Red Rubies in Coconut Milk (Tub Tim Grob)

Tub tim grob means crisp rubies, and this dessert of dyed water chestnuts glistens exactly like gemstones floating in a bowl of coconut milk. It is a Bangkok classic served at festivals and sweet shops, and its roots trace back to a royal palace chef who added the crimson pearls to coconut cream. Cool, milky, and gently sweet, it is Thailand’s answer to a hot summer day.

Jewels in a pool of coconut cream

Each water chestnut cube wears a translucent tapioca shell that cooks into a delicate, jelly-like coating around a crisp, juicy center. The coconut milk is sweet and silky, and the crushed ice keeps everything refreshingly cold. Spoon in some jackfruit or mango for texture, and you have a dessert as beautiful as it is soothing. The contrast of cold milk and chewy, crisp pearls makes every spoonful feel like a small celebration, and a handful of crushed ice keeps it frosty to the very last bite.

Key ingredients

• Water chestnuts: the classic ‘rubies’ — canned or fresh, diced small.
• Red food coloring: the ruby red color.
• Tapioca starch: the translucent coating.
• Coconut milk and sugar: the sweet serving sauce.
• Jackfruit and crushed ice (optional): the classic additions.

Tips for perfect red rubies

Toss the diced water chestnuts with red food coloring and a little water until evenly stained, then coat them in tapioca starch — the coating is what makes them translucent and jewel-like. Drop them into boiling water in small batches and cook until they float and turn translucent, about 2 to 3 minutes, then plunge into cold water. Make the coconut sauce by simmering coconut milk with sugar and a pinch of salt until slightly thickened, then chill. Serve the rubies in the cold coconut sauce over crushed ice, with shredded jackfruit on top.

Variations and storage

Add palm seeds, tapioca pearls, or diced lychee. The rubies keep 2 days in the fridge in a little water, and the sauce keeps 3 days — assemble just before serving.

Craving more? Explore all Thai Kitchen recipes.

Thai recipes →