Uncovering a Gene for Haze

In 2022, craft brewers produced about 24 million barrels of beer, of which hazy IPA and double IPA made up about 10% (Nielsen). Most brewers use one particular yeast strain for hazy IPA, leading some consumers and industry analysts to posit that all hazy beer tastes the same. Our research into the sources of haze has demonstrated that yeast plays a crucial role in the creation and stability of haze in beer. As brewers have figured out over the years, some strains are better at creating the signature orange juice-like haze than others. We made it our mission to seek out the elusive haze gene.

Based on much of the work our team has already done, we were already certain that yeast was playing an important role in the development of haze in beer. 

Using a classical yeast genetics approach combined with modern bioinformatics, we were able to identify a yeast gene responsible for dry hop-dependent, yeast-derived haze. We crossed two strains: one of our most haze-positive strains, OYL-011, and a haze-neutral wine strain. Some of the resulting offspring of this cross were haze-positive. We then took one of these haze-positive offspring and continued backcrossing to the haze-neutral wine strain multiple times, each time taking the haze-positive offspring and crossing it to the haze-neutral wine strain. The end result was a haze-positive offspring with 99.2% of the genetics of the haze-neutral wine strain, and only 0.8% of the genetics from the haze-positive OYL-011 strain. By using whole genome sequencing, we were able to compare the genome of the haze-neutral wine strain with the haze-positive backcrossed strain to ultimately hone in on this ​“haze gene.”

To illustrate the approach, picture two decks of cards, one set blue and the other red. In the blue deck, one card confers the ability on the deck to glow in the dark, and that represents the haze gene. By shuffling the decks together and dividing in two, only one deck has this magic card. You take that deck and shuffle it back into a red deck. Split them in half and again take the deck that glows and shuffle it into a fresh red deck. The deck will increasingly be made up of more and more red cards but will have the one special card conferring the ability for the deck to glow (i.e., the haze gene). Once the glowing deck is statistically mostly of red deck origin, the cards (i.e., genes) can be examined and any blue cards remaining can be individually tested for the glowing property. 

From this genetics approach, we identified a novel gene YIL169C and named it HZY1 for its role in promoting haze in beer. Little to nothing is known about the function of HZY1. In fact, YIL169C had only been briefly characterized in a S. cerevisiae lab strain to be a potential secreted protein of 995 amino acids in length. When looking further into the HZY1 gene in the haze-positive backcrossed strain, we found that it contained expanded ​“repeats” (i.e., short sequences that repeated over and over). These repeat expansions were found in two regions of the gene, one serine-rich region at the N‑terminus and the other is a serine/threonine-rich region at the C‑terminus.

When we looked at HZY1 sequences from long-read whole genome sequencing data of our Omega Yeast strain collection, we found that expansions in the N‑terminal domain strongly correlated with haze-positive strains, whereas haze-neutral strains either didn’t have expansions or had much shorter expansions. Next, we knocked out the HZY1 gene in several haze positive strains and found that the strains were no longer haze-positive, thereby confirming the role of HZY1 in dry hop-dependent haze.

To better understand how HZY1 affects beer, we conducted numerous experiments using a standard hazy IPA recipe. The data we collected included tetrad testing among samples brewed with standard yeast strains as well as yeast strains that had their HZY1 gene deleted.

In this tetrad test, panelists were instructed to find the pairs in their four-beer flights, in which two beers per flight were hazy (brewed with the haze-positive parent strain) while the other two were not (brewed with the hzy1∆ strain). Because this was a sensory panel that aimed to discover visual differences, samples were served in opaque cups with lids to obscure tasters’ view of the samples and require them to focus solely on sensory differences.

The results showed that our panelists could not ascertain which samples were hazy with any degree of certainty or repeatability. While some panelists did select the pairs correctly, the taster comments revealed that the correct answers may have been lucky guesses: one taster with a correct answer noted, ​“honestly a guess,” while another correct taster commented, ​“I’m having difficulty picking out similar beers.” Across the three panels, the theme of the comments was primarily that all four samples were incredibly similar. 

It’s worth noting that HZY1 varies from strain to strain, like any genetic variation. The degree of this variation seems to affect the degree of haziness found in finished beers, which is to say that we believe HZY1 plays a pivotal role in yeast-dependent haze, and genetic variation explains why some strains produce more intense haze than others.

This discovery brings with it immense potential for brewers to have the opportunity to enrich their brand portfolios and use yeast strains that generate different ester profiles and degrees of attenuation. Understanding the genetic link to haze will blur the line between yeast strains specifically used for traditional West Coast IPAs and NEIPAs as we continue to explore the possibilities of engineering this gene.

Richly hoppy beer took over the craft beer scene in a swift and unexpected way, and consumers have made it clear that it isn’t going anywhere. It’s now up to brewers to experiment and discover new flavor profiles that keep the beer-drinking public excited for the next big thing.

Identification of the yeast mannoprotein gene HZY1 as a key genetic determinant for yeast-derived haze in beer by Lacy, Mormando, Smith, Gibney, Shaner, Burns
Read the full research article on bioRxiv

Omega Yeast Discovers a Yeast Gene that Makes Beer Hazy
Read the press release