Grapes

TL;DR. Every wine grape in the world grows on American roots, because an aphid called phylloxera destroyed European viticulture in the 1870s and grafting onto resistant American rootstock was the only cure. Table grapes are a high-sugar, low-fibre fruit whose main interest is the polyphenols in the skin and seeds. Resveratrol, the compound that made grapes famous, is present in quantities far too small to matter and its research literature was damaged by a major fraud case. Raisins are grapes with the water removed, which concentrates everything including sugar by a factor of about four.

1. What it is

Vitis vinifera, the Eurasian grape, plus American species (V. labrusca, V. rotundifolia) and hybrids. Family Vitaceae. A woody, deciduous, climbing liana that in the wild reaches the forest canopy and in cultivation is kept to a metre or two by relentless pruning.

The fruit is a true berry, borne in bunches. Three commercial categories, and they are genuinely different products:

• Table grapes: large berries, thin skin, often seedless, low acid, harvested at moderate sugar.
• Wine grapes: small berries, thick skin, high skin-to-juice ratio (because skin is where colour, tannin, and aroma live), high sugar at harvest, seeded.
• Raisin grapes: high sugar, thin skin, seedless. Thompson Seedless (Sultana) dominates.

2. Where it comes from

Origin: the South Caucasus, in the region of modern Georgia, Armenia, and northern Iran. Archaeological evidence for winemaking in Georgia dates to around 6000 BCE, making it one of the oldest processed foods. A large 2023 genomic study in Science found evidence for two independent domestication events, in Western Asia and the Caucasus, around 11,000 years ago.

The vine spread with Phoenician, Greek, and Roman expansion, and viticulture became a defining feature of Mediterranean agriculture and later of monastic economies. European colonists took it worldwide from the sixteenth century.

The phylloxera catastrophe. In the 1860s, Daktulosphaira vitifoliae, a root-feeding aphid native to eastern North America, arrived in France on imported vines. European V. vinifera had no resistance. Within about twenty-five years it destroyed the majority of French vineyards and spread across Europe. After enormous argument between the "chemists" (who wanted an insecticide) and the "Americanists" (who wanted grafting), the solution was grafting European scions onto American rootstocks that had co-evolved with the pest. Every significant wine region replanted. Essentially all wine grapes today grow on American roots, with a handful of exceptions on sandy soils where phylloxera cannot survive (Chapter 5).

Production: roughly 75 to 80 million tonnes a year, of which around half goes to wine. China is the largest producer overall and overwhelmingly the largest table grape producer; Italy, Spain, and France dominate wine; Chile, Peru, South Africa, and the US are the major table grape exporters; Turkey, the US, and Iran lead in raisins.

3. How it is grown

Climate. Grapes want a Mediterranean profile: mild wet winters, hot dry summers. Dry summers matter enormously because grape fungal diseases (powdery mildew, downy mildew, botrytis) thrive on wet foliage. Chilling requirement is modest (around 100 to 500 hours) but real. Frost at bud break destroys the crop. The classic wine climates sit in narrow latitude bands (roughly 30 to 50 degrees) and the effect of climate change on those bands is one of the most closely watched agricultural stories in Europe.

Soil. Famously, vines do well on poor soil. Deep, fertile soil produces vigorous vegetative growth and diluted fruit; stony, well-drained, low-fertility soil restricts vigour and concentrates the berry. Gravel, chalk, slate, and volcanic soils are all prized. Drainage matters more than fertility.

The vine year.

1. Winter pruning, the defining operation. A vine left alone produces enormous quantities of poor fruit; pruning to a set number of buds decides the crop level. Two systems: cane pruning (Guyot), retaining one or two long canes, and spur pruning (cordon), retaining short spurs on a permanent arm.
2. Bud break in spring, and the frost risk window.
3. Flowering and fruit set in early summer. Grapes are self-fertile and wind-pollinated, which spares them the pollination anxieties of tree fruit.
4. Canopy management: shoot positioning, leaf removal around the bunches for airflow and sun exposure, hedging. This is where disease pressure and fruit quality are decided.
5. Véraison, the moment the berries stop growing green and start colouring and accumulating sugar, typically mid-summer. Everything from here is ripening.
6. Green harvest in quality wine production: deliberately dropping a portion of the crop to concentrate the rest.
7. Harvest, timed by sugar (measured in degrees Brix), acidity, pH, and phenolic ripeness.

Regulated deficit irrigation is one of the few cases in agriculture where water is deliberately withheld: mild water stress after fruit set reduces berry size, raising the skin-to-juice ratio, and concentrates sugars and phenolics. Overwatered vines make dilute wine.

Table grape specifics: bunches are thinned by hand, sometimes berry by berry, to achieve uniform large berries. Gibberellic acid is routinely applied to seedless varieties to enlarge berries and elongate bunches, because seedless grapes lack the seed-derived hormones that drive berry growth. Girdling (removing a ring of bark) is also used. Table grapes are packed in the field into the final consumer bag with a sulphur dioxide generator pad, which suppresses botrytis in transit and is why table grapes ship so well.

