Yeast – a key cause of haze
Haze happens when reflections from fine particulates scatter light. In beer, these fine particulates are often yeast (S. cerevisiae). Yeast cells are on average 3-5 microns in size. As a result, they have a big impact on clarity. As charged yeast particles attach to each other, their mass increases. Influencing factors on yeast flocculation include genetics, calcium levels, temperature, and the mass of each cell. Whatever the cause, flocculation leads to higher rates of sedimentation. For example, one yeast cell might only drop around 18cm daily, while six cells bound together could drop up to 72cm every day.
Small particulates - peptides and phenols
Yeast stops creating haze once there are fewer than around one million suspended yeast cells/ml. If you’re still getting haze at this point, the cause is probably reflections from particulates sized from 2 to 0.5 microns. At this point, I could take a deep dive into Stoke’s Law, Reynolds numbers and Brownian motion. But my goal here is to help prevent confusion of mind, so I’ll keep it simple. Malt and hops are a source of peptides and phenols. These are expressed in the wort during production. On their own, they’re invisible to the naked eye. And they’re still invisible after they join together as peptide-phenol complexes. But they’re the most likely source of any smaller particulates at this point in your process.
Haze-causing polypeptide-polyphenol complexes
A particle’s size influences how long it stays suspended. When they’re sufficiently small, particles become colloidal. Colloidal particles are spread evenly through the substrate. They don’t drop out and can’t be filtered or centrifuged out. Colloidal dispersions in beer are mostly caused by polypeptide-polyphenol complexes. These form late in your process. The best way to avoid them is to get rid of the maximum possible amount of peptide-phenol reactive material through hot and cold break. You can also take certain steps during mashing and lautering to help prevent or encourage these haze-causing compounds. If you want to get rid of them after production, enzymes can help.
Tannoids and permanent haze
Catechin is an example of a simple flavonoid. It’s a monomer, so it can join with protein complexes, and still be too small to form a visible haze. But as it and other flavinoids oxidize and start to join together, they get sufficiently big to cross-link proteins. That’s something you may notice as a reversible chill haze at an intermediate state. Reversible chill haze happens when the liquid warms and the agglomerations caused by few protein-polyphenol cross-links are temporarily made soluble again. Continuing oxidation and polymerization of the flavinoids leads to tannoids, and the agglomerated molecules get bigger. This can result in permanent haze. It can also lead to sedimentation in the product container.
The rise of haze in craft brewing
When I started out in this industry, the only conversations I had about maintaining haze stability related to styles like witbier and hefeweizen. These were the only hazy style considered acceptable in craft brewing. And there was good reason. Craft brewers were keen to get away from associations with “backyard brews”. That meant decades of striving for the translucency that comes with full yeast removal and adequate conditioning time. In the more recent past, I got a lot of questions about how to achieve the clarity of a lager on dry hopped or fruited pale ales. But craft brewing – like everything else – is cyclical. Today, the conversations have moved back to how to get a stable haze. They’re subtly different however, as this time they’re mostly about IPAs. So you could say that the aim of craft brewers have shifted from producing something that looks like colored seltzer water to something more resembling a glass of orange juice.