Press Fractioning of Grape Juice: A First Step to Manage Potential Atypical Aging Development during Winemaking

Abstract

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 most abundant auxin in plants, are considered to be the primary precursors of this compound. 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 contribute directly 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 four different varieties: Cabernet Cantor, Chardonnay, Merlot, and Solaris. Chardonnay (three lots) was analyzed in more depth by evaluating precursor extraction during industrial pressing at different stages. For quantification, this study developed and validated a method using high-performance liquid chromatography coupled with high-resolution mass spectrometry. It used a pre-concentration and purification solid-phase extraction-online system and had a detection limit between 0.25 and 2 µg/L, depending on the compound. Despite significant varietal differences, indole-3-acetic acid was more abundant in seeds and skin fractions. Only ~30% of the total berry amount was extracted with free-run pressing, but ~80% was extracted at 0.6 bar. This suggests a fundamental role of pressing in managing the development of UTA during winemaking.