Lettuces (lactuca sativa var.capitata) form a more or less solid head. To harvest, the entire head is cut off just above the soil. Lettuce takes about 8 weeks from planting to harvest. The ideal harvest time can be found by feeling the heads. Once solid, the lettuce should be harvested within a week. Otherwise, it will start to form a flowering stem, which will slowly grow upwards inside the head.
Lettuce contains high levels of α- and β-carotene. As a provitamin, the latter can be converted into vitamin A (retinol) in the body. α- and β-carotene are carotenoids. Other phytochemicals contained in lettuce include flavonoids and phenolic acids, which are among the polyphenols.
The individual leaves are separated from the stalk before washing. The lettuce is dressed just before serving, as the leaves wilt quickly.
Lettuce is almost impossible to store and should be used fresh.