Rain at harvest splits berries and triggers rot, which is why the great wine vintages correlate with dry Septembers.

4. What is inside it

Per 100 g of raw grapes:

Raisins, per 100 g: 299 kcal, 79 g carbohydrate, 59 g sugar, 3.7 g fibre, 749 mg potassium, 1.9 mg iron. About four times as concentrated as fresh, which is exactly what removing the water does.

Grapes are among the higher-sugar, lower-fibre fruits, which is worth knowing. A 150 g portion carries roughly 24 g of sugar, comparable to a small chocolate bar, with the important differences that it arrives inside cell walls with water and polyphenols.

Where the interest is:

• Skins: anthocyanins (red and black varieties), flavonols including quercetin, and resveratrol, a stilbene produced as a defence against fungal attack, which is why organically grown and disease-pressured grapes have more.
• Seeds: proanthocyanidins, at high concentration. Grape seed extract is a supplement built on this.
• Flesh: essentially just sugar, water, acid (tartaric and malic), and potassium.

So a seedless, thin-skinned, pale table grape is nutritionally close to sugar water, while a thick-skinned, seeded, dark grape delivers a substantial polyphenol load. That distinction matters more than any grape-versus-other-fruit comparison.

5. What it does in your body

High glycaemic load for a fruit, though the glycaemic index is moderate at 45 to 60. The sugar arrives quickly compared with an apple, because there is very little fibre to slow it.

Polyphenols from skins and seeds have shown modest effects in trials on blood pressure and endothelial function. Grape seed extract has small blood pressure reductions in meta-analyses, in the range of a few mmHg.

Resveratrol deserves its deflation here. A glass of red wine contains roughly 0.3 to 1.5 mg. The mouse studies showing metabolic and lifespan effects used doses equivalent to hundreds of milligrams to grams per day in a human. Achieving those levels from wine would require drinking a lethal quantity many times over. Compounding this, the field suffered a major research integrity failure when a prominent resveratrol researcher was found by his university to have falsified data across dozens of papers, which were retracted. Human trials of resveratrol supplements have not shown meaningful benefit. It is the clearest cautionary tale about a compound whose reputation ran far ahead of its evidence.

The "French paradox" that resveratrol was invoked to explain (relatively low coronary heart disease in France despite high saturated fat intake) is now largely attributed to differences in death certification practices, delayed effects of historical diet changes, and overall dietary pattern, rather than to any compound in wine.

6. What the evidence actually shows

Established: grapes and raisins provide sugar, potassium, and, in dark varieties, substantial polyphenols. Sulphite treatment of table grapes and dried fruit is real and matters to sulphite-sensitive people.

Strong: whole fruit intake, including grapes, is part of the general association with lower cardiovascular risk.

Mixed: grape polyphenol effects on blood pressure and endothelial function, which are small. Raisins for blood pressure and glycaemic control, where small trials show modest benefits.

Thin to negative: resveratrol for anything in humans. Grape seed extract beyond modest blood pressure effects. Any specific anti-cancer claim.

On wine specifically, which is covered fully in Chapter 61: the long-held belief that moderate drinking protects the heart has weakened substantially. Studies correcting for the "sick quitter" problem (former drinkers who stopped because of illness being counted as abstainers) and Mendelian randomisation analyses using genetic variants in alcohol metabolism find little or no cardiovascular benefit and clear harm for cancer at any level. Whatever is good in grapes is available from eating grapes.

7. Who should eat more, who should be careful

Good for: most people, as one of several fruits. Dark, thick-skinned, seeded varieties are the better choice nutritionally.

Be careful if:

• You are managing blood glucose. Grapes are high-sugar and low-fibre. Portion matters, and they are easy to eat in quantity because there is no natural stopping point in a bunch.
• You have a sulphite sensitivity, which overlaps heavily with asthma. Table grapes are shipped with sulphur dioxide pads, and dried fruit is commonly sulphited (golden raisins and bright orange apricots are; dark ones are not). Reactions range from wheeze to, rarely, serious bronchospasm.
• You take warfarin. Grapes are moderately high in vitamin K; consistency matters more than avoidance.
• You have IBS. Grapes are low-FODMAP in normal portions. Raisins are high-FODMAP because of the concentration.
• You own a dog. Grapes and raisins cause acute kidney failure in dogs, at unpredictable doses, through a mechanism only recently identified as likely tartaric acid toxicity. This is one of the most important pieces of household food safety knowledge that has nothing to do with humans.

Ages. Whole grapes are one of the leading causes of fatal food choking in young children, because they are exactly the diameter of a small airway and their smooth, compressible shape forms a perfect seal. Cut them lengthways into quarters for children under about 5. This is worth more than everything else in this chapter.

