Fresh water chestnuts, diced into small cubes, coated in tapioca flour, and cooked until translucent — then served in sweetened coconut milk over crushed ice, with a few drops of jasmine or rosewater. The water chestnut coated in tapioca flour and cooked produces a specific textural experience: a firm, crunchy interior (the water chestnut) surrounded by a slightly translucent, slightly sticky, somewhat elastic tapioca coating. This interior crunch against the external soft-sticky coating against the cold, sweet coconut milk is the preparation's entire appeal.
**The water chestnut:** Fresh water chestnuts (the fresh corms, not canned) — peeled, diced into 1cm cubes. Fresh water chestnuts have a crispness that canned lack entirely — the freezing and canning process completely destroys the crunch. In Thailand and Asian grocery stores: fresh are standard. **The tapioca coating:** 1. Toss the diced water chestnut pieces in 2–3 tablespoons of tapioca flour (not cornflour — tapioca flour produces the characteristic translucent, slightly sticky coating that cornflour cannot). 2. Shake off excess flour. 3. Drop into vigorously boiling water. The tapioca coating gelatinises and turns from white to translucent within 1–2 minutes. 4. Remove when translucent. Rinse in cold water to prevent sticking. **The colour:** The coated water chestnuts are traditionally coloured red with red food colouring before coating in flour — producing the characteristic 'ruby' appearance (tab tim = ruby). The colouring is food dye added to the water chestnut cubes before flouring. The name tab tim grob (ruby, crunchy) describes both the colour and texture. **The assembly:** Cold sweetened coconut milk (thin coconut milk with palm sugar and a pinch of salt — Entry TH-27 principle) in a bowl, the coated water chestnuts, crushed ice, and a few drops of jasmine water (scented water prepared by soaking jasmine flowers overnight, or commercial jasmine essence). Decisive moment: The gelatinisation of the tapioca coating in the boiling water — the moment of transparency. White = still raw (the tapioca starch has not fully gelatinised). Translucent = correctly cooked. Overcooked: the coating begins to dissolve and the texture becomes gluey rather than distinctly coated.
David Thompson, *Thai Food* (2002); *Thai Street Food* (2010)