Tub Tim Grob (Thai Red Rubies in Coconut Milk)

What Is Tub Tim Grob?

Tub Tim Grob is a chilled Thai dessert of chewy, tapioca-coated water chestnuts dyed a brilliant red and served in cold, sweetened coconut milk over crushed ice. The name translates to “crunchy rubies,” a nod to how the small, vivid pieces resemble gemstones floating in the creamy liquid. It’s one of Thailand’s most recognizable cold desserts, especially popular during the country’s hot season when something icy and refreshing is exactly what’s needed after a spicy meal.

The dish belongs to a broader family of Thai desserts built around contrasting textures rather than a single dominant flavor. The water chestnuts themselves stay naturally crisp and watery at their core, while the tapioca starch coating cooks into a translucent, springy shell around each piece. That bounce-then-crunch bite is the entire point of Tub Tim Grob, and it’s what makes the dessert feel playful and distinct from Western-style puddings or ice creams.

Coconut milk ties everything together, lightly sweetened and often infused with fragrant pandan leaves for a subtle grassy, vanilla-like aroma. Some versions add jackfruit for a fruity sweetness, or swap in other tropical fruits and jellies depending on the region or the cook’s preference, since Tub Tim Grob is flexible enough to accommodate seasonal ingredients.

Despite its striking appearance, Tub Tim Grob is a relatively simple dessert to make at home, requiring no baking and only basic pantry ingredients. It’s often served in small glass bowls to show off the layered ruby-red pieces against the white coconut milk and ice, making it as visually appealing as it is refreshing.

Ingredient Notes

• Fresh water chestnuts: Fresh water chestnuts provide the dessert’s signature crisp, watery bite at the center of each ruby. Choose firm, unblemished ones and peel them just before use, since they discolor quickly once cut.
• Tapioca starch: This starch forms the chewy, translucent outer shell that defines the dish’s texture. Use a fine, pure tapioca starch rather than a blended starch mix for the most consistent, glossy coating.
• Coconut milk: Full-fat coconut milk gives the syrup its rich, silky body. Look for cans with a high fat content and minimal additives, since thinner, watered-down coconut milk makes for a less satisfying dessert.
• Pandan leaves: Pandan adds a subtle grassy, vanilla-like aroma that’s considered essential in many Thai desserts. Fresh or frozen leaves work best; dried pandan has a much fainter fragrance.

Ingredient Suggestions

1. Young coconut meat: Shredded young coconut adds another layer of chewy texture and tropical flavor alongside the rubies.

2. Jackfruit: Sweet, fragrant jackfruit slices are a traditional addition that pairs beautifully with the coconut milk.

3. Lychee: Adding a few lychees introduces a floral sweetness that complements the crisp water chestnuts.

4. A pinch of toasted sesame seeds: Sprinkled on top just before serving, they add a subtle nutty crunch.

5. Green rubies from taro: Using taro dyed green alongside the red water chestnut rubies creates a more colorful, festive presentation.

Helpful Tips & Pro Tips

• Work in small batches when coating the water chestnuts with tapioca starch. Doing too many at once causes the pieces to clump together, resulting in an uneven, lumpy coating.
• Boil the coated pieces just until they float and turn translucent; overboiling causes the tapioca shell to dissolve slightly and become mushy instead of staying pleasantly chewy.
• Shock the boiled rubies in ice water immediately, without delay. This step firms up the tapioca shell and is what gives the dessert its signature bouncy bite.
• If your coconut syrup tastes flat, a small pinch of salt makes a noticeable difference by sharpening the sweetness rather than muting it.
• Assemble the dessert right before serving. The rubies can turn soft and lose their crisp-chewy contrast if they sit submerged in the coconut milk for too long before eating.

How to Serve and Store

Tub Tim Grob is meant to be served ice cold, so keep the crushed ice generous and pour the coconut milk over the top only at the last moment before it reaches the table. For storage, keep the prepared red rubies and the sweetened coconut milk in separate airtight containers in the refrigerator, where they will each keep well for up to two days. Avoid combining and refrigerating the fully assembled dessert, since the ice will melt and dilute the coconut milk, and the rubies will gradually soften. This dessert is not suitable for freezing, as both the tapioca coating and the coconut milk separate and become grainy once thawed.

Substitutions

• Fresh water chestnuts → Jicama, diced small — Jicama offers a similarly crisp, mildly sweet bite when fresh water chestnuts aren’t available. (Budget-Friendly)
• Red food coloring → Beet juice or grenadine syrup — Both natural options tint the water chestnuts a vivid red without artificial dye.
• Coconut milk → Oat milk blended with a spoon of coconut cream — This combination approximates the richness of coconut milk for those avoiding coconut allergens, though the flavor will differ slightly.
• Tapioca starch → Cornstarch — Cornstarch can work in a pinch, though the resulting shell will be slightly less chewy and translucent. (Gluten-Free)
• Granulated sugar → Palm sugar or agave syrup — Either alternative sweetens the coconut syrup while adding a slightly more complex, less refined sweetness. (Vegan)

Suggested Recipes

1. Khao Niew Ma Muang: Both are classic Thai coconut-based desserts, ideal for offering guests a choice of textures at the end of a meal.

2. Khanom Buang: Pair this chilled dessert with the crispy, warm shells of Khanom Buang for a contrast of temperatures and textures.

3. Pla Nueng Manao: A refreshing, icy dessert like this one is the perfect way to cool the palate after a bold, spicy fish dish.

4. Gai Pad Med Mamuang: Serve as a light, sweet finish after this savory cashew chicken stir-fry.