Agricultural Research Service have published, as of early 2014, several studies that identify the nutritional make-up and the shelf life of microgreens. Twenty-five varieties were tested, with the key nutrients measured being ascorbic acid (vitamin C), tocopherols (vitamin E), phylloquinone (vitamin K), and beta-carotene (a vitamin A precursor), plus other related carotenoids in the cotyledons. Among the 25 microgreens tested, red cabbage, cilantro, garnet amaranth, and green daikon radish had the highest concentrations of vitamin C, carotenoids, vitamin K, and vitamin E, respectively. In general, microgreens contained considerably higher levels of vitamins and carotenoids—about five times greater—than their mature plant counterparts. Comparison of microgreens to sprouts Sprouts are germinated or partially germinated seeds. A sprout consists of the seed, root, stem, while microgreens are harvested without the roots. Microgreens have stronger flavors compared to sprouts, and come in a wider selection of leaf shapes, textures, and colors. Microgreens are grown in soil or soil-like materials such as peat moss. Microgreens require high light levels, preferably natural sunlight with low humidity and good air circulation. Microgreens are planted with very low seed density compared to sprout processing. Crop times are generally one to two weeks for most varieties, although some can take four to six weeks. Microgreens are ready to harvest when the cotyledons are fully expanded. Harvesting is usually with scissors cutting just above the soil surface, excluding any roots. Some growers sell them while still growing, rooted in the growing trays so that they may be cut later. Once removed from their growing environment, these trays of microgreens must be used quickly, or they will rapidly begin to elongate and lose color and flavor. Sprout seeds are soaked in water, usually for eight hours, and then drained. A high density of seed is placed inside of sprouting equipment or enclosed containers. The seed germinates rapidly due to the high moisture and humidity levels maintained in the enclosures. Seeds can also be sprouted in cloth bags that are repeatedly soaked in water. The sprouting process occurs in dark or very low light conditions. After a few days of soaking and repeated rinsing in water (several times a day to minimize spoilage), the processing is complete, and the sprouts are ready to consume. The conditions that are ideal for properly grown microgreens do not encourage the growth of dangerous pathogens. These growing methods would not work for the production of sprouts.