Seeds

Seeds, also referred to as pips, are one of the structural components of the grape berry and play an important role in both grape development and wine composition, primarily through their contribution of phenolic compounds and tannins.^[1]

Botanical role

Grape seeds are the reproductive organs of the berry, typically numbering between one and four per grape depending on variety and pollination success.^[2] Their primary biological function is to protect and disperse genetic material, supported by a hard outer coat that becomes lignified during ripening.

Seed development is closely linked to berry growth, and the number and size of seeds influence berry size, shape and skin-to-pulp ratio.

Chemical composition

Seeds are rich in phenolic compounds, particularly flavan-3-ols and proanthocyanidins, which form a major source of tannins in red wine.^[3] Compared with skin-derived tannins, seed tannins tend to be more bitter and astringent, especially when extracted before full phenolic maturity.

In addition to tannins, seeds contain lipids, proteins and trace minerals, although these components are generally of limited oenological significance.

Seed maturity

The sensory impact of seed tannins is strongly influenced by seed ripeness. As seeds mature, their colour typically changes from green to brown, and their tannins become less harsh and more polymerised.^[4]

Assessment of seed maturity, through visual inspection and tasting, is often used by growers and winemakers as an indicator of phenolic ripeness when determining harvest timing.

Role in winemaking

During fermentation and maceration, seed tannins are extracted into the must through physical contact and alcohol-mediated solubilisation. Extended maceration or aggressive cap management can increase seed tannin extraction, potentially leading to bitterness and excessive astringency if not carefully managed.^[5]

[[Winemaking techniques]] such as gentle pressing, reduced pump-overs, or early seed removal may be employed to limit seed-derived phenolics, particularly in varieties prone to harsh tannins.

Analytical and regulatory context

Seed tannins are a recognised component of total grape and wine phenolics and are included in analytical frameworks for phenolic assessment.^[6] Laboratory methods for measuring seed-derived compounds are well established and form part of standard must and wine analysis.^[7]

Research institutions continue to study the relationship between seed development, extraction kinetics and wine style, particularly in relation to harvest decisions and maceration strategies.^[8]

References

↑ Robinson (ed.), The Oxford Companion to Wine, Oxford University Press, 2015, ISBN 978-0198705383.
↑ Keller, The Science of Grapevines, Academic Press, 2015, ISBN 978-0124199873.
↑ Jackson, Wine Science, Academic Press, 2020, ISBN 978-0128161180.
↑ Ribéreau-Gayon et al., Handbook of Enology, Vol. 2, Wiley, 2006, ISBN 978-0470010396.
↑ Waterhouse et al., Understanding Wine Chemistry, Wiley, 2016, ISBN 978-1118627808.
↑ OIV, “Phenolic compounds in grapes”. ISBN 9781800627048.
↑ Amerine & Ough, Methods for Analysis of Musts and Wines, Wiley, 1980, ISBN 978-0471036732.
↑ UC Davis, “Seed tannins and extraction”.

[1] Robinson (ed.), The Oxford Companion to Wine, Oxford University Press, 2015, ISBN 978-0198705383.

[2] Keller, The Science of Grapevines, Academic Press, 2015, ISBN 978-0124199873.

[3] Jackson, Wine Science, Academic Press, 2020, ISBN 978-0128161180.

[4] Ribéreau-Gayon et al., Handbook of Enology, Vol. 2, Wiley, 2006, ISBN 978-0470010396.

[5] Waterhouse et al., Understanding Wine Chemistry, Wiley, 2016, ISBN 978-1118627808.

[6] OIV, “Phenolic compounds in grapes”. ISBN 9781800627048.

[7] Amerine & Ough, Methods for Analysis of Musts and Wines, Wiley, 1980, ISBN 978-0471036732.

[8] UC Davis, “Seed tannins and extraction”.

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