Raisins are made primarily by sun drying several different types of grapes. They are small and sweetly flavored with a wrinkled texture. The technique for making raisins has been known since ancient times and evidence of their production has been found in the writings of ancient Egyptians. Currently, over 500 million lb (227 million kg) of raisins are sold each year in the United States, and that number is expected to increase because raisins are recognized as a healthy snack.
Most raisins are small, dark, and wrinkled. They have a flavor similar to the grapes from which they are made, but the drying process which creates them concentrates the amount of sugar making them taste much sweeter. They are a naturally stable food and resist spoilage due to their low moisture and low pH.
Raisins are composed of important food elements such as sugars, fruit acids, and mineral salts. The sugars provide a good source for carbohydrates. Fruit acids such as folic acid and pantothenic acid, which have been shown to promote growth, are also significant components. Vitamin B6 is found in raisins and is an essential part of human nutrition. Important minerals in raisins include calcium, magnesium, and phosphorus. Additionally, iron, copper, zinc, and other nutrients are found in trace amounts in raisins. Considering the composition of raisins and the fact that they have no fat, it is no wonder that this fruit is considered a healthy snack.
The majority of grapes used for making raisins in the United States are grown in California. This area has an ideal climate for grape growing because it has plenty of sun during the summer and very mild winters. Five other countries, which produce a substantial amount of raisins include Greece, Australia, Turkey, Iran, and Afghanistan. Each of these countries have their own variety of raisin that they consistently grow.
The primary raw material for making raisins is grapes. To make 1 lb (453.59 g) of raisins, over 4 lb (1,814.36 g) of fresh grapes are required. These grapes must have certain qualities in order to produce quality raisins. For example, they must ripen early and be easy to dry. Additionally, they must have a soft texture, not stick together when stored, have no seeds, and have a pleasing flavor. The most important grapes for raisin production include Thompson Seedless, Black Corinth, Fiesta, Muscats, and Sultans.
By far, the most widely grown raisin grape is the Thompson Seedless variety. They are used in the production of over half the world’s raisins. Ninety percent of these come from California. The Thompson was first developed in 1872 by William Thompson, who created it by taking cuttings from an English seedless grape and grafting them with a Muscat grape vine. The resulting plant produced the first Thompson seedless grapes. It is believed that all of the subsequent Thompson seedless vines came from this original grafting.
The Thompson seedless is a white, thinskinned grape, which produces the best raisins available today. Its small berries are oval and elongated. It does not contain seeds and has a high sugar content. From a raisin production standpoint, Thompson grapes are ideal because they ripen fairly early in the season and do not stick to each other during shipping.
The Black Corinth is a grape that originated in Greece, which has become an important variety of raisin grape. They are about one fourth the size of the Thompson grapes and have a juicy, tangy/tart flavor. These grapes are quite small, spherical in shape, and reddish-black in color. They are thin skinned and nearly seedless. They make good raisins and are excellent for production because they ripen early and dry easily. Because of their flavor, they are more often used for baking cookies, specialty breads, and fruitcakes than for eating.
A cast iron raisin seeder made by A.C. Williams of Ravenna, Ohio, circa 1900.
(From the collections of Henry Ford Musevm & Greenfield Village, Dearborn, Michigan.)
How lucky we are that many of our foodstuffs are already dried, seeded, and otherwise prepared for inclusion in our favorite recipes. We purchase seedless raisins and don’t even have the option of purchasing raisins with seeds. However, this was not the case over TOO years ago. Then, seedless raisins (expensive) were sold alongside those with seeds (noted as cheaper and “more commonly used”).
One might have saved pennies buying raisins with seeds but invested time in seeding those tiny fruits. How? One cookbook suggests that Valencia raisins be heated slightly with water in order to plump them, and then cut with a knife and de-seeded by hand! However, enterprising manufacturers produced labor-saving devices for women’s kitchen chores, including deseeding raisins. First, the housewife clamped her Boss brand raisin seeder to her kitchen table. Then, she loaded the raisins into the hopper at the top. As the housewife cranked the handle, the raisins were squeezed between two grooved rubber and toothed-metal rollers, which exposed the seeds. The seeds were then forced out a chute at the front (pushed out by the metal-toothed rollers) and the raisins dropped below the rollers into a pile.
Next in line of importance to raisin production is the Muscat grapes. These are large, sweet grapes that contain some seeds. Originally grown in Alexandria, Egypt, these grapes were the primary raisin grape before the advent of the Thompson. They were introduced in the United States in 1851. Muscat grapes are juicy, dull green in color, and have a sweet, muscat flavor. They have moderately tough skins and result in excellent tasting, large, soft-textured raisins. When they are used for raisin making, they are subjected to a mechanical process, which removes the seeds after the grapes are dried. These seeds are a significant drawback to using the muscat, and additionally, they do not ship well.
Grapes are harvested in August through September. While drying on trays, the grapes’ moisture content is reduced from 75% to under 15% and the color of the fruit changes to a brownish purple. After the fruit is dried, the paper trays are rolled up around the raisins to form a package. The rolls are gathered and stored in boxes or bins before being transported by truck to a processing plant, where they are cleaned, inspected, and packaged.
Two minor varieties of grape that find some use as raisins include the Fiesta and the Sultana. The Fiesta is a white seedless grape with a good flavor. A major problem with these grapes is that their stems are more difficult to remove. The Sultana grape is nearly seedless, but they make inferior raisins because they are less meaty, have a high acid content, and have some small, very hard seeds. Both Fiesta and Sultana raisins are used more often as baking raisins.
There are four primary methods for producing raisins including the natural, dehydration, continuous tray, and dried-on-the-vine methods. The most popular of these is the natural method which will be explained in some detail. The basic steps in natural raisin manufacturing include harvesting, processing, and packaging. While a small portion of raisins are made by mechanically dehydrating grapes, the majority of them are produced by sun drying.
Vineyards are susceptible to various diseases and insect attacks, so it is important for these factors to be controlled. Chemical and biological agents are used to control mites and other insects. Sulfur dusting is used to prevent the growth of mildew and other fungi. Since these compounds can have an effect on the overall grape quality, attempts are made to minimize the amounts used
Whether or not some of the fruit will be stored for later processing or moved to the production lines, is determined by the needs of the manufacturer. If the raisins are moved for storage, they are stacked outside the plant in temporary storage enclosures. These enclosures are constructed with polyethylene sheeting fastened to wooden frames. They are made tight enough to hold the fumigation gasses, which are applied periodically to inhibit insect growth. Methyl bromide and phosphine gases are the primary fumigants used.
Quality control is an important part of each step in the raisin making process. While the grapes are growing, they are checked for ripeness by squeezing the juice from a grape and using a refractometer. This allows the growers to determine how much sugar is in the grape. They are also tasted and their weight per volume is measured to give a measure of the quality of the fruit. During picking, workers are careful not to place bunches with insects or mold on the trays. They also try not to break berries as the liquid will attract insects. Knives are used to cut down the grape bunches to prevent damage. At the factory, the raisins are thoroughly inspected. They are also subjected to a variety of laboratory analyses to ensure the production of a consistent, high quality product.
Advancements in raisin production will focus on improvements in raisin yield, variety, and processing. Currently, the amount of grapes that can be produced are limited by the amount of land available. To increase yield, researchers are developing improved farming methods and new, genetically modified vine types. Experimentation is also being done on improving grape variety and characteristics through traditional grafting and biochemical means. It is expected that processing equipment will improve to reduce the amount of time required and improve the quality of the finished product.