Tamarind concentrate, also known as tamarind paste, is made from the tamarind fruit. It's commonly used in Asian and Middle Eastern cooking, but it's sometimes difficult to find outside an Asian specialty grocery store. It adds a sour note to dishes, with a hint of sweetness, so there are several substitutes you can use to get a similar flavor.
Amchoor powder is an Indian ingredient that's made by cutting up and sun drying green mangoes, and then crushing them into a powder. Green mangoes are unripe, which gives them a similar, slightly sour, flavor to tamarind concentrate. However, unlike tamarind concentrate, amchoor powder doesn't add any moisture to the dish, so you if you use it as a substitute, you should mix it with equal parts of water.
Lemon or Lime Juice
Lemon or lime juice is another substitute for tamarind concentrate. Although neither gives you the same complexity of flavor, they can provide the sweet and sour notes that your dish needs. Just mix the juice with an equal amount of light brown sugar. Use 2 tablespoons of lemon or lime juice with equal amounts of brown sugar for every teaspoon of tamarind concentrate you're replacing in your recipe.
A mixture of several dried fruits and lemon juice will act as a substitute for tamarind concentrate. Measure out equal parts of dried apricots, prunes, dates and lemon juice. Blend them in a blender or food processor until they form a smooth paste. You can use this mixture in the same proportions that you would tamarind concentrate. For instance, use 1 teaspoon of this paste to replace 1 teaspoon of tamarind.
Vinegar and Sugar
A mixture of vinegar and sugar is another possible substitute for tamarind concentrate. Mix together equal parts of sugar and a mild-flavored vinegar, such as distilled white, apple cider, white wine or rice vinegar. Avoid vinegars with a strong flavor such as malt or balsamic vinegar. Use this mixture to replace tamarind concentrate like for like.