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Raisins: Rancho product of the week

October 09, 2015
Raisins made from a variety of grapes.


It takes about four tons of grapes to make one ton of raisins. One-third of the weight of every grape is water!

Some 97% of all raisins produced in California are made from the Sultana grape variety, making it the most widely planted grape for raisin production. The Sultana is a thin-skinned grape cultivated for its decreased drying time.

In some areas, Sultana raisins are synonymous with Thompson Seedless, the difference being the method with which they are dried.

Sultana raisins.
Sultana raisins.

Sultanas are sometimes sold as golden raisins and are subject to a hot dip in a caustic soda to break down the tough cuticle which improves drying time, and then they are treated with sulphur dioxide to give them a golden colour.

After the sulphur dioxide treatment, the grapes are tunnel-dried. Thompson Seedless are a darker colour than Sultanas because they do not go through the hot dip or sulphur dioxide process. Thompson Seedless are also naturally dried or sun-dried, and require more time to dehydrate.

Some dark-coloured, tunnel-dried varieties of raisins are exempt from the caustic soda treatment (which gives them the golden colour) and only receive a hot water dip to break down the skin.

The outer surface of grapes is naturally resistant to water loss. The skin is typically thick and layered, hence the cultivation of the thin-skinned Sultana varietal.

When raisins are dried their natural sugars crystallize. Over a period of prolonged storage, the raisin can develop what is known as sugaring, a physical-chemical disorder that can result in external sugar crystals, discolouration and grittiness in texture. Raisins can be soaked in tepid water to rehydrate them, eliminating some of the grittiness.

Ventilated sheds (chunche) for drying raisins in Xinjiang, north-west China.
Ventilated sheds (chunche) for drying raisins in Xinjiang, north-west China.

There are three standard methods of drying used today. Natural drying methods and tunnel drying are the most common. Less common is a shade drying procedure which results in the raisins having a greenish hue. Low-maturity fruit and clusters of grapes that mature in the shade of the vine canopy helps the grapes retain their chlorophyll as they dry. Some raisin varieties, such as Green Naturals, produced primarily in China and Afghanistan, retain much of their original green colour due to the tradition of using dark, ventilated drying houses.

Let’s talk about currants for a minute. In 1911 commercial cultivation of currants was outlawed in the USA. The lumber industry was concerned a botanical disease could wipe out the valuable white pine tree. The disease, white pine blister rust, needs both currant bushes and white pine trees in close proximity to each other to complete its cycle. The law was only recently overturned in New York due to the development of a disease-resistant variety of currant. In the 1920s Greece started exporting raisins made from the Corinth grape to the U.S. When the first shipment arrived in New York port the word “Corinth” was mistranslated as “currant.” The Americans had not seen currants on the market for so long that the term stuck and another thought was never given to the fact that dried currants are grapes after all.

History and Usage

Traditional dried fruits have been a staple food of the Mediterranean diet for thousands of years. An area known as the Fertile Crescent was a starting point for most of the original dried fruits: countries such as Iran, Iraq, Syria, northern Egypt and south-west Turkey. Dried fruits were founded in about 1700 BC when the produce fell from the tree and dried on the ground in the hot sun. It wasn’t until about 1500 BC, during a particularly hot season, when what we now call raisins were found shrivelled and dried on the vines. It was quite a different thing for the fruit to dry out on the tree!

Ancient Phoenicians and Armenians took the first steps in perfecting viticulture (the grape growing and selection process). Between 120 BC and 900 BC the Phoenicians established vineyards in Spain and Greece while the Armenians founded their own in Turkey, Iran and Iraq. Raisins were consumed in large quantities by Greeks and Romans, given as prizes in sporting events and used as a barter for trade. Ancient physicians even prescribed raisins as a potion to cure everything from mushroom poisoning to old age.

Exportation of raisins started in the eleventh century when the demand in Europe increased. Knights returning from the Crusades brought the sweet fruit home with them, creating a craving all over the continent. Initial shipping methods were too poor to maintain the quality of the raisins for such a long travel period, and when methods eventually improved the demand skyrocketed. The fifteenth and sixteenth centuries saw a rapid spread of viticulture to France and Germany. In the eighteenth century Spain’s Queen Isabella sent missionaries to Mexico to teach natives about religion. While preaching and teaching, the missionaries also passed on their knowledge of grape growing. When Spain turned power over to the colonial government of Mexico in 1834 the mission system declined, but the viticulture remained. Mexico’s adoption of Mediterranean agricultural techniques had a strong influence on the raisin industry in modern-day California, where over 50% of the world’s current raisin production now stems from.

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