Sweet-tart, dark brownish-red tamarind is a necessary ingredient for an authentic-looking and tasting pad thai. It's commonly sold in paste (also called pulp) and in concentrate form. But don't fret if neither is available—you can still make an excellent pad thai using the lime juice and water substitute below.
Tamarind Paste or Pulp
Tamarind paste, or pulp, is firm, sticky, and filled with seeds and fibers. We favored this product because it had the freshest, brightest flavor. To use it in the pad thai recipe, soak 2 tablespoons in 3/4 cup boiling water for about 10 minutes, then push it through a mesh strainer to remove the seeds and fibers and extract as much pulp as possible.
Tamarind concentrate looks more like a scary pomade than foodstuff. It's black, thick, shiny, and gooey. Its flavor approximates that of tamarind paste, but it tastes less fruity and more "cooked," and it colors the pad thai a shade too dark. To use in the pad thai recipe, mix 1 tablespoon with 2/3 cup hot water.
Lime Juice and Water Substitute
If tamarind is out of the question, combine 1/3 cup lime juice and 1/3 cup water and use it in its place; use light brown sugar instead of granulated sugar to give the noodles some color and a faint molasses flavor. Because it will already contain a good hit of lime, do not serve this version with lime wedges.