One Bamboo Tray, Two Very Different Noodles

July is peak cold noodle season, and across Japan, home cooks are reaching for two beloved dishes to beat the summer heat: zaru soba and zaru udon. Both are served on a zaru, the woven bamboo strainer that gives these dishes their name. The tray keeps noodles elevated so excess water drains away, leaving each strand perfectly chilled and ready for dipping.

The two noodles couldn't be more different. One is made from buckwheat, thin and earthy. The other is thick wheat udon, chewy and satisfying. The choice between them is more interesting than most people realize.

We've spent over 20 years at Tomato Japanese Grocery sharing Japanese food culture with our community here in Marietta, GA, and cold dipping noodles are one of our favorite topics. By the end of this guide, you'll know which noodle suits you, how to make the perfect tsuyu dipping sauce, and how to eat it exactly the way it's done in Japan.

A Tale of Two Noodles: Origins and Key Differences

Zaru soba traces its roots to Japan's Edo period (1603–1868), when soba shops began serving chilled buckwheat noodles on bamboo strainers. The format stuck, and the bamboo tray became inseparable from the dish itself. If you've heard of mori soba, you might wonder what separates it from zaru soba. The answer is a single topping: shredded nori. During the Meiji era, restaurants began garnishing zaru soba with fine strips of seaweed to position it as a slightly more upscale option. That tradition persists to this day.

Zaru udon is a much younger dish. It was invented around 1952 in Kagawa Prefecture, when a shop owner adapted the zaru soba format using thick udon noodles and special techniques to perfect their smooth, springy texture. Compared to centuries-old zaru soba, it's practically brand new.

The flavor and texture contrast between the two is striking. Soba noodles are thin, with an earthy, nutty aroma that registers almost aromatically on the palate. Udon noodles are thick, chewy, and relatively neutral in flavor, letting the dipping sauce do more of the talking. Soba is lighter and works beautifully as a quick summer lunch. Udon is more filling and makes a satisfying dinner centerpiece.

Regionally, soba dominates the Kanto area around Tokyo, while udon enjoys nationwide popularity in Japan. Chains like Marugame Seimen have helped spread udon culture broadly. And the cold dipping concept keeps expanding: zaru ramen is now an emerging format, proving that soba and udon are the originals of a growing trend.

The Sauce That Makes It All Work: Mentsuyu (Tsuyu)

No matter which noodle you choose, the dipping sauce is the flavor backbone of the dish. Mentsuyu (also called tsuyu) is a concentrated blend of dashi, soy sauce, mirin, and sugar. It's savory, slightly sweet, and deeply umami. The preparation is nearly identical for both zaru soba and zaru udon; the noodle is the variable, not the sauce.

Making tsuyu from scratch is rewarding, but bottled mentsuyu is a widely used shortcut, even in Japanese households. You can find it at any well-stocked Japanese grocery. One important note: bottled mentsuyu must be diluted with cold water before serving, and dilution ratios vary by brand. Always read the label. A common mistake is using it straight from the bottle, which results in an overly salty, intense sauce.

There's a subtle nuance worth knowing. Tsuyu for udon is sometimes diluted a bit more generously, because udon's neutral flavor benefits from a gentler sauce. Soba's earthiness can hold up to a stronger concentration, so the dip can be a touch more intense.

The real customization happens with yakumi, the small condiments served alongside. Wasabi, finely chopped scallions, grated daikon radish, grated ginger, and tenkasu (tempura flakes) are the classics. Stir them into your tsuyu cup a little at a time to adjust flavor and intensity to your liking.

For plant-based eaters, traditional tsuyu uses katsuobushi (bonito flakes) for its dashi base, but a version made with kombu seaweed and dried shiitake mushrooms is a fully authentic alternative with deep roots in Japanese Buddhist cuisine. It delivers rich umami without any animal products.

