Raisins

Drying removes water until the sugar concentration in what remains is high enough that microorganisms cannot grow in it — the fruit preserves itself by becoming too sweet to spoil, the same principle that makes the ripest dates shelf-stable. The sugars, acids, and minerals of the grape are all still there; they are simply no longer diluted.

The dried vine fruit trade uses a vocabulary that confuses outsiders, because its names mix up cultivar, method, and treatment rather than following any one system. Sultanas, raisins, and currants are distinguished in the trade by the cultivar used and by how the fruit was treated and dried, and the same term does not always mean the same thing in different markets. What is consistent is that the name signals cultivar and process together.

Sun drying is the classic route: bunches are cut and laid on trays or on paper between the vine rows, and the sun does the work over a period of weeks. It is cheap and it produces the darker, characteristically flavoured fruit many markets prefer, but it is a gamble against the weather — rain on drying fruit causes mould, splitting, and loss, and the crop is exposed for the whole time it takes.

Dehydration in tunnels or chambers removes the weather from the equation at the cost of energy and capital. A third route, dry-on-the-vine, cuts the fruiting canes and lets the bunches dry while still hanging, which mechanises harvest and keeps the fruit off the ground. Fruit destined for the pale golden types is treated before drying — dipped to break the skin's waxy layer so water escapes faster, and in some cases sulphured to preserve colour, with permitted treatments varying by market.

Raisins are graded on size, colour, moisture, texture, and defect incidence — sugared or crystallised fruit, mould, damaged and immature berries, capstems left attached, and foreign material. Moisture sits at the centre of it: too moist and the fruit moulds and ferments in the pack, too dry and it goes hard, dark, and unpalatable. Ochratoxin is a documented concern for dried vine fruit and is regulated, with the risk originating in mould growth on the fruit during drying rather than in storage afterwards.

• Mould and fermentation in fruit dried in poor weather or packed too moist
• Sugaring — sugar crystallising out on or in the fruit during storage
• Immature and undersized berries in the lot
• Capstems and foreign material carried through from harvest
• Excessive darkening and hardening in over-dried fruit
• Insect infestation in stored fruit

Once correctly dried, raisins store at ambient temperature in bags, cartons, and bulk, and cold storage is used to preserve colour and texture rather than to prevent spoilage. Sugar-rich stored fruit attracts stored-product insects, so hygiene and monitoring in store are routine — the same problem the date trade has, and for the same reason.

Raisins are eaten as dried fruit, packed for retail and in snack formats, and used heavily as a bakery and confectionery ingredient — in breads, cakes, biscuits, and breakfast cereals — where their sweetness and their stability both matter. They go into savoury cooking across many cuisines, and smaller volumes are used in brewing and distilling and as a natural sweetening ingredient in processed foods.

• Food — retail dried fruit and snack formats
• Food — a bakery, cereal, and confectionery ingredient
• Food — savoury culinary use and as a fruit-derived sweetener