Canh Khoai Mỡ (Vietnamese Purple Yam Soup)

What is Canh Khoai Mo?

Canh khoai mỡ is a traditional Vietnamese vegetable soup from Central Vietnam, easily recognized by its natural purple color from purple yam.

Canh khoai means “potato/yam soup.” Mỡ means “fat,” which is referring to the slimy texture of raw, grated purple yam that feels like grease.

Purple yam, also known as khoai tím or purple water yam (Dioscorea alata), is called ube in Filipino cooking, where it is usually used in sweet desserts.

In Vietnamese cuisine, it is most often grated or more traditionally, scraped with a sharp spoon, and added to savory dishes like vegetable soups.

This purple yam is not to be confused with yampi root (sometimes spelled yampee) or Okinawan purple sweet potato, which are different root vegetables. But who’s to say it can’t be used as a substitute?

In fact, yampi root is often used as a substitute when making the white version of this soup, canh khoai mỡ trắng.

When added to the soup, the grated purple yam slightly thickens the broth and most of its natural sliminess reduces.

There are many variations of this soup, with the main difference being the protein used.

When cooked with shrimp, it’s canh khoai mo nau tom. When cooked with salted dried shrimp, it’s canh khoai mo nau tom kho. And when cooked with ground pork, canh khoai mo nau thit bam.

In this recipe, I’m using shrimp because it naturally adds a subtle sweetness to the broth and it’s most traditional.

What You Will Need

To make Vietnamese canh khoai mo, gather the following ingredients:

• Purple yam: I absolutely cannot find fresh purple yam. Instead, I buy it frozen and many Asian grocery stores carry them. Look for packages labeled frozen grated purple yam. Get the one from Vietnam, as it usually contains only grated yam. The Filipino frozen grated yam, which is also labeled the same, often includes added ingredients for a brighter purple color, since it is intended for ube desserts.
• Shrimp: fresh shrimp of any size. I’m using frozen, peeled and already devein shrimp.
• Water: for the stock.
• Seasonings: chicken bouillon powder or mushroom seasoning powder (Vietnamese secret umami seasoning ingredient), fish sauce, and salt, and ground black pepper.
• Oil: Any cooking oil works. You can also use rendered animal fat such as lard or talo for more flavor.
• Aromatics: The usual culprits, fresh garlic and shallot.
• Fresh garnish: chopped rice paddy herbs, green onions, and/or cilantro. I’m currently herb-poor so I’m just using cilantro here.

How to Make Canh Khoai Moi

Step 1: Toast aromatics

Heat oil in a pot over medium heat. Add garlic and shallot. Pan fry until lightly toasted (about 30 seconds).

Step 2: Add shrimp

Add minced shrimp and cook until just pink. Add water and bring the pot to a low simmer.

Step 3: Add purple yam

Add the grated purple yam and cook for about 15 minutes to allow the flavors to meld. Stir occasionally, making sure to scrape the bottom of the pot, as the grated yam will settle and can burn.

Step 4: Season, serve and garnish

Add your seasonings a little at a time, adjusting to taste.

Transfer the soup to a serving bowl and garnish with a handful of roughly chopped rice paddy herbs, cilantro, green onions, or a combination of all three.

Finish with a crack of fresh black pepper for aroma, and enjoy.