Name: Japanese Lotus Root Salad with Tuna and Mustard Mayo
Prep time: 5 min
Cook time: 10 min
Total time: 15 min
Ingredients: 300 g lotus root (renkon) (about 10 oz, peeled); 70 g canned tuna in oil (1 small can, drained); 2 tbsp Japanese mayonnaise; 1 heaping tbsp whole-grain mustard; 1 tbsp mentsuyu (3x concentrate); sugar (a pinch); green onion (finely chopped, to taste); coarsely ground black pepper (to taste); 1 liter water (for boiling); 1 tbsp vinegar (for boiling)

This Japanese lotus root salad is thin slices of renkon (lotus root), boiled until just tender and still crunchy, then tossed with canned tuna, mayonnaise, and whole-grain mustard. A splash of mentsuyu (Japanese noodle soup base) gives it a savory, slightly sweet Japanese flavor. It’s the kind of small side dish that sits next to the main and the rice in a Japanese set meal.

I followed a recipe from Nadia, a Japanese recipe site, with the same amounts. The only changes were cutting the lotus root into full rounds instead of half-moons and draining the oil from the tuna. Everything else came from the pantry: a can of tuna, Japanese mayo, a jar of whole-grain mustard, and a bottle of mentsuyu. It takes about 15 minutes.

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Japanese lotus root salad with tuna and whole-grain mustard mayonnaise in a blue ceramic bowl, topped with chopped green onion

The Short Answer

If you just want the method:

What it is: a Japanese side salad of thinly sliced lotus root and tuna in a mayonnaise and whole-grain mustard dressing.
The dressing: for 300g lotus root, 2 tbsp mayonnaise, 1 heaping tbsp whole-grain mustard, 1 tbsp mentsuyu (3x concentrate), and a pinch of sugar, plus a 70g can of tuna.
The method: slice the lotus root 2–3 mm thick, soak it in water, boil it for 5 minutes in water with 1 tbsp vinegar, pat dry, and toss with the dressing and tuna.
Don’t skip: the vinegar in the boiling water. It keeps the lotus root white and crunchy, which is how Japanese cooks always boil it.

Why You’ll Love This Recipe

Great crunch. Lotus root stays crisp even after boiling, unlike potatoes or most root vegetables.
15 minutes, pantry dressing. Mayo, mustard, mentsuyu, and a can of tuna — no special shopping beyond the lotus root.
It looks pretty with no effort. The round slices with their lace-like holes do all the work.
Good for making ahead. It keeps in the fridge for a couple of days, so it’s handy as a side dish or for bento.

What is Lotus Root (Renkon)?

Lotus root, or renkon in Japanese, is the underground stem of the lotus plant. Sliced across, it shows a ring of holes, which makes it a lucky food in Japan — you can “see through to the future.” It has a mild, slightly sweet taste and a crisp texture, a bit like a water chestnut. Japanese home cooks use it in stir-fries like lotus root kinpira, in simmered dishes, in tempura, and in salads like this one.

Outside Japan, you can usually find fresh lotus root at Asian supermarkets. Look for firm pieces without soft or dark spots.

Ingredients (Serves 3–4)

Ingredient	Amount	Notes
Lotus root (renkon)	About 300g (10 oz)	Peeled
Canned tuna in oil	1 small can (70g)	We drained the oil
Mayonnaise	2 tbsp	Japanese mayo (Kewpie) is best
Whole-grain mustard	1 heaping tbsp	Add more if you like
Mentsuyu	1 tbsp	3x concentrate
Sugar	A pinch
Green onion	To taste	Finely chopped
Black pepper	To taste	Coarsely ground
Water	1 liter (4 cups)	For boiling
Vinegar	1 tbsp	For boiling; any plain vinegar

The Kewpie mayonnaise makes a difference here. It’s richer and tangier than American mayo, which suits the mustard. For the mentsuyu, check the strength on the label. If yours is 2x concentrate, use about 1½ tbsp; if it’s 4x, use a little less than 1 tbsp. Whole-grain mustard is easy to find in any US supermarket.

Mayonnaise, whole-grain mustard, mentsuyu, and drained canned tuna in a steel mixing bowl, with the bottles of Kewpie mayo and mentsuyu and a jar of mustard behind

How to Make Japanese Lotus Root Salad

Step 1: Slice and Soak the Lotus Root

Peel the lotus root and slice it into 2–3 mm (about ⅛ in) rounds. The original recipe cuts it in half first for half-moons, but I left the rounds whole. Put the slices in water right away so they don’t turn brown.

Thin rounds of lotus root soaking in water in a pink colander

Step 2: Boil in Vinegar Water for 5 Minutes

Bring the water to a boil with the vinegar. I used a frying pan, which is plenty for a batch this size. Drain the lotus root, add it to the pan, and boil over medium heat for 5 minutes. It should still have a little crunch.

Adding grain vinegar from a bottle to a frying pan of water on an induction cooktop

Step 3: Drain and Pat Dry

Drain the lotus root in a colander, then press it with paper towels to remove the extra water. If it’s wet, the dressing turns watery.

Boiled lotus root slices on paper towels in a colander to remove excess water

Step 4: Mix the Dressing and Toss

In a bowl, mix the mayonnaise, mustard, mentsuyu, and sugar, and add the drained tuna. The original recipe adds the tuna with its oil, but we drained it to keep the salad lighter. Add the lotus root and toss until every slice is coated.

Lotus root slices tossed with tuna and mustard mayonnaise dressing in a steel bowl

Step 5: Finish with Pepper and Green Onion

Grind some black pepper over the top, pile it into a small bowl, and sprinkle with chopped green onion.

Grinding black pepper over the lotus root salad in the mixing bowl

A small blue bowl of lotus root salad with tuna, whole-grain mustard, and green onion, with chopsticks on a wooden tray behind

Tips and Variations

Don’t overboil. 5 minutes is enough. Longer and the lotus root loses its crunch and turns starchy.
Tuna oil or not. Keep the oil for a richer salad, or drain it (or use tuna in water) for a lighter one.
More mustard. If you like the pop of the mustard seeds, add an extra spoonful.
No mentsuyu? A little soy sauce with a pinch more sugar is the usual swap. I haven’t tested it in this salad, so add it a bit at a time and taste.

What to Serve It With

As one of the small sides in a Japanese set meal, next to a main dish, rice, and miso soup. That’s how we ate it.
With other mayo-based Japanese salads like gobo salad or Japanese potato salad, if you want to try a few.
Packed into a bento box — it holds up well.

Storing

Keep it covered in the fridge for up to 2 days. The lotus root stays crunchy, but the dressing gets a little more watery over time, so give it a stir before serving. I don’t recommend freezing it, since mayonnaise separates when it thaws.

Frequently Asked Questions

Why boil lotus root in vinegar water?

Vinegar keeps lotus root white and helps it stay crisp. Without it, the slices can turn grayish and a little soft. Any plain vinegar works — just 1 tbsp in a liter of water.

Can you eat lotus root raw?

In Japanese home cooking it’s almost always cooked. Boiling it briefly, like in this salad, keeps the crunch while making it pleasant to eat.

How do you cook lotus root Japanese style?

The most common ways are boiled and dressed as a salad like this, stir-fried with soy sauce and sugar as kinpira, simmered in dashi, or fried as tempura. For salads, slice it thin and boil it briefly in vinegar water.

Where can I buy lotus root?

Asian supermarkets usually carry fresh lotus root in the produce section, and some also sell it pre-sliced and frozen.

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