IRC7 AND VOLATILE THIOLS IN BEER

Genetic and functional diversity of IRC7 in brewing strains and its implications for aroma profile development

Understanding why genetically similar ale yeast strains can produce markedly different thiol-driven aroma profiles remains a key challenge in brewing science.

A study conducted at the University of Modena and Reggio Emilia and supported by AEB S.p.A. within the National Recovery and Resilience Plan (NRRP), analyzed 15 Saccharomyces cerevisiae ale brewing strains to investigate the genotype–phenotype relationship underlying thiol release during beer fermentation.

Published in the Journal of Food Biochemistry (Nasuti et al., 2026), the study links IRC7 genetic diversity to differences in β-lyase activity, the enzyme responsible for releasing aroma-active volatile thiols from hop- and malt-derived precursors, offering new insight into this variability.

ABOUT THE STUDY

Volatile thiols are powerful aroma compounds that contribute fruity, tropical, and citrus notes in beer, even at extremely low concentrations.

Their release depends on yeast metabolism, particularly on the enzyme β-lyase encoded by the IRC7 gene.

The IRC7 gene exists in two allelic variants: a full-length, functional form, and a short-length, non-functional form.

However, the presence of the full-length (functional) IRC7 alone is not sufficient: internal point mutations can reduce its activity, thereby affecting aroma output. The combination of genotypic and phenotypic analyses enables the assessment of the true potential of yeast strains.

Genotypic analyses

The presence of the IRC7 gene, responsible for β-lyase production, was verified, and its allelic form (long or short) was determined. In addition, potential genetic mutations that could reduce or abolish enzyme functionality were investigated.

To achieve this, Sanger sequencing was used, a precise and well-established laboratory technique that enables the reading of the DNA sequence. From this sequence, it’s then possible to reconstruct the encoded protein and assess its functional capability.

Scientific workflow illustrating yeast sporulation, ascus dissection, single-spore germination, genomic DNA extraction, PCR and electrophoresis analysis

Phenotypic analyses

An indirect enzymatic assay was performed to evaluate the actual activity of β-lyase. In this assay, the initial compound is transformed by β-lyase and, through a secondary reaction, a measurable change over time is generated. This change is detected by spectrophotometry, by monitoring absorbance variation at a specific wavelength. The greater the change in absorbance, the higher the enzymatic activity.

This “in vitro” assay simulates what occurs during fermentation and allows a reliable estimation of how effectively a yeast strain can release fruity and tropical aromas from initially non-aromatic compounds.

Conclusions

The results show that most Saccharomyces cerevisiae ale brewing strains possess the functional form of the gene (IRC7L). However, the presence of this allele alone does not fully explain the observed enzymatic activity or the resulting aromatic profile. The results highlight the complexity of the relationship between genotype and phenotype, showing that genetic characteristics, gene expression, enzyme activity and substrate availability can all contribute to the final aromatic outcome. In particular, the alleles and the substrate on which the enzyme acts are key factors in determining aroma intensity.

YEAST	Beta-lyase activity
FERMOALE BEL-ABBEY	HIGH
FERMOALE	HIGH
FERMOALE WEISS	HIGH
FERMOALE AY4	HIGH
FERMOALE GERMAN K	MEDIUM
FERMOALE NEW-E	MEDIUM
FERMOALE AY3	MEDIUM
FERMO KVEIK SV	MEDIUM

How to read the table: while β-lyase activity alone does not fully determine the final aromatic profile, the classification below provides a useful reference for comparing the thiol-release potential of different brewing strains.

Author: Tania Porcu – R&D Manager AEB Brewing

22 October 2026

Sources and acknowledgements

This article is freely available in open access format thanks to the Wiley – CRUI-CARE agreement, facilitated by the University of Modena and Reggio Emilia.

The study was conducted at the Lactic Acid Bacteria and Yeast Biotechnology (LYB) Lab and the Nutritional Biochemistry Lab, both part of the Department of Life Sciences, University of Modena and Reggio Emilia (Via Amendola 2, 42122 Reggio Emilia, Italy).

Authors: C. Nasuti, V. Papiani Ceramelli, D. Tagliazucchi, A. Cattivelli, L. Solieri.

The IRC7 sequences characterised in this study have been deposited in the GenBank database under accession numbers PV876887–PV876904.

Full bibliographic reference: Nasuti C., Papiani Ceramelli V., Tagliazucchi D., Cattivelli A., Solieri L. — "Functional Link Between IRC7 Allelic Variation and Carbon-Sulfur-β-Lyase Activity in Brewing Saccharomyces cerevisiae Strains" — Journal of Food Biochemistry, 2026; 2026:7937512. DOI: 10.1155/jfbc/7937512 — Open Access.

Received: 28 July 2025 | Revised: 27 February 2026 | Accepted: 2 March 2026 | Academic Editor: Anupama Bose.

Thanks for your request. We will contact you as soon as possible.

CONTACT US

Name *

Surname *

Telephone *

Email *

Company *

City *

Country *

Select the country you wish to contact *

Message

Category*

I'm a AEB customer

I have read the privacy policy published on this website and I consent to the processing of my data, for purposes of Research and Selection of Personnel and business contacts.

Send