Beyond oak: impacts of juniper versus oak on red‑wine colour, phenolic composition, and volatiles

Abstract

Wood ageing remains one of the most fascinating processes in winemaking. Wood can act as a catalyst for wine quality through the release of volatile and non‑volatile constituents. Historically, a range of species has been employed according to local availability, most notably oak, but also chestnut and walnut. In recent years, novel woods have entered practice together with diversified formats and toasting regimes. While the medium‑toast barrique endures as the gold standard, modular formats (e.g., staves, chips, shavings) allow more practical, scalable and, in many cases, more sustainable solutions. Untoasted or lightly toasted woods are also increasingly adopted to better preserve the wine matrix, especially its aroma profile. In parallel, new botanical species (e.g., acacia, mulberry) are gaining attention for their distinctive impacts on wine attributes, enabling trials with woods unsuited to cooperage and opening new oenological possibilities. This study evaluated juniper (Juniperus communis) for the treatment of red wines, a Mediterranean species never previously applied to wine, though traditional in the ageing of Italian balsamic vinegar. Juniperus species are among the greatest accumulators of terpenoids in the plant kingdom. Two formats (cubes and shavings) at the same 4 g/L dose were added to Pinot noir and Merlot for 1, 2, 4, 6, 10, and 14 weeks. In parallel, the same wines were treated with untoasted French oak or no wood, providing positive and negative controls. Conventional spectrophotometric assays for polyphenols and colour (CIELab and anthocyanin classes per Boulton) were coupled by UHPLC–qTOF–IMS for non‑volatiles (ca. 350 identified compounds) and GC×GC–MS for volatiles (ca. 140 identified molecules); identical analyses were performed on wood extracts to test effects in the absence of the wine matrix. The most pronounced effects concerned wine pigments and volatiles. Despite pigments being present in juniper wood, no direct transfer to wines was detected; nevertheless, wood contact consistently promoted chromatic evolution and stabilisation of the colour compounds. Volatile composition exhibited species‑specific and format‑dependent signatures, with relevant release of sesquiterpenes and terpenes in juniper samples, differentiating juniper from oak and cubes from chips. Overall, juniper additions modulated colour development as for oak, but conferred a distinctive volatile fingerprint, expanding the array of woods available to oenology.