FERMOPLUS® AromaGlow is a cutting-edge yeast nutrient designed to improve beer aroma, flavour, and mouthfeel. It’s composition of grape skin tannins, yeast cell walls, and yeast autolysates are designed to work synergistically. FERMOPLUS® AromaGlow increases the yeast’s production of terpenes, esters and thiols, enhancing the aromatic complexity and intensity of the beer. The yeast autolysates improve mouthfeel providing body and volume. Additionally, it reduces ageing compounds and can reduce the dry hopping rates required, offering brewers both economic advantages and quality improvements. 

The typical dosage rate of AromaGlow is 40 g/hl of cold wort/beer, It is recommended to add 20 g/hl of FERMOPLUS® Aromaglow directly into the cold wort, with a further 20 g/hl during dry-hopping or beer spunding (at 2°P or ~8 SG points above the targeted final gravity). This double addition has proven to have the greatest measurable effect however the ideal addition will depend upon the beer style and the brewer’s preference.

Many key biological processes play pivotal roles in aroma compound production in fermentation, three of them are the Ehrlich pathway, esterification and the IRC7 gene pathway. In this article, we’ll explore each of them in-depth and how FERMOPLUS® AromaGlow optimizes them.

The Ehrlich Pathway: A Key Process in Yeast Metabolism

The Ehrlich pathway is a metabolic route used by yeast and other microorganisms to convert amino acids into higher alcohols and related aroma compounds. This pathway plays a vital role in fermentation processes, in brewing, and winemaking, it contributes significantly to the flavour and aroma profiles of beverages. The Ehrlich pathway primarily converts amino acids into higher alcohols and, subsequently esters through esterification reactions.

Central to the Ehrlich pathway are amino acids, especially branched-chain ones like leucine, isoleucine and valine. Yeast metabolises these amino acids to produce specific higher alcohols, such as isoamyl alcohol (banana-like aroma) from leucine and isobutanol (alcoholic aroma) from valine.

The availability of these amino acids in the fermentation medium directly affects the intensity, variety, and balance of higher alcohols produced. A higher concentration of amino acids typically leads to a more robust production of these compounds, enriching the beverage's sensory characteristics. Conversely, a deficiency can limit the metabolic potential of yeast, resulting in a less complex flavour profile. Beyond higher alcohols, the metabolites of these amino acids can further interact with other compounds to form esters, which are responsible for fruity and floral aromas. For example, isoamyl alcohol can combine with acetic acid to produce isoamyl acetate, known for its characteristic banana-like fragrance.

Maintaining an optimal supply of amino acids, along with other essential nutrients like nitrogen, is critical for balancing the production of higher alcohols and avoiding undesirable outcomes. Complex yeast nutrient formulations, such as FERMOPLUS® AromaGlow, are designed to provide a balanced source of amino acids and other nutrients. 

The Ehrlich pathway involves three main steps:

  1. Amino acid uptake: Specific amino acids (e.g., leucine, valine, phenylalanine) are absorbed by yeast cells.

  2. Transamination and deamination: These amino acids are converted into corresponding α-keto acids through enzymatic reactions.

  3. Reduction to higher alcohols: The α-keto acids are decarboxylated into aldehydes, which are subsequently reduced to higher alcohols.

Key Amino Acids and Their Products via the Ehrlich Pathway

  1. Threonine → Propanol:

    • Threonine is metabolized to propanol (n-propanol), a higher alcohol with a mild aroma. It also produces intermediate compounds like propanal and butyric acid.

  2. Isoleucine → 2-Methyl-1-butanol:

    • Isoleucine is converted into 2-methyl-1-butanol, which has a fruity aroma, enhancing the complexity of fermented beverages.

  3. Valine → Isobutanol:

    • Valine produces isobutanol, contributing an alcoholic aroma. It passes through intermediates like α-keto-isovalerate and isobutanal.

  4. Leucine → Isoamyl Alcohol:

    • Leucine is metabolized into isoamyl alcohol, known for its banana-like aroma. It forms intermediates such as α-keto-isocaproate and isoamylaldehyde.

  5. Phenylalanine → 2-Phenylethanol:

    • Phenylalanine produces 2-phenylethanol, a higher alcohol with a floral, rose-like aroma. This involves phenylpyruvate and phenylacetaldehyde as intermediates.

Key Enzymes Involved in the Erlich pathway

BAT1/BAT2 (Branched-Chain Aminotransferases): Catalyze the initial transamination of branched-chain amino acids like leucine, isoleucine, and valine to their respective α-keto acids.

PDC (Pyruvate Decarboxylase) and ARO10: Decarboxylate α-keto acids into aldehydes.

ADHs (Alcohol Dehydrogenases): Reduce aldehydes to their corresponding higher alcohols.

CHA1, ILV1, and ILV2: Enzymes specific to threonine and branched-chain amino acid metabolism.

   Overview of the Ehrlich Pathway


Production of Esters (via Alcohol Acetyltransferase Enzymes)

Esters are key aromatic compounds in beer and other fermented beverages, providing fruity, floral, and complex sensory notes. FERMOPLUS® AromaGlow enhances ester production by optimizing yeast health, metabolic activity, and the availability of precursors and cofactors necessary for esterification.

