Introducing two new original strains: Bananza and Sundew

The POF– Project

Academic research has shown that the naturally-occurring spicy, clove flavors in phenolic strains mask much of a finished beer’s perceived fruitiness, which comes from both yeast-derived esters and from hops.

For years, we’ve helped brewers with yeast handling tips to enhance the overall fruitiness produced by our traditional Belgian and Hefeweizen strains.

A brewer can enhance a yeast strain’s ester production to compete with phenolic character using fermentation temperature control, for example, but cannot eliminate the phenolic flavor component.

This sparked our curiosity:

1. What would the fruity esters in phenolic strains contribute without the phenolics that partially obscure them?
2. How would their fully-revealed ester profiles be perceived differently in a finished beer?
3. Would the absence of phenolics improve a beer’s overall perceived fruitiness, contributed to by both yeast and hops?

Wait, What is POF-?

Though phenolic character is considered desirable in Belgian styles and German wheat beers, phenols are considered an off-flavor and unwanted in most modern, hoppy styles.

Brewing strains that are positive for phenolic off-flavor (POF+) produce a spicy or clovey compound called 4‑vinyl guaiacol (4VG) – the same compound present in clove spice for baking.

4VG is produced by an enzyme encoded by the FDC1 gene, present in all brewing yeast.

Though all brewers yeast carries this gene, most brewing strains in use today naturally acquired an inactive copy of the FDC1 gene from a centuries-old mutation that brewers have perpetuated historically through use.

Because POF- strains’ flavor profiles were favored by brewers and selected for during the advancement of pure culturing techniques in the late 1800s, the vast majority of the brewing strains we use today are from those POF- heritages. One specific historic inactivation that caused POF- in brewing strains is called the fdc1-C460T substitution.

POF+ (positive for phenolic off-flavor) phenolic-producing yeast. For example, Belgian and Hefeweizen strains.

POF- (negative for phenolic off-flavor) the most common category of brewing strains, strains that do not make phenolic compounds. A standard example is West Coast Ale I (Chico).

4VG (4‑viny) guaiacol) a spicy, peppery or clovey compound.

FDC1 the gene that encodes the enzyme that produces 4VG, common to all brewing strains. However, most brewing strains brewers use today have inherited an inactivated version of this gene.

fdc1-C460T the specific substitution responsible for inactivating 4VG production resulting in a POF- subset of brewing yeast.

Phenolics a class of spicy, clovey, medicinal, herbal flavor compounds. 4VG is one example.

Esters a class of fruity flavor and aroma compounds.

Making Bananza and Sundew

Inspired by the effect of this historic fdc1-C460T inactivation in POF- yeast, we selected a group of phenolic strains whose perceivable ester profile and brewing characteristics were already popular and were likely to stand out even more without the phenolic tagalong.

We used the naturally-occurring FDC1 substitution as a roadmap.

Using CRISPR-Cas9, a modern gene-editing process, we introduced the same inactivation of the FDC1 gene into these phenolic brewing strains.

The FDC1 substitution could have been accomplished through hybridization. However, with CRISPR Cas9 – unlike with hybridization – it was possible to make a very targeted change and leave the rest of the strain’s characteristics untouched.

As expected, the process disrupted the production of 4VG and eliminated the expression of clove-like phenolics, revealing the full-impact of the strains’ fruit esters without the muting interference of phenolic character for the first time.

These strains now carried the same inactivation of the FDC1 gene the brewing industry’s favorite workhorse strain, West Coast Ale I (OYL-004) has, for example.

Hefeweizen I (OYL-021) and Belgian Ale A (OYL-024) were the phenolic parent strains. The resulting POF- strains are Bananza (OYL-400) and Sundew (OYL-401), named for their newly uncovered predominant ester character.

Recipes

During test brewing, the absence of phenolic character allowed both yeast esters and complementary hop fruitiness to come forward in a new way, and was indeed perceived as an increase in the beer’s overall fruitiness.

Test recipes included a double NEIPA, a banana milkshake IPA, a West Coast IPA, a banana-split pastry stout, a hoppy blonde, an all banana hefeweizen, a roasty porter, and a few others. More recipes available soon!