Press fractioning of grape juice: a first step to manage potential atypical aging development during winemaking

The development in young white wines of 2-aminoacetophenone, commonly known as atypical aging defect (UTA), leads to unpleasant notes such as mothball, wet mop, sweaty, acacia blossom or soap. Tryptophan and indole-3-acetic acid, the auxin most present in plants, are considered the main precursors of this compound. Also indole-3-acetonitrile, indole-3-lactic acid, skatole, tryptophol and the inactivated form of the auxin, N-(3-indolylacetyl)-L-alanine, N-(3-indolylacetyl)-DL-aspartic acid and methyl-indole-3-acetate, can act as potential precursors of 2-aminoacetophenone and directly contribute to UTA scents in wines. This paper investigates the distribution of 2-aminoacetophenone precursors or intermediate metabolites (n=9) in grape berry tissues (pulp, skin and seeds) in 12 samples of 4 different varieties (Cabernet Cantor, Chardonnay, Merlot, and Solaris). The issue regarding Chardonnay (3 lots) was analyzed more in depth by evaluating the precursor extraction of industrial pressing at different stages. For the quantification, this study developed and validated a high performance liquid chromatography coupled with a high-resolution mass spectrometry method. Owing to the use of a pre-concentration and purification SPE-online system, a detection limit was detected between 0.25 and 2 µg/L, depending on the compound. Despite significant varietal differences, the research showed that indole-3-acetic acid is more present in seeds and skin fractions. Indeed, only ~30% of the total berry amount were extracted with free run pressing, whereas ~80% were reached with 0.6 bar. This indicates a fundamental role of pressing in managing the development of UTA during winemaking