Esterification is a chemical process in which an alcohol reacts with an acid (usually an organic acid) to form an ester and water. Esters are organic compounds that are often characterized by their fruity and floral aromas, making them essential contributors to the sensory profiles of beer, wine, and other fermented beverages. 

The Esterification Process in Fermentation

In brewing and fermentation, esterification is catalyzed by specific yeast enzymes known as alcohol acetyltransferases (e.g., ATF1 and ATF2). These enzymes facilitate the reaction between:

  1. Alcohols: Produced by yeast during fermentation (e.g., ethanol, isoamyl alcohol, phenylethanol).

  2. Acyl-CoA Compounds: Derived from fatty acid metabolism in yeast (e.g., acetyl-CoA, propionyl-CoA, butyryl-CoA).

Steps in Esterification:

  1. Alcohol Formation:

    Alcohols are produced through yeast metabolism, particularly via the Ehrlich pathway (e.g., isoamyl alcohol, phenylethanol) or glycolysis (e.g., ethanol).

  2. Fatty Acid Metabolism:

    • Acyl-CoA intermediates (like acetyl-CoA) are generated during yeast fatty acid metabolism. These serve as the acid component in the reaction.

  3. Enzymatic Catalysis:

    • Alcohol acetyltransferases catalyze the esterification reaction, combining alcohols with acyl-CoA to form esters.

  4. Ester Formation:

Esters like isoamyl acetate (banana aroma) or ethyl butanoate (pineapple aroma) are formed and released into the fermentation medium, contributing to the beverage's aroma.

Types of Esters in Fermentation

Common esters formed during fermentation include:

  • Ethyl acetate: Fruity, pear-like aroma (ethanol + acetyl-CoA).

  • Isoamyl acetate: Banana-like aroma (isoamyl alcohol + acetyl-CoA).

  • Ethyl butanoate: Pineapple, tropical aroma (ethanol + butyryl-CoA).

  • Phenylethyl acetate: Floral, honey-like aroma (phenylethanol + acetyl-CoA).

The IRC7 Gene Pathway: A Key Process in Thiol Release

The IRC7 gene pathway is a specialized metabolic route in yeast, particularly in Saccharomyces cerevisiae, which enables the release of volatile thiols from sulphur-containing compounds. These thiols are potent aromatic compounds that significantly enhance the fruity, floral, and tropical aromas in fermented beverages such as beer and wine. Click here to read the article where we go in-depth about the metabolism of thiol precursors.

FERMOPLUS® AromaGlow enhances the performance of the IRC7 gene pathway by providing essential precursors, nutrients, and a fermentation environment conducive to thiol release.

Key Steps in the IRC7 Gene Pathway

  1. Uptake of Sulfur-Containing Amino Acids

    • Yeast absorbs amino acids like cysteine or their derivatives (e.g., cysteine-S-conjugates) from the wort or must.

    • These compounds serve as the precursors for thiol production.

  2. Cysteine Cleavage by IRC7-Encoded Enzyme

    • The IRC7 gene encodes a beta-lyase enzyme that cleaves sulfur-containing amino acids.

    • This enzymatic activity breaks down cysteine-S-conjugates to release volatile thiols, along with other by-products.

  3. Release of Volatile Thiols

    • Thiols such as 4-mercapto-4-methylpentan-2-one (4-MMP) and 3-mercaptohexanol (3-MH) are released.

    • These thiols contribute intense tropical, citrus, and floral aromas.

Mouthfeel Improvement

A balanced mouthfeel in beer is achieved through the interaction of specific compounds that affect the sensory perception of fullness, smoothness, and harmony in the beverage. In the case of FERMOPLUS® AromaGlow, several key mechanisms contribute to creating this balanced mouthfeel.

The role of Grape Skin Tannins

 Impact on Structure and Astringency: Tannins naturally bind with proteins and other compounds in beer, which helps to moderate astringency and add a sense of structure to the body of the beer. This contributes to a clean, round, and pleasant sensation on the palate.

Stabilization of Polyphenols: These tannins protect against the oxidation of polyphenols, ensuring they contribute positively to the sensory texture. This preservation helps maintain the smooth and rounded feel of the beer.

The role of Yeast Cell Walls and Autolysate

 Polysaccharides and Mannoproteins: The yeast cell walls release mannoproteins and other polysaccharides during fermentation. These compounds increase the viscosity and richness of the beer, adding a creamy texture and enhancing the perception of the body.

 

Improved Protein-Tannin Interactions: The presence of yeast-derived compounds promotes desirable interactions between proteins and tannins, which smooth out rough edges and reduce perceived harshness or bitterness.

 

 Reduction of Harsh By-Products: Autolysates contribute amino acids and peptides that enhance yeast metabolism, reducing the risk of undesirable by-products like excessive higher alcohols, which can negatively impact mouthfeel.

Grape Skin Tannins and Yeast Derivatives in Beer Flavor Stability

Grape skin tannins and yeast derivatives naturally rich in specific amino acids and glutathione improve beer flavour stability by mitigating the effects of oxidation and aging.

