catalyse haze formation and concentrate in the haze complexes.

In the BBT/FPT, rousing should be avoided where possible as this can lead to the abovementioned collapsed foam particles.

Good quality packaging materials that are free of defects, residual bottle washing additives and conveyor lubricant, must be ensured.