Canh Khoai Mỡ (Vietnamese Purple Yam Soup)

What is Canh Khoai Mo?

Canh khoai mỡ is a traditional Vietnamese vegetable soup from Central Vietnam. 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.

There are two types of yams commonly used in Vietnamese cooking that have a distinct slimy texture. Both are Dioscorea alata. The two different varieties are:

• White yam: Known as khoai mỡ trắng, though it is often labeled simply as khoai mỡ in Asian supermarkets. I typically can find this fresh in the markets.
• Purple yam: Known as khoai mỡ tím. In Filipino cooking, this is the same yam you may already know as ube, which is commonly used in sweet desserts. This variety is harder to find fresh in markets.

In Vietnamese cuisine, these yams are most often grated or traditionally scraped with a sharp spoon, then added to savory dishes such as vegetable soups.

When the purple yam is used, it’s easily recognizable by its natural magenta color.

The 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. The most common proteins are fresh shrimp, dried salted shrimp, or ground pork.

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.
• 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.