barberries
Small dried red berries from the barberry shrub, intensely sour with a light fruity note. In Persian cooking they are briefly warmed in butter and scattered over rice.
Barberries are the dried berries of a thorny shrub, known in Iran as zereshk. They are only a few millimetres across, bright red, and distinctly sour with very little sweetness, much like a concentrated redcurrant. Because they contain a lot of sugar for their size, they burn very quickly in hot fat and turn bitter, so they are warmed only briefly over gentle heat, often with a little sugar. Before use they should be picked over, as stems and small stones are common, then soaked briefly in cold water and drained. They can be found in Persian, Afghan and some Turkish or Middle Eastern grocers as well as by mail order; kept airtight in the fridge or freezer they hold their colour and sourness for a long time.
Substitute:
There is no true equivalent. The closest options are unsweetened dried sour cherries or dried cranberries, finely chopped and sprinkled with a little lemon juice; they are larger, sweeter and less sharply sour, so the dish turns milder and fruitier. Dried redcurrants match the sourness better but are rarely available.