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.
Polyphenol Precipitation and measurement
Tannoid value
Polyvinylpyrrolidone (PVP) is a molecule that will bind and precipitate low and medium MW polyphenols, collectively called tannoids. Beer is titrated with a PVP solution until a maximum peak is formed. This is the Tannoid value expressed in mg PVP / 100 mL. This test only precipitates around 10% of beer polyphenols, so has its limitations.
HPLC
This is the examination of beer polyphenols by high-performance liquid chromatography. The polyphenols are separated using a Sephadex LH-20 resin column. Eluted polyphenols are measured by UV detection. HPLC is covered in more detail in the quality unit.
The brewer may feel these tests to be tricky to perform routinely; fortunately, an instrument called Tannometer has been developed in Germany, which performs all tests described above. Unfortunately these are no longer made but some are still in use.