Proportional Mass of Seeds in the Grape Crop
From the perspective of quantitative analysis and evaluation of raw material processing yields, the total mass of seeds accounts for 2% to 6% of the aggregate weight of ripe grape berries. When considered in relation to the weight of the entire grape cluster (including the mass of the peduncle and all branches of the rachis), this indicator fluctuates between 1.5% and 4%, depending on the biological characteristics of the specific variety. The proportion of seeds in the overall volume of the harvested crop is directly influenced by pollination conditions during the flowering period, as well as the susceptibility of the specific variety to millerandage (shot berries), which substantially reduces the average number of fully formed seeds per cluster.
Biochemical Profile of Grape Seeds
The study of the precise chemical composition of grape seeds has formed the basis of many fundamental scientific investigations in the fields of plant physiology and enology. The most authoritative and detailed works in this area are recognized as the classic studies by researchers A. Girard and L. Lindet. Based on a series of precise laboratory analyses, they identified patterns in the distribution of key chemical components and recorded significant variations in the biochemical composition of seeds across different cultivated grape varieties.
The consolidated analytical data from Girard and Lindet, reflecting the percentage content of major substances within the seed mass for leading grape varieties, are presented in the following table:
| Grape Variety | Water, % | Fixed Oil, % | Volatile Acids*, % | Tannins (Tannic Matter), % | Resinous and Gummy Matter, % | Lignin (Woody Fiber), % | Mineral Matter (Ash), % |
|---|---|---|---|---|---|---|---|
| Aramon | 38.82 | 6.92 | 0.57 | 2.56 | 4.45 | 48.82 | 1.86 |
| Carignane | 33.28 | 7.81 | 0.81 | 0.31 | 1.35 | 54.66 | 1.78 |
| Petit-Bouschet | 38.02 | 4.48 | — | 2.26 | 4.07 | 49.41 | 1.76 |
| Piquepoul | 31.31 | 8.81 | 0.64 | 0.81 | 1.40 | 55.66 | 1.33 |
| Pinot | 29.54 | 7.98 | 1.04 | 4.17 | 5.40 | 50.12 | 1.75 |
*Note: The concentration of volatile acids is calculated in terms of sulfuric acid equivalent.
The second half of the varietal analyses by Girard and Lindet covers equally important technical varieties, demonstrating a unique biochemical balance of tannic substances and lignin characteristic of each individual grape variety:
| Grape Variety | Water, % | Fixed Oil, % | Volatile Acids*, % | Tannins (Tannic Matter), % | Resinous and Gummy Matter, % | Lignin (Woody Fiber), % | Mineral Matter (Ash), % |
|---|---|---|---|---|---|---|---|
| Gamay | 36.46 | 5.56 | 0.82 | 2.62 | 3.17 | 49.50 | 1.87 |
| Chardonnay | 39.49 | 7.38 | 0.55 | 2.06 | 6.39 | 42.39 | 1.74 |
| César | 29.38 | 7.20 | 0.70 | 5.56 | 6.62 | 48.57 | 1.97 |
| Cabernet-Sauvignon | 32.80 | 7.25 | 0.72 | 1.81 | 3.35 | 52.38 | 1.69 |
| Merlot | 32.28 | 5.92 | — | 2.62 | 1.50 | 55.99 | 1.69 |
*Note: The concentration of volatile acids is calculated in terms of sulfuric acid equivalent.
Grape Seed Oil and Its Technological Potential
Additional chemical analyses indicate that the concentration of fixed oil in the seeds of certain grape varieties can reach 10% to 12% of their total dry weight. Historically, the extraction of this oil was carried out in significant volumes for subsequent practical application. In large wine-producing regions with high volumes of secondary raw material processing (grape pomace), the large-scale extraction of grape seed oil can serve as an important and economically efficient element of waste-free production.
The Role of Grape Seed Oil and Seed Tannins in Winemaking
Fixed oil localized within the grape seed possesses unique physicochemical properties that dictate the nature of its interaction with the wine material. During alcoholic fermentation and subsequent technological processing of the must, this oil does not dissolve in the liquid medium and is fundamentally incapable of blending with the wine. However, its biological role in shaping the organoleptic profile of the beverage is realized through an entirely different pathway.
Following the passage of the berry into the stage of veraison (the onset of ripening), processes of partial oxidation of fixed oils are triggered within the seed, resulting in the formation of specific related volatile acids. It is precisely these oxidation products that possess the ability to dissolve and pass into the wine in a small proportion. During subsequent long-term aging, these volatile components enter into biochemical interactions with other elements of the young wine, exerting a direct and profound influence on the maturation, development, and refinement of the varietal bouquet.
The second highly valuable product contained within the seeds, capable of yielding immense benefits in the winemaking process, is tannins (tannic matter). During fermentation, their partial dissolution and extraction proceed under the influence of alcohol and heat. Upon transferring into the must, seed tannins act as powerful natural antioxidants, shaping the structure, fullness of flavor (the "body" of the wine), and its potential for long-term storage, while also ensuring its natural stability and high potential for multi-year aging.
Historical validation of the high efficiency of utilizing this resource is found in the traditional winemaking practices of Burgundy. In this prestigious region, from very ancient times, practical winemakers purposefully applied pure alcoholic extracts obtained from grape seeds to enrich noble wines with soluble phenolic compounds. The authors of the original academic work emphasize that this Burgundian experience deserves a more constant, systemic, and widespread implementation in commercial winemaking across all large wine estates.
Conducted research clearly proves that the nature of a specific grape variety exerts a determining influence on the final concentration of oil and tannic substances in the processing by-products. At the same time, the authors establish a distinct pattern: it is precisely the red technical grape varieties that possess seeds most rich in active tannins. This factor is of decisive importance when calculating the phenolic maturity of the crop and directly predetermines the leading role of seed components in establishing the structure and varietal character of finished red wines.