In essence, compost tea results when fully composted materials are steeped in water. The resulting liquid, which may be quite aromatic depending on the type of material, is applied to plants to improve growth and to increase the number of soil microorganisms around the plant roots. Using compost tea was part of farming technique centuries ago, when animal manures were steeped in water and the resulting liquid was poured around plants. Some changes in the method of production have currently given the tea idea a high-tech twist. New equipment, somewhat more expensive than would be practical for the average gardener, results in a tea with more oxygen incorporated, super-oxygenated through air being incorporated while the compost ferments.
Compost tea can improve soil quality by increasing the number of beneficial soil organisms.
Plants depend on soil microorganisms for help with gathering and incorporating nutrients in their roots. Plants can't take up all the nutrients they need for growth. They must rely on tiny organisms to convert the nutrients into forms they can use. Compost teas contain substantial quantities of microorganisms, which are released into the soil when the tea is added around plants. If you want to experiment with compost teas, they have traditionally been made by a fermentation process.