Lalbrew Pomona is the newest yeast in the Lallemand LalBrew range, selected by Escarpment Labs in Canada. The strain was chosen for its ability to produce delicious hop-forward and hazy IPAs with a variety of strengths. Here Alix Blease, technical sales representative at Lallemand Brewing, delves into the origin story of this yeast and looks at where it came from.
Yeast hybridisation can be used to improve a number of yeast characteristics, for example; sugar utilisation, temperature tolerance or, in this case, aroma production. Lalbrew Pomona actually started its life as two different yeasts.
Sterling, a Scottish-British yeast with great fermentation characteristics but low aroma; and Cerberus, an STA1 positive saison strain, which has excellent aromatic qualities but is a diastatic yeast, meaning it would break down unfermentable sugars.
These yeasts were selected as the two parent strains from which a variety of hybrid yeasts were created using the “rare mating” technique.
There are two methods for creating hybrids from mating yeast, spore-to-spore and rare mating. In spore-to-spore the parent yeast cells create spores which are then selected and combined. The equipment required for this is very expensive, however this method is incredibly efficient.
The second method, and the one used to create LalBrew Pomona, is rare mating; in this case thousands of cells from each parent yeast are mixed together and then the mixture is “screened” for the occurrence of hybridisation events.
To make sure that the hybrids are identifiable, the parent cells are modified so that the synthesis of one compound is inhibited in each.
In the case of Lalbrew Pomona one parent cell was unable to synthesise uracil and the other lysine (this might sound familiar because it’s how they “contained” the dinosaurs in Jurassic Park).
Hybrid cells can be identified because they will be able to produce both compounds, lysine and uracil, proving that genetic material has been exchanged and a hybrid has formed. This method is more labour intensive, but it can be achieved with relatively basic equipment.
Once all the hybrid cells have been identified their genetics need to be evaluated as well as their fermentation characteristics. In the case of LalBrew Pomona, one of the parents was a vigorous fermenter, while the other had great aroma.
The resulting hybrid needed to have broad attenuation and good aromatic qualities; as well as not being diastatic (containing the STA1 gene).
Once the desired hybrids were selected, it became apparent that these hybrids didn’t have the required attenuation range or haze formation.
The hybrids were further transformed using Adaptive Laboratory Evolution, coincidentally, ALE for short. ALE can be used to expose yeast to specific environmental conditions or to enhance certain metabolic capabilities.
Yeast is grown and then repitched in controlled stressful environments, for example extreme temperatures or high alcohol concentrations. This promotes mutations in the yeast to become resistant to these conditions. It is essentially survival of the fittest but on fast forward.
Throughout this process the yeast population are regularly screened to identify any beneficial genetic mutations which may have occurred.
The hybrid selected from the rare mating of Stirling and Cerberus parent strains went through ALE in high gravity and heavily dry-hopped worts.
This happened over 107 days and 48 successive transfers or re-pitches. The resulting yeast was screened for attenuation, haze formation and biotransformation ability.
The LalBrew Pomona strain pushes peach and stone fruit aromatics and is also compatible with a wide range of ABVs from session pale ales to triple IPAs.
Research from Oregon State University and Niagara College compared LalBrew Pomona and LalBrew Verdant IPA fermentations.
LalBrew Pomona showed a slightly higher affinity for fermenting maltotriose than LalBrew Verdant IPA resulting in a slightly higher ABV beer.
LalBrew Pomona also showed excellent liberation of (the very trendy) thiols, as well as a lesser known group of compounds called lactones.
Lactones are very well studied in wine-making, however there is very little research on their aromatic impact in beer.
Lactone compounds are generally described as oily, coconut and peachy. In wine (and beer) they have been shown to have a compounding effect on the aromatic thresholds of terpenes and thiols.
This means that the presence of lactones in concentrations lower than threshold amounts will increase the perceived aroma and flavour imparted by terpenes and thiols.
An analogy which can be made in beer is adding a handful of Sabro (coconut) hops when brewing a tropical IPA. Although the beer won’t taste like coconut, the presence of this flavour increases the perception of tropical fruit in the beer.
The feedback on LalBrew Pomona from our commercial trials was overwhelmingly positive; the beers created were described as citrus, tropical and peach!
If you want more information on this topic and tricks to maximising these flavours, then check out our Biotransformation and IPA Solutions document on the Lallemand website.