8. When and how to eat it

• Eat the skin and the seeds, where nearly all the polyphenols are. Seeded grapes are better food than seedless ones, which is an inconvenient fact given what the market sells.
• Portion deliberately. Put a portion in a bowl rather than eating from the bunch.
• Pair with cheese or nuts to slow absorption, which happens to be the traditional pairing for other reasons.
• Freeze them. Frozen grapes are an excellent slow-eaten snack and the freezing forces small bites.
• Raisins on teeth are a genuine dental issue: sticky, sugary, and slow to clear. Eat them with a meal rather than as a grazing snack.
• Wash them. Table grapes carry residues and the sulphite pad dust. Rinse and rub.

9. Choosing, storing, and ripening

Choosing. Grapes are non-climacteric and will not sweeten after picking.

• The stems should be green and flexible, not brown and brittle. This is the single most reliable freshness test.
• The bloom (that dusty white coating) is a natural wax and a sign the grapes have not been handled. Do not choose shiny, rubbed grapes.
• Berries firmly attached. If they fall off when you lift the bunch, they are old.
• Colour: green grapes with a slight yellow cast are riper and sweeter than uniformly green ones. Red and black grapes should be deeply and uniformly coloured.

Storing. Fridge, unwashed, in the perforated bag they came in, in the coldest part. They hold 1 to 2 weeks, which is exceptional among berries and is largely thanks to the sulphite pad. Wash only at the point of eating. They absorb odours, so keep them away from onions.

10. The varieties worth knowing

Table grapes:

Wine grapes worth naming because their names appear on bottles: Cabernet Sauvignon (a 1600s spontaneous cross of Cabernet Franc and Sauvignon Blanc, confirmed by DNA in 1996), Merlot, Pinot Noir, Syrah, Tempranillo, Sangiovese, Chardonnay, Sauvignon Blanc, Riesling. There are around 10,000 named wine grape varieties and roughly a dozen dominate global plantings, which is a diversity problem of the same shape as the banana's.

Raisin types: raisins (dried dark, usually Thompson), sultanas (dried Thompson, treated to stay golden), currants (dried Black Corinth, small and tart, unrelated to blackcurrants and a persistent source of confusion).

11. Myths and confusions

Don't be confused: dried currants, blackcurrants, and redcurrants are three different things. Dried currants are tiny raisins from the Black Corinth grape, named after Corinth. Black and redcurrants are Ribes berries and unrelated. Recipes that call for "currants" in baking almost always mean the raisins.

• "Red wine is good for your heart because of resveratrol." The dose is negligible and the cardiovascular benefit of moderate drinking has largely dissolved under better methods.
• "Grape seed extract is a proven supplement." Modest blood pressure effects at best.
• "Grapes are too sugary to be healthy." They are high-sugar for a fruit and still whole fruit, with skin polyphenols and water. Portion, do not avoid.
• "The white coating on grapes is pesticide." It is the natural bloom, a wax the plant produces, and it indicates good handling.
• "Seedless grapes are genetically modified." They are not. Seedlessness arose by natural mutation (stenospermocarpy: the seed begins to form and aborts) and is propagated by cutting, which humans have done for centuries.

12. The bottom line

• Grapes are one of the oldest domesticated crops and the only major one whose entire cultivated population sits on grafted foreign roots, because of an aphid.
• Nutritionally they are high-sugar and low-fibre, and the value is in the skins and seeds. Dark, thick-skinned, seeded grapes are meaningfully better food than pale seedless ones.
• Resveratrol is present in doses far below anything shown to do anything, and its research literature was damaged by fraud. It is the clearest superfood cautionary tale in the book.
• Raisins are grapes at roughly four times the concentration, including four times the sugar, and they are sticky on teeth.
• Cut grapes lengthways for young children. They are a leading cause of fatal choking. And keep grapes and raisins away from dogs entirely.

Sources and notes

Composition figures are from USDA FoodData Central; production figures are approximate FAOSTAT values for the early 2020s. Grape domestication follows Dong et al., Science, 2023, which found two independent domestication events. Phylloxera history and the grafting solution follow Campbell, Phylloxera, 2004, and Gale, Dying on the Vine, 2011. Viticulture practice, regulated deficit irrigation, and gibberellic acid use on seedless table grapes follow UC Davis and Australian viticulture extension publications. Sulphur dioxide pads in table grape shipping are industry standard and are the basis of the sulphite declaration requirement. Resveratrol content in wine and the doses used in animal studies follow Baur and Sinclair's work and its critiques; the research misconduct case is the University of Connecticut investigation and the resulting retractions. The French paradox reassessment follows Law and Wald, BMJ, 1999. Grape seed extract and blood pressure follows meta-analyses by Feringa et al. Grape and raisin nephrotoxicity in dogs follows ASPCA Animal Poison Control reporting, with tartaric acid identified as the likely agent in 2021.

Open questions. Why some dogs are affected by grapes and others are not remains unexplained even with tartaric acid as the leading candidate. Whether grape polyphenols do anything meaningful at dietary intakes, as opposed to extract doses, is not established.

👉 Next: stone fruit: peaches, plums, cherries, apricots, and the family that carries cyanide in its seeds.