Technical Yearbook 2023

AUGUST

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Fruit salad vs varnish – nitrogen sources and their impact on aroma production in wine By James Duncan & Benoit Divol Understanding the impact and differences of amino acids versus ammonium to produce aroma compounds can help winemakers optimise their processes and produce high-quality wines with desired aromatic profiles. Yeasts’ metabolism of some nitrogenous compounds can contribute aromas to the wine that include chemical and delicate fruit – think varnish versus a summer fruit salad.

Nitrogen is a key element necessary for synthesising amino acids, nucleic acids, vitamins and various other compounds in living organisms, including wine yeasts. It is present in various compounds in grape juice, including ammonium, amino acids, nitrates, peptides and proteins. Nevertheless, wine yeasts can only make use of two sources of yeast assimilable nitrogen (YAN) for their metabolism and growth, namely, amino acids (organic nitrogen) and ammonium (inorganic nitrogen). The uptake of these

nitrogen sources is subject to complex regulatory processes, and the timing and order of uptake vary significantly depending on the yeast species, strains and also on environmental conditions. During wine fermentation, the skeleton of selected amino acids may be used by the yeasts to produce aromas (i.e., the so-called “fermentative” or “secondary” aromas). Alternatively, yeasts can make some of these aromas “from scratch” (i.e., from the breakdown of sugars).

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TECHNICAL YEARBOOK 2023