Raisins are dried grapes. Most commercially sold raisins come from seedless grape varieties grown in hot, dry climates, where the fruit is either sun-dried in vineyards or mechanically dehydrated after harvest. It takes about 4 to 4.5 pounds of fresh grapes to produce a single pound of raisins, which is why their flavor and nutrients are so concentrated compared to the original fruit.
The Grapes Behind the Raisin
Of the thousands of domesticated grape varieties in the world, only a handful are used for raisin production. The dominant variety is Thompson Seedless, also known as Sultanina. This grape is small, pale green, naturally seedless, and high in sugar, all traits that make it ideal for drying. Its thin skin allows moisture to escape quickly, and its sweetness intensifies as water evaporates. Most dark raisins you find in grocery stores started as Thompson Seedless grapes.
Other varieties produce specialty raisins. Muscat grapes, which are larger and have seeds, yield a darker, more intensely flavored raisin. Zante currants, despite the name, are actually tiny dried Black Corinth grapes. Flame Seedless grapes are sometimes used for red raisins. But Thompson Seedless dominates global production by a wide margin.
How Grapes Become Raisins
The traditional method is sun-drying. After grapes are harvested, workers lay them on paper or plastic trays between the vineyard rows. Over the next two to three weeks, the sun and dry air pull moisture from the fruit until the grapes shrink to about a quarter of their original weight. Untreated grapes typically need 15 to 20 days to fully dry. When grapes are pretreated with a solution of potassium carbonate and olive oil (a technique that’s been used for centuries to soften the skin and speed moisture loss), drying time drops to 7 to 12 days.
During this process, the grapes’ skin darkens through a natural browning reaction. The sugars and acids in the fruit oxidize in the open air, which is why sun-dried raisins turn that familiar deep brown color. Once dried, the raisins are collected, cleaned, sorted by size and quality, and packaged.
Some producers use mechanical dehydrators instead of sunlight. These temperature-controlled tunnels can dry grapes faster and more consistently, which matters in regions where weather is less predictable. The end product tastes similar, though purists argue sun-dried raisins develop a slightly richer flavor.
Why Golden Raisins Look Different
Golden raisins start from the same Thompson Seedless grapes as regular dark raisins. The difference is entirely in how they’re processed. Before drying, golden raisins are treated with sulfur dioxide, a preservative that prevents the natural browning reaction. They’re then dried in mechanical dehydrators rather than in the sun. The result is a lighter color, a slightly tangier flavor, and a plumper, moister texture. Sulfur dioxide also acts as an antimicrobial agent, helping preserve the fruit’s color and flavor over time. If you have a sulfite sensitivity, this distinction matters: golden raisins contain sulfite residues, while natural sun-dried raisins generally do not.
What Changes When a Grape Dries
Removing water doesn’t just shrink a grape. It fundamentally changes the fruit’s nutritional profile. Raisins are about 60% sugar by weight, mostly fructose and glucose, which makes them one of the sweetest dried fruits. But the drying process also creates something grapes don’t have at all: fructans. These are a form of dietary fiber produced when grape sugars partially convert during dehydration. Fructan content in raisins can reach up to 8%, and fructans act as prebiotics, feeding beneficial gut bacteria. Raisins also contain 3.3 to 4.5 grams of fiber per 100 grams, along with concentrated amounts of iron, potassium, and boron.
The calorie density jumps significantly too. A cup of fresh grapes has roughly 100 calories. A cup of raisins packs close to 430. The nutrients are the same ones found in grapes, just squeezed into a much smaller package.
Where Most Raisins Are Grown
Raisins need a specific climate: long, hot summers with low humidity and minimal rain during harvest season. That limits major production to a few regions worldwide. Turkey leads global production at roughly 353,000 metric tons per year, followed closely by the United States at about 333,000 metric tons. Iran ranks third at around 123,000 metric tons. Other significant producers include India, Chile, South Africa, and Australia.
In the U.S., nearly all raisins come from California’s San Joaquin Valley, centered around the city of Fresno. The valley’s combination of hot, dry summers and fertile soil creates near-perfect conditions for growing and sun-drying grapes. Turkey’s Aegean coast, particularly the area around Manisa and Izmir, plays a similar role for Sultanina raisins exported across Europe and Asia.
A Very Old Food
Raisins were almost certainly discovered by accident. Grapes left on the vine or dropped to the ground in hot climates would have dried naturally, and someone eventually tried eating them. Evidence of raisin consumption dates back to at least 2000 BC. Ancient wall paintings in Mediterranean regions depict dried fruits being eaten and used as decorations. The Phoenicians and Armenians were among the first to refine grape cultivation and begin trading raisins with Greeks and Romans, who consumed them in enormous quantities.
In the ancient world, raisins served as far more than a snack. They were awarded as prizes in sporting events, used as currency for barter, and prescribed by physicians as medicine for ailments ranging from poisoning to aging. The Roman Emperor Augustus reportedly feasted on small birds stuffed with raisins. Hannibal packed them as rations for his troops when crossing the Alps. Their light weight, high calorie density, and long shelf life made them one of the most practical foods of the ancient world, a role they still fill today in trail mix, baking, and portable snacks.