The sharpness of radishes and arugula comes from mustard-family compounds released when their cells are ruptured. The sharpness varies with how the vegetables are cut, their age, and the season. There are four ways to mellow it: soak in ice water, salt lightly and rinse, serve with a fatty ingredient, or apply heat. Heat removes the sharpness completely.
Radishes, arugula, watercress, and mustard greens belong to the same plant family and share the same defense mechanism. Two substances are stored separately in the plant’s cells; when a cell is ruptured, they combine to produce a pungent compound that can sting the nose. This is why a whole radish is nearly odorless, while grated radish is much sharper. The sharpness is not present in the same way beforehand; it develops when the vegetable is cut. The same radish can taste like two different vegetables when sliced thickly or grated. The same mechanism explains why mustard seeds become pungent when crushed.
The first method is to change how you cut the vegetables. Radishes cut into thick slices or left whole are noticeably milder than finely grated radishes. The second method is ice water: soaking sliced radishes in ice water for half an hour makes them crisp and draws some of their sharpness into the water. The same method works for arugula, but keep the soak brief because its thin leaves wilt quickly. Drain and dry radishes after soaking, or water will collect at the bottom of the salad.
The third method is salt. Lightly salt sliced radishes, let them sit for a few minutes, then rinse and dry them; salt draws out water and removes some of the sharpness. This method is common in radish salads. Do not overdo it: prolonged salting makes radishes soft and watery. Do not salt arugula, since its leaves wilt immediately and collapse into a limp pile on the plate. Do not skip rinsing after salting; unrinsed radishes remain salty and continue to release water onto the plate.
The fourth method is what you serve alongside them. Fat does the most to soften the perception of pungent compounds; yogurt, olive oil, cheese, or avocado can noticeably mellow both radishes and arugula. Acid works in a similar way: lemon and pomegranate molasses cut the sharpness. A sweet note, such as pear or pomegranate seeds, rounds out the balance and brings the two flavors together. Fatty nuts such as walnuts and almonds do the same while adding textural contrast.
Heat is the most decisive solution. It breaks down the mechanism that creates pungency; roasted radishes become mildly sweet, while sautéed arugula behaves almost like spinach. Consider the vegetable’s age when choosing: small, fresh radishes are mild, while large, late-season radishes are much more pungent. Thin-leaved arugula is milder as well. Do not discard radish leaves; they are pungent too and can be used in soup or sautéed. Radishes bought out of season are generally more pungent, so adjust the amount you serve accordingly.