Yeast Hybrids: Recreating our favorite strains . . . with a twist

Harking back to high school biology class, diploid cells contain two sets of chromosomes while haploid cells only contain one. All images courtesy of Renaissance Biosciences

Let’s take a second to picture this: You’ve decided to brew a lager this week. After all the time and effort of purchasing ingredients and spending a full day brewing, it’s now fermenting and all you’re getting is sulfur coming out of the airlock. Yuck – definitely not what you were hoping for! Alternatively maybe you want to try a brut IPA and you want it dry, so you’re thinking of using a saison yeast, but the last thing you want is all that phenolic flavor overpowering the hop character. Or on the flip side, you want to produce a saison, but you’re concerned about using a yeast strain with diastatic capabilities. (Saccharomyces cerevisiae var. diastaticus is a common saison strain that secretes glucoamylase enzyme that breaks down dextrins and is seen as a contaminant in most instances.) If only your favorite lager strain didn’t produce H2S, or your saison strain didn’t produce phenolics, or didn’t have diastatic capabilities! This may sound like a brewer’s sci-fi dream, but it’s surprisingly not! All three of these strains exist today. The interesting thing is all these strains are not classified as genetically modified organisms (GMOs) (there is no splicing or dicing of genetic material) and they are not packed blends of two different strains. These are true genetic hybrids. All created through hybridization — breeding techniques that can develop novel strains with selectable traits. An option to solve some pesky brewing concerns. But what are hybrid yeast strains and how are they developed?

In the simplest of terms, hybridization (in the context of yeast) is a technique where you combine the genetic material of two different yeast strains to produce a genetically different offspring, a hybrid. This is not new technology, but it is newer to the brewing industry. In the past, hybrids were most commonly seen in the wine industry. This has to do with the differences between brewing and wine strains. Wine yeast strains are typically diploid cells. Now if you can stretch your memory all the way back to high school biology, you may remember that diploid cells have two sets of chromosomes. When cells go through sexual reproduction, the diploid cell will split its paired set and create haploid cells. A haploid cell only has one set of chromosomes. Two haploid cells will create a new diploid cell (which will come back to the full two sets of chromosomes and will be a 50/50 mix of genetic material from each haploid cell). This is an easier process for scientists when creating hybrid yeast strains.

In the simplest of terms, hybridization (in the context of yeast) is a technique where you combine the genetic material of two different yeast strains to produce a genetically different offspring, a hybrid.

Brewing strains on the other hand are a bit difficult to work with. Why? Well, first they’re not diploids. Brewer’s yeast is polyploid, meaning there are more than just two sets of chromosomes in each cell and second, they’re poor at sporulating. This is due to brewers historically, and probably unknowingly, getting rid of strains that sporulate. Since brewers rely on consistency, if a yeast wasn’t working as planned (potentially hybridized) they would switch strains to a fresh propagation and would throw out that yeast. Also, yeast cells sporulate when they are stressed out. Brewing yeast strains have been spoiled in nutritious wort for years. Thus, over generations and generations of these factors, brewing yeasts have pretty much lost the capability to sporulate altogether. But this doesn’t mean that it’s impossible to create a hybrid yeast strain that is good at fermenting in brewing environments. It’s just more complex, and scientists have found that brewing strains that are closer genetically to wine or Champagne strains (e.g. saison strains) tend to be easier to work with.

There are two common methods to produce hybrids. One method is adaptive evolution; this is where scientists place yeast cells into an environment that they will eventually adapt to. However, this can take between 100–200 generations (as it uses evolution for survival of cells), which is a slow and time-consuming process. The other method used to create these hybrid strains is called selective breeding. Selective breeding is the process of selecting parent strains to breed together, to then produce offspring that contain specifically selected and more desirable characteristics.

Typically, when yeast cells want to create more yeast cells, they will go through asexual reproduction. This is what brewers are most used to — one yeast cell yielding clones or genetically identical offspring (i.e. mother yeast cell budding a daughter yeast cell). For the selective breeding technique to work, the cells must undergo sexual reproduction. This is when two cells mate, or in other words, when the genetic material between the two parent cells mix and produce more genetic diversity in their offspring. For a cell to undergo sexual reproduction, instead of asexual reproduction, the cells need to be under a stressed environment to induce sporulation. According to Jessica Swanson, the Lead Development Scientist and Beverage Unit Manager at Renaissance Biosciences, low nitrogen and poor sugar source media is used to stress the cells out. Swanson explained that the reason these “cells produce spores is to survive stressful conditions. When these spores find themselves in a more favorable environment, they will produce cells (germinate), which may then undergo sexual reproduction to create a new generation of hybrid cells that are more genetically diverse allowing them to potentially be better suited in their new environment.”

