What is grape seed extract, and what is in it?

Grape seed extract is made from the seeds of wine grapes, Vitis vinifera. The seeds are mostly a by-product of winemaking, left over in the pomace after the grapes are pressed. The main compounds in the extract are proanthocyanidins, chains built from small units such as catechin and epicatechin. How much of them a seed contains depends on the grape variety, the year and how the vines were grown.

In short:

• What it is: an extract of the seeds of wine grapes (Vitis vinifera)
• Where the seeds come from: mainly the pomace left over from winemaking
• Main compounds: proanthocyanidins (also called condensed tannins), plus catechin, epicatechin and gallic acid
• What changes the amounts: grape variety, harvest year, ripeness and water supply to the vines
• Daily value: none in the Thai RDIs
• Watch out for: little is known about use in pregnancy or breastfeeding; anyone on regular medication should ask a doctor or pharmacist

What is grape seed extract?

NCCIH, part of the US National Institutes of Health, says grape seed extract is made from the seeds of wine grapes and gives its Latin name as Vitis vinifera. Memorial Sloan Kettering describes it as containing proanthocyanidins and minor phenolic compounds, which also occur naturally in many foods.

Which plants are used?

Vitis vinifera is the common grape used for wine and also eaten as fresh grapes (องุ่น in Thai). Memorial Sloan Kettering lists three scientific names under grape seed: Vitis vinifera, Vitis coignetiae and Vitis rotundifolia, and gives "grape seed oil", "grape seed extract" and "muskat" as common names.

Where do grape seeds come from?

Most come from wineries. A 2022 study by Salem and colleagues in Plants explains that every stage of winemaking leaves residues. The organic part includes grape pomace, which holds the seeds, pulp and skins, as well as stems and leaves. Winemaking produces 1.3 to 1.5 kg of waste for every litre of wine, about 75% of it wastewater. The researchers describe grape seeds as the main by-product of wineries, and note that much of the pomace still ends up in ponds and landfills.

What is inside a grape seed?

Salem and colleagues worked with seeds from the pomace of two traditional Lebanese grape varieties, Obeidi (white) and Asswad Karech (red), and separated them step by step into oil, polyphenols and protein.

Source: Salem and colleagues (2022). The same paper notes that grape seeds also contain carbohydrates, with glucose the most abundant. The figures come from two varieties grown in one country and show the order of size, not a fixed recipe for every grape seed.

What fats are in grape seed oil?

Grape seeds also yield an oil, known as grape seed oil. Salem and colleagues summarise its fatty acids from earlier studies:

What are proanthocyanidins (OPCs)?

Proanthocyanidins are the group of compounds most associated with grape seeds. They are also called condensed tannins: Wang and colleagues (2023) note that the condensed tannins in wine come from grape seeds and skins and contribute to its bitterness and astringency.

What are they made of?

A 2017 study by Kyraleou and colleagues in Molecules explains that grape tannins are polymers built from small units called flavan-3-ols, mainly catechin, epicatechin, epicatechin gallate and epigallocatechin, linked through carbon-carbon bonds (C4–C6 or C4–C8). The units at the end of a chain are called terminal units, and those in between are extension units.

Sources: formulas and weights from PubChem; structure from Kyraleou and colleagues (2017).

What does "degree of polymerisation" mean?

It is the number of units in a chain. Researchers usually report the mean degree of polymerisation (mDP), the average chain length in a sample. A 2004 study by Gu and colleagues at the US Department of Agriculture grouped the proanthocyanidins in the American diet by size: monomers made up 7.1%, dimers 11.2%, trimers 7.8% and larger chains 73.9%.

How do seed tannins differ from skin tannins?

Kyraleou and colleagues (2017) summarise the differences found in grape research:

In their own study of Syrah grapes, the larger seed tannins (mDP above 6) had less galloylation, while high galloylation was seen only in monomers, dimers and trimers.

Do grape seeds from different varieties and years differ?

Yes, noticeably. A study by Sochorova and colleagues at Mendel University (2020) measured total polyphenols in the seeds of 10 grape varieties grown around the university's viticulture institute in the Czech Republic, over three harvests (2015, 2016 and 2017).

Seeds from dark-skinned (blue) varieties had higher values than seeds from white varieties, and the highest values came in 2017. The researchers also measured 14 individual compounds in 2015. Across the varieties, the averages included gallic acid at 225.4 µg per gram of dry matter, catechin at 181.3 µg per gram and epicatechin at 138.2 µg per gram. The limits of this study: the grapes came from one area of the Czech Republic, and total polyphenols were measured with the Folin–Ciocalteu method, which gives a combined figure rather than separate compounds. The authors note that comparing results between studies is difficult because varieties, years, ripeness, drying and test methods differ.

Does ripeness or water supply change the seeds?

It can change the make-up of the tannins. Kyraleou and colleagues (2017) studied Syrah grapes grown in a semi-arid climate under three watering levels over the 2011 and 2012 seasons. The total amount of seed tannin did not change as the grapes ripened, but the seeds of fully watered vines had more flavan-3-ol monomers and tannin oligomers in both years.

Wang and colleagues (2023) followed Cabernet Sauvignon seeds from two vineyards over two years. The soluble tannins in the seeds drifted slightly downward as the berries developed, while the insoluble tannins rose before the berries began to change colour and stayed high afterwards. Epigallocatechin gallate, which dominated the end units of the soluble tannins, fell as the seeds matured; the researchers link it to bitterness.

Which foods contain proanthocyanidins?

Proanthocyanidins are not unique to grape seeds. Gu and colleagues (2004) analysed common foods in the United States and, combining their results with a national food survey from 1994–1996, estimated that people over 2 years old in the US eat about 57.7 mg of proanthocyanidins a day. The main sources were apples (32.0%), chocolate (17.9%) and grapes (17.8%). The study reflects the American diet, not the Thai one.

Proanthocyanidins belong to the flavonoid family. For more on how flavonoids are grouped, see which foods contain quercetin?

Are procyanidins found in Thai plants?

Yes. A 2025 study by Potijun and colleagues at Chulalongkorn University looked at durian flowers, which durian trees produce in large numbers but which do not all develop into fruit. The researchers identified epicatechin and procyanidins B1, B2 and C1 in the flowers. An 80% ethanol extract had a total procyanidin content of 7.68 mg per gram of crude extract. This shows that the same group of compounds is found in a plant grown widely in Thailand.

Is there a recommended daily amount of grape seed extract?

No. Grape seed extract and proanthocyanidins are not nutrients in the Thai Reference Daily Intakes (Thai RDIs), which cover nutrients such as vitamins and minerals, so there is no Thai daily value for them. As shown above, the amount of polyphenols in grape seeds also differs from variety to variety and from year to year.

Who should be careful with grape seed extract?

People who are pregnant or breastfeeding

NCCIH says little is known about the use of grape seed extract during pregnancy or while breastfeeding.

People taking regular medication

NCCIH advises anyone who takes any type of medicine to talk with their health care provider before using grape seed extract or other herbal products, because some herbs and medicines interact in harmful ways. Memorial Sloan Kettering also notes that grape seed extract may interact with some medicines. Anyone taking regular medication should speak to a doctor or pharmacist.

Effects that can occur

NCCIH says grape seed extract is generally well tolerated when taken by mouth. Memorial Sloan Kettering notes possible stomach upset.

If you are pregnant, breastfeeding, take regular medication or are under a doctor's care, speak to a doctor or pharmacist before taking dietary supplements.

Dietary supplements are not intended to prevent, treat or cure any disease.