How to Serve, Dip, and Slurp Like You Mean It

The presentation of zaru noodles is part of the experience. Cold noodles rest on a bamboo zaru tray (or a flat plate if you don't have one), with individual cups of chilled tsuyu alongside. Small dishes of yakumi are arranged nearby so each person can customize their own dipping cup. Simple, elegant, and inviting.

Here's the proper technique: pick up a small bundle of noodles with your chopsticks and dip only the bottom third into the tsuyu. This lets the noodle's own flavor register first before the sauce hits. Submerging the entire bite drowns out the subtle character of the noodle itself.

And yes, slurping is not just acceptable. It's encouraged. When you slurp, you aerate the noodles and sauce together, which helps release volatile aromatic compounds and intensifies the flavor you perceive. It's also considered a genuine sign of appreciation to the cook.

For home entertaining, prepare your tsuyu ahead of time and refrigerate it. Set up a communal condiment plate with all the yakumi so guests can build their own dipping cups. It's one of the easiest, most impressive summer meals you can put together.

Want to turn it into a full dinner? Add crispy tempura. When paired with tempura (shrimp and anago, or saltwater eel, are the classics), the dish becomes tenzaru. Tenzaru soba and tenzaru udon are restaurant staples that are surprisingly easy to recreate at home. The contrast of hot, crispy tempura against cold, slippery noodles is one of summer's great pleasures.

The Sobayu Ritual: The Secret Final Course

Sobayu (蕎麦湯) is the starchy, slightly cloudy water left in the pot after boiling soba noodles. At traditional soba restaurants in Japan, it arrives at your table in a small teapot after you've finished eating. The ritual is simple: pour the warm sobayu into the leftover tsuyu in your dipping cup and drink it as a light broth.

The flavor is mild, slightly nutty, and warming. The sobayu softens the remaining saltiness of the tsuyu into something almost soup-like. It's a deeply satisfying close to the meal, both nutritionally (the cooking water retains B vitamins and minerals from the buckwheat) and emotionally.

This ritual is unique to soba dining and does not apply to udon. It's one of those cultural details that makes zaru soba a distinctly ceremonial experience. Most Western-facing content skips it entirely, but we think it's one of the best parts. Don't pour that cooking water down the drain.

Which Should You Choose? A Simple Decision Guide

• Flavor: Soba is earthy and nutty. Udon is neutral and mild.
• Texture: Soba is thin and light. Udon is thick, chewy, and filling.
• Dietary considerations: Soba has a lower glycemic index (approximately 50–56, compared to 100 for white rice, according to Japanese nutritional research). Buckwheat is also a complete plant-based protein containing all nine essential amino acids. Udon is wheat-based and higher on the glycemic scale.
• Occasion: Soba is ideal for a light summer lunch. Udon works well as a more substantial dinner.

A note on gluten: if you need gluten-free noodles, look for juwari soba, made from 100% buckwheat flour and naturally gluten-free. Most commercially available soba is hachiwari (80% buckwheat, 20% wheat), which contains gluten. Always check the ingredient list when shopping.

For zaru udon, frozen Sanuki-style udon noodles deliver the best chewy, authentic texture. Dried udon works in a pinch but yields a thinner, less springy result. We carry both at Tomato Japanese Grocery.

Our recommendation: if you're new to cold dipping noodles, start with udon for its approachable, neutral flavor. If you want the full traditional Japanese experience, go with soba, and don't skip the sobayu.

Bring the Zaru Experience Home

Cold dipping noodles are one of Japan's most elegant yet effortless summer dishes. A bamboo tray, a cup of tsuyu, and the right noodle are genuinely all it takes.

Everything you need to get started, from mentsuyu and dashi to dried and frozen noodles, nori, wasabi, and mirin, is available at Tomato Japanese Grocery. Visit us in person here in Marietta, GA, or shop online with nationwide UPS shipping.

July is the heart of cold noodle season. There's no better time to try zaru soba or zaru udon for the first time, or to make it a summer ritual you look forward to every year. Browse our noodle and pantry selection, and if you have questions about which products to pick, reach out. We love talking about this stuff. It's what our family has been doing for over 20 years.