When the two distinct spore isolates are put together, they will eventually mate. The mating process will take around 1–4 hours to complete. The spores (haploid cells) will release mating factors (pheromones) to induce the hybridization events. The cells will start growing in the direction of the other cells, which is referred to as “shmooing” — one of my favorite scientific phrases! This elongation of cells will allow them to join or fuse together, and eventually the genetic material of the two spores will mix to create a new diploid cell; a.k.a. the new hybrid cell.

Creating hybrid brewer’s yeast requires sexual reproduction of cells, the process of which is seen here. But pushing brewer’s yeast to reproduce sexually is not an easy task.

So now we have a new hybrid diploid cell, let’s call it an equal 50/50 mix of genetic material from each parent. What if you only wanted a specific trait from one of the strains, but wanted the rest of the genetic material to be that of the other selected strain? Let’s break it down in a basic example. Say you have Strain A (a good brewing strain, with strong attenuating abilities) and you have strain B (a wild strain with aromatics that you wish Strain A had, but not a good fermenter). If these went through sexual reproduction and produced a simple hybrid (50/50 mix of each), you now have 50% Strain A’s genetic material and 50% Strain B’s genetic material. But this isn’t what you’re looking for as the 50% of Strain B may cause this hybrid to be a poor fermenter. Preferably, the ideal strain would be >99% Strain A (brewing strain), but still have that 1% technical yeast trait (in this example, the sensory profile) from Strain B. To accomplish this, the process of backcrossing needs to occur.

After the first round of sexual reproduction, the new yeast strain would be considered a hybrid, but may not perform in the way brewers want. It often takes roughly eight rounds of backcrossing events to reach the goal.

Backcrossing requires multiple rounds of breeding the first hybrid strain back with one of the original parent strains until the hybrid has all the desired traits. In the case of this simple hybrid example, the 50% Strain A/50% Strain B hybrid will be backcrossed with the original brewing strain (Strain A) over and over again. The first hybrid was 50/50, but after a second round the new hybrid would be 75%/25%, the third would be 87.5%/12.5% and so on. This process is done until the daughter strain has all the desirable brewing traits along with the one specific trait (in this example: sensory profile) of Strain B. Once it reached that >99%/<1% ratio, it’s officially a fully functioning, true genetic hybrid strain that is ready to be brewed with!

There are countless possibilities out there when you start looking at the potential of yeast hybridization. According to Jessica Swanson, a wide variety of selectable traits can be targeted when developing hybrids. Some examples are “increasing or decreasing attenuation, flocculation, fermentation kinetics, specific flavors and aromas, stress tolerance, temperature profile, and enzyme activity to just name a few.” But the end goal doesn’t always have to be so specific and only about explicit traits. Lance Shaner, Co-Owner of Omega Yeast, provided another perspective of hybridization techniques, “You can go after targeted traits. But sometimes, instead of always having an end goal in mind, you can go through an exploratory process with no bias involved.” Maybe one of those initial 50/50 hybrids or other percent of genetic mix could turn out to do something unique and great?! The possibilities are endless.

The brewing and homebrew communities are continually pushing boundaries and bringing new, innovative ideas forward. Hybrid yeast strains not only solve potential brewing problems (as listed in the introduction) but can open new doors for some fun experimentation. That’s always been the beauty of brewing — sometimes it’s about trying to recreate a specific beer and sometimes it’s about trying something new to see how it goes. Or in the words of Lance, “Let’s just see what happens!”
If you are interested in learning more about the strains listed in the introduction of this article, find them here:

Renaissance Yeast – offers a full portfolio of hydrogen sulfide preventing wine and cider yeast
Omega Yeast – Gulo Ale (Irish ale x French saison) and Saisonstein (Belgian saison x French saison)
Lallemand Brewing – Farmhouse Hybrid Saison-Style Yeast

A special thank you to Jessica Swanson and Renaissance Biosciences for providing amazing amounts of research and information on the topic of hybridization techniques, along with supplying the graphics for this article.

Issue: September 2021