What Are Aldehydes, Ketones, and Lactones?

These compounds are by-products of oxidation and aging in beer and can negatively affect its flavour profile:

  • Aldehydes:

    • Examples include acetaldehyde (green apple aroma) and hexanal (grassy aroma).

    • These compounds form when lipids (fats) and polyphenols oxidize, contributing to stale or "papery" off-flavours.

  • Ketones:

    • Examples include diacetyl (buttery aroma) and other oxidative degradation products.

    • They add undesirable buttery, sour, or solvent-like notes.

  • Lactones:

    • While some lactones (e.g., coconut-like aromas) can be desirable in certain contexts, oxidative lactones often create unwanted woody or cardboard-like flavours.

Role of Grape skins on flavour stability.

Polyphenol Stabilization: Grape skin tannins, a type of polyphenol, stabilize other polyphenols in beer by reducing their susceptibility to oxidation. This prevents the formation of aldehydes and ketones that degrade flavour over time.

Antioxidant Properties: Tannins act as natural antioxidants, scavenging oxygen and free radicals that contribute to the oxidation of beer compounds. By limiting oxidation, they preserve the fresh and vibrant flavours of the beer.

Interaction with Proteins: Tannins interact with proteins in beer to create a balanced flavour and texture, which can also shield sensitive compounds from oxidation.

Role of Yeast Derivatives in flavour stability.

Amino Acids: Yeast derivatives supply amino acids that support healthy yeast metabolism during fermentation, reducing the risk of unwanted oxidative compounds being formed.

Glutathione: Glutathione is a powerful antioxidant naturally present in yeast derivatives. It prevents oxidation by Binding to reactive oxygen species (ROS), neutralizing their ability to oxidize other compounds and stabilizing sulphur compounds and thiols, which are highly prone to degradation during oxidation.

Reduction of Off-Flavor Precursors: By reducing oxidative stress in the fermentation environment, yeast derivatives minimize the formation of compounds like acetaldehyde, diacetyl, and stale ketones.

Click here to look at our full range of beer nutrients and bioregulators.

Click here if you’d like to read our previous article on our Fermoplus range of nutrients

Ana Victoria Vasquez de la Peña

ana@neumaker.com.au

24 January 2025

References:

Boulton, C., & Quain, D. (2006). Brewing yeast and fermentation. Wiley-Blackwell.

Hazelwood, L. A., Daran, J. M., van Maris, A. J. A., Pronk, J. T., & Dickinson, J. R. (2008). The Ehrlich pathway for fusel alcohol production: A century of research on Saccharomyces cerevisiae metabolism. Applied and Environmental Microbiology, 74(8), 2259–2266. https://doi.org/10.1128/AEM.02625-07

Howell, K. S., Cozzolino, D., Bartowsky, E. J., Fleet, G. H., & Henschke, P. A. (2006). Metabolic profiling as a tool for revealing Saccharomyces interactions during wine fermentation. FEMS Yeast Research, 6(1), 91–101. https://doi.org/10.1111/j.1567-1364.2005.00015.x

Roland, A., Schneider, R., Razungles, A., & Cavelier, F. (2011). Varietal thiols in wine: Discovery, analysis, and applications. Chemical Reviews, 111(11), 7355–7376. https://doi.org/10.1021/cr100205b

Winter, G., Kromer, J. O., Daran, J. M., & Pronk, J. T. (2014). Enhancement of volatile thiol release of Saccharomyces cerevisiae by expression of various copies of the IRC7 gene. Applied Microbiology and Biotechnology, 98(16), 7545–7556. https://doi.org/10.1007/s00253-014-5896-6

Saerens, S. M. G., Verstrepen, K. J., Van Laere, S. D. M., Voet, A. R. D., Van Dijck, P., Delvaux, F. R., & Thevelein, J. M. (2006). The Saccharomyces cerevisiae acetyl-CoA synthetase-encoding gene ACS2 is essential for optimal ester production during fermentation. Applied and Environmental Microbiology, 72(11), 7130–7136. https://doi.org/10.1128/AEM.01062-06

Pires, E. J., Teixeira, J. A., Brányik, T., & Vicente, A. A. (2014). Yeast: The soul of beer's aroma—A review of flavour-active esters and higher alcohols produced during fermentation. Applied Microbiology and Biotechnology, 98(5), 1937–1949. https://doi.org/10.1007/s00253-013-5470-0

Keyzers, R. A., & Boss, P. K. (2010). Changes in volatile thiols and other aroma compounds during wine fermentation. Journal of Agricultural and Food Chemistry, 58(22), 12360–12365. https://doi.org/10.1021/jf103128y

Maltman, C., & Gramlich, M. (2017). Biotransformation of hop-derived precursors and yeast contributions to beer aromas. Journal of the Institute of Brewing, 123(1), 35–46. https://doi.org/10.1002/jib.389

Furukawa, A., Porcu, T., & Brilli, C. (2024). Aromatic yeast nutrients as beer flavour boosters. AEB Group. [PowerPoint slides].