The lacquer pot that arrives after your soba, and what it holds

The bowls are cleared and you reach for your wallet, but what arrives is not the bill. It is a small square pot with a wooden handle across the top, set down without explanation. Inside is cloudy water, still hot. This is the last course, and nobody is going to tell you that.

What is actually in the pot

Sobayu (そば湯) is the water the noodles were boiled in, carried straight from the pot behind the counter. Buckwheat gives up a great deal in three minutes of boiling — starch, protein, the faintly green cast of freshly milled flour — and the water thickens with it. In shops that mill their own grain that morning it pours like thin cream. In shops working from delivered flour it is closer to weak tea.

How the counter expects you to drink it

Your dipping cup, the soba choko, still holds tsuyu, the dark soy-and-dashi sauce you were dunking into. Pour the sobayu straight in and watch the colour go pale. That is the entire technique. The wasabi and the shredded negi left on the plate go in as well; nothing on the tray was meant to be thrown away.

Then taste and adjust — more sobayu if it is sharp, more tsuyu if it has gone flat. Two cups is usual, drunk slowly, while the shop cleans the counter around you.

It costs nothing, and it tells you more about the flour than the noodles did.

When it does not come

Sobayu belongs to the cold orders — mori, seiro, zaru — where the sauce sits in a cup beside you rather than in the bowl. Order kake soba, hot in broth, and there is nothing left to dilute. Some shops bring the pot the moment your plate is empty; others wait to be asked, which is sobayu o onegaishimasu (そば湯をお願いします). Standing shops in station concourses, where a bowl is ninety seconds of somebody's morning, often do not serve it at all.

そば湯は蕎麦を茹でた湯そのもので、最後に猪口へ注いで飲みます。