Why Are Artichokes and Celeriac Soaked in Lemon Water?

Artichokes and celeriac contain an enzyme that becomes active when exposed to air. While the plant is intact, the enzyme is kept in a separate compartment and does not do anything; as soon as a knife opens the tissue, the enzyme comes into contact with its target and with oxygen. The resulting compounds combine to produce a dark color. This is not spoilage; it is only a color reaction. But it happens so quickly in artichokes that the surface turns brown in a few minutes. The same reaction occurs in potatoes, apples, and avocados, but at different rates.

Lemon works through chemistry. Acid lowers the pH, and the enzyme works much more slowly at this lower pH; the reaction does not stop, but it slows until it is barely visible. Water works physically by keeping oxygen away from the surface. The 2 work on their own, but they work clearly better together. Vinegar or citric acid can be used instead of lemon. More acidity gives more protection, but beyond a certain point it also noticeably changes the vegetable’s flavor.

The amount is judged by eye in practice, but there is a limit. Squeeze the juice of 1 or 2 lemons into a wide bowl of water; you can add the peel too. Too much lemon leaves celeriac noticeably sour and makes its texture firmer, so do not overdo it. You can use more acid with artichokes. Put the pieces in the water as soon as they are trimmed; a piece left on the cutting board has already started to brown. To keep seeds out of the water, squeeze the lemons through your hand or a strainer.

One detail is often overlooked: artichokes float. Any part above the surface is exposed to air and browns right there. To prevent this, place an upside-down plate over the bowl, or lay a clean cloth over the pieces and submerge them in the water. Celeriac is heavier and usually sinks on its own, but keeping it covered makes sure it stays submerged. If you put the bowl in the refrigerator, cover it with plastic wrap because the lemon water easily picks up odors from the refrigerator.

You can also use this same water for cooking, and doing so is recommended. Boiling artichokes and celeriac in lemon water helps them retain their color; you can add a few lemon slices to the pot as well. Also cut both vegetables with a stainless-steel knife; some metals speed up the reaction and leave grayish spots on the surface. If you let the vegetables cool in their own cooking liquid after cooking, they retain their color longer. If you are not going to cook a trimmed artichoke right away, keep it in a covered container in the refrigerator with the lemon water.