How I keep half a celeriac from going soft

I halved a celeriac for the soup — the second half lies cut-side up on the board. The flesh greys quickly, the edge turns soft, and you no longer want it in a soffritto. I shut the cut tight with film or set the flat side against the wall of a box and put it on a cold shelf — until the next soup the root stays firm.

How I keep half a celeriac from going soft. Courgette and squash are about soft summer flesh; a celery stick is about stick crunch in a glass; swede and turnip are about a dry or woody cut. Here it is a heavy bulb with an earthy smell: a closed cut face — not a speech about a new root from the market.

If the cut already greyed — I take a thin slice with the knife and put the firm part into soup or mash. I don’t stand this root in water like greens on the window. I take only the half already cut at ours.

I don’t need a grey soft edge by lunch. I need a root that still clicks under the knife. In your kitchen is half a celeriac shut at once — or left cut-side up on the board?