{"id":1278965,"date":"2026-02-23T17:10:03","date_gmt":"2026-02-23T17:10:03","guid":{"rendered":"https:\/\/www.hopstore.fr\/biotransformation-the-fundamentals\/"},"modified":"2026-07-29T16:09:28","modified_gmt":"2026-07-29T16:09:28","slug":"biotransformation-the-fundamentals","status":"publish","type":"page","link":"https:\/\/www.hopstore.fr\/en\/biotransformation-the-fundamentals\/","title":{"rendered":"Biotransformation: The Fundamentals"},"content":{"rendered":"

[vc_row][vc_column][vc_column_text css=”” woodmart_inline=”no” text_larger=”no”]<\/p>\n

Biotransformation<\/h1>\n

Long considered an intuitive “trade secret”, it is now at the heart of the creation of modern beers, especially NEIPAs and highly aromatic beers.<\/p>\n

In the world of brewing, fermentation is no longer seen simply as the conversion of sugar into alcohol and CO2. It is a veritable chemical laboratory where yeast interacts with hop compounds to create new aromas that did not previously exist. <\/p>\n

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  1. What is biotransformation?<\/strong><\/li>\n<\/ol>\n

    Biotransformation refers to the chemical modification of organic compounds by microorganisms. In beer, this mainly concerns the action of yeast enzymes on two types of molecules derived from hops: terpenes<\/strong> and thiols<\/strong> . <\/p>\n

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    1. Key mechanisms:<\/strong><\/li>\n<\/ol>\n
      \"The<\/a>

      Three biochemical biotransformation processes – HOPSTORE<\/p><\/div>\n

      Terpene alcohol conversion: Reductase<\/strong><\/h3>\n

      Hop oils are rich in geraniol (rose\/floral). During active fermentation, yeast can transform geraniol into citronellol<\/strong> (citrus\/lemongrass). This process radically alters the beer’s aroma profile. <\/p>\n

      This is a modification of the molecular structure. Geraniol<\/strong> (rose-scented) is the main precursor. Under the action of yeast reductases, it undergoes a transformation: <\/p>\n

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      1. Geraniol -> Citronellol:<\/strong> Yeast reduces the double bond of geraniol. Citronellol has a much fresher lemon\/citrus scent. <\/li>\n
      2. Nerol -> Geraniol:<\/strong> Yeast can isomerize nerol into geraniol, increasing the floral potential before transforming it again.<\/li>\n<\/ol>\n

        Glycoside Hydrolysis: Beta-glucosidase<\/strong><\/h3>\n

        Many terpenes are “trapped”: they are bound to a sugar molecule (often glucose). These are called glycosides<\/strong> . In this form, the molecule is too heavy to evaporate (therefore, there is no odor)<\/strong> . <\/p>\n

        Yeast produces an enzyme, beta-glucosidase<\/strong> , which acts like a chemical scissor. It breaks the glycosidic bond, thus releasing the aromatic terpene into the beer. <\/p>\n

        Beta-lyase Release<\/strong><\/h3>\n

        Thiols are organic sulfur compounds. They are responsible for the notes of passion fruit, guava, and boxwood<\/strong> . <\/p>\n

        The mechanism of the precursor linked<\/strong><\/p>\n

        In hops, thiols are mostly present as precursors bound to cysteine<\/strong> \u200b\u200bor glutathione<\/strong> . Example: 3-sulfanylhexan-1-ol<\/em> (3SH) is bound to cysteine \u200b\u200b(Cys-3SH). <\/p>\n

        Yeast comes into play with the enzyme beta-lyase<\/strong> :<\/p>\n

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        1. The yeast absorbs the precursor (Cys-3SH) through its cell membrane.<\/li>\n
        2. The Beta-lyase enzyme breaks the carbon-sulfur bond of cysteine.<\/li>\n
        3. Free thiol (3SH) is released into the must.<\/li>\n<\/ol>\n

          Most strains of Saccharomyces cerevisiae<\/em> possess the gene (IRC7) encoding this enzyme, but it is often “switched off” or inefficient. This is why laboratories select or modify strains. <\/p>\n

          These enzymes are produced by yeast for its own metabolism (often to capture carbon or nitrogen). Once fermentation is complete and the yeast enters dormancy (flocculation), enzyme production drops. This is why dry hopping<\/strong> must take place while the yeast is highly active. <\/p>\n

          <\/strong><\/p>\n

          The chemical balance of the must<\/h1>\n

          The chemical balance of the wort<\/strong> (pH, nutrients) can promote the expression of these specific enzymes: To optimize these organic chemistry reactions, the brewer must act on the physico-chemical environment in the fermenter.<\/p>\n

          Yeast is a complex biological machine: its enzymes only function optimally under certain conditions of pH, temperature and availability of co-factors.<\/p>\n

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          1. \n

            The influence of pH on enzyme activity<\/strong><\/h3>\n<\/li>\n<\/ol>\n

            The pH of the must changes drastically during fermentation (from ~5.2 to ~4.2). However, each enzyme involved in biotransformation has a catalytic optimum<\/strong> : <\/p>\n