Kansui: why ramen noodles are yellow and springy

Put a strand of udon next to a strand of ramen and you might guess they're close relatives. Both are wheat, both are boiled, both are slurped from a bowl of hot soup. Bite into them, though, and they're clearly different animals. Ramen is yellow where udon is white, springy where udon is soft, and it carries a faint aroma all its own.

The reason usually isn't egg, as you might assume. It's a small dose of alkaline salts called kansui (かん水), and once you know what it does, you'll never look at a ramen noodle quite the same way.

The bowl's secret ingredient

Kansui, traditionally written 鹹水, is alkaline water: a solution of mineral salts, mainly sodium carbonate and potassium carbonate, that noodle makers mix into wheat dough. Blends vary from maker to maker, but the principle is the same.

It's what makes ramen noodles, called chūka-men (中華麺, "Chinese noodles") in Japan, a category of their own. Udon is made from wheat flour, water and salt. Soba is buckwheat. Neither uses kansui, and that single ingredient explains much of the gap between a bowl of udon and a bowl of ramen.

What the alkali actually does

Kansui works on three things at once: texture, colour and smell.

Texture. Wheat flour contains proteins that link up into gluten when you add water and knead. In alkaline dough those proteins behave differently, forming a tighter, more elastic network. The noodles come out firmer and springier, with the bounce that ramen fans prize. They also stand up better to hot soup, staying firm instead of turning soft and bloated quite so quickly.

Colour. Flour contains natural pigments called flavonoids that are almost invisible in ordinary dough. In alkaline conditions they turn yellow. That's where ramen's golden colour comes from, no egg required. It's the same family of chemistry that makes red cabbage change colour when you add vinegar or baking soda. Some noodles do contain egg, and some makers add colouring, but the basic yellow is chemistry.

Aroma. Kansui gives noodles a distinctive smell, slightly mineral and sometimes described as eggy. In balance, it's part of what makes ramen smell like ramen. Overdo it, and the noodles can taste bitter or faintly soapy.

An old Chinese idea

Alkaline noodles are much older than ramen. In Chinese the alkaline water is called jiǎn shuǐ (碱水), and the technique runs through many Chinese noodle traditions. A story often told is that cooks in northern China discovered the effect using water from naturally alkaline lakes, though, like most noodle origin stories, that's hard to pin down.

The most famous example may be the hand-pulled noodles, lamian, of Lanzhou, which were traditionally made with an alkaline ash from a desert plant. The alkali helps the dough stretch, so it can be pulled, folded and pulled again into long, even strands. Our piece on Lanzhou beef noodles goes into that bowl.

Japanese ramen is generally traced to Chinese noodle cooking that arrived in Japan's port cities, and one of its old names, chūka soba (中華そば), "Chinese soba", still points back to that origin. You can read the longer story in our history of ramen.

Water, thickness and curls

Kansui is one dial on the noodle maker's control panel. There are several others, and together they decide how a noodle behaves in the bowl.

Hydration. Noodle makers talk about kasui-ritsu (加水率), the amount of water relative to flour. Low-water noodles are firm, almost snappy, and they soak up soup quickly, which is one reason the thin noodles of Hakata tonkotsu ramen are best eaten fast. High-water noodles are chewier, glossier and more forgiving; the plump, wavy noodles of Kitakata are a classic example.

Thickness. There's no single rule. Hakata pairs very thin noodles with a rich pork broth, while tsukemen, ramen's dipping-noodle cousin, leans on thick noodles that can drag a heavy sauce up with them.

Curls. Wavy noodles, called chijire (縮れ), are made by squeezing or crumpling the strands after cutting. The kinks catch soup, trap a little air and add bite. Straight noodles feel sleeker and slip through a broth more cleanly. Neither is better; it depends on what the bowl needs.

Fresh, dried and the home kitchen

Most ramen shops use fresh noodles, nama-men (生麺). Some make their own and advertise it as jika-seimen (自家製麺), "house-made noodles", while many buy from specialist noodle makers who produce noodles to each shop's specification. Dried ramen and instant noodles generally rely on kansui too.

If you want to try this at home, Asian grocery stores often sell kansui as a liquid or powder. A widely shared alternative is to bake ordinary baking soda (sodium bicarbonate) in a low oven for about an hour, which turns it into sodium carbonate. Be careful with the result: it's more strongly alkaline than the raw powder and can irritate skin and eyes, so handle it with gloves and store it clearly labelled. A gentler trick is to add a spoonful of baking soda to the water when you boil spaghetti, which gives it a springier, more ramen-like texture.

Next time a bowl arrives, look at the noodle before you taste the broth. That colour and that bounce are a small piece of chemistry, carried from old Chinese kitchens all the way to the counter in front of you.